Volume 49,Issue 1,2020 Table of Contents
2020, 49(1):1-9.
DOI: 10.12442/j.issn.1002-185X.20180734
Abstract:
The microstructures and precipitated phases of as-extruded Mg-Al-Ca-xNd alloys with 0-1.76wt.% Nd were studied by OM, SEM and XRD. The mechanical properties of the alloys at room temperature and high temperature were also tested. Experimental results showed that the addition of Nd resulted in the formation of Al2Nd and Al11Nd3phases in the matrix and the grain refinement in Mg-Al-Ca alloy, and the amounts of Al2Nd and Al11Nd3 phases increase with the increase of Nd addition. The average grain size of alloys changed from 4.80 μm without Nd to 2.39 μm when added 1.76% Nd. The mechanical properties at room temperature were improved due to the precipitation of second phases and grain refinement. With increment of Nd, the tensile strength increased from 267 MPa to 304 MPa, the yield strength increased from 144 MPa to 203 MPa and the elongation decreased from 20.0 % to 16.9% at room temperature in these alloys. At 150℃, the tensile strength increased from 192 MPa to 229 MPa, the yield strength increased from 140 MPa to 159 MPa and the elongation decreased from 48.6 % to 29.3% with increasing Nd content.
The microstructures and precipitated phases of as-extruded Mg-Al-Ca-xNd alloys with 0-1.76wt.% Nd were studied by OM, SEM and XRD. The mechanical properties of the alloys at room temperature and high temperature were also tested. Experimental results showed that the addition of Nd resulted in the formation of Al2Nd and Al11Nd3phases in the matrix and the grain refinement in Mg-Al-Ca alloy, and the amounts of Al2Nd and Al11Nd3 phases increase with the increase of Nd addition. The average grain size of alloys changed from 4.80 μm without Nd to 2.39 μm when added 1.76% Nd. The mechanical properties at room temperature were improved due to the precipitation of second phases and grain refinement. With increment of Nd, the tensile strength increased from 267 MPa to 304 MPa, the yield strength increased from 144 MPa to 203 MPa and the elongation decreased from 20.0 % to 16.9% at room temperature in these alloys. At 150℃, the tensile strength increased from 192 MPa to 229 MPa, the yield strength increased from 140 MPa to 159 MPa and the elongation decreased from 48.6 % to 29.3% with increasing Nd content.
2020, 49(1):10-20.
DOI: 10.12442/j.issn.1002-185X.20180842
Abstract:
In hot stamping, the high strength aluminum alloy AA7075 blank was first fully solutionized and then transferred into room temperature tools, stamped and quenched. To characterize the AA7075 alloy hot deformation behavior, tensile tests employing the heating path representative of the hot stamping process were performed over the temperature range of 200-480 °C and strain rate range of 0.01-10 s-1. Modified constitutive models based on the Arrhenius type model, Johnson-Cook model and Zerilli-Armstrong model were proposed and calibrated with the hot tensile test data. The proposed models coupled the strain, strain rate and temperature effects on flow stress by expressing the model parameters as polynomial functions of strain, strain rate and temperature. The prediction accuracy of the constitutive models on flow stress was evaluated by the mean square error (MSE) and the correlation coefficient R value. The results indicated that the modified Johnson-Cook model can provide most accurate prediction for the AA7075 hot flow behavior.
In hot stamping, the high strength aluminum alloy AA7075 blank was first fully solutionized and then transferred into room temperature tools, stamped and quenched. To characterize the AA7075 alloy hot deformation behavior, tensile tests employing the heating path representative of the hot stamping process were performed over the temperature range of 200-480 °C and strain rate range of 0.01-10 s-1. Modified constitutive models based on the Arrhenius type model, Johnson-Cook model and Zerilli-Armstrong model were proposed and calibrated with the hot tensile test data. The proposed models coupled the strain, strain rate and temperature effects on flow stress by expressing the model parameters as polynomial functions of strain, strain rate and temperature. The prediction accuracy of the constitutive models on flow stress was evaluated by the mean square error (MSE) and the correlation coefficient R value. The results indicated that the modified Johnson-Cook model can provide most accurate prediction for the AA7075 hot flow behavior.
Tingzhuang Han
,
Guangsheng Huang
,
Lifei Wang
,
Bin Jiang
,
Guangang Wang
,
Aitao Tang
,
Fusheng Pan
2020, 49(1):21-26.
DOI: 10.12442/j.issn.1002-185X.E20180019
Abstract:
AZ31 alloy sheets were subjected to continuous bending (CB) process with various accumulated strain in a single pass at room temperature, and followed by annealing treatment. The corresponding microstructure and mechanical properties of as-received and CB sheets were investigated in the present paper. The obtained results indicated that no twins were observed in all microstructures during CB process. Abnormal grain growth occurred in the surface part after annealing and the depth of coarse-grained layer increased with the accumulated strain increasing. Moreover, the CB sheets in annealing condition exhibited a RD-tilt basal texture, and the inclination angle increased with the accumulated strain increasing. Compared to the as-received sample with a strong basal texture, the CB processed samples exhibited better stretch formability (2.3mm vs. 4.9mm, increased by ~113%), due to smaller r-value and larger n-value, which was related to the texture evolution.
AZ31 alloy sheets were subjected to continuous bending (CB) process with various accumulated strain in a single pass at room temperature, and followed by annealing treatment. The corresponding microstructure and mechanical properties of as-received and CB sheets were investigated in the present paper. The obtained results indicated that no twins were observed in all microstructures during CB process. Abnormal grain growth occurred in the surface part after annealing and the depth of coarse-grained layer increased with the accumulated strain increasing. Moreover, the CB sheets in annealing condition exhibited a RD-tilt basal texture, and the inclination angle increased with the accumulated strain increasing. Compared to the as-received sample with a strong basal texture, the CB processed samples exhibited better stretch formability (2.3mm vs. 4.9mm, increased by ~113%), due to smaller r-value and larger n-value, which was related to the texture evolution.
2020, 49(1):27-33.
DOI: 10.12442/j.issn.1002-185X.20180727
Abstract:
This paper investigated the formation and the growth of intermetallic compound (IMC) layer at the interface between Sn0.7Ag0.5Cu (SAC0705) solder and Cu or graphene-coated Cu (G-Cu) substrates during soldering and aging. The samples were soldered on a heating platform by aging treatment at 120 °C for up to 600 h. The experimental results showed that the thickness of IMC increased with the increasing aging time. The Cu6Sn5 IMC layer was observed between SAC0705/Cu and SAC0705/G-Cu interfaces. As the addition of Ni element in the solder, Cu6Sn5 transform into (Cu, Ni)6Sn5. With the increase of Ni content, the thickness of IMC showed an increase trend first and then decreased on the two kinds of substrates. Moreover, as the Ni content adds, the growth rate constant of interfacial IMC layer decreased. Since the graphene layer works as a diffusion barrier, the IMC on G-Cu is thinner than that on Cu substrate. And the growth rate constant of the interfacial IMC on G-Cu substrate is lower than that on Cu substrate.
This paper investigated the formation and the growth of intermetallic compound (IMC) layer at the interface between Sn0.7Ag0.5Cu (SAC0705) solder and Cu or graphene-coated Cu (G-Cu) substrates during soldering and aging. The samples were soldered on a heating platform by aging treatment at 120 °C for up to 600 h. The experimental results showed that the thickness of IMC increased with the increasing aging time. The Cu6Sn5 IMC layer was observed between SAC0705/Cu and SAC0705/G-Cu interfaces. As the addition of Ni element in the solder, Cu6Sn5 transform into (Cu, Ni)6Sn5. With the increase of Ni content, the thickness of IMC showed an increase trend first and then decreased on the two kinds of substrates. Moreover, as the Ni content adds, the growth rate constant of interfacial IMC layer decreased. Since the graphene layer works as a diffusion barrier, the IMC on G-Cu is thinner than that on Cu substrate. And the growth rate constant of the interfacial IMC on G-Cu substrate is lower than that on Cu substrate.
2020, 49(1):34-41.
DOI: 10.12442/j.issn.1002-185X.20190413
Abstract:
The electrical ablation properties of typical pantograph materials Ti3AlC2 as well as Cu-Ti3AlC2 were analyzed under 2, 5, 7, 9 kV. The arc life of Cu-Ti3AlC2 was shorter than that of Ti3AlC2. The breakdown current showed the same condition. High speed camera was employed to record the arc morphologies of the two materials. The arc on Ti3AlC2 was more concentrated than that of Cu-Ti3AlC2, accompanying with much more droplet splashes. The eroded surfaces of the two materials were observed by Scanning Electron Microscopy (SEM). Comparing to the eroded Cu-Ti3AlC2, Ti3AlC2 surface was more uneven, covered with "holes", "microcracks", "splashes". The arc energy at different voltages were calculated. It was shown that the arc energy of Cu-Ti3AlC2 material was less than that of Ti3AlC2 material under the same voltage. Raman spectrometer was carried out to determine the compositions of the eroded surfaces. Summarizing the experimental results, it could be found out that Cu-Ti3AlC2 is more suitable for pantograph material.
The electrical ablation properties of typical pantograph materials Ti3AlC2 as well as Cu-Ti3AlC2 were analyzed under 2, 5, 7, 9 kV. The arc life of Cu-Ti3AlC2 was shorter than that of Ti3AlC2. The breakdown current showed the same condition. High speed camera was employed to record the arc morphologies of the two materials. The arc on Ti3AlC2 was more concentrated than that of Cu-Ti3AlC2, accompanying with much more droplet splashes. The eroded surfaces of the two materials were observed by Scanning Electron Microscopy (SEM). Comparing to the eroded Cu-Ti3AlC2, Ti3AlC2 surface was more uneven, covered with "holes", "microcracks", "splashes". The arc energy at different voltages were calculated. It was shown that the arc energy of Cu-Ti3AlC2 material was less than that of Ti3AlC2 material under the same voltage. Raman spectrometer was carried out to determine the compositions of the eroded surfaces. Summarizing the experimental results, it could be found out that Cu-Ti3AlC2 is more suitable for pantograph material.
6 Investigation of the microstructure of pressure-assisted Ag sintering layer by deep-etching method
2020, 49(1):42-47.
DOI: 10.12442/j.issn.1002-185X.20180788
Abstract:
In this study, nano silver (Ag) film was used as the bonding material. High quality bonding layers with low porosity (1.2% to 1.4%) were obtained when the sintering pressure ranged from 5 to 10 MPa at 250 ℃. As the sintering pressure increased from 5 to 10 MPa, the shear strength of the pressure-assisted sintering specimens was improved. The microstructure of the sintered layers was investigated in comparison with the bulk Ag by deep-etching method. The results revealed that the deep-etched morphology of the sintered layer was quite different from that of the bulk Ag. Micron-scale polyhedral Ag grains were observed in the deep-etched morphology of the sintered layers. The grain size and the area of the interfaces between these polyhedral Ag grains changed as the sintering pressure increased from 5 to 10 MPa. This is considered as the dominate factor in the bonding properties of the sintered layers.
In this study, nano silver (Ag) film was used as the bonding material. High quality bonding layers with low porosity (1.2% to 1.4%) were obtained when the sintering pressure ranged from 5 to 10 MPa at 250 ℃. As the sintering pressure increased from 5 to 10 MPa, the shear strength of the pressure-assisted sintering specimens was improved. The microstructure of the sintered layers was investigated in comparison with the bulk Ag by deep-etching method. The results revealed that the deep-etched morphology of the sintered layer was quite different from that of the bulk Ag. Micron-scale polyhedral Ag grains were observed in the deep-etched morphology of the sintered layers. The grain size and the area of the interfaces between these polyhedral Ag grains changed as the sintering pressure increased from 5 to 10 MPa. This is considered as the dominate factor in the bonding properties of the sintered layers.
2020, 49(1):48-58.
DOI: 10.12442/j.issn.1002-185X.20180787
Abstract:
Comparison effect of microwave power, irradiation time and mass quantity on activation desulfurization of molybdenite and conventional oxidative roasting was experimentally studied; unreacted shrinkage nucleus model of gas-solid heterogeneous reaction was adopted to study reaction kinetics. Results showed that molybdenite concentrate had good microwave absorption performance, and optimum desulfurization effect was obtained with 0.64kW microwave irradiation on 30g molybdenite for 6 minutes, the relative sulfur content rate was reduced 65.47% by contrast with traditional oxidizing roasting; the oxidation of molybdenite is highly exothermic with faster oxidation rate at higher reaction temperature; the conversion rate is obviously increased at 540~630 °C with interfacial chemical reaction as rate controlling step. The effect of microwave activation of molybdenite concentrate prior to conventional oxidative roasting has been tested and verified. As for industrial application, a short-time activated calcination pretreatment can be used to assist conventional oxidative roasting, and an optimized process with fast reaction rate and a low sulfur content of molybdenum calcine can be obtained.
Comparison effect of microwave power, irradiation time and mass quantity on activation desulfurization of molybdenite and conventional oxidative roasting was experimentally studied; unreacted shrinkage nucleus model of gas-solid heterogeneous reaction was adopted to study reaction kinetics. Results showed that molybdenite concentrate had good microwave absorption performance, and optimum desulfurization effect was obtained with 0.64kW microwave irradiation on 30g molybdenite for 6 minutes, the relative sulfur content rate was reduced 65.47% by contrast with traditional oxidizing roasting; the oxidation of molybdenite is highly exothermic with faster oxidation rate at higher reaction temperature; the conversion rate is obviously increased at 540~630 °C with interfacial chemical reaction as rate controlling step. The effect of microwave activation of molybdenite concentrate prior to conventional oxidative roasting has been tested and verified. As for industrial application, a short-time activated calcination pretreatment can be used to assist conventional oxidative roasting, and an optimized process with fast reaction rate and a low sulfur content of molybdenum calcine can be obtained.
2020, 49(1):59-67.
DOI: 10.12442/j.issn.1002-185X.20180849
Abstract:
In order to obtain better comprehensive performances of Zr/Ti/steel composite plate, the effect of heat treatment on Zr/Ti/steel composite plate was investigated. Based on shear test analysis of titanium-steel interface, the trend that shear strength decreases along with the heat treatment temperature has been found. Besides, the shear strength of vertical to wave direction is higher than that of parallel to wave direction. Based on orthogonal test and variance analysis, it was found out that the significance of heat treatment on shear strength and bonding strength is that: holding temperature > holding time > temperature change rate. The fracture appearance of shear specimen is ductile fracture including local brittle fracture. The heat treatments of 500℃+2h+60℃/h and 540℃+1h+60℃/h are both appropriate heat treatment processes through the analysis of microstructure and micro-hardness on interface. With the holding temperature increasing, the grains become coarsening and the brittle intermetallic compounds-FeTi is formed. The micro-hardness of interface drops along with the increase of heat treatment temperature.
In order to obtain better comprehensive performances of Zr/Ti/steel composite plate, the effect of heat treatment on Zr/Ti/steel composite plate was investigated. Based on shear test analysis of titanium-steel interface, the trend that shear strength decreases along with the heat treatment temperature has been found. Besides, the shear strength of vertical to wave direction is higher than that of parallel to wave direction. Based on orthogonal test and variance analysis, it was found out that the significance of heat treatment on shear strength and bonding strength is that: holding temperature > holding time > temperature change rate. The fracture appearance of shear specimen is ductile fracture including local brittle fracture. The heat treatments of 500℃+2h+60℃/h and 540℃+1h+60℃/h are both appropriate heat treatment processes through the analysis of microstructure and micro-hardness on interface. With the holding temperature increasing, the grains become coarsening and the brittle intermetallic compounds-FeTi is formed. The micro-hardness of interface drops along with the increase of heat treatment temperature.
2020, 49(1):68-74.
DOI: 10.12442/j.issn.1002-185X.20180855
Abstract:
A kind of massive microstructure αm along the primary α phase(αP) has been characterized in the microstructure quenched from the α+β phase field. The obvious interface between αm and αP can be realized under the optical observation, and the concentrations of Al, Sn, Zr elements in αm are in between the αP and β matrix, but the orientation of the αm keeps consistent with the αP as evidenced by EBSD analysis. The appearence of the αm is considered as the result of limited diffusion controlled transformation from the β phase during the cooling, becasue the αm initiates from the α/β interface and keeps the consistent orientation with αP, and the growth is limited around the α/β interface. As the diffusion is limited by decreasing the solution periods from 30min to 5min, and the dissolving of αP is accelerated by increasing the solution temperature from 1040℃ to 1060℃, the volume fraction of αm increases from 5.2% to 30.7% significantly
A kind of massive microstructure αm along the primary α phase(αP) has been characterized in the microstructure quenched from the α+β phase field. The obvious interface between αm and αP can be realized under the optical observation, and the concentrations of Al, Sn, Zr elements in αm are in between the αP and β matrix, but the orientation of the αm keeps consistent with the αP as evidenced by EBSD analysis. The appearence of the αm is considered as the result of limited diffusion controlled transformation from the β phase during the cooling, becasue the αm initiates from the α/β interface and keeps the consistent orientation with αP, and the growth is limited around the α/β interface. As the diffusion is limited by decreasing the solution periods from 30min to 5min, and the dissolving of αP is accelerated by increasing the solution temperature from 1040℃ to 1060℃, the volume fraction of αm increases from 5.2% to 30.7% significantly
2020, 49(1):75-84.
DOI: 10.12442/j.issn.1002-185X.20180856
Abstract:
To study the precipitation behavior and strengthening effect of (Ti,Mo)C particles, one Cr-MoSsteel with added Ti was austenitized at 880 ℃ and 1350 ℃ followed by oil quenching and tempering. The chemical extraction phase analysis results showed that some (Ti,Mo)C particles were found to have size distributions within the range of 18–36 nm, 36–60 nm, and 60–96 nm when the steel was austenitized at 880 ℃ and particles were precipitated during hot rolling. When the austenitized temperature was 1350 ℃, some new (Ti,Mo)C particles appeared with sizes ranging from 1–5 nm, precipitated during tempering. These (Ti,Mo)C particles demonstrated a distinct secondary hardening platform with a strengthening increment of approximately 165 MPa. The atomic ratio of Ti/Mo in the (Ti,Mo)C particles precipitated during tempering decreased to approximately 1 as the tempering temperature increased.
To study the precipitation behavior and strengthening effect of (Ti,Mo)C particles, one Cr-MoSsteel with added Ti was austenitized at 880 ℃ and 1350 ℃ followed by oil quenching and tempering. The chemical extraction phase analysis results showed that some (Ti,Mo)C particles were found to have size distributions within the range of 18–36 nm, 36–60 nm, and 60–96 nm when the steel was austenitized at 880 ℃ and particles were precipitated during hot rolling. When the austenitized temperature was 1350 ℃, some new (Ti,Mo)C particles appeared with sizes ranging from 1–5 nm, precipitated during tempering. These (Ti,Mo)C particles demonstrated a distinct secondary hardening platform with a strengthening increment of approximately 165 MPa. The atomic ratio of Ti/Mo in the (Ti,Mo)C particles precipitated during tempering decreased to approximately 1 as the tempering temperature increased.
2020, 49(1):85-92.
DOI: 10.12442/j.issn.1002-185X.20180900
Abstract:
The interfacial microstructure and fractography of Cu/Al laminated composite fabricated by asymmetrical roll bonding and annealing were studied by scanning electron microscope. The peeling and tension tests were carried out to investigate the mechanical properties of interface. The results show that the interfacial interlayer is improved by heat treatment and higher annealing tenmperature weaken the interfacial bonding. The tensile properties of laminated composites fall in between two metal components. After annealed at 340 °C, copper substrate is nearly equal to aluminium substrate in ductility, and the crack degree of interface is lower. The mismatch elongation of metal substrates leads to the internal fracture of interlayer during tension tests. The interface plays an important role in strengthening the laminated composite as a transition between copper and aluminum.
The interfacial microstructure and fractography of Cu/Al laminated composite fabricated by asymmetrical roll bonding and annealing were studied by scanning electron microscope. The peeling and tension tests were carried out to investigate the mechanical properties of interface. The results show that the interfacial interlayer is improved by heat treatment and higher annealing tenmperature weaken the interfacial bonding. The tensile properties of laminated composites fall in between two metal components. After annealed at 340 °C, copper substrate is nearly equal to aluminium substrate in ductility, and the crack degree of interface is lower. The mismatch elongation of metal substrates leads to the internal fracture of interlayer during tension tests. The interface plays an important role in strengthening the laminated composite as a transition between copper and aluminum.
2020, 49(1):93-100.
DOI: 10.12442/j.issn.1002-185X.20180879
Abstract:
Micro-fine lightweight Nb-Ti based alloy powder was fabricated by hydride-dehydride method, and the hydrogen absorption/desorption behavior was investigated. The obvious hydrogen absorption occurs at 300 oC, and the absorbed hydrogen quantity reaches a saturation value of 1.12 wt.% at 400 oC. Binary and ternary hydrides (Nb0.803V0.197H, Nb0.696V0.304H and TiHx) were formed after hydrogenation. Hydrogen-induced embrittlement facilitates the pulverization of the thin alloy plate. During dehydrogenation process, hydrogen content was effectively reduced to 0.001 wt.% at 300 oC. Phase transformation from niobium or titanium hydrides to single phase solid solution alloy (β phase) was achieved. Oxygen content of the powder increases with increasing hydrogenation or dehydrogenation temperature due to the high reactivity of constituent elements with oxygen, both hydrogenation and dehydrogenation temperature of 400 oC is selected in order to prevent severe oxygen intake. Micro-fine Nb-based alloy powder with average particle size of 16 μm and oxygen content of 2980 ppm was obtained. Superfacial contamination of the obtained powder is detected, and oxygen impurity exists in the form of Nb2O5 and TiO2.
Micro-fine lightweight Nb-Ti based alloy powder was fabricated by hydride-dehydride method, and the hydrogen absorption/desorption behavior was investigated. The obvious hydrogen absorption occurs at 300 oC, and the absorbed hydrogen quantity reaches a saturation value of 1.12 wt.% at 400 oC. Binary and ternary hydrides (Nb0.803V0.197H, Nb0.696V0.304H and TiHx) were formed after hydrogenation. Hydrogen-induced embrittlement facilitates the pulverization of the thin alloy plate. During dehydrogenation process, hydrogen content was effectively reduced to 0.001 wt.% at 300 oC. Phase transformation from niobium or titanium hydrides to single phase solid solution alloy (β phase) was achieved. Oxygen content of the powder increases with increasing hydrogenation or dehydrogenation temperature due to the high reactivity of constituent elements with oxygen, both hydrogenation and dehydrogenation temperature of 400 oC is selected in order to prevent severe oxygen intake. Micro-fine Nb-based alloy powder with average particle size of 16 μm and oxygen content of 2980 ppm was obtained. Superfacial contamination of the obtained powder is detected, and oxygen impurity exists in the form of Nb2O5 and TiO2.
2020, 49(1):101-108.
DOI: 10.12442/j.issn.1002-185X.20180888
Abstract:
The inhibitive effect of NO3- on the corrosion behavior of U-0.79wt.%Ti alloy in 0.01 M NaCl solution was studied by electrochemical methods. The experiment results show that NO3- ions possess inhibitive effect on the corrosion of U-0.79wt.%Ti alloy in the solution containing Cl- ions, which has a close relationship with the concentration of NO3-. When the concentration ratio of NO3- and Cl- exceeds 0.1, NO3- could inhibit the appearance of the pitting on U-0.79 wt.%Ti alloy effectively; however, when the ratio is less than 0.1, NO3- show hardly any inhibitive effect on the corrosion behavior of U-0.79 wt.%Ti alloy. In the viewpoint of electrochemical process, the NO3- could increase the open circuit potential (OCP) of the alloy and lower the concentration polarization, meanwhile, increase the limited diffusion current density. At the same time, NO3- could also lower the rate of active anode dissolution, and increase the pitting corrosion potential of U-0.79 wt.%Ti alloy. The surface scratches experiments exhibit that the inhibitive effect of NO3- may root from that the NO3- ions have precedence over Cl- ions in being absorbed at the surface defects, which would inhibit the nucleation of pitting corrosion.
The inhibitive effect of NO3- on the corrosion behavior of U-0.79wt.%Ti alloy in 0.01 M NaCl solution was studied by electrochemical methods. The experiment results show that NO3- ions possess inhibitive effect on the corrosion of U-0.79wt.%Ti alloy in the solution containing Cl- ions, which has a close relationship with the concentration of NO3-. When the concentration ratio of NO3- and Cl- exceeds 0.1, NO3- could inhibit the appearance of the pitting on U-0.79 wt.%Ti alloy effectively; however, when the ratio is less than 0.1, NO3- show hardly any inhibitive effect on the corrosion behavior of U-0.79 wt.%Ti alloy. In the viewpoint of electrochemical process, the NO3- could increase the open circuit potential (OCP) of the alloy and lower the concentration polarization, meanwhile, increase the limited diffusion current density. At the same time, NO3- could also lower the rate of active anode dissolution, and increase the pitting corrosion potential of U-0.79 wt.%Ti alloy. The surface scratches experiments exhibit that the inhibitive effect of NO3- may root from that the NO3- ions have precedence over Cl- ions in being absorbed at the surface defects, which would inhibit the nucleation of pitting corrosion.
2020, 49(1):109-115.
DOI: 10.12442/j.issn.1002-185X.20180875
Abstract:
Based on the CALPHAD (Calculated of Phase Diagrams) approach, series micro-scale amorphous/crystalline composite powders of (Fe0.75Si0.1B0.15)100-xCux (x = 30, 45, 55, 65, at.%) with core/shell microstructure were designed and successfully fabricated by using the gas atomization method. The obtained gas-atomized powder exhibits a Fe-Si-B-rich amorphous-core/Cu-rich crystalline-shell composite microstructure. Results indicate that the coercive force of the composite powders is almost the same as Fe75Si10B15 amorphous powder, but their saturation magnetization decreases with increasing Cu concentration. The formation mechanism of such amorphous-core/crystalline-shell composite powders is originated from the occurrence of liquid phase separation at high temperature and the different glass-forming ability (GFA) of the two separated liquids (Cu-rich and FeSiB-rich) during the rapid solidification process.
Based on the CALPHAD (Calculated of Phase Diagrams) approach, series micro-scale amorphous/crystalline composite powders of (Fe0.75Si0.1B0.15)100-xCux (x = 30, 45, 55, 65, at.%) with core/shell microstructure were designed and successfully fabricated by using the gas atomization method. The obtained gas-atomized powder exhibits a Fe-Si-B-rich amorphous-core/Cu-rich crystalline-shell composite microstructure. Results indicate that the coercive force of the composite powders is almost the same as Fe75Si10B15 amorphous powder, but their saturation magnetization decreases with increasing Cu concentration. The formation mechanism of such amorphous-core/crystalline-shell composite powders is originated from the occurrence of liquid phase separation at high temperature and the different glass-forming ability (GFA) of the two separated liquids (Cu-rich and FeSiB-rich) during the rapid solidification process.
2020, 49(1):116-124.
DOI: 10.12442/j.issn.1002-185X.20180911
Abstract:
A composite ceramic coating containing B4C and TiO2 with excellent wear resistance and corrosion resistance was formed on the pure Ti via micro-arc oxidation. The influence of the concentration of B4C particles added into electrolyte on the microstructure, phase composition, adhesion, wear resistance and corrosion resistance of the coatings was investigated. The results show that TiO2-B4C composite coatings consisting of rutile TiO2, anatase TiO2 and B4C phases were more uniform and denser than TiO2 coating. With the increase of B4C particle concentration, the adhesion, the wear resistance and corrosion resistance of the coatings increased firstly and then decreased. TiO2-0.9B4C coating displayed strongest adhesion of 22.6 N due to the most compact microstructure. TiO2-0.9B4C coating exhibited the best wear resistance. Its breakage time was 19.24 min and its wear width was 384.53 μm. The wear mechanisms were abrasive wear and fatigue wear. TiO2-0.9 B4C coating showed the best corrosion resistance. The self-corrosion potential, corrosion current density and polarization resistance of the coating were -213.38 mV, 5.47×104 Ω?cm2 and 2.37×10-6 A?cm2, respectively. According to the Bode-phase diagram, it can be speculated that the coatings were composed of two oxide layers, a porous outer layer and a dense inner layer.
A composite ceramic coating containing B4C and TiO2 with excellent wear resistance and corrosion resistance was formed on the pure Ti via micro-arc oxidation. The influence of the concentration of B4C particles added into electrolyte on the microstructure, phase composition, adhesion, wear resistance and corrosion resistance of the coatings was investigated. The results show that TiO2-B4C composite coatings consisting of rutile TiO2, anatase TiO2 and B4C phases were more uniform and denser than TiO2 coating. With the increase of B4C particle concentration, the adhesion, the wear resistance and corrosion resistance of the coatings increased firstly and then decreased. TiO2-0.9B4C coating displayed strongest adhesion of 22.6 N due to the most compact microstructure. TiO2-0.9B4C coating exhibited the best wear resistance. Its breakage time was 19.24 min and its wear width was 384.53 μm. The wear mechanisms were abrasive wear and fatigue wear. TiO2-0.9 B4C coating showed the best corrosion resistance. The self-corrosion potential, corrosion current density and polarization resistance of the coating were -213.38 mV, 5.47×104 Ω?cm2 and 2.37×10-6 A?cm2, respectively. According to the Bode-phase diagram, it can be speculated that the coatings were composed of two oxide layers, a porous outer layer and a dense inner layer.
Luo Guoqiang
,
Qian Yichang
,
Chen Ben
,
Hu Yeyuan
,
Wei Qinqin
,
Hu qilin
,
Zhang Jian
,
Shen Qiang
2020, 49(1):125-130.
DOI: 10.12442/j.issn.1002-185X.20181034
Abstract:
In order to improve the room temperature strength and toughness of W-5Re alloy, SiC was added to form W-5Re-xSiC composites with high performance using vacuum arc melting. The relationship between the SiC content and the microstructure and mechanical properties of W-5Re-xSiC composites was investigated. The results show that the W-5Re-xSiC composites are mainly composed of W(Re) solid solution, W2C and W5Si3. As the SiC content is increased, the grain size of the W(Re) is refined and the contents of brittle intermetallic compounds are increased. The strength and fracture toughness of W-5Re-xSiC composites firstly increase and then decrease. When the SiC content is 1wt%, the strength and fracture toughness of the W-5Re-1SiC composite reach the maximum values of 1859 MPa and 32.87%, respectively, originating from the combination of grain refinement and W5Si3 toughening.
In order to improve the room temperature strength and toughness of W-5Re alloy, SiC was added to form W-5Re-xSiC composites with high performance using vacuum arc melting. The relationship between the SiC content and the microstructure and mechanical properties of W-5Re-xSiC composites was investigated. The results show that the W-5Re-xSiC composites are mainly composed of W(Re) solid solution, W2C and W5Si3. As the SiC content is increased, the grain size of the W(Re) is refined and the contents of brittle intermetallic compounds are increased. The strength and fracture toughness of W-5Re-xSiC composites firstly increase and then decrease. When the SiC content is 1wt%, the strength and fracture toughness of the W-5Re-1SiC composite reach the maximum values of 1859 MPa and 32.87%, respectively, originating from the combination of grain refinement and W5Si3 toughening.
2020, 49(1):131-137.
DOI: 10.12442/j.issn.1002-185X.20181090
Abstract:
The research in the area of grain boundary engineering was mainly focused on the relationship between process, microstructure and properities. However, little attention has been paid to the formation and evolution process of low ∑CSL grain boundary. To better understand the dynamic process, electron backscatter diffraction (EBSD) was used to analyse the grain boundary migration and evolution in J75 alloy. Single-step deformation heat treatment with 5% pre-deformation and 1000 °C annealing was used to increase the proportion of low-∑CSL grain boundary to over 70%, and formed grain clusters with ∑3n orientation relationship to break the connectivity of random grain boundaries. During the annealing process, the migration ability of ∑3ic grain boundary is strong, and when it encounters other ∑3, ∑9 would be formed; In addition, ∑3 with ∑9 would lead to∑3+∑9→ ∑27 or ∑9+∑3→∑3 processes, and the latter was more likely to occur. The ∑3 regeneration was closely related to the ∑3ic grain boundary; A mechanism for breaking the connectivity of random grain boundary network was proposed. When random boundary met low ∑CSL grain boundary, R/∑ grain boundary would form. If the ratio (R/∑)≤29, the connectivity of random grain boundary network could be interrupted.
The research in the area of grain boundary engineering was mainly focused on the relationship between process, microstructure and properities. However, little attention has been paid to the formation and evolution process of low ∑CSL grain boundary. To better understand the dynamic process, electron backscatter diffraction (EBSD) was used to analyse the grain boundary migration and evolution in J75 alloy. Single-step deformation heat treatment with 5% pre-deformation and 1000 °C annealing was used to increase the proportion of low-∑CSL grain boundary to over 70%, and formed grain clusters with ∑3n orientation relationship to break the connectivity of random grain boundaries. During the annealing process, the migration ability of ∑3ic grain boundary is strong, and when it encounters other ∑3, ∑9 would be formed; In addition, ∑3 with ∑9 would lead to∑3+∑9→ ∑27 or ∑9+∑3→∑3 processes, and the latter was more likely to occur. The ∑3 regeneration was closely related to the ∑3ic grain boundary; A mechanism for breaking the connectivity of random grain boundary network was proposed. When random boundary met low ∑CSL grain boundary, R/∑ grain boundary would form. If the ratio (R/∑)≤29, the connectivity of random grain boundary network could be interrupted.
2020, 49(1):138-146.
DOI: 10.12442/j.issn.1002-185X.20181115
Abstract:
Cast rods of TiAl alloy with lamellar microstructure were prepared by cold crucible levitation melting using the Ti-47.5Al-3.7 (Cr, V, Zr) alloys with 0.05-0.2% C (at.%, the same below) addition. The effects of carbon content on microstructure and mechanical properties of TiAl alloys was investigated by means of microstructure observation, tensile test at room temperature and creep properties measurement. The results show that the preferred orientation lamellar microstructure can still be obtained after adding 0.05~0.2% C. The volume fraction of the α2 lamellae increases slightly and the lamellar spacing tends to refine with the increase of C content. When the carbon content exceeds 0.1%, fine Ti2AlC-type carbides precipitated inside the α2 and γ lamellae and at the lamellar interfaces as well, and the size and quantity of the carbides increase with the increase of carbon content. The ultimate tensile strength and yield strength of the alloy at room temperature were improved by adding 0.05~0.2% C, and the improvement gradually increased with the increase of C content. The tensile strength and yield strength were increased by 101 MPa and 123 MPa respectively when the carbon content was 0.2%. The creep resistance has been improved significantly by adding carbon. When the carbon content is 0.1%, the creep performance is the best. When compared with the alloy without carbon addition, the plastic creep strain is reduced by half, and the creep rate at the same strain is reduced by more than one order of magnitude. The addition of C element can restrain the generation and multiplication of dislocations at the initial stage of creep. In the primary creep stage, the formation of jogs and debris in the gamma lamellae hindered the movement of dislocation which contributed to the remarkable increase of strain hardening effect of the C-containing alloy. At the same time, the Ti2AlC-type carbides further strengthened the lamellar interfaces and the matrix, and the refinement of the lamellar spacing together improved the gliding resistance of dislocation across the lamellar interface.
Cast rods of TiAl alloy with lamellar microstructure were prepared by cold crucible levitation melting using the Ti-47.5Al-3.7 (Cr, V, Zr) alloys with 0.05-0.2% C (at.%, the same below) addition. The effects of carbon content on microstructure and mechanical properties of TiAl alloys was investigated by means of microstructure observation, tensile test at room temperature and creep properties measurement. The results show that the preferred orientation lamellar microstructure can still be obtained after adding 0.05~0.2% C. The volume fraction of the α2 lamellae increases slightly and the lamellar spacing tends to refine with the increase of C content. When the carbon content exceeds 0.1%, fine Ti2AlC-type carbides precipitated inside the α2 and γ lamellae and at the lamellar interfaces as well, and the size and quantity of the carbides increase with the increase of carbon content. The ultimate tensile strength and yield strength of the alloy at room temperature were improved by adding 0.05~0.2% C, and the improvement gradually increased with the increase of C content. The tensile strength and yield strength were increased by 101 MPa and 123 MPa respectively when the carbon content was 0.2%. The creep resistance has been improved significantly by adding carbon. When the carbon content is 0.1%, the creep performance is the best. When compared with the alloy without carbon addition, the plastic creep strain is reduced by half, and the creep rate at the same strain is reduced by more than one order of magnitude. The addition of C element can restrain the generation and multiplication of dislocations at the initial stage of creep. In the primary creep stage, the formation of jogs and debris in the gamma lamellae hindered the movement of dislocation which contributed to the remarkable increase of strain hardening effect of the C-containing alloy. At the same time, the Ti2AlC-type carbides further strengthened the lamellar interfaces and the matrix, and the refinement of the lamellar spacing together improved the gliding resistance of dislocation across the lamellar interface.
2020, 49(1):147-152.
DOI: 10.12442/j.issn.1002-185X.20181072
Abstract:
The effects of different WC particle sizes on WC/10Co injection molding process (PIM) were investigated in this study. The influence mechanisms of WC particle size on feedstock flowability, molded compact’s quality, degreasing process and sintering process were analyzed. The results show that as the WC particle size decreases, the flowability of WC/10Co feedstock, the molded compacts’ quality and the dimensional accuracy decrease, only the solvent degreasing rate increases. For the ultrafine WC/10Co feedstock with powder agglomerated particles and insufficient binder coating, the heat stability is lower and the flowability reduces by 56%, which lead to the density of molded compacts reduced by 5%. As to as-sintered ultrafine WC-10Co which is prone to be decarburization during degreasing-vacuum sintering, the line shrinkage is 20.80% and the dimensional deviation is 2.85%.
The effects of different WC particle sizes on WC/10Co injection molding process (PIM) were investigated in this study. The influence mechanisms of WC particle size on feedstock flowability, molded compact’s quality, degreasing process and sintering process were analyzed. The results show that as the WC particle size decreases, the flowability of WC/10Co feedstock, the molded compacts’ quality and the dimensional accuracy decrease, only the solvent degreasing rate increases. For the ultrafine WC/10Co feedstock with powder agglomerated particles and insufficient binder coating, the heat stability is lower and the flowability reduces by 56%, which lead to the density of molded compacts reduced by 5%. As to as-sintered ultrafine WC-10Co which is prone to be decarburization during degreasing-vacuum sintering, the line shrinkage is 20.80% and the dimensional deviation is 2.85%.
2020, 49(1):153-160.
DOI: 10.12442/j.issn.1002-185X.20181081
Abstract:
Due to the low color rendering of high-power white light-emitting diodes (LEDs) based on yttrium aluminum garnet-based (YAG) yellow phosphors, high color-rendering white LEDs by mixing multiple-phosphors have been accepted by LED industry. However, the difference of phosphors can result in the luminous-chromatic-thermal stability and reliability problems in LED packages. This study selects yellow, red and orange phosphors used in high color rendering white packages, analyzes their luminescence and thermal properties, crystal structures and micro morphologies during both the high temperature and high moisture ageing test and the water-soaking test, and finally figures out the degradation mechanisms of different phosphors. The results show that: 1) the hydrolysis reaction of phosphors under hygrothermal environment produces OH- and increases the environment’s pH, that can lower the crystallinity of phosphor hosts, increase the lattice vibration and light-induced heat, and enhance the thermal quenching effect of phosphors. Meanwhile, the surface roughening of phosphor particles can increase the blue light scattering and lower its absorption and conversion efficiency. 2) the degradation trends of both luminescence and thermal properties of phosphors under the water-soaking test are similar to those aged under high temperature and high moisture ageing test. So it is an effective method to assess the reliability of LED phosphors under hygrothermal environment.
Due to the low color rendering of high-power white light-emitting diodes (LEDs) based on yttrium aluminum garnet-based (YAG) yellow phosphors, high color-rendering white LEDs by mixing multiple-phosphors have been accepted by LED industry. However, the difference of phosphors can result in the luminous-chromatic-thermal stability and reliability problems in LED packages. This study selects yellow, red and orange phosphors used in high color rendering white packages, analyzes their luminescence and thermal properties, crystal structures and micro morphologies during both the high temperature and high moisture ageing test and the water-soaking test, and finally figures out the degradation mechanisms of different phosphors. The results show that: 1) the hydrolysis reaction of phosphors under hygrothermal environment produces OH- and increases the environment’s pH, that can lower the crystallinity of phosphor hosts, increase the lattice vibration and light-induced heat, and enhance the thermal quenching effect of phosphors. Meanwhile, the surface roughening of phosphor particles can increase the blue light scattering and lower its absorption and conversion efficiency. 2) the degradation trends of both luminescence and thermal properties of phosphors under the water-soaking test are similar to those aged under high temperature and high moisture ageing test. So it is an effective method to assess the reliability of LED phosphors under hygrothermal environment.
2020, 49(1):161-168.
DOI: 10.12442/j.issn.1002-185X.20181234
Abstract:
The ΔHθf,298 and ΔGθf,298of 56 solid inorganic compounds were first estimated by the group contribution method. The estimated ΔHθf,298 and ΔGθf,298 were compared with the literature values, and the absolute value of the relative error is within 4%. Based on the group contribution method, a mathematical model for estimating LiNixCoyMnzO2 cathode materials ΔHθf,298 and ΔGθf,298 was constructed, and LiNi0.6Co0.2Mn0.2O2, LiNi0.5Co0.2Mn0.3O2, LiNi0.8Co0.1Mn0.1O2 and LiNi1/3Co1/3Mn1/3O2 were constructed, ΔHθf,298 are -705.39kJ.mol-1, -703.90kJ.mol-1, -695.67kJ.mol-1 and -705.17kJ.mol-1; ΔGθf,298are -647.98kJ.mol-1, -640.04kJ.mol-1, -631.10kJ.mol-1 and -642.41kJ.mol-1, respectively.
The ΔHθf,298 and ΔGθf,298of 56 solid inorganic compounds were first estimated by the group contribution method. The estimated ΔHθf,298 and ΔGθf,298 were compared with the literature values, and the absolute value of the relative error is within 4%. Based on the group contribution method, a mathematical model for estimating LiNixCoyMnzO2 cathode materials ΔHθf,298 and ΔGθf,298 was constructed, and LiNi0.6Co0.2Mn0.2O2, LiNi0.5Co0.2Mn0.3O2, LiNi0.8Co0.1Mn0.1O2 and LiNi1/3Co1/3Mn1/3O2 were constructed, ΔHθf,298 are -705.39kJ.mol-1, -703.90kJ.mol-1, -695.67kJ.mol-1 and -705.17kJ.mol-1; ΔGθf,298are -647.98kJ.mol-1, -640.04kJ.mol-1, -631.10kJ.mol-1 and -642.41kJ.mol-1, respectively.
2020, 49(1):169-176.
DOI: 10.12442/j.issn.1002-185X.20181177
Abstract:
The influence of Ni-Al interatomic potential from the first-nearest neighbor to the fourth-nearest neighbor on the precipitation process of L10 pre-precipitation phase in Ni75Al14Cr11 alloy was investigated by the Microscopic Phase-Field method. As the third-nearest Ni-Al interatomic potential increases or the fourth-nearest interatomic potential decreases, L10 pre-precipitation phase and L12 phase appears in advance; besides, the volume fraction of L10 pre-precipitated phase decreases while the final volume fraction of L12 phase almost remains unchanged. Whereas the opposite, L10 pre-precipitation phase and L12 phase appears later; besides, the volume fraction of both phases increases. Compared with the above two, the first-nearest interatomic potential has the less impact and the second-nearest Ni-Al interatomic potential has the least impact on the precipitation process of L10 pre-precipitation phase and L12 phase. Further research shows that Ni-Al interatomic potential does not affect the precipitation mechanism of the alloy and will affect the precipitation time, speed, volume fraction and precipitation morphology of L10 pre-precipitation phase and L12 equilibrium phase, thus affecting the structure and properties of Ni75Al14Cr11 superalloy, which has guiding significance for alloy optimization design.
The influence of Ni-Al interatomic potential from the first-nearest neighbor to the fourth-nearest neighbor on the precipitation process of L10 pre-precipitation phase in Ni75Al14Cr11 alloy was investigated by the Microscopic Phase-Field method. As the third-nearest Ni-Al interatomic potential increases or the fourth-nearest interatomic potential decreases, L10 pre-precipitation phase and L12 phase appears in advance; besides, the volume fraction of L10 pre-precipitated phase decreases while the final volume fraction of L12 phase almost remains unchanged. Whereas the opposite, L10 pre-precipitation phase and L12 phase appears later; besides, the volume fraction of both phases increases. Compared with the above two, the first-nearest interatomic potential has the less impact and the second-nearest Ni-Al interatomic potential has the least impact on the precipitation process of L10 pre-precipitation phase and L12 phase. Further research shows that Ni-Al interatomic potential does not affect the precipitation mechanism of the alloy and will affect the precipitation time, speed, volume fraction and precipitation morphology of L10 pre-precipitation phase and L12 equilibrium phase, thus affecting the structure and properties of Ni75Al14Cr11 superalloy, which has guiding significance for alloy optimization design.
2020, 49(1):177-184.
DOI: 10.12442/j.issn.1002-185X.20181182
Abstract:
The hot deformation behavior of Ti-6Al-4V-0.1Ru titanium alloy was investigated by isothermal compression on Gleeble-3500 thermal simulator under the conditions of deformation temperature ranging from 800℃ to 1100℃ and strain rate ranging from 0.01 s-1 to 10 s-1. The results revealed that the peak stress of Ti-6Al-4V-0.1Ru titanium alloy increased with decreasing the deformation temperature and increasing the strain rate, the softening mechanism was dynamic recovery below 950℃ and dynamic recrystallization above 950℃. The constitutive equation of Ti-6Al-4V-0.1Ru alloy was calculated by a linear regression analysis in two phase regions in the form of Arrhenius-type relationships. It is found that the apparent activation energies were calculated to be 720.477 kJ/mol and strain rate sensitivity index was 4.809. By introducing the influence of strain on the material constants of α, n, A and Q, the fixed constitutive model of flow stress was established, through comparing the experimental and predicted results, the correlation coefficient reached 96.9%, it was illustrated that this constitutive model had better prediction precision.
The hot deformation behavior of Ti-6Al-4V-0.1Ru titanium alloy was investigated by isothermal compression on Gleeble-3500 thermal simulator under the conditions of deformation temperature ranging from 800℃ to 1100℃ and strain rate ranging from 0.01 s-1 to 10 s-1. The results revealed that the peak stress of Ti-6Al-4V-0.1Ru titanium alloy increased with decreasing the deformation temperature and increasing the strain rate, the softening mechanism was dynamic recovery below 950℃ and dynamic recrystallization above 950℃. The constitutive equation of Ti-6Al-4V-0.1Ru alloy was calculated by a linear regression analysis in two phase regions in the form of Arrhenius-type relationships. It is found that the apparent activation energies were calculated to be 720.477 kJ/mol and strain rate sensitivity index was 4.809. By introducing the influence of strain on the material constants of α, n, A and Q, the fixed constitutive model of flow stress was established, through comparing the experimental and predicted results, the correlation coefficient reached 96.9%, it was illustrated that this constitutive model had better prediction precision.
2020, 49(1):185-192.
DOI: 10.12442/j.issn.1002-185X.20181204
Abstract:
The microstructure and mechanical properties of Mg-2Zn-1.5Cu(at%) alloy were investigated by means of metallographic microscope, scanning electron microscopy, transmission electron microscopy, XRD phase analysis and mechanical properties test. The results show that the as-cast alloy has obvious element segregation, and the main second phase is MgCuZn phase; the mechanical properties of the alloy decrease when the temperature rises with the plasticity changes are significantly higher than the strength, and the fracture mode of the alloy also changes from intergranular fracture at low temperature to transgranular fracture at high temperature; at the same temperature, the steady-state creep rate of the alloy increases and the creep mechanism is transformed from grain boundary control to joint control of grain boundary and dislocation with the increase of the stress; at the same stress, there are orders of magnitude increase in the steady-state creep rate of the alloy with the increase of the temperature, and the creep activation energy decreases from 130 kJ/mol to 36.4 kJ/mol; the alloy reaches acceleration creep stage at 200℃~45MPa and occurs creep fracture with obvious transgranular fracture characteristics in the fracture position and a large number of dislocations along the base surface in the matrix. Part of these dislocations climb and the MgZnCu phase has the effect of slowing creep deformation.
The microstructure and mechanical properties of Mg-2Zn-1.5Cu(at%) alloy were investigated by means of metallographic microscope, scanning electron microscopy, transmission electron microscopy, XRD phase analysis and mechanical properties test. The results show that the as-cast alloy has obvious element segregation, and the main second phase is MgCuZn phase; the mechanical properties of the alloy decrease when the temperature rises with the plasticity changes are significantly higher than the strength, and the fracture mode of the alloy also changes from intergranular fracture at low temperature to transgranular fracture at high temperature; at the same temperature, the steady-state creep rate of the alloy increases and the creep mechanism is transformed from grain boundary control to joint control of grain boundary and dislocation with the increase of the stress; at the same stress, there are orders of magnitude increase in the steady-state creep rate of the alloy with the increase of the temperature, and the creep activation energy decreases from 130 kJ/mol to 36.4 kJ/mol; the alloy reaches acceleration creep stage at 200℃~45MPa and occurs creep fracture with obvious transgranular fracture characteristics in the fracture position and a large number of dislocations along the base surface in the matrix. Part of these dislocations climb and the MgZnCu phase has the effect of slowing creep deformation.
25 Evolution of In-Plane Electrical Transport Properties of Ru doped BaFe2As2 system Ba(Fe1-xRux)2As2
2020, 49(1):193-200.
DOI: 10.12442/j.issn.1002-185X.20181229
Abstract:
Single crystals of Ba(Fe1-xRux)2As2 were grown out of self flux using conventional high- temperature solution growth techniques, a T- x (0 ≤ x ≤ 0.425) phase diagram is summarized using the data derivated from temperature dependent resistances. The longitudinal in-plane magnetoresistance (LMR) has been measured on different superconducting Ba(Fe1-xRux)2As2 single crystals, for all the samples, a negtive LMR was found in the paramagnetic state whose magnitude increases as H2, the suppression of spin fluctuations by the applied magnetic field could account for this minus LMR. The temperature dependent LMR coefficient curves are found to shift down systematically with the increasing doping level x, which shows the detailed procedure of suppression and the existence of drastic magnetic fluctuation in the underdoped samples. The analysis of its T dependence in an 2D itinerant nearly antiferromagnetic metal model evidences that the mode coupling coefficient a(T) exhibits a qualitative change of T variation with increasing Ru content. The latter occurs exactly at quantum critical point (QCP) where the antiferromagnetic ground state is completely suppressed, indicating the change of interaction between the conduction electrons and the fluctuating magnetic moments. LMR provides a powerful tool for studying the coupling effect between the charge carriers and the spin degrees of freedom in such iron pnictide materials.
Single crystals of Ba(Fe1-xRux)2As2 were grown out of self flux using conventional high- temperature solution growth techniques, a T- x (0 ≤ x ≤ 0.425) phase diagram is summarized using the data derivated from temperature dependent resistances. The longitudinal in-plane magnetoresistance (LMR) has been measured on different superconducting Ba(Fe1-xRux)2As2 single crystals, for all the samples, a negtive LMR was found in the paramagnetic state whose magnitude increases as H2, the suppression of spin fluctuations by the applied magnetic field could account for this minus LMR. The temperature dependent LMR coefficient curves are found to shift down systematically with the increasing doping level x, which shows the detailed procedure of suppression and the existence of drastic magnetic fluctuation in the underdoped samples. The analysis of its T dependence in an 2D itinerant nearly antiferromagnetic metal model evidences that the mode coupling coefficient a(T) exhibits a qualitative change of T variation with increasing Ru content. The latter occurs exactly at quantum critical point (QCP) where the antiferromagnetic ground state is completely suppressed, indicating the change of interaction between the conduction electrons and the fluctuating magnetic moments. LMR provides a powerful tool for studying the coupling effect between the charge carriers and the spin degrees of freedom in such iron pnictide materials.
2020, 49(1):201-208.
DOI: 10.12442/j.issn.1002-185X.20181233
Abstract:
To study the fogging of GH4720Li nickel-based superalloy sufficiently, the hot deformation of the homogenization heat treated GH4720Li was carried out on Gleeble-3800 hot simulation experiment machine, and the microstructure evolution during high temperature deformation was also analyzed. Results show that the flow stress of GH4720Li at 1100℃/0.1s-1 is about 250MPa hich is sensitive to the deformation temperature and strain rate, also dynamic recrystallization is the main softening mechanism. Coarse grain improves the critical deformation temperature and strain rate for dynamic recrystallization, and complete dynamic recrystallization is obtained at 1140~1180℃ under strain rate of 0.001 s-1. The thermal deformation activation energy is calculated as Q= 1171 kJ/mol, and the higher thermal deformation activation indicates that the coarse grain is detrimental to hot workability and dynamic recrystallization for GH4720Li alloy. It is reveals that forging temperature for coarse GH4720Li alloy is determined above 1140℃, and low stran rate is necessary to ensure the occurance of dynamic recrystallization and dendrite broken.
To study the fogging of GH4720Li nickel-based superalloy sufficiently, the hot deformation of the homogenization heat treated GH4720Li was carried out on Gleeble-3800 hot simulation experiment machine, and the microstructure evolution during high temperature deformation was also analyzed. Results show that the flow stress of GH4720Li at 1100℃/0.1s-1 is about 250MPa hich is sensitive to the deformation temperature and strain rate, also dynamic recrystallization is the main softening mechanism. Coarse grain improves the critical deformation temperature and strain rate for dynamic recrystallization, and complete dynamic recrystallization is obtained at 1140~1180℃ under strain rate of 0.001 s-1. The thermal deformation activation energy is calculated as Q= 1171 kJ/mol, and the higher thermal deformation activation indicates that the coarse grain is detrimental to hot workability and dynamic recrystallization for GH4720Li alloy. It is reveals that forging temperature for coarse GH4720Li alloy is determined above 1140℃, and low stran rate is necessary to ensure the occurance of dynamic recrystallization and dendrite broken.
2020, 49(1):209-215.
DOI: 10.12442/j.issn.1002-185X.20181086
Abstract:
The unique ultrathin electrolyte layer deposition process is helpful for the investigation of the pattern formation and the pattern selection of metal and metal oxides with the micro-nanometer scale. Under different growth driving force, the electrodeposits will present the different patterns. Moreover, the distribution of magnetic domains formed in the magnetic metals, for instance the micro-nanometer Co filaments obtained through the ultrathin electrolyte layer electrodeposition process, will be affected by their geometry such as the thickness and the width remarkbely. In this paper, through the ultrathin FeSO<sub>4</sub> solution layer electrodeposition process, the iron electrodeposits with the filament or the film like morphology grown under the different electrodeposition currents were obtained. Compared with the Fe filaments with nanometer thickness formed under the higher electrodeposition current, the film like electrodeposit formed under the lower electrodeposition current presented the sub-micron thickness. Further, based on the magnetic force microscopy (MFM), we measured the distribution of the stray magnetic field around the electrodeposits with different morphology, which is resulted from the magnetic domains formed in the electrodeposits through the self-assembled process or the magnetization process under applied static magnetic field. Finally, the magnetic property of samples were measured with the alternating gradient magnetometer (AGM), the obtained hysteresis loops presented that the ease axis is located in the plane of the electrodeposits growth, and the saturation magnetization at different directions should be determined by the growth direction, the geometry, and the morphological characteristics of electrodeposits.
The unique ultrathin electrolyte layer deposition process is helpful for the investigation of the pattern formation and the pattern selection of metal and metal oxides with the micro-nanometer scale. Under different growth driving force, the electrodeposits will present the different patterns. Moreover, the distribution of magnetic domains formed in the magnetic metals, for instance the micro-nanometer Co filaments obtained through the ultrathin electrolyte layer electrodeposition process, will be affected by their geometry such as the thickness and the width remarkbely. In this paper, through the ultrathin FeSO<sub>4</sub> solution layer electrodeposition process, the iron electrodeposits with the filament or the film like morphology grown under the different electrodeposition currents were obtained. Compared with the Fe filaments with nanometer thickness formed under the higher electrodeposition current, the film like electrodeposit formed under the lower electrodeposition current presented the sub-micron thickness. Further, based on the magnetic force microscopy (MFM), we measured the distribution of the stray magnetic field around the electrodeposits with different morphology, which is resulted from the magnetic domains formed in the electrodeposits through the self-assembled process or the magnetization process under applied static magnetic field. Finally, the magnetic property of samples were measured with the alternating gradient magnetometer (AGM), the obtained hysteresis loops presented that the ease axis is located in the plane of the electrodeposits growth, and the saturation magnetization at different directions should be determined by the growth direction, the geometry, and the morphological characteristics of electrodeposits.
2020, 49(1):216-224.
DOI: 10.12442/j.issn.1002-185X.20181238
Abstract:
The Mg-3%Al melt was inoculated by carbon combining with Sr addition. The trace impurity Fe was introduced into the melt and the holding time after carbon-inoculation was adjusted. The effect of impurity Fe on grain refinement and structure characteristics of the nucleating particle was studied by adjusting the sequence of Fe introduction and holding time. The results show that the Mg-3%Al alloy was significantly refined by carbon inoculation combining with Sr addition. The addition of impurity Fe and its sequence had no obvious effect on the grain refinement. The grain size was refined from 560 μm to the range between 100 and 130 μm. The grain size after been inoculated kept stable with increasing in the holding time to 80 min. The presence of Sr could effectively inhibit the adverse effects of Fe-induced grain coarsening and accelerating the fading of carbon inoculation. There existed two types of particles could be easily observed in the inoculated Mg-3%Alloy containing with trace Fe impurity. One was the Al4C3 particles. The other one is dual-phased particles of Al-Fe phase coated with Al4C3. Both of the particles should be the potent nuclei of α-Mg grains. Higher Sr content in the particles was measured. Active element Sr easily segregate and enrich towards the surface of particles, reducing the surface energy and interfacial energy of particles. The segregation of Sr can promote the formation of dual-phase particles and improve the stability of potent nuclei. Consequently, the Fe-induced nuclei-poisoning and the fading of inoculation could be effectively inhibited due to Sr addition in the carbon-inoculated Mg-Al melt.
The Mg-3%Al melt was inoculated by carbon combining with Sr addition. The trace impurity Fe was introduced into the melt and the holding time after carbon-inoculation was adjusted. The effect of impurity Fe on grain refinement and structure characteristics of the nucleating particle was studied by adjusting the sequence of Fe introduction and holding time. The results show that the Mg-3%Al alloy was significantly refined by carbon inoculation combining with Sr addition. The addition of impurity Fe and its sequence had no obvious effect on the grain refinement. The grain size was refined from 560 μm to the range between 100 and 130 μm. The grain size after been inoculated kept stable with increasing in the holding time to 80 min. The presence of Sr could effectively inhibit the adverse effects of Fe-induced grain coarsening and accelerating the fading of carbon inoculation. There existed two types of particles could be easily observed in the inoculated Mg-3%Alloy containing with trace Fe impurity. One was the Al4C3 particles. The other one is dual-phased particles of Al-Fe phase coated with Al4C3. Both of the particles should be the potent nuclei of α-Mg grains. Higher Sr content in the particles was measured. Active element Sr easily segregate and enrich towards the surface of particles, reducing the surface energy and interfacial energy of particles. The segregation of Sr can promote the formation of dual-phase particles and improve the stability of potent nuclei. Consequently, the Fe-induced nuclei-poisoning and the fading of inoculation could be effectively inhibited due to Sr addition in the carbon-inoculated Mg-Al melt.
Yuan Junhao
,
Dong Dandan
,
Wang Qing
,
Wang Yingmin
,
Qiang Jianbin
,
Li Xiaona
,
Dong Chuang
,
Huang Huogen
,
Ke Haibo
,
Zhang Pei
,
Zhang Pengguo
,
Liu Tianwei
2020, 49(1):225-232.
DOI: 10.12442/j.issn.1002-185X.20181259
Abstract:
As an important nuclear fuel, γ-U alloys with the body centered cubic(BCC) structure have high temperature stability and comprehensive performance among Uranium alloys, which are the target of recent alloys design. In the present paper, cluster-plus-glue-atoms structure model, which used to describesolid solution alloys, are applied to build the component formulas of γ-U solution alloys, and clarify that the structural unit of γ-U alloys is composed by BCC first neighbor coordination polyhedron cluster and three glue atoms. Further, an enormous amount of the existing alloy components are analyzed based on the model, which shows that all the BCC-stable alloys satisfy the model, such as [Mo-U14]Mo3(U-10.7Mo), [Zr-U14]Nb3(U-7.5Nb-2.5Zr, i.e., Mulberry alloy), which are all exhibit best structural stability in their respective systems and show excellent corrosion resistance. Therefore, the component design method based on cluster-plus-glue-atoms model clusters has important guiding value on predicting alloys composition and performance.
As an important nuclear fuel, γ-U alloys with the body centered cubic(BCC) structure have high temperature stability and comprehensive performance among Uranium alloys, which are the target of recent alloys design. In the present paper, cluster-plus-glue-atoms structure model, which used to describesolid solution alloys, are applied to build the component formulas of γ-U solution alloys, and clarify that the structural unit of γ-U alloys is composed by BCC first neighbor coordination polyhedron cluster and three glue atoms. Further, an enormous amount of the existing alloy components are analyzed based on the model, which shows that all the BCC-stable alloys satisfy the model, such as [Mo-U14]Mo3(U-10.7Mo), [Zr-U14]Nb3(U-7.5Nb-2.5Zr, i.e., Mulberry alloy), which are all exhibit best structural stability in their respective systems and show excellent corrosion resistance. Therefore, the component design method based on cluster-plus-glue-atoms model clusters has important guiding value on predicting alloys composition and performance.
2020, 49(1):233-240.
DOI: 10.12442/j.issn.1002-185X.20190539
Abstract:
The effect of the content of TiO2 in CaF2-CaO-Al2O3-MgO-Li2O-(TiO2) slag on the content of Al and Ti in Incoloy 825 alloy was discussed by the high temperature slag-metal equilibrium experiment. The relationship between the activity of TiO2 and Al2O3 in slag and the compositions of slag was analyzed by FactSage 7.3 thermodynamic software. The influence rule of components in slag on Gibbs free energy of reaction 4[Al]+3(TiO2) = 3[Ti]+2(Al2O3) and the content of equilibrium Al and Ti in alloy were studied. The results show that the Gibbs free energy of the reaction is negatively correlated with TiO2, CaF2 and MgO in the slag, and positively correlated with CaO and Al2O3. When the content of TiO2 in slag is 0-7.27%, the effect of burning Ti to increase Al is gradually reduced. When the content of TiO2 is 11.27%, the effect of burning Al to increase Ti is appeared. At the same temperature, with the increase of CaO and Al2O3 content in slag, the equilibrium Ti content in alloy decreases and the equilibrium Al content increases. With the increase of TiO2 content in slag, the equilibrium Ti content in alloy increases and the equilibrium Al content decreases. The change of CaF2 and MgO content in slag has little effect on the equilibrium Al and Ti content in the alloy. The experimental results are in good agreement with the thermodynamic calculation results.
The effect of the content of TiO2 in CaF2-CaO-Al2O3-MgO-Li2O-(TiO2) slag on the content of Al and Ti in Incoloy 825 alloy was discussed by the high temperature slag-metal equilibrium experiment. The relationship between the activity of TiO2 and Al2O3 in slag and the compositions of slag was analyzed by FactSage 7.3 thermodynamic software. The influence rule of components in slag on Gibbs free energy of reaction 4[Al]+3(TiO2) = 3[Ti]+2(Al2O3) and the content of equilibrium Al and Ti in alloy were studied. The results show that the Gibbs free energy of the reaction is negatively correlated with TiO2, CaF2 and MgO in the slag, and positively correlated with CaO and Al2O3. When the content of TiO2 in slag is 0-7.27%, the effect of burning Ti to increase Al is gradually reduced. When the content of TiO2 is 11.27%, the effect of burning Al to increase Ti is appeared. At the same temperature, with the increase of CaO and Al2O3 content in slag, the equilibrium Ti content in alloy decreases and the equilibrium Al content increases. With the increase of TiO2 content in slag, the equilibrium Ti content in alloy increases and the equilibrium Al content decreases. The change of CaF2 and MgO content in slag has little effect on the equilibrium Al and Ti content in the alloy. The experimental results are in good agreement with the thermodynamic calculation results.
2020, 49(1):241-246.
DOI: 10.12442/j.issn.1002-185X.20190642
Abstract:
ZrB2-SiC and La2O3 modified ZrB2-SiC coated C/C composites were prepared by high temperature reactive infiltration process. The oxidation resistance of the two coated samples in three temperature ranges, i.e. medium temperature (700-1100℃), high temperature (1200-1500℃) and super high temperature (over 2000℃), was compared. The results show that the oxidation resistance of La2O3 modified coatings increases gradually with the increase of temperature in the range of 700-1100 C. The coating exhibited good long-term oxidation resistance in the range of 1200-1500℃. The weight loss rate of ZrB2-SiC modified by La2O3 was only 0.6% after 250 h oxidation at 1200℃ and 550 h oxidation at 1500℃. This is mainly due to the synergistic effect of La-Si-O composite glass layer and pinning phase ZrSiO4 formed on the surface of the coating during oxidation, which improves the high temperature stability of the oxide film. The mass and linear ablation rates of ZrB2-SiC coatings were reduced by nearly 50% with the addition of La2O3 under the flame ablation environment of acetylene and oxygen above 2000℃.
ZrB2-SiC and La2O3 modified ZrB2-SiC coated C/C composites were prepared by high temperature reactive infiltration process. The oxidation resistance of the two coated samples in three temperature ranges, i.e. medium temperature (700-1100℃), high temperature (1200-1500℃) and super high temperature (over 2000℃), was compared. The results show that the oxidation resistance of La2O3 modified coatings increases gradually with the increase of temperature in the range of 700-1100 C. The coating exhibited good long-term oxidation resistance in the range of 1200-1500℃. The weight loss rate of ZrB2-SiC modified by La2O3 was only 0.6% after 250 h oxidation at 1200℃ and 550 h oxidation at 1500℃. This is mainly due to the synergistic effect of La-Si-O composite glass layer and pinning phase ZrSiO4 formed on the surface of the coating during oxidation, which improves the high temperature stability of the oxide film. The mass and linear ablation rates of ZrB2-SiC coatings were reduced by nearly 50% with the addition of La2O3 under the flame ablation environment of acetylene and oxygen above 2000℃.
2020, 49(1):247-256.
DOI: 10.12442/j.issn.1002-185X.20181171
Abstract:
Nickel base single crystal superalloys are widely used to fabricate turbine blade materials, since they have high temperature capability, excellent mechanical and environmental properties. Appropriate heat treatment process can improve alloy performance by changing its microstructure. The second generation single crystal alloy CMSX-4 was prepared by screw selecting method and low segregation technology. The homogenizing heat treatment carried out in an antivacuum chamber oven and followed by air cooling (AC), in order to investigate the effect of heat treatment on microstructure and stress rupture properties. The results show that elemental segregation of alloy is obviously improved after multistage solid solution heat treatment 1280 ℃, 1 h+1290 ℃, 2 h+1300 ℃, 6 h AC+1140 ℃, 4 h AC+870 ℃, 16 h AC (process 1). The rupture life of the alloy is 207.50 h under the condition of 980℃/250MPa and 280.84 h under the condition of 1070℃/140MPa. During heat treatment, homogenization micropores formed in the solution process and the size of solidification micropores increased. These micropores are the weak and crack initiation points during the creep tests of the alloy. Elemental segregation of the alloy was also improved after over melting point heat treatment heat treatment 1320℃, 3 h AC+1140℃, 4 h AC+870℃, 16 h AC (process 2). It can be concluded that the homogenization effect of process 2 is not as good as that of process 1 by measuring the segregation coefficient. However, the rupture property performs well and the rupture life of the alloy is 293.08 h under the condition of 980℃/250MPa and 310.10 h under the condition of 1070℃/140MPa. The solid solution time of process 2 is shorter and the number of micropores is less.
Nickel base single crystal superalloys are widely used to fabricate turbine blade materials, since they have high temperature capability, excellent mechanical and environmental properties. Appropriate heat treatment process can improve alloy performance by changing its microstructure. The second generation single crystal alloy CMSX-4 was prepared by screw selecting method and low segregation technology. The homogenizing heat treatment carried out in an antivacuum chamber oven and followed by air cooling (AC), in order to investigate the effect of heat treatment on microstructure and stress rupture properties. The results show that elemental segregation of alloy is obviously improved after multistage solid solution heat treatment 1280 ℃, 1 h+1290 ℃, 2 h+1300 ℃, 6 h AC+1140 ℃, 4 h AC+870 ℃, 16 h AC (process 1). The rupture life of the alloy is 207.50 h under the condition of 980℃/250MPa and 280.84 h under the condition of 1070℃/140MPa. During heat treatment, homogenization micropores formed in the solution process and the size of solidification micropores increased. These micropores are the weak and crack initiation points during the creep tests of the alloy. Elemental segregation of the alloy was also improved after over melting point heat treatment heat treatment 1320℃, 3 h AC+1140℃, 4 h AC+870℃, 16 h AC (process 2). It can be concluded that the homogenization effect of process 2 is not as good as that of process 1 by measuring the segregation coefficient. However, the rupture property performs well and the rupture life of the alloy is 293.08 h under the condition of 980℃/250MPa and 310.10 h under the condition of 1070℃/140MPa. The solid solution time of process 2 is shorter and the number of micropores is less.
2020, 49(1):257-266.
DOI: 10.12442/j.issn.1002-185X.20181108
Abstract:
In order to improve oxidation resistance of niobium alloy, an Al-Si coating was obtained on the surface of the niobium alloy by Al-Si co-deposition method and then a MoSi2 coating was prepared continuously by laser cladding technique. The growth mechanism of the Al-Si co-deposition was investigated and the high-temperature oxidation resistance was discussed by comparing the Al-Si layer to the MoSi2/Al-Si coating. The results showed that the formation process of the Al-Si coating is derived from the sequential deposition of Al and Si elements, and Al3Nb phase is preferentially formed. The thickness X and the holding time t follow the relationship: x=At1/2+7.4, here A= 11.6 at 1000 ℃ and A= 16.2 at 1050 ℃. The MoSi2/ Al-Si coating prepared by laser cladding was uniformly continuous and compact, which was tightly bound to the substrate without cracks and holes found. MoSi2, Al3Nb, NbSi2, Nb5Si3 and Mo(Si,Al)2 phases were detected in the as-deposited duplex coatings. After oxidation at 1200 ℃, a large amount of SiO2 were formed to prevent the inward diffusion of oxygen atoms on the Al-Si coating and the MoSi2/Al-Si coating, respectively. Compared with the Al-Si coating, presence of continuous oxide scales on the duplex coatings effectively avoids rapid consumption of the Al-Si layer, so that the MoSi2/Al-Si coating exhibited more excellent high temperature oxidation resistance.
In order to improve oxidation resistance of niobium alloy, an Al-Si coating was obtained on the surface of the niobium alloy by Al-Si co-deposition method and then a MoSi2 coating was prepared continuously by laser cladding technique. The growth mechanism of the Al-Si co-deposition was investigated and the high-temperature oxidation resistance was discussed by comparing the Al-Si layer to the MoSi2/Al-Si coating. The results showed that the formation process of the Al-Si coating is derived from the sequential deposition of Al and Si elements, and Al3Nb phase is preferentially formed. The thickness X and the holding time t follow the relationship: x=At1/2+7.4, here A= 11.6 at 1000 ℃ and A= 16.2 at 1050 ℃. The MoSi2/ Al-Si coating prepared by laser cladding was uniformly continuous and compact, which was tightly bound to the substrate without cracks and holes found. MoSi2, Al3Nb, NbSi2, Nb5Si3 and Mo(Si,Al)2 phases were detected in the as-deposited duplex coatings. After oxidation at 1200 ℃, a large amount of SiO2 were formed to prevent the inward diffusion of oxygen atoms on the Al-Si coating and the MoSi2/Al-Si coating, respectively. Compared with the Al-Si coating, presence of continuous oxide scales on the duplex coatings effectively avoids rapid consumption of the Al-Si layer, so that the MoSi2/Al-Si coating exhibited more excellent high temperature oxidation resistance.
2020, 49(1):267-273.
DOI: 10.12442/j.issn.1002-185X.20181176
Abstract:
In order to enhance the stability of the materials and reduce the influence of friction and wear on the material properties in the wide temperature range. Ni60 alloy powder was used as the matrix materials, and the composite materials of nickel-based self-lubrication with different LaF3 content were prepared by spark plasma sintering(SPS) technology in this paper. The wide-temperature tribological properties of composite materials in air environment were tested by using HT-1000 high temperature friction and wear tester, GBS-SmartWLI white light interference three-dimensional profiler, SEM, EDS, XRD, etc. Research results indicate that the prepared nickel-based self-lubricating composites have excellent tribological properties in a wide temperature range. When the content of LaF3 is 6%, the average friction coefficient varies from 0.189 to 0.288 ranges in the temperature range from 200°C to 800°C, and the low friction coefficient was showed 0.189 and the average wear rate was on the order of 10-5mm3/N?m at 600℃. SrSiO3, SrMoO4, La6MoO12. were formed at a high temperature of the composite materials with the content of 6%. The direct contact of the surface was prevented by formed salt transfer films and the shear strength of the contact layer was reduced, thereby the stability of the material was improved significantly in a wide temperature range. As the test temperature was increased to 800°C, the friction coefficient of the composite increased slightly due to high temperature oxidations, but remained at a low level of 0.2.
In order to enhance the stability of the materials and reduce the influence of friction and wear on the material properties in the wide temperature range. Ni60 alloy powder was used as the matrix materials, and the composite materials of nickel-based self-lubrication with different LaF3 content were prepared by spark plasma sintering(SPS) technology in this paper. The wide-temperature tribological properties of composite materials in air environment were tested by using HT-1000 high temperature friction and wear tester, GBS-SmartWLI white light interference three-dimensional profiler, SEM, EDS, XRD, etc. Research results indicate that the prepared nickel-based self-lubricating composites have excellent tribological properties in a wide temperature range. When the content of LaF3 is 6%, the average friction coefficient varies from 0.189 to 0.288 ranges in the temperature range from 200°C to 800°C, and the low friction coefficient was showed 0.189 and the average wear rate was on the order of 10-5mm3/N?m at 600℃. SrSiO3, SrMoO4, La6MoO12. were formed at a high temperature of the composite materials with the content of 6%. The direct contact of the surface was prevented by formed salt transfer films and the shear strength of the contact layer was reduced, thereby the stability of the material was improved significantly in a wide temperature range. As the test temperature was increased to 800°C, the friction coefficient of the composite increased slightly due to high temperature oxidations, but remained at a low level of 0.2.
2020, 49(1):274-280.
DOI: 10.12442/j.issn.1002-185X.20181089
Abstract:
For the high temperature and high rotational speed working conditions of K418 superalloy impeller, the problems of deformation out of tolerance and reduction of mechanical properties after remanufacture for layer become the research focus. Basing on the optimized process of waveform modulation pulsed laser, the Inconel 718 alloy layer was remanufactured. The metallographic microscope, SEM, XRD, EDS, microhardness, and dynamic balance testing machine were used to research the microstructure morphology, phase structure, interface composition distribution, basic mechanical properties of Inconel 718 layer. The test results show, there is metallurgical bonding between the cladding layer and the substrate. The middle layer is a coarse dendrite, there is a 30~45 degree angle between the coarse dendrite and the laser scanning direction. From the middle of the forming layer to the top and bottom, the coarse dendrite degenerate into equiaxed and cellular crystals.The microhardness of the forming layer is 410~440 HV0.1, which is slightly higher than the substrate. A small amount of Laves phase is precipitated in the grains and intergranular, which reduces the impact on the hard-brittleness of the forming layer, the friction and wear coefficient is slightly lower than that of the matrix, but the requirements of remanufacture is still met.
For the high temperature and high rotational speed working conditions of K418 superalloy impeller, the problems of deformation out of tolerance and reduction of mechanical properties after remanufacture for layer become the research focus. Basing on the optimized process of waveform modulation pulsed laser, the Inconel 718 alloy layer was remanufactured. The metallographic microscope, SEM, XRD, EDS, microhardness, and dynamic balance testing machine were used to research the microstructure morphology, phase structure, interface composition distribution, basic mechanical properties of Inconel 718 layer. The test results show, there is metallurgical bonding between the cladding layer and the substrate. The middle layer is a coarse dendrite, there is a 30~45 degree angle between the coarse dendrite and the laser scanning direction. From the middle of the forming layer to the top and bottom, the coarse dendrite degenerate into equiaxed and cellular crystals.The microhardness of the forming layer is 410~440 HV0.1, which is slightly higher than the substrate. A small amount of Laves phase is precipitated in the grains and intergranular, which reduces the impact on the hard-brittleness of the forming layer, the friction and wear coefficient is slightly lower than that of the matrix, but the requirements of remanufacture is still met.
2020, 49(1):281-287.
DOI: 10.12442/j.issn.1002-185X.20181183
Abstract:
An advanced Cu-FeC composite material with good interface bonding was prepared by vacuum induction melting and rapid solidification technology. The microstructure evolution and deformation behaviors of the composites in the as-cast, austenitizing + quenching and cold rolling states were studied by OM, SEM, TEM, XRD characterization and mechanical property measurements. The results show that, γ-Fe、α-Fe and martensite phase coexist in the as-cast composite, however, after the treatment of austenitizing (820℃/4min) + quenching the primary Fe-C phase in the matrix can be transformed into martensite, and a large number of nano-sized γ-Fe phase particles can be also formed. The composite in the as-cast state possesses a better deformability during cold rolling process, while micro cracks could be formed in the coarse Fe-C martensite phases or around them in the quenched composite during cold rolling. The strengths of the composites could be both increased significantly after cold rolling, and the highest tensile strength could reach about 515MPa, but the plastic deformation characteristics still can be seen in them. Additionally, their elongations are much higher than those of the reported ceramic particles reinforced copper matrix composites with similar strengthes. Finally, based on the microstructure evolution of Cu-FeC composite material, the deformation and fracture models of the composites with different microstructure characteristics were put forward in this paper.
An advanced Cu-FeC composite material with good interface bonding was prepared by vacuum induction melting and rapid solidification technology. The microstructure evolution and deformation behaviors of the composites in the as-cast, austenitizing + quenching and cold rolling states were studied by OM, SEM, TEM, XRD characterization and mechanical property measurements. The results show that, γ-Fe、α-Fe and martensite phase coexist in the as-cast composite, however, after the treatment of austenitizing (820℃/4min) + quenching the primary Fe-C phase in the matrix can be transformed into martensite, and a large number of nano-sized γ-Fe phase particles can be also formed. The composite in the as-cast state possesses a better deformability during cold rolling process, while micro cracks could be formed in the coarse Fe-C martensite phases or around them in the quenched composite during cold rolling. The strengths of the composites could be both increased significantly after cold rolling, and the highest tensile strength could reach about 515MPa, but the plastic deformation characteristics still can be seen in them. Additionally, their elongations are much higher than those of the reported ceramic particles reinforced copper matrix composites with similar strengthes. Finally, based on the microstructure evolution of Cu-FeC composite material, the deformation and fracture models of the composites with different microstructure characteristics were put forward in this paper.
2020, 49(1):288-296.
DOI: 10.12442/j.issn.1002-185X.20181190
Abstract:
This paper aims at investigating the mechanical properties and texture evolution of extruded AZ31 magnesium alloy rods under cyclic torsion. Thus, cyclic torsion tests were performed at different temperatures such as room temperature, 373, 443, 503, and 573K, respectively. Measured mechanical properties of magnesium alloy cyclic torsion revealed that, stress-strain hysteresis loops of cyclic torsions were strictly symmetric which means that the dominant deformation mechanism is sliding. Additionally, due to the thermal influence of cyclic torsion, the peak stresses in stress-strain hysteresis loops were decreased with the increase of number of cycles. The grain orientations were changed due to the activation of prismatic slips. The texture of {11-20} prismatic planes perpendicular to ED in initial rods was transformed into the texture of {10-10} prismatic planes after cyclic torsion. Also, two types of grain orientation variations occurred due to the activation of extension twin.
This paper aims at investigating the mechanical properties and texture evolution of extruded AZ31 magnesium alloy rods under cyclic torsion. Thus, cyclic torsion tests were performed at different temperatures such as room temperature, 373, 443, 503, and 573K, respectively. Measured mechanical properties of magnesium alloy cyclic torsion revealed that, stress-strain hysteresis loops of cyclic torsions were strictly symmetric which means that the dominant deformation mechanism is sliding. Additionally, due to the thermal influence of cyclic torsion, the peak stresses in stress-strain hysteresis loops were decreased with the increase of number of cycles. The grain orientations were changed due to the activation of prismatic slips. The texture of {11-20} prismatic planes perpendicular to ED in initial rods was transformed into the texture of {10-10} prismatic planes after cyclic torsion. Also, two types of grain orientation variations occurred due to the activation of extension twin.
Chen Guanfang
,
Zhang Jinyong
,
Zhang shuai
,
Fu Yangyang
,
Chen Zheng
,
Meng Qingkun
,
Zhang Ping
,
Shen Chengjin
,
Shen Baolong
2020, 49(1):297-303.
DOI: 10.12442/j.issn.1002-185X.20181118
Abstract:
In this work, we investigate the strain hardening behavior of the metastable β Ti-12Mo-5Zr (wt. %) alloy combined with TWIP/TRIP effects (TRIP for Transformation Induced Plasticity and TWIP for Twinning Induced Plasticity). The evolution of the strain hardening exponent is analyzed by classical Hollomon theory. The three stages of strain-hardening behavior are divided, labeled as Stage ?, Stage ?? and Stage ???, respectively. Stage I corresponds to the transition from the elastic to plastic regimes (ε≈0~0.02). Stage II relates to a continuously increase of the strain-hardening rate and the hardening exponent (ε≈0.02~0.15). Then, the strain-hardening rate decreases and the hardening exponent reaches stable value 0.34 in Stage III (ε≈0.15~0.34). The evolution of microstructure within three stages is observed by employing techniques of optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the experimental results, the governing mechanisms for deformation at different stages and strain-hardening behavior of Ti-12Mo-5Zr alloy are discussed.
In this work, we investigate the strain hardening behavior of the metastable β Ti-12Mo-5Zr (wt. %) alloy combined with TWIP/TRIP effects (TRIP for Transformation Induced Plasticity and TWIP for Twinning Induced Plasticity). The evolution of the strain hardening exponent is analyzed by classical Hollomon theory. The three stages of strain-hardening behavior are divided, labeled as Stage ?, Stage ?? and Stage ???, respectively. Stage I corresponds to the transition from the elastic to plastic regimes (ε≈0~0.02). Stage II relates to a continuously increase of the strain-hardening rate and the hardening exponent (ε≈0.02~0.15). Then, the strain-hardening rate decreases and the hardening exponent reaches stable value 0.34 in Stage III (ε≈0.15~0.34). The evolution of microstructure within three stages is observed by employing techniques of optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the experimental results, the governing mechanisms for deformation at different stages and strain-hardening behavior of Ti-12Mo-5Zr alloy are discussed.
2020, 49(1):304-312.
DOI: 10.12442/j.issn.1002-185X.20181146
Abstract:
Pure magnesium has become a barrier to surgical transplant materials for its rapid corrosion rate. In order to control its degradation rate, this study presents a two-step procedure to prepare composite coating by BTSE(1,2-Bis(triethoxysilyl)ethane) silane treatment and covalent bond grafting crosslinking modification sodium hyaluronate via EDC-NHS. At the same time, the physical and chemical properties of the coating are analyzed by infrared spectrum (FTIR), X ray photoelectron spectroscopy(XPS), atomic force microscope (AFM) and static contact angle method (CA),the corrosion resistance of the coating in simulated body fluid is analyzed by electrochemical behavior. The results of FTIR and XPS show that the composite coating is successfully prepared on the surface of pure magnesium. Other results reveal that the surface of the cross-linked sodium hyaluronate coating is more smooth than that of bare magnesium and silane, also taked on hydrophilicity to improve its biological activity. Compared with the unmodified pure magnesium, the corrosion current density of the composite coating is reduced by two orders of magnitude, the impedance value is increased by three orders of magnitude, demonstrating better corrosion resistance of the composite coating. The results show that the composite coating as surgical transplant material has great prospect in medicine.
Pure magnesium has become a barrier to surgical transplant materials for its rapid corrosion rate. In order to control its degradation rate, this study presents a two-step procedure to prepare composite coating by BTSE(1,2-Bis(triethoxysilyl)ethane) silane treatment and covalent bond grafting crosslinking modification sodium hyaluronate via EDC-NHS. At the same time, the physical and chemical properties of the coating are analyzed by infrared spectrum (FTIR), X ray photoelectron spectroscopy(XPS), atomic force microscope (AFM) and static contact angle method (CA),the corrosion resistance of the coating in simulated body fluid is analyzed by electrochemical behavior. The results of FTIR and XPS show that the composite coating is successfully prepared on the surface of pure magnesium. Other results reveal that the surface of the cross-linked sodium hyaluronate coating is more smooth than that of bare magnesium and silane, also taked on hydrophilicity to improve its biological activity. Compared with the unmodified pure magnesium, the corrosion current density of the composite coating is reduced by two orders of magnitude, the impedance value is increased by three orders of magnitude, demonstrating better corrosion resistance of the composite coating. The results show that the composite coating as surgical transplant material has great prospect in medicine.
2020, 49(1):313-319.
DOI: 10.12442/j.issn.1002-185X.20181248
Abstract:
Three groups of WC-Co-(Ni)-(Cr) cemented carbides with different binder phase compositions were prepared by powder metallurgy using WC, Co, Ni and Cr3C2 powders as raw materials. The corrosion behavior of the three alloys in neutral solution was studied by polarization curve test and immersion experiment. The corrosion mechanism was discussed by means of scanning electron microscopy, energy spectrum analysis, X-ray photoelectron spectroscopy (XPS) and EBSD. The results show that in neutral solution the corrosion of WC-Co and WC-Co-Cr cemented carbides is mainly caused by the selective dissolution of Co and the corrosion products after immersion are mainly composed of Co(OH)2. The corrosion resistance of WC-Co cemented carbide in neutral solution can be improved by the addition of Cr, which may be related to the decrease of the content of hcp-Co in the binder phase by adding Cr. Adding Ni and Cr together can further improve the corrosion resistance of WC-Co cemented carbide in neutral solution. After 480 hours immersion in Na2SO4 solution, the WC-Co-Ni-Cr alloy sample is just corroded slightly.
Three groups of WC-Co-(Ni)-(Cr) cemented carbides with different binder phase compositions were prepared by powder metallurgy using WC, Co, Ni and Cr3C2 powders as raw materials. The corrosion behavior of the three alloys in neutral solution was studied by polarization curve test and immersion experiment. The corrosion mechanism was discussed by means of scanning electron microscopy, energy spectrum analysis, X-ray photoelectron spectroscopy (XPS) and EBSD. The results show that in neutral solution the corrosion of WC-Co and WC-Co-Cr cemented carbides is mainly caused by the selective dissolution of Co and the corrosion products after immersion are mainly composed of Co(OH)2. The corrosion resistance of WC-Co cemented carbide in neutral solution can be improved by the addition of Cr, which may be related to the decrease of the content of hcp-Co in the binder phase by adding Cr. Adding Ni and Cr together can further improve the corrosion resistance of WC-Co cemented carbide in neutral solution. After 480 hours immersion in Na2SO4 solution, the WC-Co-Ni-Cr alloy sample is just corroded slightly.
2020, 49(1):320-324.
DOI: 10.12442/j.issn.1002-185X.20181253
Abstract:
AZ31 magnesium alloy was rolled and annealed after rolling in this work. The anisotropy of magnesium plate in rolling state and annealed state was studied, and the effect of annealing on anisotropy was analyzed. The results showed that rolled magnesium alloys was anisotropic visibly and the difference of texture strength between different orientations of magnesium alloys decreased after annealing. The tensile strength, yield strength and elongation anisotropy index of annealed state magnesium plate were smaller than that of rolling state magnesium, especially in elongation, which displays that annealing can improve the anisotropy of Mg alloys .
AZ31 magnesium alloy was rolled and annealed after rolling in this work. The anisotropy of magnesium plate in rolling state and annealed state was studied, and the effect of annealing on anisotropy was analyzed. The results showed that rolled magnesium alloys was anisotropic visibly and the difference of texture strength between different orientations of magnesium alloys decreased after annealing. The tensile strength, yield strength and elongation anisotropy index of annealed state magnesium plate were smaller than that of rolling state magnesium, especially in elongation, which displays that annealing can improve the anisotropy of Mg alloys .
2020, 49(1):325-330.
DOI: 10.12442/j.issn.1002-185X.20181160
Abstract:
Porous titanium (Ti) has attracted much attention due to its elastic modulus similar to that of human bone tissue and the pore architectures allowing bone ingrow.The pore architectures not only have influence on the effect of bone ingrowth but also determine the mechanical properties of porous Ti. An ideal pore architecture can be constructed by precisely regulating of implicit function parameters of triply periodic minimal surface (TPMS). The Gyroid (G) cell structure was used in this paper. The influences of implicit function parameters of G cell on pore structure characteristics, such as porosity, pore diameter and strut diameter were investigated. The homogeneous pore structures with porosity of about 77% and pore size of 300 (G300) and 500 μm (G500) were designed. Mimicking the radial gradient structure of natural long bone, the graded G pore structure was constructed. Selective laser melting (SLM) technique was ultized to fabricate the porous Ti samples. Digital microscope and scanning electron microscopy (SEM) were used to observe the pore architecture characteristics of the SLM-produced porous Ti. It was found that the measured porosities of SLM-produced Ti samples were lower than the designed values. The measured pore sizes were less than the designed values and the measured strut diameters were larger than the designed values. The compression tests were examined. The results showed that the elastic modulus of porous titanium of G300 and G500 was 2.04 GPa and 3.12 GPa, respectively, and its maximum compressive strength was 63.5 Mpa and 103.5 Mpa, respectively. The maximum compressive strength of porous titanium of gradient pore structure was 6.3 GPa and 186.9 MPa, respectively. These results indicated that the G cell gradient porous Ti could be an ideal alternative candidate for bone defect repairment in load-bearing sites.
Porous titanium (Ti) has attracted much attention due to its elastic modulus similar to that of human bone tissue and the pore architectures allowing bone ingrow.The pore architectures not only have influence on the effect of bone ingrowth but also determine the mechanical properties of porous Ti. An ideal pore architecture can be constructed by precisely regulating of implicit function parameters of triply periodic minimal surface (TPMS). The Gyroid (G) cell structure was used in this paper. The influences of implicit function parameters of G cell on pore structure characteristics, such as porosity, pore diameter and strut diameter were investigated. The homogeneous pore structures with porosity of about 77% and pore size of 300 (G300) and 500 μm (G500) were designed. Mimicking the radial gradient structure of natural long bone, the graded G pore structure was constructed. Selective laser melting (SLM) technique was ultized to fabricate the porous Ti samples. Digital microscope and scanning electron microscopy (SEM) were used to observe the pore architecture characteristics of the SLM-produced porous Ti. It was found that the measured porosities of SLM-produced Ti samples were lower than the designed values. The measured pore sizes were less than the designed values and the measured strut diameters were larger than the designed values. The compression tests were examined. The results showed that the elastic modulus of porous titanium of G300 and G500 was 2.04 GPa and 3.12 GPa, respectively, and its maximum compressive strength was 63.5 Mpa and 103.5 Mpa, respectively. The maximum compressive strength of porous titanium of gradient pore structure was 6.3 GPa and 186.9 MPa, respectively. These results indicated that the G cell gradient porous Ti could be an ideal alternative candidate for bone defect repairment in load-bearing sites.
2020, 49(1):331-336.
DOI: 10.12442/j.issn.1002-185X.20181262
Abstract:
Deformation and fracture behavior of Ti-55531 alloy with lamellar microstructure (LM) and bimodal microstructure (BM) under static loading were analyzed by the in-situ SEM tensile method. The results show that the characteristic parameters of the alpha phase have a strong influence on the deformation, crack initiation and propagation behavior of the alloy under static loading. Dislocation initiated at secondary alpha (αs) interior under pressure, because the thick αs plate is softer than residual beta (βr) lath in LM. Dislocation moves and accumulates at the αs/βr interphase during deformation, which induces that cracks initiate at and propagate along the αs/βr interphase during the process of fracture. However, beta transaction microstructure (βtrans) is greatly harder than equiaxed primary α (αp) in BM, moreover, αpwith large size could support longer slip length. Both of above reasons leads to a large number of multi-direction slips initiate at αp during deformation of BM. The intersection of slip lines in different directions promotes stress concentration at αpinner, and some dislocations accumulate at the αp/βtrans interface to produce stress concentration. These behavior results in the initiation of microcracks within αp and the αp/βtrans interface, and propagation along the weak interface of αp/βtrans, or the aggregation site of αp.
Deformation and fracture behavior of Ti-55531 alloy with lamellar microstructure (LM) and bimodal microstructure (BM) under static loading were analyzed by the in-situ SEM tensile method. The results show that the characteristic parameters of the alpha phase have a strong influence on the deformation, crack initiation and propagation behavior of the alloy under static loading. Dislocation initiated at secondary alpha (αs) interior under pressure, because the thick αs plate is softer than residual beta (βr) lath in LM. Dislocation moves and accumulates at the αs/βr interphase during deformation, which induces that cracks initiate at and propagate along the αs/βr interphase during the process of fracture. However, beta transaction microstructure (βtrans) is greatly harder than equiaxed primary α (αp) in BM, moreover, αpwith large size could support longer slip length. Both of above reasons leads to a large number of multi-direction slips initiate at αp during deformation of BM. The intersection of slip lines in different directions promotes stress concentration at αpinner, and some dislocations accumulate at the αp/βtrans interface to produce stress concentration. These behavior results in the initiation of microcracks within αp and the αp/βtrans interface, and propagation along the weak interface of αp/βtrans, or the aggregation site of αp.
2020, 49(1):337-342.
DOI: 10.12442/j.issn.1002-185X.20181120
Abstract:
In order to solve the problem of forming difficulty of TiAl alloy, Ti-47Al alloy was sintered by Micro-FAST using Ti and Al element powders as raw materials. The effects of temperatures (700~1050 °C) on the microstructures and properties of TiAl alloy were studied, and the migration mechanisms of particles during sintering were investigated. The results show that typical microstructures can’t be formed during sintering at 700°C, and the main phase was TiAl3. When sintering at 800°C and above, the island structure was formed, and the Ti-47Al alloy was mainly composed of TiAl and a small amount of Ti3Al. It has the best comprehensive mechanical properties when sintered at 1050°C. The sintering process was controlled by a variety of diffusion mechanisms. As the holding time increases, evaporation condensation, volume diffusion, grain boundary diffusion and surface diffusion occurred in sequence.
In order to solve the problem of forming difficulty of TiAl alloy, Ti-47Al alloy was sintered by Micro-FAST using Ti and Al element powders as raw materials. The effects of temperatures (700~1050 °C) on the microstructures and properties of TiAl alloy were studied, and the migration mechanisms of particles during sintering were investigated. The results show that typical microstructures can’t be formed during sintering at 700°C, and the main phase was TiAl3. When sintering at 800°C and above, the island structure was formed, and the Ti-47Al alloy was mainly composed of TiAl and a small amount of Ti3Al. It has the best comprehensive mechanical properties when sintered at 1050°C. The sintering process was controlled by a variety of diffusion mechanisms. As the holding time increases, evaporation condensation, volume diffusion, grain boundary diffusion and surface diffusion occurred in sequence.
45 Microstructure Evolution of Ti834 Alloy subjected to Laser Shock processing in Strengthening Layer
2020, 49(1):343-348.
DOI: 10.12442/j.issn.1002-185X.20181138
Abstract:
Laser shock processing (LSP), also known as laser peening, is a novel surface strengthening treatment technology, which is capable of introducing residual compressive stress, improving performance of fatigue strength and micro-hardness. With its preferable reinforcement effect, strong controllability and outstanding adaptability, LSP plays an irreplaceable role in improving the service life of key components. The evolution of microstructure in the plastic deformation layer of Ti834 alloy subjected to LSP impacts were investigated by means of transmission electron microscopy (TEM) observations, and the microstructure evolution model in the surface layer and depth direction was established. The results indicate that numerous dislocations are generated in the plastic deformation layer of Ti834 alloy subjected to LSP, and the plastic deformation becomes more intense and the dislocation density further increases as the number of impacts increases. Typical microstructure features due to decreasing strain rates can be observed along the depth direction, including mechanical twins (MTs), dense density dislocation walls (DDWs), dislocation tangles (DTs), dislocation arrays (DAs) and dislocation lines (DLs).
Laser shock processing (LSP), also known as laser peening, is a novel surface strengthening treatment technology, which is capable of introducing residual compressive stress, improving performance of fatigue strength and micro-hardness. With its preferable reinforcement effect, strong controllability and outstanding adaptability, LSP plays an irreplaceable role in improving the service life of key components. The evolution of microstructure in the plastic deformation layer of Ti834 alloy subjected to LSP impacts were investigated by means of transmission electron microscopy (TEM) observations, and the microstructure evolution model in the surface layer and depth direction was established. The results indicate that numerous dislocations are generated in the plastic deformation layer of Ti834 alloy subjected to LSP, and the plastic deformation becomes more intense and the dislocation density further increases as the number of impacts increases. Typical microstructure features due to decreasing strain rates can be observed along the depth direction, including mechanical twins (MTs), dense density dislocation walls (DDWs), dislocation tangles (DTs), dislocation arrays (DAs) and dislocation lines (DLs).
2020, 49(1):349-454.
DOI: 10.12442/j.issn.1002-185X.20181053
Abstract:
Rhenium trioxide (ReO3) has great application potential in solid-state batteries, electrochromic and liquid crystal devices owing to its relatively simple structure and high conductivity. It is also an important material for the fundamental studies in surface science, analytical chemistry, biophysics etc. However, the complicated phase diagram of rhenium oxides brings critical challenges to the synthesis of single-phased cubic ReO3 materials. In this paper, we synthesize ReO3 bulk by direct sintering of the pressed chips of ReO3 powders under the ambient pressure. With the characterizations of X-ray diffraction (XRD), electric transport and scanning electron microscope (SEM), we optimize the sintering temperature and time, and obtain the ReO3 materials in monophase of the cubic structure, with high crystalline homogeneity and high density. Preliminary growth experiments demonstrate that the obtained ReO3 can be used as the target in pulsed laser deposition technology, promising for future researches on the high-quality ReO3 films.
Rhenium trioxide (ReO3) has great application potential in solid-state batteries, electrochromic and liquid crystal devices owing to its relatively simple structure and high conductivity. It is also an important material for the fundamental studies in surface science, analytical chemistry, biophysics etc. However, the complicated phase diagram of rhenium oxides brings critical challenges to the synthesis of single-phased cubic ReO3 materials. In this paper, we synthesize ReO3 bulk by direct sintering of the pressed chips of ReO3 powders under the ambient pressure. With the characterizations of X-ray diffraction (XRD), electric transport and scanning electron microscope (SEM), we optimize the sintering temperature and time, and obtain the ReO3 materials in monophase of the cubic structure, with high crystalline homogeneity and high density. Preliminary growth experiments demonstrate that the obtained ReO3 can be used as the target in pulsed laser deposition technology, promising for future researches on the high-quality ReO3 films.
2020, 49(1):355-360.
DOI: 10.12442/j.issn.1002-185X.20181070
Abstract:
In order to reduce the manufacturing cost of fastening rings made of NiTiNb wide hysteresis memory alloy, the Influences of annealing on mechanical properties and shape memory effects of laser welding joints were investigated. The welding were annealed at 850 ℃. The results showed that the microstructure of the welding joints was coarse and uneven. The Tensile strength and elongation of the joints were significantly lower than that of the base metal. After annealing, recrystallization leads to more uniform microstructure of welding joints. The tensile strength of base metal and welding joints decreased substantially, but the elongation increased greatly. The elongation of welding joints has increased to 28.57%. After 13% bending deformation at -40 ℃, the shape recovery rate of the annealed welding joints was closed to that of the matrix.
In order to reduce the manufacturing cost of fastening rings made of NiTiNb wide hysteresis memory alloy, the Influences of annealing on mechanical properties and shape memory effects of laser welding joints were investigated. The welding were annealed at 850 ℃. The results showed that the microstructure of the welding joints was coarse and uneven. The Tensile strength and elongation of the joints were significantly lower than that of the base metal. After annealing, recrystallization leads to more uniform microstructure of welding joints. The tensile strength of base metal and welding joints decreased substantially, but the elongation increased greatly. The elongation of welding joints has increased to 28.57%. After 13% bending deformation at -40 ℃, the shape recovery rate of the annealed welding joints was closed to that of the matrix.
2020, 49(1):361-369.
DOI: 10.12442/j.issn.1002-185X.20181272
Abstract:
Ni-14Cr-10P metal powder was prepared by vacuum melting and inert gas atomization, and then Ti powder and polymer paste were added and stirred at high speed to prepare Ni-14Cr-10P-xTi paste active solder. The C/C composites were welded in the vacuum brazing furnace with the prepared active solder paste, and then the welded joint shear strength was tested. The microstructure and mechanical properties of the joints were investigated by SEM, EDS and XRD. The results show that the strength of the welded joint decreases with the increase of welding temperature and the holding time；The addition of Ti accelerates the decrease of welding strength with temperature and holding time. Combined with the microstructure, the reason why the welding strength decreases with the increase of temperature and holding time after the addition of Ti element is analyzed.
Ni-14Cr-10P metal powder was prepared by vacuum melting and inert gas atomization, and then Ti powder and polymer paste were added and stirred at high speed to prepare Ni-14Cr-10P-xTi paste active solder. The C/C composites were welded in the vacuum brazing furnace with the prepared active solder paste, and then the welded joint shear strength was tested. The microstructure and mechanical properties of the joints were investigated by SEM, EDS and XRD. The results show that the strength of the welded joint decreases with the increase of welding temperature and the holding time；The addition of Ti accelerates the decrease of welding strength with temperature and holding time. Combined with the microstructure, the reason why the welding strength decreases with the increase of temperature and holding time after the addition of Ti element is analyzed.
2020, 49(1):370-376.
DOI: 10.12442/j.issn.1002-185X.20181141
Abstract:
In this paper, the progress in study of metastable beta titanium alloys with TWIP/TRIP effect (TRIP: transformation induced plasticity; TWIP: Twin induced plasticity, twin induced plasticity) is reviewed. The alloy-design ideas of TWIP/TRIP titanium alloy are described. The members in TWIP/TRIP titanium alloy family and their mechanical properties developed in recent years are introduced. The deformation products during plastical process and their correspongding formation mechanism are discussed. Finally the possible problems encountered in development of TWIP/TRIP Ti-materials are also presented.
In this paper, the progress in study of metastable beta titanium alloys with TWIP/TRIP effect (TRIP: transformation induced plasticity; TWIP: Twin induced plasticity, twin induced plasticity) is reviewed. The alloy-design ideas of TWIP/TRIP titanium alloy are described. The members in TWIP/TRIP titanium alloy family and their mechanical properties developed in recent years are introduced. The deformation products during plastical process and their correspongding formation mechanism are discussed. Finally the possible problems encountered in development of TWIP/TRIP Ti-materials are also presented.
2020, 49(1):377-384.
DOI: 10.12442/j.issn.1002-185X.20181185
Abstract:
About 10 years of research on perovskite solar cells, it has demonstrated advantages such as higher photoelectric conversion efficiency (notarized PCE of 23.3%), lower cost, simple preparation methods, and has a broad commercial prospects. However, the stability of perovskite solar cells has not been solved, which seriously hinders its further development. This article reviews the development of perovskite solar cells at first. Then, we summarize some important factors that affecting the stability of perovskite solar cells, including water vapor, oxygen, lights, high temperature conditions, electron transport layer (ETL), hole transport layer (HTL) and preparation methods. Meanwhile, we focus on the understanding of the instability mechanism and find some ways to improve the stability of cells. In the end, basing on the current research, we forecasted the development of perovskite solar cells.
About 10 years of research on perovskite solar cells, it has demonstrated advantages such as higher photoelectric conversion efficiency (notarized PCE of 23.3%), lower cost, simple preparation methods, and has a broad commercial prospects. However, the stability of perovskite solar cells has not been solved, which seriously hinders its further development. This article reviews the development of perovskite solar cells at first. Then, we summarize some important factors that affecting the stability of perovskite solar cells, including water vapor, oxygen, lights, high temperature conditions, electron transport layer (ETL), hole transport layer (HTL) and preparation methods. Meanwhile, we focus on the understanding of the instability mechanism and find some ways to improve the stability of cells. In the end, basing on the current research, we forecasted the development of perovskite solar cells.
