Volume 43,Issue 2,2014 Table of Contents
2014, 43(2):264-268.
Abstract:
CrMoN/MoS2 composite coatings were prepared on the surfaces of the CrMoN composite coatings with different Mo contents by means of a low temperature ion sulfurizing process. The structural and mechanical properties of these coatings as a function of Mo content have been studied. SEM analysis shows that the CrMoN coating reveals a dense and compact surface structure, the CrMoN/MoS2 composite coatings display loose grain structures; In the sulfurizing process, a preferential growth does not happen, the sulfide size is inhibited, The products of the reaction between MoNx and S are the main origin of MoS2.Nanoindentation test shows that the hardness and Young’s modulus of CrMoN/MoS2 coatings are higher than that of CrMoN composite coatings.
CrMoN/MoS2 composite coatings were prepared on the surfaces of the CrMoN composite coatings with different Mo contents by means of a low temperature ion sulfurizing process. The structural and mechanical properties of these coatings as a function of Mo content have been studied. SEM analysis shows that the CrMoN coating reveals a dense and compact surface structure, the CrMoN/MoS2 composite coatings display loose grain structures; In the sulfurizing process, a preferential growth does not happen, the sulfide size is inhibited, The products of the reaction between MoNx and S are the main origin of MoS2.Nanoindentation test shows that the hardness and Young’s modulus of CrMoN/MoS2 coatings are higher than that of CrMoN composite coatings.
2014, 43(2):269-273.
Abstract:
La0.7Sr0.3Cr0.5Mn0.5O3-δ (LSCM) ultrafine powder was synthesized using glycine-nitrate process. Three kinds of pore-formers(activated carbon, starch and graphite) with different ratios were mixed with the LSCM powders to prepare porous anode substrates. The porosity of the anode substrate was measured by the Archimedes method, and the maximum porosity was 45%. The morphology and the structure of the anode substrates were characterized by SEM, XRD and EDS. XRD analysis displays that the LSCM substrates are main perovskite phases after sintering. SEM analyses show that the pore distribution of the anode substrate prepared by adding 20 wt% activated carbon is more uniform than those of the substrates prepared by starch and graphite, and no cracks appear. The catalytic experiments results demonstrate that the porous anode substrate prepared by adding 20 wt% activated carbon as the pore-former has the best methane catalytic performance at high temperature, and the corresponding conversion efficiency is 71.88%.
La0.7Sr0.3Cr0.5Mn0.5O3-δ (LSCM) ultrafine powder was synthesized using glycine-nitrate process. Three kinds of pore-formers(activated carbon, starch and graphite) with different ratios were mixed with the LSCM powders to prepare porous anode substrates. The porosity of the anode substrate was measured by the Archimedes method, and the maximum porosity was 45%. The morphology and the structure of the anode substrates were characterized by SEM, XRD and EDS. XRD analysis displays that the LSCM substrates are main perovskite phases after sintering. SEM analyses show that the pore distribution of the anode substrate prepared by adding 20 wt% activated carbon is more uniform than those of the substrates prepared by starch and graphite, and no cracks appear. The catalytic experiments results demonstrate that the porous anode substrate prepared by adding 20 wt% activated carbon as the pore-former has the best methane catalytic performance at high temperature, and the corresponding conversion efficiency is 71.88%.
2014, 43(2):274-277.
Abstract:
The Fe-Cr-Si-P amorphous composite coatings were fabricated on 304L stainless steel by laser cladding. The microstructure, the phase composition, the microhardness, the corrosion and wear resistance of the coatings were analyzed by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), a microhardness tester, an electrochemical measurement system and a friction and wear tester. The results show that the cladding coating mainly contains plum-like dendrite crystals in the surface, an amorphous in center region and a dendrite crystals in binding zone. A good metallurgical bond is obtained between the coating and substrate. Except amorphous phase, the cladding coating contains a small amount of Fe3P and Fe2Si phases. The coating has a good performance. The microhardness HV0.2 is about 8000 MPa; the Ecorr and icorr are –449.3 mV and 4.34 μA/cm2, respectively; the frictions coefficient at the load of 100 N is 0.076.
The Fe-Cr-Si-P amorphous composite coatings were fabricated on 304L stainless steel by laser cladding. The microstructure, the phase composition, the microhardness, the corrosion and wear resistance of the coatings were analyzed by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), a microhardness tester, an electrochemical measurement system and a friction and wear tester. The results show that the cladding coating mainly contains plum-like dendrite crystals in the surface, an amorphous in center region and a dendrite crystals in binding zone. A good metallurgical bond is obtained between the coating and substrate. Except amorphous phase, the cladding coating contains a small amount of Fe3P and Fe2Si phases. The coating has a good performance. The microhardness HV0.2 is about 8000 MPa; the Ecorr and icorr are –449.3 mV and 4.34 μA/cm2, respectively; the frictions coefficient at the load of 100 N is 0.076.
2014, 43(2):291-295.
Abstract:
A low modulus near b type titanium alloy (Ti-25Nb-3Zr-2Sn-3Mo, or TLM alloy) was subjected to hydrothermal treatments with a urea solution at different temperatures followed by heat treatment. The surface structure, the chemical composition, adhesion and hydrophilicity of the treated TLM alloy were investigated by SEM, XRD, XPS, Rockwell-C indentation test and contact angle measurement. The results show that nanosheet films of ammonium titanate can be formed at 105 and 120 °C, while the nanoparticle film of anatase TiO2 containing Nb2O5 is formed at 150 °C on the alloy surface. The subsequent annealing heat treatment at 400 °C can decompose the ammonium salts and crystallize titania. The obtained oxide films have a good adhesion. The duplex treatment has enhanced the hydrophilicity of the TLM alloy, and it would be good for its biocompatibility.
A low modulus near b type titanium alloy (Ti-25Nb-3Zr-2Sn-3Mo, or TLM alloy) was subjected to hydrothermal treatments with a urea solution at different temperatures followed by heat treatment. The surface structure, the chemical composition, adhesion and hydrophilicity of the treated TLM alloy were investigated by SEM, XRD, XPS, Rockwell-C indentation test and contact angle measurement. The results show that nanosheet films of ammonium titanate can be formed at 105 and 120 °C, while the nanoparticle film of anatase TiO2 containing Nb2O5 is formed at 150 °C on the alloy surface. The subsequent annealing heat treatment at 400 °C can decompose the ammonium salts and crystallize titania. The obtained oxide films have a good adhesion. The duplex treatment has enhanced the hydrophilicity of the TLM alloy, and it would be good for its biocompatibility.
2014, 43(2):296-300.
Abstract:
For isothermal local loading process by means of partitioned die, the partition at a rib is generally adopted in order to reduce the disadvantageous influence of loading area on unloaded area. In the local loading process, some metal (flow-into metal) in loading area flow into unloaded area due to the local loading characteristic. The distribution of the metal flowing into unloaded area plays an important role in analyzing the forming process, controlling the metal flow, and improving the forming quality. The distribution of flow-into metal coming from loading area is mainly determined by the shape of the unloaded area and the geometric parameters near the die partitioning boundary. If the unloaded area is a formed area then some of the flow-into metal will fill the cavity of partitioning rib. A predicted model for the ratio of flow-into metal distributed to cavity of partitioning rib has been established by using partial least squares regression. The numerical simulation result indicates that the analysis on distribution of flow-into metal and the predicted model are reasonable.
For isothermal local loading process by means of partitioned die, the partition at a rib is generally adopted in order to reduce the disadvantageous influence of loading area on unloaded area. In the local loading process, some metal (flow-into metal) in loading area flow into unloaded area due to the local loading characteristic. The distribution of the metal flowing into unloaded area plays an important role in analyzing the forming process, controlling the metal flow, and improving the forming quality. The distribution of flow-into metal coming from loading area is mainly determined by the shape of the unloaded area and the geometric parameters near the die partitioning boundary. If the unloaded area is a formed area then some of the flow-into metal will fill the cavity of partitioning rib. A predicted model for the ratio of flow-into metal distributed to cavity of partitioning rib has been established by using partial least squares regression. The numerical simulation result indicates that the analysis on distribution of flow-into metal and the predicted model are reasonable.
2014, 43(2):301-305.
Abstract:
In order to obtain the diagrams of stability relations (namely, predominance area phase diagram, PAPD) for carbothermal reduction and nitridation (CRN) of zircon, the thermodynamic calculation and the analysis on the Zr-Si-C-N-O system were carried on by the method of , and PAPD of the Zr-Si-C-N-O system was constructed. The CRN of zircon may lead to the formation of different oxide-nitride composites such as ZrO2-Si2N2O, ZrN-Si2N2O, and ZrN-Si3N4 by controlling reaction conditions of carbon proportion, temperature, and partial pressures of CO and N2. Zircon powder (45 μm), activated carbon and N2 (99.999%) were used as the starting materials, the effect of carbon proportion on the mass loss and the product phase composition after CRN of zircon was investigated. Carbon proportion affects the yielded reaction products obviously; and the higher the carbon proportion, the lower the starting temperature for the CRN to occur.
In order to obtain the diagrams of stability relations (namely, predominance area phase diagram, PAPD) for carbothermal reduction and nitridation (CRN) of zircon, the thermodynamic calculation and the analysis on the Zr-Si-C-N-O system were carried on by the method of , and PAPD of the Zr-Si-C-N-O system was constructed. The CRN of zircon may lead to the formation of different oxide-nitride composites such as ZrO2-Si2N2O, ZrN-Si2N2O, and ZrN-Si3N4 by controlling reaction conditions of carbon proportion, temperature, and partial pressures of CO and N2. Zircon powder (45 μm), activated carbon and N2 (99.999%) were used as the starting materials, the effect of carbon proportion on the mass loss and the product phase composition after CRN of zircon was investigated. Carbon proportion affects the yielded reaction products obviously; and the higher the carbon proportion, the lower the starting temperature for the CRN to occur.
2014, 43(2):306-310.
Abstract:
The hydrogenated commercially pure titanium and Ti-6AL-4V alloy with 0.11wt%H were diffusion-bonded in the temperature range from 800 to 860 °C. The interface and elements diffusion were observed by OM, SEM and EPMA. The results show that hydrogen significantly improves the rate of diffusion bonding (bonding rate is up to 98% under the condition of 0.11 wt%H at 840 °C). An equiaxed microstructure is maintained due to the addition of 0.11 wt%H after bonding while the higher amount of hydrogen (0.32 wt%~0.48 wt%H) results in a coarse widmanstatten structure. The improved performance of the diffusion bonding induced by hydrogen is mainly attributed to the weak-bond effect and the increase of diffusion coefficient of the elements. The addition of 0.11 wt%H brings one order increase of magnitude to the diffusion coefficient of Al and V element, as well as 40 °C lower diffusion bonding temperature compared with non-hydrogen Ti-6Al-4V alloy.
The hydrogenated commercially pure titanium and Ti-6AL-4V alloy with 0.11wt%H were diffusion-bonded in the temperature range from 800 to 860 °C. The interface and elements diffusion were observed by OM, SEM and EPMA. The results show that hydrogen significantly improves the rate of diffusion bonding (bonding rate is up to 98% under the condition of 0.11 wt%H at 840 °C). An equiaxed microstructure is maintained due to the addition of 0.11 wt%H after bonding while the higher amount of hydrogen (0.32 wt%~0.48 wt%H) results in a coarse widmanstatten structure. The improved performance of the diffusion bonding induced by hydrogen is mainly attributed to the weak-bond effect and the increase of diffusion coefficient of the elements. The addition of 0.11 wt%H brings one order increase of magnitude to the diffusion coefficient of Al and V element, as well as 40 °C lower diffusion bonding temperature compared with non-hydrogen Ti-6Al-4V alloy.
2014, 43(2):311-315.
Abstract:
The composite piezomagnetic film was prepared by using Fe73.5CulNb1.5Si13.5B9Mo1.5 amorphous powder with particles size of 40 μm as dispersing agent and silicon rubber as the matrix. Meanwhile, the Fe73.5CulNb3Si13.5B9 amorphous ribbon was selected as piezoelectric layer. The testing frequency was ranged from 10 kHz to 1 MHz, and the pressure stress was from 0 to 0.14 MPa. The tiny stress impedance (TST) effects of the two types of layer structures were compared in the experiment, the two types included piezomagnetic/piezoelectric/piezomagnetic (pm/pe/pm) layer and piezoelectric/piezomagnetic/piezoelectric (pe/pm/pe) layer. It is found that both of the layer structures have magnetoelectricity coupling effects. The magnetoelectricity coupling effect enhances with the increase of pressure stress before 0.02 MPa, and afterward the magnetoelectricity coupling effect comes to a maximum value, which has little contribution to TSI. Since two types of layer structure are both of varying magnetoelectricity coupling effect, pm/pe/pm is piezomagnetic based and pe/pm/pe is piezoelectric based.
The composite piezomagnetic film was prepared by using Fe73.5CulNb1.5Si13.5B9Mo1.5 amorphous powder with particles size of 40 μm as dispersing agent and silicon rubber as the matrix. Meanwhile, the Fe73.5CulNb3Si13.5B9 amorphous ribbon was selected as piezoelectric layer. The testing frequency was ranged from 10 kHz to 1 MHz, and the pressure stress was from 0 to 0.14 MPa. The tiny stress impedance (TST) effects of the two types of layer structures were compared in the experiment, the two types included piezomagnetic/piezoelectric/piezomagnetic (pm/pe/pm) layer and piezoelectric/piezomagnetic/piezoelectric (pe/pm/pe) layer. It is found that both of the layer structures have magnetoelectricity coupling effects. The magnetoelectricity coupling effect enhances with the increase of pressure stress before 0.02 MPa, and afterward the magnetoelectricity coupling effect comes to a maximum value, which has little contribution to TSI. Since two types of layer structure are both of varying magnetoelectricity coupling effect, pm/pe/pm is piezomagnetic based and pe/pm/pe is piezoelectric based.
2014, 43(2):316-321.
Abstract:
In order to select a good cost-performance ratio?magnesium alloy as anode material, the electrochemical properties of AZ31B magnesium alloy under different processing conditions were investigated by electrochemical workstation, optical?microscope (OM), scanning electron microscopy (SEM) and energy dispersed spectroscopy (EDS). Extruded, rolled, cast-rolled and as-cast AZ31 magnesium alloys were prepared as the anode materials. The results show that under different processing conditions, the extruded alloy is the best cost-performance ratio anode material among the four alloys. It possesses?the most?negative equilibrium potential, the lowest?corrosion current?density and the smallest free corrosion rate indicating the highest electrochemical?activity due to the uniform fine grains and the second phase. Its corrosiun products are loose, dispersing uniformly on the extruded anode surface, prone to falling off which decrease the polarization?and increase the utilization of the anode. The electrochemical activity and the corrosion resistance of the rolled and the cast-rolled alloys are relatively low, compared with the extrude samples. Due to the coarse grains, as-cast defects and coarse second phase distributed along the grain boundaries, the as-cast alloy has unstable discharge curve and positive discharge potential. The corrosions of AZ31 magnesium alloy under different conditions are almost pitting corrosion.
In order to select a good cost-performance ratio?magnesium alloy as anode material, the electrochemical properties of AZ31B magnesium alloy under different processing conditions were investigated by electrochemical workstation, optical?microscope (OM), scanning electron microscopy (SEM) and energy dispersed spectroscopy (EDS). Extruded, rolled, cast-rolled and as-cast AZ31 magnesium alloys were prepared as the anode materials. The results show that under different processing conditions, the extruded alloy is the best cost-performance ratio anode material among the four alloys. It possesses?the most?negative equilibrium potential, the lowest?corrosion current?density and the smallest free corrosion rate indicating the highest electrochemical?activity due to the uniform fine grains and the second phase. Its corrosiun products are loose, dispersing uniformly on the extruded anode surface, prone to falling off which decrease the polarization?and increase the utilization of the anode. The electrochemical activity and the corrosion resistance of the rolled and the cast-rolled alloys are relatively low, compared with the extrude samples. Due to the coarse grains, as-cast defects and coarse second phase distributed along the grain boundaries, the as-cast alloy has unstable discharge curve and positive discharge potential. The corrosions of AZ31 magnesium alloy under different conditions are almost pitting corrosion.
10 Numerical Stimulation and Experimental Validation of Stress in C/SiC Riveted Joints under Shear Load
2014, 43(2):327-330.
Abstract:
The stress concentration and fracture form of C/SiC riveted joints under shear load were investigated by using a FEM model and its accuracy was validated by experiments. The calculation results show that the stress concentration in C/SiC riveted joints is reasonable under shear load and the riveted joints in given size will be damaged in shear fracture form. All riveted joints are damaged in shear fracture form in the experimental validation. All of the starting fracture points occur at the inner of junction plates, which demonstrates that the established model for analysis of fracture form of C/SiC rivet is correct.
The stress concentration and fracture form of C/SiC riveted joints under shear load were investigated by using a FEM model and its accuracy was validated by experiments. The calculation results show that the stress concentration in C/SiC riveted joints is reasonable under shear load and the riveted joints in given size will be damaged in shear fracture form. All riveted joints are damaged in shear fracture form in the experimental validation. All of the starting fracture points occur at the inner of junction plates, which demonstrates that the established model for analysis of fracture form of C/SiC rivet is correct.
2014, 43(2):331-335.
Abstract:
Tensile tests, compression tests and three point bending tests have been conducted on longitudinal and transverse specimens of as-cast full lamellar Ti-46Al-0.5W-0.5Si alloy with columnar grains at room temperature. The fracture surfaces of tensile samples have been investigated to analysis the reason of different mechanical properties. Results show that the alloy exhibits mechanical property anisotropy, the tensile and bending properties of transverse specimens are much better than those of longitudinal specimens, but the compression yield strength is lower. The mechanical properties of the alloy strongly depend on the angle between the loading axis and the lamellar interface, do not depend on the growth direction of columnar grains. When the tensile stress of the transverse specimen is parallel to the lamellar interface, the interface of α2/γ lamellar can effectively block the crack growth, which plays an important role on improving their tensile properties. When the compression stress of the longitudinal specimens is perpendicular to the lamellar interface, the microcracks between lamellae can close up, without any more growing, resulting in obtaining higher compression yield strength.
Tensile tests, compression tests and three point bending tests have been conducted on longitudinal and transverse specimens of as-cast full lamellar Ti-46Al-0.5W-0.5Si alloy with columnar grains at room temperature. The fracture surfaces of tensile samples have been investigated to analysis the reason of different mechanical properties. Results show that the alloy exhibits mechanical property anisotropy, the tensile and bending properties of transverse specimens are much better than those of longitudinal specimens, but the compression yield strength is lower. The mechanical properties of the alloy strongly depend on the angle between the loading axis and the lamellar interface, do not depend on the growth direction of columnar grains. When the tensile stress of the transverse specimen is parallel to the lamellar interface, the interface of α2/γ lamellar can effectively block the crack growth, which plays an important role on improving their tensile properties. When the compression stress of the longitudinal specimens is perpendicular to the lamellar interface, the microcracks between lamellae can close up, without any more growing, resulting in obtaining higher compression yield strength.
2014, 43(2):336-340.
Abstract:
The microstructure evolution and the recrystallization of undercooled Ni-1at%Fe alloy were investigated by employing the glass fluxing technique in combination with cyclical superheating. The experiments of rapid quenching and naturally cooling on Ni-1at%Fe alloy after recalescence were conducted. It is proved that the fine structure is the product of recrystallization under high undercooling. The evolution of microstructure was systematically investigated by applying the calculation of dimensionless superheating. Two grain refinements were detected. The first grain refinement occurs owing to the dendrite break-up or ripening induced by remelting. The second grain refinement occurs due to the recrystallization induced by stress cumulation.
The microstructure evolution and the recrystallization of undercooled Ni-1at%Fe alloy were investigated by employing the glass fluxing technique in combination with cyclical superheating. The experiments of rapid quenching and naturally cooling on Ni-1at%Fe alloy after recalescence were conducted. It is proved that the fine structure is the product of recrystallization under high undercooling. The evolution of microstructure was systematically investigated by applying the calculation of dimensionless superheating. Two grain refinements were detected. The first grain refinement occurs owing to the dendrite break-up or ripening induced by remelting. The second grain refinement occurs due to the recrystallization induced by stress cumulation.
2014, 43(2):346-350.
Abstract:
The reduction stage in the process of using NiO-YSZ of solid oxide fuel half-cell at 800 °C has been experimentally investigated. The analysis of the microstructure and the reduction degree of anode support materials have been addressed. As well as the residual stress variation of electrolyte film after different reduction times has been studied from which the full curve variation of the reduction degree with different reduction time has been obtained. It can be seen from energy spectrum that the mass fraction of oxygen decreases with the increase of reduction time and the minimum value is 13.24%, while the mass fraction of nickel increases with the increase of reduction time and the maximum value is 49.56%. It can be indicated from the X-ray stress analysis that the residual stress of the electrolyte film reduces gradually with the increase of reduction time. The value of the residual stress in the film reaches 394.35 MPa when the reduction time reaches 12 h, which accounts for 48.54% of the residual stress before reduction. It is revealed from the scanning micrographs that the porosity increases in the anode support materials after reduction.
The reduction stage in the process of using NiO-YSZ of solid oxide fuel half-cell at 800 °C has been experimentally investigated. The analysis of the microstructure and the reduction degree of anode support materials have been addressed. As well as the residual stress variation of electrolyte film after different reduction times has been studied from which the full curve variation of the reduction degree with different reduction time has been obtained. It can be seen from energy spectrum that the mass fraction of oxygen decreases with the increase of reduction time and the minimum value is 13.24%, while the mass fraction of nickel increases with the increase of reduction time and the maximum value is 49.56%. It can be indicated from the X-ray stress analysis that the residual stress of the electrolyte film reduces gradually with the increase of reduction time. The value of the residual stress in the film reaches 394.35 MPa when the reduction time reaches 12 h, which accounts for 48.54% of the residual stress before reduction. It is revealed from the scanning micrographs that the porosity increases in the anode support materials after reduction.
2014, 43(2):351-355.
Abstract:
Titanium and aluminum were deposited on the SiC fiber by magnetron sputtering according to a certain power ratio. The precursor wires of SiC fibers with Ti-Al matrix were fabricated and then close-packed in the canning. The specimens of SiC fiber reinforced titanium-aluminium intermetallic compound matrix composites were prepared by hot isostatic pressing. Microstructure was observed by SEM, the effects of hot isostatic pressing and vacuum heat treatment on the interfacial layer were analyzed. The influences of magnetron sputtering power on the Ti/Al atomic ratio and variation of phase composition during titanium aluminum in-situ reaction were researched using X-ray diffraction and energy spectrum analysis. Kinetic analysis of Ti-Al reaction was conducted through differential scanning calorimetry. The results show that Ti/Al atomic ratio is directly affected by the sputtering power of Ti and Al targets. When the power of TC4 and Al targets is 13 and 4.5 kW/m2, respectively, the Al content is 27at%; when the power of TC4 and Al targets is 13 and 8.3 kW/m2, respectively, the Al content is 49at%. In addition, studies on kinetics show that Al3Ti is the priority generation phase of Ti-Al in-situ reaction. TiAl, Al2Ti and Ti3Al will be gradually formed with the diffusion of Al. However, after full diffusing of Al, the final stable reaction product depends on Ti/Al atomic ratio. When the Ti/Al atomic ratio is 1:1, TiAl can be obtained, and TiAl and Ti3Al can coexist in the region with the different Ti/Al atomic ratios.
Titanium and aluminum were deposited on the SiC fiber by magnetron sputtering according to a certain power ratio. The precursor wires of SiC fibers with Ti-Al matrix were fabricated and then close-packed in the canning. The specimens of SiC fiber reinforced titanium-aluminium intermetallic compound matrix composites were prepared by hot isostatic pressing. Microstructure was observed by SEM, the effects of hot isostatic pressing and vacuum heat treatment on the interfacial layer were analyzed. The influences of magnetron sputtering power on the Ti/Al atomic ratio and variation of phase composition during titanium aluminum in-situ reaction were researched using X-ray diffraction and energy spectrum analysis. Kinetic analysis of Ti-Al reaction was conducted through differential scanning calorimetry. The results show that Ti/Al atomic ratio is directly affected by the sputtering power of Ti and Al targets. When the power of TC4 and Al targets is 13 and 4.5 kW/m2, respectively, the Al content is 27at%; when the power of TC4 and Al targets is 13 and 8.3 kW/m2, respectively, the Al content is 49at%. In addition, studies on kinetics show that Al3Ti is the priority generation phase of Ti-Al in-situ reaction. TiAl, Al2Ti and Ti3Al will be gradually formed with the diffusion of Al. However, after full diffusing of Al, the final stable reaction product depends on Ti/Al atomic ratio. When the Ti/Al atomic ratio is 1:1, TiAl can be obtained, and TiAl and Ti3Al can coexist in the region with the different Ti/Al atomic ratios.
2014, 43(2):356-360.
Abstract:
Graphene supported nickel catalysts (Ni/Graphene) were synthesized by physical method and chemical method, respectively. The as prepared Ni/Graphene was further mixed with Mg by ball milling pretreatment or ultrasonic dispersion. Then the well mixed powders were used to prepare Mg-Ni/Graphene composites by the combined process of hydriding combustion synthesis and mechanical milling (HCS+MM). The phase compositions, surface morphologies and hydriding/dehydriding properties of the samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas reaction controller (GRC). Results show that the Mg-Ni/Graphene composite which mixed Ni/Graphene synthesized by chemical method and Mg through ball milling pretreatment exhibits the best hydriding/dehydriding properties. It has the lowest onset hydrogen desorption temperature and faster dehydrogenation rate. About 6.21 % hydrogen can be absorbed within 100 s at 373 K, and 6.05 % hydrogen can be desorbed within 1800 s at 553 K. Ball milling pretreatment makes Ni/Grapheme and Mg contact homogeneous, thus the excellent thermal?and?electrical conductivity of Grapheme and the catalytic effect of Ni are enhanced. In addition, nano-crystalline Ni with smaller grain size synthesized by chemical method is helpful to the formation of nanosized Mg2NiH4 grains, leading to the improvement in hydrogen storage properties of the composite.
Graphene supported nickel catalysts (Ni/Graphene) were synthesized by physical method and chemical method, respectively. The as prepared Ni/Graphene was further mixed with Mg by ball milling pretreatment or ultrasonic dispersion. Then the well mixed powders were used to prepare Mg-Ni/Graphene composites by the combined process of hydriding combustion synthesis and mechanical milling (HCS+MM). The phase compositions, surface morphologies and hydriding/dehydriding properties of the samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas reaction controller (GRC). Results show that the Mg-Ni/Graphene composite which mixed Ni/Graphene synthesized by chemical method and Mg through ball milling pretreatment exhibits the best hydriding/dehydriding properties. It has the lowest onset hydrogen desorption temperature and faster dehydrogenation rate. About 6.21 % hydrogen can be absorbed within 100 s at 373 K, and 6.05 % hydrogen can be desorbed within 1800 s at 553 K. Ball milling pretreatment makes Ni/Grapheme and Mg contact homogeneous, thus the excellent thermal?and?electrical conductivity of Grapheme and the catalytic effect of Ni are enhanced. In addition, nano-crystalline Ni with smaller grain size synthesized by chemical method is helpful to the formation of nanosized Mg2NiH4 grains, leading to the improvement in hydrogen storage properties of the composite.
2014, 43(2):361-363.
Abstract:
The WC coating was produced on the surface of BT20 titanium alloy in Ar atmosphere by electro-spark deposition technique using WC as electrode. The microstructures and the phase compositions of WC coatings were characterized by SEM，EDS and XRD. The microhardness distribution of the deposition coating was studied by microhardness tester. The results show that the coating consists of TiC, WC, W and W2C phases. TiC is a new phase formed by the reaction between the electrode material and the substrate which is the main phase of the deposited layer. The excellent metallurgical bonding between the coating and the substrate is obtained. The coating surface displays a "splash" shape. The nanometer crystallite stacking structure and a small amount of dendritic structure can be observed in the cross section morphology which reflects the electric spark deposition process for rapid heating and the cooling mechanism. The maximum microhardness of the coating is three times of that of the substrate.
The WC coating was produced on the surface of BT20 titanium alloy in Ar atmosphere by electro-spark deposition technique using WC as electrode. The microstructures and the phase compositions of WC coatings were characterized by SEM，EDS and XRD. The microhardness distribution of the deposition coating was studied by microhardness tester. The results show that the coating consists of TiC, WC, W and W2C phases. TiC is a new phase formed by the reaction between the electrode material and the substrate which is the main phase of the deposited layer. The excellent metallurgical bonding between the coating and the substrate is obtained. The coating surface displays a "splash" shape. The nanometer crystallite stacking structure and a small amount of dendritic structure can be observed in the cross section morphology which reflects the electric spark deposition process for rapid heating and the cooling mechanism. The maximum microhardness of the coating is three times of that of the substrate.
2014, 43(2):364-368.
Abstract:
Novel calcium ferrites with magnetoplumbite structure were prepared by the ceramic technology. The structure, the morphology and the magnetic properties of the samples were investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating-sample magnetometer (VSM) and B-H hysteresis curve measurements. The experimental results show that the magnetic properties of calcium ferrites with Ca2+-La3+-Co2+ substitution can be significantly improved. The remanence, the magnetic induction coercivity, the intrinsic coercivity and the maximum magnetic energy of calcium ferrites have a significant improvement compared with that of strontium ferrites substituted by La3+-Co2+. In addition, the high residual flux density of the magnet can be still kept even the sintered magnet is thin and small.
Novel calcium ferrites with magnetoplumbite structure were prepared by the ceramic technology. The structure, the morphology and the magnetic properties of the samples were investigated systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating-sample magnetometer (VSM) and B-H hysteresis curve measurements. The experimental results show that the magnetic properties of calcium ferrites with Ca2+-La3+-Co2+ substitution can be significantly improved. The remanence, the magnetic induction coercivity, the intrinsic coercivity and the maximum magnetic energy of calcium ferrites have a significant improvement compared with that of strontium ferrites substituted by La3+-Co2+. In addition, the high residual flux density of the magnet can be still kept even the sintered magnet is thin and small.
2014, 43(2):369-374.
Abstract:
In order to study the size effect of melting of silver nanoparticles, the melting process of silver nanoparticles of different sizes were simulated by molecular dynamics in this paper. Simulation results show that the system potential energy has an obvious mutation within a certain temperature range when solid state transforms into liquid state, which is similar to amorphous body. And, the melting temperature of nanoparticles is significantly lower than that of the bulk materials and the melting point decreases with the reduction in the size of nanoparticles. The dominant mechanism and the relationship between melting point and nanoparticle size were also analyzed.
In order to study the size effect of melting of silver nanoparticles, the melting process of silver nanoparticles of different sizes were simulated by molecular dynamics in this paper. Simulation results show that the system potential energy has an obvious mutation within a certain temperature range when solid state transforms into liquid state, which is similar to amorphous body. And, the melting temperature of nanoparticles is significantly lower than that of the bulk materials and the melting point decreases with the reduction in the size of nanoparticles. The dominant mechanism and the relationship between melting point and nanoparticle size were also analyzed.
2014, 43(2):375-380.
Abstract:
The isothermal compression tests for air-cooled titanium alloy TC11 were carried out in the temperature range of 750~1100 ℃ and strain rate range of 0.001~10.0 s-1, and the high temperature flow behavior, the flow instability and the deformation mechanism were investigated inphase field andphase field for this alloy by using flow stress-strain curve and processing map. The results show that in excess of peak stress the flow stress decreases continuously with increasing of strain at low temperatures inphase, but first decreases and then reaches an approximately constant value at moderate and high temperatures inphase; the flow stress decreases slightly and then tends gradually toward a constant value with increasing of stain inphase field. In the processing maps of this alloy, the domains with high value of in phase are about (750~900 ℃, 0.001~0.006 s-1) and (900~1000 ℃, 0.001~0.02 s-1). In these two domains, the spheroidization oflamellae occurs, and the combination of spheroidization of lamellae andphase transformation happens, respectively. The domain with high value of inphase field is about (1000~1100 ℃, 0.003~0.3 s-1), where dynamic recrystallization undergoes. The above domains are desirably to be selected for hot working. The domains of flow instability are (750~875 ℃, 0.006~10.0 s-1), (875~975 ℃, 0.03~10.0 s-1) and (975~1100 ℃, 1.0~10.0 s-1), and the manifestations of flow instability are macroscopic shear, adiabatic shear band and non-uniform deformation of grains.
The isothermal compression tests for air-cooled titanium alloy TC11 were carried out in the temperature range of 750~1100 ℃ and strain rate range of 0.001~10.0 s-1, and the high temperature flow behavior, the flow instability and the deformation mechanism were investigated inphase field andphase field for this alloy by using flow stress-strain curve and processing map. The results show that in excess of peak stress the flow stress decreases continuously with increasing of strain at low temperatures inphase, but first decreases and then reaches an approximately constant value at moderate and high temperatures inphase; the flow stress decreases slightly and then tends gradually toward a constant value with increasing of stain inphase field. In the processing maps of this alloy, the domains with high value of in phase are about (750~900 ℃, 0.001~0.006 s-1) and (900~1000 ℃, 0.001~0.02 s-1). In these two domains, the spheroidization oflamellae occurs, and the combination of spheroidization of lamellae andphase transformation happens, respectively. The domain with high value of inphase field is about (1000~1100 ℃, 0.003~0.3 s-1), where dynamic recrystallization undergoes. The above domains are desirably to be selected for hot working. The domains of flow instability are (750~875 ℃, 0.006~10.0 s-1), (875~975 ℃, 0.03~10.0 s-1) and (975~1100 ℃, 1.0~10.0 s-1), and the manifestations of flow instability are macroscopic shear, adiabatic shear band and non-uniform deformation of grains.
2014, 43(2):391-394.
Abstract:
The Bi3+-doped GdVO4:Tm3+ Blue Phosphors were synthesized by co-precipitation method. The crystal structure, the morphology and the luminescence properties of the (Gd, Bi)VO4:Tm3+ Blue Phosphors were investigated by X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Fluorescence Spectrophotometer (PL). The results show that the crystal structure of the prepared Gd0.99-xVO4:Tm0.013+, Bix3+ phosphors is a tetragonal zircon type structure as same as GdVO4:Tm3+ phosphor. Nevertheless, the crystal structure of GdVO4:Tm3+ is not changed with Bi3+-doping. The SEM image reveals Gd0.99-xVO4:Tm0.013+, Bix3+ phosphor powders are composed of relatively uniform particles and its particle average size is about 70 nm. The photoluminescence intensity of （Gd, Bi）VO4:Tm3+ phosphor is enhanced by Bi3+ doping. When the concentration rate of Bi3+/Tm3+=0.5, the maximum photoluminescence intensity can be achieved at wavelengths 417 nm and the bright blue luminescence is displayed.
The Bi3+-doped GdVO4:Tm3+ Blue Phosphors were synthesized by co-precipitation method. The crystal structure, the morphology and the luminescence properties of the (Gd, Bi)VO4:Tm3+ Blue Phosphors were investigated by X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Fluorescence Spectrophotometer (PL). The results show that the crystal structure of the prepared Gd0.99-xVO4:Tm0.013+, Bix3+ phosphors is a tetragonal zircon type structure as same as GdVO4:Tm3+ phosphor. Nevertheless, the crystal structure of GdVO4:Tm3+ is not changed with Bi3+-doping. The SEM image reveals Gd0.99-xVO4:Tm0.013+, Bix3+ phosphor powders are composed of relatively uniform particles and its particle average size is about 70 nm. The photoluminescence intensity of （Gd, Bi）VO4:Tm3+ phosphor is enhanced by Bi3+ doping. When the concentration rate of Bi3+/Tm3+=0.5, the maximum photoluminescence intensity can be achieved at wavelengths 417 nm and the bright blue luminescence is displayed.
2014, 43(2):395-398.
Abstract:
Mg(NH2)2 was synthesized first by high energy milling MgH2 powder in a 99.995% NH3 atmosphere and then via crystallization heat treating at 300 ℃, and the hydrogen storage properties of Mg(NH2)2+2.2LiH (molar ratio) were investigated in the temperature range of 150~240 ℃. It is found that mechanical milling of Mg(NH2)2 and LiH with molar ratio 1:2.2 followed by heat treatment under static hydrogen pressure and dehydrogenating at 208.5 ℃ yields the desired reversible hydrogen storage phase:Li2Mg(NH)2. Desorption kinetics reveal that the reversible hydrogen capacity for the system can reach 4.5wt% in the temperature range of 200~240 ℃.The system starts to dehydrogenate at 150 ℃ and the Arrhenius activation energy Ea of desorption reaction can be determined to be 51.7 kJ/mol H2 based on the data of kinetics. Additionally, the dehydrogenating reaction enthalpy (△H) and entropy (△S) are calculated to be 42.8 kJ/mol H2 and 149.2 J·K-1/mol H2, respectively, by P-C-T measurements.
Mg(NH2)2 was synthesized first by high energy milling MgH2 powder in a 99.995% NH3 atmosphere and then via crystallization heat treating at 300 ℃, and the hydrogen storage properties of Mg(NH2)2+2.2LiH (molar ratio) were investigated in the temperature range of 150~240 ℃. It is found that mechanical milling of Mg(NH2)2 and LiH with molar ratio 1:2.2 followed by heat treatment under static hydrogen pressure and dehydrogenating at 208.5 ℃ yields the desired reversible hydrogen storage phase:Li2Mg(NH)2. Desorption kinetics reveal that the reversible hydrogen capacity for the system can reach 4.5wt% in the temperature range of 200~240 ℃.The system starts to dehydrogenate at 150 ℃ and the Arrhenius activation energy Ea of desorption reaction can be determined to be 51.7 kJ/mol H2 based on the data of kinetics. Additionally, the dehydrogenating reaction enthalpy (△H) and entropy (△S) are calculated to be 42.8 kJ/mol H2 and 149.2 J·K-1/mol H2, respectively, by P-C-T measurements.
2014, 43(2):408-412.
Abstract:
The thermal deformation tests of Cu-0.90Cr-0.18Zr alloy were conducted at the deformation temperature of 500~800 °C and the strain rate of 0.01~1 s-1 on the Gleeble-1500 thermal-mechanical simulator. The flow stress, the constitutive equation and the critical conditions of dynamic recrystallization were studied. The results show that the flow stress decreases with the increasing of deformation temperature or with the decreasing of strain rate, The constitutive equation was established with the activation energy 584.87 kJ/mol. The critical strain of dynamic recrystallization was studied by inflection point of lnθ-ε curve and minimum value of -e curve.
The thermal deformation tests of Cu-0.90Cr-0.18Zr alloy were conducted at the deformation temperature of 500~800 °C and the strain rate of 0.01~1 s-1 on the Gleeble-1500 thermal-mechanical simulator. The flow stress, the constitutive equation and the critical conditions of dynamic recrystallization were studied. The results show that the flow stress decreases with the increasing of deformation temperature or with the decreasing of strain rate, The constitutive equation was established with the activation energy 584.87 kJ/mol. The critical strain of dynamic recrystallization was studied by inflection point of lnθ-ε curve and minimum value of -e curve.
2014, 43(2):418-422.
Abstract:
The valence electron structures and the properties of ANi5 (A=La, Ca, Y) hydrogen storage alloys were calculated according to the empirical electron theory of solids and molecules (EET). Results show that there exist good correlations among their electron structures and hardness, anti-pulverization abilities together with equilibrium hydrogen pressures at the room temperature. The theoretical results agree with that of experiments and have a theoretical guiding significance to improving the hydrogen storage properties of ANi5 alloys with the element substitution method and exploring versatile hydrogen storage alloys suitable for different situations.
The valence electron structures and the properties of ANi5 (A=La, Ca, Y) hydrogen storage alloys were calculated according to the empirical electron theory of solids and molecules (EET). Results show that there exist good correlations among their electron structures and hardness, anti-pulverization abilities together with equilibrium hydrogen pressures at the room temperature. The theoretical results agree with that of experiments and have a theoretical guiding significance to improving the hydrogen storage properties of ANi5 alloys with the element substitution method and exploring versatile hydrogen storage alloys suitable for different situations.
24 Study on Formation Mechanism about the Cr3C2-NiCr/NiAl Coating of CuCo2Be Alloy by Plasma Spraying
2014, 43(2):423-428.
Abstract:
Cr3C2-NiCr/NiAl coating on the CuCo2Be alloy was prepared by plasma spraying. The formation mechanism, phase composition in the Cr3C2-NiCr/NiAl coating and the phase characteristics were analyzed by DTA, XRD, SEM, EDS etc. The DTA analysis shows that in thermal spray process, Ni2Al3, NiAl3, NiAl phase may be generated for the exothermic reaction. SEM, EDS analysis results showed that the coating displays an obviously layered structure and nickel-aluminum compounds exhibit a angular. XRD analysis shows that the compounds of the coating conformed exhibit different changes and types in the different forming stages and time. The phase formation at the interface and the distribution of elements were investigated by XRD, EDS, it is shown that a certain element diffusion appears?in the boundary, So the interface has the micro-metallurgical bonding.
Cr3C2-NiCr/NiAl coating on the CuCo2Be alloy was prepared by plasma spraying. The formation mechanism, phase composition in the Cr3C2-NiCr/NiAl coating and the phase characteristics were analyzed by DTA, XRD, SEM, EDS etc. The DTA analysis shows that in thermal spray process, Ni2Al3, NiAl3, NiAl phase may be generated for the exothermic reaction. SEM, EDS analysis results showed that the coating displays an obviously layered structure and nickel-aluminum compounds exhibit a angular. XRD analysis shows that the compounds of the coating conformed exhibit different changes and types in the different forming stages and time. The phase formation at the interface and the distribution of elements were investigated by XRD, EDS, it is shown that a certain element diffusion appears?in the boundary, So the interface has the micro-metallurgical bonding.
2014, 43(2):429-434.
Abstract:
Based on an overall review of the research achievements and the problems of rare earth metal conversion coatings for aluminum alloys at home and abroad and combined with our early study of aluminum alloy’s inhibition mechanism and coating formation mechanism, this paper studied the chemically formed cerium conversion coatings on aluminum alloys with the aid of oxidation accelerator. The morphology and the structure and the composition of rare earth metal conversion coating were investigated by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that rare metal conversion coating on B95 surface formed by Ce(III) is mainly composed of Al and the Ce oxides, the Ce oxides are mainly made up of Ce(IV)(CeO2 and Ce(OH)4 compounds. During the whole process, Ce is distributed evenly; the conversion coating is compact and even. Some deposits rich in Ce stay locally. The conversion coating is non-crystal structure. The mechanism of the corrosion resistance of the coating was studied by electrochemical methods together with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results indicate that H2O2 helps to make the conversion coating on the B95 surface becoming more compact and non-crystal structure , it is able to prevent water and Cl+ from permeating the conversion coating, it will inhibit simultaneously both the cathodic and anodic reactions of corrosion on the alloy surface. The rare earth conversion coating still retains the self-rehabilitation ability after pitting.
Based on an overall review of the research achievements and the problems of rare earth metal conversion coatings for aluminum alloys at home and abroad and combined with our early study of aluminum alloy’s inhibition mechanism and coating formation mechanism, this paper studied the chemically formed cerium conversion coatings on aluminum alloys with the aid of oxidation accelerator. The morphology and the structure and the composition of rare earth metal conversion coating were investigated by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that rare metal conversion coating on B95 surface formed by Ce(III) is mainly composed of Al and the Ce oxides, the Ce oxides are mainly made up of Ce(IV)(CeO2 and Ce(OH)4 compounds. During the whole process, Ce is distributed evenly; the conversion coating is compact and even. Some deposits rich in Ce stay locally. The conversion coating is non-crystal structure. The mechanism of the corrosion resistance of the coating was studied by electrochemical methods together with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results indicate that H2O2 helps to make the conversion coating on the B95 surface becoming more compact and non-crystal structure , it is able to prevent water and Cl+ from permeating the conversion coating, it will inhibit simultaneously both the cathodic and anodic reactions of corrosion on the alloy surface. The rare earth conversion coating still retains the self-rehabilitation ability after pitting.
2014, 43(2):435-439.
Abstract:
For the cold pre-deformed Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy, the high density of dislocation could still be observed after traditional aging treatment, which could lead to detrimental influences on mechanical properties. To resolve this problem, a second aging treatment process was proposed. Transmitting electron microscopy (TEM) investigations show that the dislocation density may be dramatically decreased by the secondary aging treatment in predeformed TB3 samples. Variant selection effect was observed in predeformed and aged TB3 samples. Low cycle fatigue (LCF) tests were carried out to the conventional peak aged TB3 samples (FA) and the predeformed and secondary aging treated TB3 samples(SA). The LCF results show that fatigue lifetime is slightly higher for SA samples when the total strain amplitude is lower than 1%, but it has an opposite result when the total strain amplitude is higher than 1%. TEM investigations on the TB3 samples after fatigue tests show that dislocation slip is the predominant deformation mode. The dislocation bands resulting form cyclic deformation are wide and discontinuous in FA sample, however they are fine and homogeneous in SA samples.
For the cold pre-deformed Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy, the high density of dislocation could still be observed after traditional aging treatment, which could lead to detrimental influences on mechanical properties. To resolve this problem, a second aging treatment process was proposed. Transmitting electron microscopy (TEM) investigations show that the dislocation density may be dramatically decreased by the secondary aging treatment in predeformed TB3 samples. Variant selection effect was observed in predeformed and aged TB3 samples. Low cycle fatigue (LCF) tests were carried out to the conventional peak aged TB3 samples (FA) and the predeformed and secondary aging treated TB3 samples(SA). The LCF results show that fatigue lifetime is slightly higher for SA samples when the total strain amplitude is lower than 1%, but it has an opposite result when the total strain amplitude is higher than 1%. TEM investigations on the TB3 samples after fatigue tests show that dislocation slip is the predominant deformation mode. The dislocation bands resulting form cyclic deformation are wide and discontinuous in FA sample, however they are fine and homogeneous in SA samples.
2014, 43(2):445-449.
Abstract:
Two thick-wall parts of TA15 alloy were formed by laser rapid forming (LRF) process using unidirectional scanning pattern and weaving scanning pattern, respectively. The investigation on the effect of scanning pattern and heat treatment on the microstructures and the tensile properties of the LRFed TA15 alloy was carried out. Results show that the LRFed TA15 alloy has a good thermal stability of metallographic microstructures. The tensile properties of TA15 alloy formed by the weaving scanning pattern are superior to that of TA15 alloy fabricated by the undirectional scanning pattern due to finer metallographic microstructures of TA15 alloy obtained by the weaving scanning pattern. The tensile properties of as-deposited and heat-treated TA15 alloy prepared by the both scanning patterns are anisotropic, after the heat treatment of 940 °C/1 h/AC，the tensile properties of the formed TA15 alloy are better than that of the wrought annealed TA15 alloy.
Two thick-wall parts of TA15 alloy were formed by laser rapid forming (LRF) process using unidirectional scanning pattern and weaving scanning pattern, respectively. The investigation on the effect of scanning pattern and heat treatment on the microstructures and the tensile properties of the LRFed TA15 alloy was carried out. Results show that the LRFed TA15 alloy has a good thermal stability of metallographic microstructures. The tensile properties of TA15 alloy formed by the weaving scanning pattern are superior to that of TA15 alloy fabricated by the undirectional scanning pattern due to finer metallographic microstructures of TA15 alloy obtained by the weaving scanning pattern. The tensile properties of as-deposited and heat-treated TA15 alloy prepared by the both scanning patterns are anisotropic, after the heat treatment of 940 °C/1 h/AC，the tensile properties of the formed TA15 alloy are better than that of the wrought annealed TA15 alloy.
2014, 43(2):460-464.
Abstract:
The elements W and Nb with paremagnetism and grain refinement was selected according to the magnetostrictive theory and the fine grain strengthening method. The thermodynamic software Factsage was used in alloy aided design. The samples with a low coefficient of thermal expansion (CTE) and a high strength were made by W+Nb binary alloying of FeNi36, forging and heat treatment. The mechanism of the low coefficient of thermal expansion and the high strength was analyzed by means of the results of Chemical analysis, metallographic and scanning electron microscopy, grain size, microhardness and CTE testing. The result shows that the elements of W+Nb have good grain refinement effect, the binary alloying can make the microhardness of matrix improved and maintain it at the lower CTE.
The elements W and Nb with paremagnetism and grain refinement was selected according to the magnetostrictive theory and the fine grain strengthening method. The thermodynamic software Factsage was used in alloy aided design. The samples with a low coefficient of thermal expansion (CTE) and a high strength were made by W+Nb binary alloying of FeNi36, forging and heat treatment. The mechanism of the low coefficient of thermal expansion and the high strength was analyzed by means of the results of Chemical analysis, metallographic and scanning electron microscopy, grain size, microhardness and CTE testing. The result shows that the elements of W+Nb have good grain refinement effect, the binary alloying can make the microhardness of matrix improved and maintain it at the lower CTE.
2014, 43(2):481-484.
Abstract:
Tm doped Y2O3-ZrO2 (YSZ) powders and coatings are prepared in order to enhance the adaptation of the coating to thermal barrier coatings. The powders were prepared by chemical process and the coatings were deposited by plasma spraying method. The effects of plasma spraying parameters on the luminescent intensity of YSZ:Tm coating were investigated. It is found that yttria solid solutes into the powder completely when the aging time is over 15 h and Zr4+ concentration is 0.2 mol/L. The luminescent intensity of powder increases with the decrement of doped concentration of Tm. Plasma spraying distance and power have obvious influence on the luminescent intensity of YSZ:Tm coatings. The lower the spraying distance and power, the higher the luminescent intensity of coatings is in the present studying range.
Tm doped Y2O3-ZrO2 (YSZ) powders and coatings are prepared in order to enhance the adaptation of the coating to thermal barrier coatings. The powders were prepared by chemical process and the coatings were deposited by plasma spraying method. The effects of plasma spraying parameters on the luminescent intensity of YSZ:Tm coating were investigated. It is found that yttria solid solutes into the powder completely when the aging time is over 15 h and Zr4+ concentration is 0.2 mol/L. The luminescent intensity of powder increases with the decrement of doped concentration of Tm. Plasma spraying distance and power have obvious influence on the luminescent intensity of YSZ:Tm coatings. The lower the spraying distance and power, the higher the luminescent intensity of coatings is in the present studying range.
2014, 43(2):485-489.
Abstract:
A navel technology for resistance spot welding with interventional powder thermite was proposed, which is characterized with energy saving and high efficiency. The influences of the interventional powder thermite ZnO+Al upon the nugget formation, the microstructure and the mechanical property were studied in the resistance spot welding of 2024 aluminum alloy. The results indicate that the powder thermite ZnO+Al can effectively increase the dimension of the nugget and the dentrite region with the extra help of the heat of the metallurgical reaction from the powder thermite ZnO+Al. The ZnO+Al addition increases the heterogeneous nucleation in the nugget and prompts the appearing of a large scale constituent supercooling in the solid-liquid interface front during the process of solidification, which makes the distribution of equiaxed grains more uniform and refines the dentritic bundles of the equiaxed grains in the nugget. According to the aforementioned facts, the tensile-shear strength of the nugget is improved. The experimental results show that the spot strength can increase by over 28%~200% in the range of experiments with the help of the ZnO+Al addition.
A navel technology for resistance spot welding with interventional powder thermite was proposed, which is characterized with energy saving and high efficiency. The influences of the interventional powder thermite ZnO+Al upon the nugget formation, the microstructure and the mechanical property were studied in the resistance spot welding of 2024 aluminum alloy. The results indicate that the powder thermite ZnO+Al can effectively increase the dimension of the nugget and the dentrite region with the extra help of the heat of the metallurgical reaction from the powder thermite ZnO+Al. The ZnO+Al addition increases the heterogeneous nucleation in the nugget and prompts the appearing of a large scale constituent supercooling in the solid-liquid interface front during the process of solidification, which makes the distribution of equiaxed grains more uniform and refines the dentritic bundles of the equiaxed grains in the nugget. According to the aforementioned facts, the tensile-shear strength of the nugget is improved. The experimental results show that the spot strength can increase by over 28%~200% in the range of experiments with the help of the ZnO+Al addition.
2014, 43(2):490-494.
Abstract:
Cu/Ag core-shell powders have been prepared by liquid phase reduction reaction using ascorbic acid as a reducing agent through inhibiting substitution reaction. The composition and the content for the pretreated and coated copper powder, the morphology and the particle size distribution of Cu/Ag core-shell powders, the composition of the coated-surface were characterized by XRD, SEM, EDS, TAG and laser particle analyzer, etc. The results show that a continuous silver film is formed on the surface of copper powder by coating for a time. The observed Cu/30%Ag (mass fraction) powder has a good oxidation resistance and thermal stability. The paste prepared with ready-made silver powder and Cu/30%Ag were printed on the silicon，and the square resistance of the sintered film tested by four-point probe is 12.35 mΩ/□, indicating the electrical property of the prepared Cu/Ag core-shell powders is qualified for solar cell．
Cu/Ag core-shell powders have been prepared by liquid phase reduction reaction using ascorbic acid as a reducing agent through inhibiting substitution reaction. The composition and the content for the pretreated and coated copper powder, the morphology and the particle size distribution of Cu/Ag core-shell powders, the composition of the coated-surface were characterized by XRD, SEM, EDS, TAG and laser particle analyzer, etc. The results show that a continuous silver film is formed on the surface of copper powder by coating for a time. The observed Cu/30%Ag (mass fraction) powder has a good oxidation resistance and thermal stability. The paste prepared with ready-made silver powder and Cu/30%Ag were printed on the silicon，and the square resistance of the sintered film tested by four-point probe is 12.35 mΩ/□, indicating the electrical property of the prepared Cu/Ag core-shell powders is qualified for solar cell．
2014, 43(2):506-512.
Abstract:
This paper reviewed the recent development of the Cu(In, Ga)Se2 (CIGS) layer in terms of the target sources and the layer structures of the as-deposited metallic precursors, the Se-sources and selenization techniques for the post-selenization. The advantages, problems and possible solutions of each technique involved were discussed.
This paper reviewed the recent development of the Cu(In, Ga)Se2 (CIGS) layer in terms of the target sources and the layer structures of the as-deposited metallic precursors, the Se-sources and selenization techniques for the post-selenization. The advantages, problems and possible solutions of each technique involved were discussed.
