Volume 47,Issue 3,2018 Table of Contents
2018, 47(3):717-722.
Abstract:
: The coupling field of electrodepositing process under the supercritical fluid was simulated by COMSOL Multiphysics software to study the distribution of the current density and the growth of the electrodepositing coating which was verified by the experimental supercritical composite electrodepositing coating. Simultaneously the surface morphology and microhardness of the experimental supercritical nickel-diamond electrodepositing coating were studied and discussed. The results show that the current density on cathodic edge is much higher than that of the middle section and the predicted growth of the electrodepositing coating accords with current density distribution. The error between predicted and experimental thickness of the central supercritical electrodepositing coating is smaller. The biggest microhardness of the composite supercritical electrodepositing coating can reach 951.47HV(200g), a figure that is 80% higher than that of ordinary composite electrodepositing coating. The supercritical composite electrodepositing coating has smooth surface and compact structure.
: The coupling field of electrodepositing process under the supercritical fluid was simulated by COMSOL Multiphysics software to study the distribution of the current density and the growth of the electrodepositing coating which was verified by the experimental supercritical composite electrodepositing coating. Simultaneously the surface morphology and microhardness of the experimental supercritical nickel-diamond electrodepositing coating were studied and discussed. The results show that the current density on cathodic edge is much higher than that of the middle section and the predicted growth of the electrodepositing coating accords with current density distribution. The error between predicted and experimental thickness of the central supercritical electrodepositing coating is smaller. The biggest microhardness of the composite supercritical electrodepositing coating can reach 951.47HV(200g), a figure that is 80% higher than that of ordinary composite electrodepositing coating. The supercritical composite electrodepositing coating has smooth surface and compact structure.
2018, 47(3):723-728.
Abstract:
To improve the corrosion resistance of Ti6Al4V alloys in acid solution, a W-Mo co-penetrated top layer was prepared using hollow-cathode glow discharge plasma technique below the β phase transition point. The surface morphology, chemical composition and crystal structure of the coatings were determined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray power diffraction (XRD), respectively. It indicated that a dense co-penetrated layer was produced with maximum thickness of approximately 23 μm. The layer was composed of AlMoTi2 and TixW1-x phases. The static corrosion test was conducted in acid (H2SO4 and HCl, respectively) at room temperature (RT) by using the electrochemical workstation. The results showed that the W-Mo co-penetrated layer could achieve relatively stable corrosion potential in reducing acid and the Icorr of co-penetrated layers occupy merely 1/10 and 1/6 that of Ti6Al4V substrates. In addition, there is barely any corroded product and crack on the corroded surface of co-penetrated layers, indicating no corroded shedding phenomenon occurred. So the corrosion resistance are obviously improved in the premise of keeping the basic properties of the substrate.
To improve the corrosion resistance of Ti6Al4V alloys in acid solution, a W-Mo co-penetrated top layer was prepared using hollow-cathode glow discharge plasma technique below the β phase transition point. The surface morphology, chemical composition and crystal structure of the coatings were determined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray power diffraction (XRD), respectively. It indicated that a dense co-penetrated layer was produced with maximum thickness of approximately 23 μm. The layer was composed of AlMoTi2 and TixW1-x phases. The static corrosion test was conducted in acid (H2SO4 and HCl, respectively) at room temperature (RT) by using the electrochemical workstation. The results showed that the W-Mo co-penetrated layer could achieve relatively stable corrosion potential in reducing acid and the Icorr of co-penetrated layers occupy merely 1/10 and 1/6 that of Ti6Al4V substrates. In addition, there is barely any corroded product and crack on the corroded surface of co-penetrated layers, indicating no corroded shedding phenomenon occurred. So the corrosion resistance are obviously improved in the premise of keeping the basic properties of the substrate.
2018, 47(3):729-735.
Abstract:
The influence of Mn doping on the Ca2SiO4:Eu2+ phosphors is investigated by the First principle calculation. Comparing with the Ca2SiO4:Eu2+ phosphor, it is found that red-shift of the absorption spectrum for the Mn-doped Ca2SiO4:Eu2+ phosphor takes place. Mn2+ ions substitution on Ca2+ sites causes an increase of the crystal ?eld strength, which results in Eu5d level moving down ward in energy. Besides, Mn3d partly enters into the top of the conduction band and the bottom of the valence band. These two reasons bring about narrow band gap and red shift of absorption spectrum.
The influence of Mn doping on the Ca2SiO4:Eu2+ phosphors is investigated by the First principle calculation. Comparing with the Ca2SiO4:Eu2+ phosphor, it is found that red-shift of the absorption spectrum for the Mn-doped Ca2SiO4:Eu2+ phosphor takes place. Mn2+ ions substitution on Ca2+ sites causes an increase of the crystal ?eld strength, which results in Eu5d level moving down ward in energy. Besides, Mn3d partly enters into the top of the conduction band and the bottom of the valence band. These two reasons bring about narrow band gap and red shift of absorption spectrum.
4 Microstructure and Mechanical properties of AZ31B magnesium alloy prepared by solid -state recycling
2018, 47(3):736-741.
Abstract:
Machined chips of AZ31B magnesium alloy were consolidated by cold pressing and then hot extruding under different processing temperatures and extrusion ratios. Being compared with ingot extruding alloy, the influences of processing technology on mechanical properties were analyzed from two main aspects that involving the dynamic recrystallization microstructure and the bonding condition between chips. With the increasing extrusion temperature, the ultimate tensile strength and elongation to failure of the recycled alloys firstly increase and then decrease. The combined action of grain growth and improvement of the bonding between chips with the increasing extrusion temperature results in the variations of mechanical properties of the recycled alloy. With the increasing extrusion ratio from 4:1 to 44:1, grain is refined, and the bonding between chips is enhanced. This contribute to the increased ultimate tensile strength of recycled alloy. Whereas elongation to failure decrease when extrusion ratio is higher than 25:1 due to the significant deformation strengthening.
Machined chips of AZ31B magnesium alloy were consolidated by cold pressing and then hot extruding under different processing temperatures and extrusion ratios. Being compared with ingot extruding alloy, the influences of processing technology on mechanical properties were analyzed from two main aspects that involving the dynamic recrystallization microstructure and the bonding condition between chips. With the increasing extrusion temperature, the ultimate tensile strength and elongation to failure of the recycled alloys firstly increase and then decrease. The combined action of grain growth and improvement of the bonding between chips with the increasing extrusion temperature results in the variations of mechanical properties of the recycled alloy. With the increasing extrusion ratio from 4:1 to 44:1, grain is refined, and the bonding between chips is enhanced. This contribute to the increased ultimate tensile strength of recycled alloy. Whereas elongation to failure decrease when extrusion ratio is higher than 25:1 due to the significant deformation strengthening.
2018, 47(3):742-747.
Abstract:
The effects of Sr modification on the microstructure and properties of Al3Ti/ADC12 composite were systematically investigated. The microstructures and fracture surfaces of composites were examined by optical microscope and SEM. Results showed that the addition of Sr reduced the sizes of the α-Al primary phase and Al3Ti particles and modified the morphology of composites. The optimum level of added Sr content was 0.25 wt%, and the eutectic silicon changed from a acicular or short rod shape into a granule one. Coarse dendritics of the primary α-A1 phases were fully refined. Results also showed that Sr addition led to the improvement inSmechanical properties. Compared with matrix alloys, the tensile strength and elongation of the composite were increased by 36.9% and 58% when the Sr addition was 0.25 wt.%. Furthermore, fractographic examinations revealed that cleavage surfaces and brittle plain area could hardly be seen from the Al3Ti/ADC12 composite with addition of 0.25wt.% Sr. The dimples were increased in quantity and diminished in size, deeper and well-distributed. The fracture appearances matched the tendency of the tensile properties.
The effects of Sr modification on the microstructure and properties of Al3Ti/ADC12 composite were systematically investigated. The microstructures and fracture surfaces of composites were examined by optical microscope and SEM. Results showed that the addition of Sr reduced the sizes of the α-Al primary phase and Al3Ti particles and modified the morphology of composites. The optimum level of added Sr content was 0.25 wt%, and the eutectic silicon changed from a acicular or short rod shape into a granule one. Coarse dendritics of the primary α-A1 phases were fully refined. Results also showed that Sr addition led to the improvement inSmechanical properties. Compared with matrix alloys, the tensile strength and elongation of the composite were increased by 36.9% and 58% when the Sr addition was 0.25 wt.%. Furthermore, fractographic examinations revealed that cleavage surfaces and brittle plain area could hardly be seen from the Al3Ti/ADC12 composite with addition of 0.25wt.% Sr. The dimples were increased in quantity and diminished in size, deeper and well-distributed. The fracture appearances matched the tendency of the tensile properties.
2018, 47(3):748-753.
Abstract:
As recent advances on the performance of the YBCO coated conductor (CC) tape, its attractive perspectives for application have opened up for us. Joining process of CC tapes is inevitable for development of coated superconductor based apparatuses where single tape is not long enough or needed to be looped. Generally the joint was completed at a certain temperature and under a constant pressure that were investigated in prior literatures. Because the CC tape is very thin, easy to damage caused by deformation in some region of the tape, the surface of the joint making table should be flat and smooth enough, which have not been yet paid serious attention. Meanwhile, the smoothness of the pressing table is crucial to obtain the joint with low resistance. In this paper, a simple and effective joint of coated superconductor tapes making process depended on a soldering table with high smoothness less than 5 μm/100 mm was investigated. In the process, the non-superconducting lapped joint method with face-to-face configuration was employed, and the solder layer thickness and the joint lapped length varied. The current-voltage characteristic of the jointed tapes was measured in liquid nitrogen bath by a standard four-probe technique. The joint with sufficiently low resistance of 6.3 nΩ was easily achieved with a lapped length of 14 cm, which is ascribed to the use of a soldering table with high smoothness. In addition, the joints microstructure was observed by the metallographic microscope and scanning electron microscopy (SEM) to reveal the distribution of the solder between the joined CC tapes.
As recent advances on the performance of the YBCO coated conductor (CC) tape, its attractive perspectives for application have opened up for us. Joining process of CC tapes is inevitable for development of coated superconductor based apparatuses where single tape is not long enough or needed to be looped. Generally the joint was completed at a certain temperature and under a constant pressure that were investigated in prior literatures. Because the CC tape is very thin, easy to damage caused by deformation in some region of the tape, the surface of the joint making table should be flat and smooth enough, which have not been yet paid serious attention. Meanwhile, the smoothness of the pressing table is crucial to obtain the joint with low resistance. In this paper, a simple and effective joint of coated superconductor tapes making process depended on a soldering table with high smoothness less than 5 μm/100 mm was investigated. In the process, the non-superconducting lapped joint method with face-to-face configuration was employed, and the solder layer thickness and the joint lapped length varied. The current-voltage characteristic of the jointed tapes was measured in liquid nitrogen bath by a standard four-probe technique. The joint with sufficiently low resistance of 6.3 nΩ was easily achieved with a lapped length of 14 cm, which is ascribed to the use of a soldering table with high smoothness. In addition, the joints microstructure was observed by the metallographic microscope and scanning electron microscopy (SEM) to reveal the distribution of the solder between the joined CC tapes.
2018, 47(3):754-758.
Abstract:
The hydrolysis process of NaBH4 using mixed catalyst Co2B/Pr6O11 was studied by drainage method. The effects of the ratios of Co2B to Pr6O11 and amount of mixed catalyst Co2B/Pr6O11 on the amount of hydrogen release of NaBH4 are very obvious. When the doping amount is varied between 1-6%, the hydrogen desorption rate of doped samples increasesSfirstlySandSthenSdecreases with the doping amount increases. Comparatively, the effect rule of the amount and the ratio of mixed catalyst Co2B / Pr6O11 on the hydrogen desorption amount of NaBH4 is not obvious. However, after NaBH4 is being catalyzed by the mixed catalyst Co2B / Pr6O11, the hydrogen desorption amount of the sample is obviously changed and the hydrogen desorption amounts of most samples are between 410-525ml. In all samples, the sample doped with 4% 70%Co2B/30% Pr6O11 has the maximum hydrogen desorption rate for 540ml/min and the maximum hydrogen desorption amount for 540ml.
The hydrolysis process of NaBH4 using mixed catalyst Co2B/Pr6O11 was studied by drainage method. The effects of the ratios of Co2B to Pr6O11 and amount of mixed catalyst Co2B/Pr6O11 on the amount of hydrogen release of NaBH4 are very obvious. When the doping amount is varied between 1-6%, the hydrogen desorption rate of doped samples increasesSfirstlySandSthenSdecreases with the doping amount increases. Comparatively, the effect rule of the amount and the ratio of mixed catalyst Co2B / Pr6O11 on the hydrogen desorption amount of NaBH4 is not obvious. However, after NaBH4 is being catalyzed by the mixed catalyst Co2B / Pr6O11, the hydrogen desorption amount of the sample is obviously changed and the hydrogen desorption amounts of most samples are between 410-525ml. In all samples, the sample doped with 4% 70%Co2B/30% Pr6O11 has the maximum hydrogen desorption rate for 540ml/min and the maximum hydrogen desorption amount for 540ml.
8 Surface Metallization of SiC Ceramic by Mo-Ni-Si Coatings for improving its wettability by molten Ag
Zhao Santuan
,
Zhang Xiangzhao
,
Liu Guiwu
,
Valenza Fabrizio
,
Muolo Maria Luigia
,
Qiao Guanjun
,
Passerone Alberto
2018, 47(3):759-765.
Abstract:
Three Mo-Ni-Si metallizing coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interface microstructure were analyzed. The wetting and spreading of molten Ag on the coated SiC ceramic substrates were investigated by the sessile drop technique, and the interfacial behavior of the Ag/coated SiC systems was analyzed and discussed. The experimental results showed that the coatings were mainly composed of Mo5Si3, MoSi2, Ni2Si, NiSi2 and MoNiSi. The tetragonal MoSi2 grains located on the coating surface disappeared with the concentration of Mo increasing from 20 at.% to 40 at.%. The final contact angles of Ag/coated SiC systems at 1000 oC for holding 30 min were 45o, 79o and 85o for Mo20-Ni32-Si48, Mo30-Ni28-Si42 and Mo40-Ni24-Si36, respectively. This result can be closely related to the interactions between the Ag drop and the microstructure of the three Mo-Ni-Si coatings. No visible reaction layers were observed at all the coating/substrate interfaces before and after the wetting tests.
Three Mo-Ni-Si metallizing coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interface microstructure were analyzed. The wetting and spreading of molten Ag on the coated SiC ceramic substrates were investigated by the sessile drop technique, and the interfacial behavior of the Ag/coated SiC systems was analyzed and discussed. The experimental results showed that the coatings were mainly composed of Mo5Si3, MoSi2, Ni2Si, NiSi2 and MoNiSi. The tetragonal MoSi2 grains located on the coating surface disappeared with the concentration of Mo increasing from 20 at.% to 40 at.%. The final contact angles of Ag/coated SiC systems at 1000 oC for holding 30 min were 45o, 79o and 85o for Mo20-Ni32-Si48, Mo30-Ni28-Si42 and Mo40-Ni24-Si36, respectively. This result can be closely related to the interactions between the Ag drop and the microstructure of the three Mo-Ni-Si coatings. No visible reaction layers were observed at all the coating/substrate interfaces before and after the wetting tests.
2018, 47(3):766-772.
Abstract:
In the present work, 2-hydroxyethyl methacrylate(HEMA)-1,6-hexanediol diacrylate(HDDA) non-aqueous gelcasting system was adopted to prepare concentrated slurry of Mo/Cu powders. The effect of dispersant dosage, monomer content and solid loading on rheological behavior of slurry was studied. The effect of processing parameters such as monomer content, monomer/cross-linker ratio, initiator dosage, temperature on the gelation behavior and green bodies’s flexural strength was studied. Results show that, solid loading influence the viscosity of slurry the most, followed by dispersant dosage and monomer content. The flexural strength of green bodies increases with the increasing of monomer content and the decreasing of monomer/cross-linker ratio, initiator dosage has a relatively slightly effect. On the basis of these, the optimum processing parameters for Mo/Cu non-aqueous gelcasting are as follows: HEMA content is 25 vol.% ~ 30 vol.%, monomer/cross-linker ratio is 10:1 ~ 15:1, initiator dosage is 1.5 vol.% ~ 2.5 vol.%, and gelation temperature is 60oC ~ 80oC.
In the present work, 2-hydroxyethyl methacrylate(HEMA)-1,6-hexanediol diacrylate(HDDA) non-aqueous gelcasting system was adopted to prepare concentrated slurry of Mo/Cu powders. The effect of dispersant dosage, monomer content and solid loading on rheological behavior of slurry was studied. The effect of processing parameters such as monomer content, monomer/cross-linker ratio, initiator dosage, temperature on the gelation behavior and green bodies’s flexural strength was studied. Results show that, solid loading influence the viscosity of slurry the most, followed by dispersant dosage and monomer content. The flexural strength of green bodies increases with the increasing of monomer content and the decreasing of monomer/cross-linker ratio, initiator dosage has a relatively slightly effect. On the basis of these, the optimum processing parameters for Mo/Cu non-aqueous gelcasting are as follows: HEMA content is 25 vol.% ~ 30 vol.%, monomer/cross-linker ratio is 10:1 ~ 15:1, initiator dosage is 1.5 vol.% ~ 2.5 vol.%, and gelation temperature is 60oC ~ 80oC.
10 The influence of hot extrusion and age treatment on the properties of biodegradable Mg-Zn-Y alloy
Qiao Xueyan
,
Yu Kun
,
Chen Liangjian
,
Dai Yilong
,
Xiao Tao
,
Deng Youwen
,
Shuai Cijun
,
Yan Yang
2018, 47(3):773-779.
Abstract:
Mg-6Zn-1Y (mass fraction, %) alloys were prepared for degradable biomaterials. The billets of the alloy were produced by powder metallurgy (PM) method and then hot extruded. The extruded samples were aged for 24h and 72h at 150°C respectively. The microstructure and corrosion behavior of the experimental alloys were comprehensively investigated. The microstructure observations show that the alloys contain α-Mg, MgZn, MgZn2 and Mg3YZn6 (I-phase) phases. The hot extrusion process significantly refined the grains and led to better mechanical properties with the value of compressive strength in the range of 365~399MPa, and better corrosion resistance for the PM alloy shows higher hydrogen volume in the immersion test. Furthermore, due to more uniform corrosion behavior, the alloy aged for 72h shows lower corrosion rate and corrosion current density in the immersion test and potentiodynamic polarization test respectively, and higher resistance value (Rp) results from the electrochemical impedance spectroscopy (EIS), which means the alloy aged for 72h exhibits better corrosion resistance than the other three alloys.
Mg-6Zn-1Y (mass fraction, %) alloys were prepared for degradable biomaterials. The billets of the alloy were produced by powder metallurgy (PM) method and then hot extruded. The extruded samples were aged for 24h and 72h at 150°C respectively. The microstructure and corrosion behavior of the experimental alloys were comprehensively investigated. The microstructure observations show that the alloys contain α-Mg, MgZn, MgZn2 and Mg3YZn6 (I-phase) phases. The hot extrusion process significantly refined the grains and led to better mechanical properties with the value of compressive strength in the range of 365~399MPa, and better corrosion resistance for the PM alloy shows higher hydrogen volume in the immersion test. Furthermore, due to more uniform corrosion behavior, the alloy aged for 72h shows lower corrosion rate and corrosion current density in the immersion test and potentiodynamic polarization test respectively, and higher resistance value (Rp) results from the electrochemical impedance spectroscopy (EIS), which means the alloy aged for 72h exhibits better corrosion resistance than the other three alloys.
2018, 47(3):780-787.
Abstract:
The tensile properties of friction stir weld (FSW) joint of 2195-T8 Al-Li alloy plate with 5 mm thickness prepared by straight cylindrical pin and threaded cylindrical pin at different rotational speed and welding speed were investigated. The structures of the FSW joint were detected. As prepared by straight cylindrical pin at improper welding speed, continuous hole was formed in the FSW joint along the welding direction, leading to lower joint strength. Threaded cylindrical pin alleviated the formation of hole in the weld, and the joint strength was increased with the rotational speed increasing from 700 r/min to 1100 r/min. The grains in the nugget zone (NZ) were recrystallized, and their size was decreased along the direction from the top to the bottom. Meanwhile, the grain size in the NZ adjacent to the thermo-mechanically affect zone (TMAZ) was smaller than that in the central NZ. The precipitates of T1 (Al2CuLi) and q￠ (Al2Cu) in the NZ were completely dissolved. All q￠ precipitates but most T1 precipitates were dissolved in the TMAZ. Meanwhile, dislocations were formed in the NZ.
The tensile properties of friction stir weld (FSW) joint of 2195-T8 Al-Li alloy plate with 5 mm thickness prepared by straight cylindrical pin and threaded cylindrical pin at different rotational speed and welding speed were investigated. The structures of the FSW joint were detected. As prepared by straight cylindrical pin at improper welding speed, continuous hole was formed in the FSW joint along the welding direction, leading to lower joint strength. Threaded cylindrical pin alleviated the formation of hole in the weld, and the joint strength was increased with the rotational speed increasing from 700 r/min to 1100 r/min. The grains in the nugget zone (NZ) were recrystallized, and their size was decreased along the direction from the top to the bottom. Meanwhile, the grain size in the NZ adjacent to the thermo-mechanically affect zone (TMAZ) was smaller than that in the central NZ. The precipitates of T1 (Al2CuLi) and q￠ (Al2Cu) in the NZ were completely dissolved. All q￠ precipitates but most T1 precipitates were dissolved in the TMAZ. Meanwhile, dislocations were formed in the NZ.
2018, 47(3):788-793.
Abstract:
By inserting Ti sheet between ceramic powder and Ti alloy steel, (TiC-TiB2)/Ti-6Al-4V graded composites were rapidly prepared by SHS centrifugal-casting process under different Ti sheet thickness from 0.5 mm to 1.5 mm. XRD, FESEM and EDS results showed that there was no significant change in phase composition of the ceramic matrix, but promoted the microstructure refinement of the reaction products with the thickness increased. Meanwhile, the introduction of Ti sheet not only enhances the thickness of the gradient interface, but also decreased the thermal infected zone of interface. Moreover, fusion bonding and atomic interdiffusion between liquid TiC-TiB2 and excessive Ti liquid in thermal vacuum circumstances were considered to initiate peritectic reaction of , direct growth of TiB solids from liquid Ti and eutectic reaction of TiB solids and liquid Ti at the final stage of joint solidification, so that consumption of TiB2 solids and increase of TiB crystal improved the interface residual stress, and the joint of the ceramic to Ti alloy was achieved in multilevel and multiscale. The joint in better thermal match and continuously-graded microstructure represents not only a transitional change in Vickers hardness but also the high shear strength of 316±25 MPa between the ceramic and Ti alloy.
By inserting Ti sheet between ceramic powder and Ti alloy steel, (TiC-TiB2)/Ti-6Al-4V graded composites were rapidly prepared by SHS centrifugal-casting process under different Ti sheet thickness from 0.5 mm to 1.5 mm. XRD, FESEM and EDS results showed that there was no significant change in phase composition of the ceramic matrix, but promoted the microstructure refinement of the reaction products with the thickness increased. Meanwhile, the introduction of Ti sheet not only enhances the thickness of the gradient interface, but also decreased the thermal infected zone of interface. Moreover, fusion bonding and atomic interdiffusion between liquid TiC-TiB2 and excessive Ti liquid in thermal vacuum circumstances were considered to initiate peritectic reaction of , direct growth of TiB solids from liquid Ti and eutectic reaction of TiB solids and liquid Ti at the final stage of joint solidification, so that consumption of TiB2 solids and increase of TiB crystal improved the interface residual stress, and the joint of the ceramic to Ti alloy was achieved in multilevel and multiscale. The joint in better thermal match and continuously-graded microstructure represents not only a transitional change in Vickers hardness but also the high shear strength of 316±25 MPa between the ceramic and Ti alloy.
13 Studies on the correlation between microstructure and corrosion behavior of Zr-0.8Sn-1Nb-0.3Fe alloy
2018, 47(3):794-798.
Abstract:
Zr-0.8Sn-1Nb-0.3Fe zirconium alloy sheets were prepared by different heat treatment processes, then OM and TEM were used to analyze the microstructure of the samples, and static autoclave tests were carried out in 360℃/18.6MPa/0.01mol/L LiOH solution and 400℃/10.3MPa superheated steam to investigate the corrosion behavior. The results showed that the second phase particles(SPPs) are mainly C14 type Zr(Nb,Fe)2 with a HCP structure, and the uniformity of SPPs distribution gradually become worse when the hot-rolling temperature increases from 600℃ to 700℃. Aging treatment before hot-rolling not only improved the uniformity of SPPs distribution, but also promoted the diffusion of Nb, which increased the amount of βNb SPPs. Extension of final annealing time had little influence on size and distribution of the SPPs, but increased the Nb/Fe ratio in the SPPs. After long time corrosion tests, the corrosion resistance became worse when the hot-rolling temperature increased in both corrosion conditions. Aging treatment before hot-rolling could increase the corrosion resistance. Extension of final annealing time also could increase the corrosion resistance in LiOH solution, but decrease the corrosion resistance in superheated steam. The relationship between microstructure and corrosion resistance was discussed, and the size, distribution and the Nb content of SPPs were considered to be the main reason for the difference of the corrosion resistance of Zr-Sn-Nb-Fe zirconium alloys.
Zr-0.8Sn-1Nb-0.3Fe zirconium alloy sheets were prepared by different heat treatment processes, then OM and TEM were used to analyze the microstructure of the samples, and static autoclave tests were carried out in 360℃/18.6MPa/0.01mol/L LiOH solution and 400℃/10.3MPa superheated steam to investigate the corrosion behavior. The results showed that the second phase particles(SPPs) are mainly C14 type Zr(Nb,Fe)2 with a HCP structure, and the uniformity of SPPs distribution gradually become worse when the hot-rolling temperature increases from 600℃ to 700℃. Aging treatment before hot-rolling not only improved the uniformity of SPPs distribution, but also promoted the diffusion of Nb, which increased the amount of βNb SPPs. Extension of final annealing time had little influence on size and distribution of the SPPs, but increased the Nb/Fe ratio in the SPPs. After long time corrosion tests, the corrosion resistance became worse when the hot-rolling temperature increased in both corrosion conditions. Aging treatment before hot-rolling could increase the corrosion resistance. Extension of final annealing time also could increase the corrosion resistance in LiOH solution, but decrease the corrosion resistance in superheated steam. The relationship between microstructure and corrosion resistance was discussed, and the size, distribution and the Nb content of SPPs were considered to be the main reason for the difference of the corrosion resistance of Zr-Sn-Nb-Fe zirconium alloys.
2018, 47(3):799-802.
Abstract:
The tensile strength stability of aging hardened Mg-10Y-1.5Sm (mass fraction, %) alloy was investigated by microstructure analysis and tensile tests. The results show that the microstructure of Mg-10Y-1.5Sm alloy consists of α-Mg matrix and Mg24Y5 phase and the formation of Sm-containing phase is not observed. With the increase of temperature from 20 oC to 300 oC, the tensile strength exceeds 200 MPa and has no obvious change. It is insensitive to temperature and the variation range is less than 10 MPa. The strength stability is superior to that of heat resistant magnesium alloy WE54 developed most successfully. The reason is mainly attributed to the hardness stability of strengthening phase Mg24Y5 enhanced by dissolved Sm.
The tensile strength stability of aging hardened Mg-10Y-1.5Sm (mass fraction, %) alloy was investigated by microstructure analysis and tensile tests. The results show that the microstructure of Mg-10Y-1.5Sm alloy consists of α-Mg matrix and Mg24Y5 phase and the formation of Sm-containing phase is not observed. With the increase of temperature from 20 oC to 300 oC, the tensile strength exceeds 200 MPa and has no obvious change. It is insensitive to temperature and the variation range is less than 10 MPa. The strength stability is superior to that of heat resistant magnesium alloy WE54 developed most successfully. The reason is mainly attributed to the hardness stability of strengthening phase Mg24Y5 enhanced by dissolved Sm.
2018, 47(3):803-809.
Abstract:
The effects of Ti content to the microstructure of high-boron steel were studied by using SEM and XRD. The effects of Ti on impact properties at room temperature, high-temperature mechanical properties and oxidation resistance at 850 °C of the steel were researched by using impact tester, dynamic thermal-mechanical simulation testing machine and oxidation weight increase method. The experimental results showed that the boride granules which distributed in a discrete manner within the matrix exhibited a round and smooth morphology and the boride size decreased greatly after adding Ti. The optimization of boride morphology and distribution made the absorbed impact energy of the steels increased. TiC particles would precipitate and ferrite would form after adding Ti. At a low level of boron content, the high temperature mechanical properties increased with increasing of born content, while at a higher level of boron content, the high temperature mechanical properties had little change. Optimum high temperature mechanical properties were obtained when boron content was at 0.33wt.%. The 850 °C oxidation test results of the steels pro and after adding Ti were all in accordance with grade 2 oxidation resistance standard in GB/T 13303-1991. Ti was conducive to the improvement of the high temperature oxidation resistance properties.
The effects of Ti content to the microstructure of high-boron steel were studied by using SEM and XRD. The effects of Ti on impact properties at room temperature, high-temperature mechanical properties and oxidation resistance at 850 °C of the steel were researched by using impact tester, dynamic thermal-mechanical simulation testing machine and oxidation weight increase method. The experimental results showed that the boride granules which distributed in a discrete manner within the matrix exhibited a round and smooth morphology and the boride size decreased greatly after adding Ti. The optimization of boride morphology and distribution made the absorbed impact energy of the steels increased. TiC particles would precipitate and ferrite would form after adding Ti. At a low level of boron content, the high temperature mechanical properties increased with increasing of born content, while at a higher level of boron content, the high temperature mechanical properties had little change. Optimum high temperature mechanical properties were obtained when boron content was at 0.33wt.%. The 850 °C oxidation test results of the steels pro and after adding Ti were all in accordance with grade 2 oxidation resistance standard in GB/T 13303-1991. Ti was conducive to the improvement of the high temperature oxidation resistance properties.
2018, 47(3):810-815.
Abstract:
The hot deformation behaviors of a new type high strength and toughness TB17 titanium alloy was investigated on the thermo mechanical simulator (Gleeble3800). The experiment conducted at temperatures ranging from 775 °C to 905 °C and strain rates various from 0.001 s?1 to 1 s?1. The softening mechanism of flow stress and microstructure were investigated during hot deformation process and the Arrhenius type constitutive equation were established as well. The stress of TB17 titanium alloy varies with sensitivity of the strain rate at defferent deformation temperatures. Duing deforming at α+β field，the peak stress was sensitive to low strain rates，while at β field deforming，the peak stress was sensitive to high strain rates. The strain rate has a major impact on the microstructure of TB17 titanium alloy. The dynamic recovery mechanisms plays an dominant role as the strain rate exceeds 0.1s-1. Dynamic recrystallization plays an significant role while the strain rate is in the range of 0.001 s-1~0.1s-1. Recrystallization processing can be promoted with the decreasing of strain rate. The microstructure of equiaxed grains with a size of 25μm was obtained with a strain rate of 0.001 s-1. The temperature also has great influence on the dynamic recrystallization. During deformed at α+β field lead to primary α phase recrystallization, while at β field lead to the β grain recrystallization. The activation energy for hot deformation below and above the temperature of phase transformation point is 538.4KJ/mol and 397.4KJ/mol, respectively. The softening mechanism of hot deformation temperature ranged from 775 to 905℃ transformation point is grain boundary glide.
The hot deformation behaviors of a new type high strength and toughness TB17 titanium alloy was investigated on the thermo mechanical simulator (Gleeble3800). The experiment conducted at temperatures ranging from 775 °C to 905 °C and strain rates various from 0.001 s?1 to 1 s?1. The softening mechanism of flow stress and microstructure were investigated during hot deformation process and the Arrhenius type constitutive equation were established as well. The stress of TB17 titanium alloy varies with sensitivity of the strain rate at defferent deformation temperatures. Duing deforming at α+β field，the peak stress was sensitive to low strain rates，while at β field deforming，the peak stress was sensitive to high strain rates. The strain rate has a major impact on the microstructure of TB17 titanium alloy. The dynamic recovery mechanisms plays an dominant role as the strain rate exceeds 0.1s-1. Dynamic recrystallization plays an significant role while the strain rate is in the range of 0.001 s-1~0.1s-1. Recrystallization processing can be promoted with the decreasing of strain rate. The microstructure of equiaxed grains with a size of 25μm was obtained with a strain rate of 0.001 s-1. The temperature also has great influence on the dynamic recrystallization. During deformed at α+β field lead to primary α phase recrystallization, while at β field lead to the β grain recrystallization. The activation energy for hot deformation below and above the temperature of phase transformation point is 538.4KJ/mol and 397.4KJ/mol, respectively. The softening mechanism of hot deformation temperature ranged from 775 to 905℃ transformation point is grain boundary glide.
2018, 47(3):816-821.
Abstract:
The samples of TiAl-3Ta-x(Cr,W)(at%) were hot compressed by Gleeble-3800 in the temperature range of 1150~1300℃ from 0.1~1s-1 for high temperature fracture behavior and microstructure evolution study. The results show that the main fracture modes consist of 45° shear fracture and longitudinal fracture on free-surface, but which crack location is different. Moreover, the cracking degree increased with the decreasing of deformation temperature, the increasing of strain rate and height reduction.In the high strain rate range, deformation twinning dominated the entire deformation process.Morever, the cracks nucleation sites were observed at grain boundary of the colonies and/or interfaces between lamellae of the specimens, and initiate and propagate perpendicular to the compression axis.
The samples of TiAl-3Ta-x(Cr,W)(at%) were hot compressed by Gleeble-3800 in the temperature range of 1150~1300℃ from 0.1~1s-1 for high temperature fracture behavior and microstructure evolution study. The results show that the main fracture modes consist of 45° shear fracture and longitudinal fracture on free-surface, but which crack location is different. Moreover, the cracking degree increased with the decreasing of deformation temperature, the increasing of strain rate and height reduction.In the high strain rate range, deformation twinning dominated the entire deformation process.Morever, the cracks nucleation sites were observed at grain boundary of the colonies and/or interfaces between lamellae of the specimens, and initiate and propagate perpendicular to the compression axis.
2018, 47(3):822-828.
Abstract:
The load-displacement curves, elastic modulus, indent morphology, nanohardness and elastic recovery of high purity Molybdenum-Niobium single crystal were investigated by nanoindentation and scanning probe microscopy. The results show that Mo - Nb single crystal has a good plastic deformation ability. Mo-Nb crystal plane undergo elastic deformation and plastic deformation during the loading-unloading process, and the load-displacement curve do not show discontinuity, which demonstrates that cracks and brittle fracture are not formed in the indents. Moreover, the pile-up behavior around indents reveals that Mo-Nb single crystal has the low work hardening tend. The nanohardness and elastic modulus of Mo-Nb single crystal were measured by continuous stiffness measurement (CSM), and a size effect on the nanohardness and elastic modulus was observed, which decrease with the increase of indentation depth. The relationship the different nanohardness and elastic modulus is: (110) crystal plane > (112) crystal plane > (111) crystal plane. The Nix-Gao model was employed to analyze the nanoindentation mechanical characteristics of Mo-Nb single crystal, and the intrinsic hardness in the limit of infinite depth (H_0) are 3.96GPa, 2.61GPa and 3.47GPa, respectively; the size effect index(i) were calculated to be 0.18, 0.16 and 0.18, respectively. The characteristic length(h^*) of (110), (111), (112) crystal plane are 1196 nm, 2753nm and 1559 nm, respectively. Mo-Nb single crystal has a significant size effect when the indentation depth is below the characteristic length, and the size effect becomes more insignificant when indentation depth is deeper than the characteristic length. The nanoindentation size effect will disappear as the impression are deeper than 4106nm、5645nm和4693nm, respectively.
The load-displacement curves, elastic modulus, indent morphology, nanohardness and elastic recovery of high purity Molybdenum-Niobium single crystal were investigated by nanoindentation and scanning probe microscopy. The results show that Mo - Nb single crystal has a good plastic deformation ability. Mo-Nb crystal plane undergo elastic deformation and plastic deformation during the loading-unloading process, and the load-displacement curve do not show discontinuity, which demonstrates that cracks and brittle fracture are not formed in the indents. Moreover, the pile-up behavior around indents reveals that Mo-Nb single crystal has the low work hardening tend. The nanohardness and elastic modulus of Mo-Nb single crystal were measured by continuous stiffness measurement (CSM), and a size effect on the nanohardness and elastic modulus was observed, which decrease with the increase of indentation depth. The relationship the different nanohardness and elastic modulus is: (110) crystal plane > (112) crystal plane > (111) crystal plane. The Nix-Gao model was employed to analyze the nanoindentation mechanical characteristics of Mo-Nb single crystal, and the intrinsic hardness in the limit of infinite depth (H_0) are 3.96GPa, 2.61GPa and 3.47GPa, respectively; the size effect index(i) were calculated to be 0.18, 0.16 and 0.18, respectively. The characteristic length(h^*) of (110), (111), (112) crystal plane are 1196 nm, 2753nm and 1559 nm, respectively. Mo-Nb single crystal has a significant size effect when the indentation depth is below the characteristic length, and the size effect becomes more insignificant when indentation depth is deeper than the characteristic length. The nanoindentation size effect will disappear as the impression are deeper than 4106nm、5645nm和4693nm, respectively.
2018, 47(3):829-834.
Abstract:
Spall microstructure characteristics and failure mechanism of Ti-6Al-4V and Ti-47Nb titanium alloys were studied through plate impact experiments and “sample soft-capture” technology at the dynamic high-pressure loading, as well as careful microscopic analyses using optical microscopy and scanning electronic microscopy. The experiment indicates that Ti-6Al-4V alloys have stronger ability of spall resistance than Ti-47Nb alloys because of the high strength of Ti-6Al-4V alloys. The micro-voids in the spalled Ti-6Al-4V alloys almost nucleate at the α/β phase boundaries and propagate along the phase boundaries, and the micro-cracks of Ti-47Nb alloys are direct connected through micro-voids. Subsequently, adiabatic shear band formed between macroscopic voids or main cracks promote the spall fracture of samples. Ti-6Al-4V and Ti-47Nb alloys fracture with ductile characteristics.
Spall microstructure characteristics and failure mechanism of Ti-6Al-4V and Ti-47Nb titanium alloys were studied through plate impact experiments and “sample soft-capture” technology at the dynamic high-pressure loading, as well as careful microscopic analyses using optical microscopy and scanning electronic microscopy. The experiment indicates that Ti-6Al-4V alloys have stronger ability of spall resistance than Ti-47Nb alloys because of the high strength of Ti-6Al-4V alloys. The micro-voids in the spalled Ti-6Al-4V alloys almost nucleate at the α/β phase boundaries and propagate along the phase boundaries, and the micro-cracks of Ti-47Nb alloys are direct connected through micro-voids. Subsequently, adiabatic shear band formed between macroscopic voids or main cracks promote the spall fracture of samples. Ti-6Al-4V and Ti-47Nb alloys fracture with ductile characteristics.
2018, 47(3):835-839.
Abstract:
The flow stress behavior of powder metallurgy (PM) Ti-47Al-2Nb-2Cr alloy during hot deformation was investigated at temperature of 950-1150oC and strain rates of 0.001-0.1s-1. In this paper, the influence of deformation parameters on the critical conditions of the dynamic recrystallization behavior was studied systematically. Based on the analysis of flow stress curves under different hot processing parameters, the critical strain (εc) and critical stress (σc) were obtained with the help of the critical condition theory proposed by Poliak and Jonas. It is also shown that the critical condition model was established by employing the strain rate and temperature compensation factor (Z): εc=1.2×10-3Z0.147. The occurrence of dynamic recrystallization behavior will be promoted with the increase of deformation temperature and the decrease of strain rate. Moreover, the reliability of the established model was verified by the observation of deformed microstructure.
The flow stress behavior of powder metallurgy (PM) Ti-47Al-2Nb-2Cr alloy during hot deformation was investigated at temperature of 950-1150oC and strain rates of 0.001-0.1s-1. In this paper, the influence of deformation parameters on the critical conditions of the dynamic recrystallization behavior was studied systematically. Based on the analysis of flow stress curves under different hot processing parameters, the critical strain (εc) and critical stress (σc) were obtained with the help of the critical condition theory proposed by Poliak and Jonas. It is also shown that the critical condition model was established by employing the strain rate and temperature compensation factor (Z): εc=1.2×10-3Z0.147. The occurrence of dynamic recrystallization behavior will be promoted with the increase of deformation temperature and the decrease of strain rate. Moreover, the reliability of the established model was verified by the observation of deformed microstructure.
2018, 47(3):840-845.
Abstract:
The interface reactions between DD6 single crystal superalloy and ceramic shells were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X ray diffraction analysis (XRD) in this paper. The results show that the black reaction products were α-Al2O3, accompanied by FeCr2O4、taenite-(Fe, Ni) at the same time. The thickness of the reaction layer was about 5~6μm. The reaction products TaO, NiO, HfO2 were observed on the prime coat of the ceramic shell. The interface reactions can be inhibited by reducing the roughness of the facecoat and controlling the content of Fe2O3 in the mineralizer simultaneously.
The interface reactions between DD6 single crystal superalloy and ceramic shells were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X ray diffraction analysis (XRD) in this paper. The results show that the black reaction products were α-Al2O3, accompanied by FeCr2O4、taenite-(Fe, Ni) at the same time. The thickness of the reaction layer was about 5~6μm. The reaction products TaO, NiO, HfO2 were observed on the prime coat of the ceramic shell. The interface reactions can be inhibited by reducing the roughness of the facecoat and controlling the content of Fe2O3 in the mineralizer simultaneously.
2018, 47(3):846-852.
Abstract:
The effects of high pressure on mechanical properties and electronic structures of Ni-Mo binary compounds (Ni4Mo、Ni3Mo(DOa)、Ni3Mo(DO22)、Ni2Mo) have been studied by first-principles calculation based on density functional theory method.Studies have shown that：The values of V/V0 decrease with pressure and the rates of change decrease gradually. The formation enthalpy are negative, and decrease with pressure.Thus high pressure can improve the ability of alloying.The calculated results of bulk modulus B、shear modulus G、Young"s modulus E、Lama constant λ and Hardness H illustrate that pressure can improve the resistance to deformation、compression resistance and hardness of four compounds. In addition,ratio of bulk modulus to shear modulus B/G and poisson"s ratio ν shows that all the considered compounds are ductile materials.The state density are also analyzed to explain the physical origin of the pressure effect on four compounds.Thus suggests that increasing pressure can improve?the stability and hardness of all compounds.
The effects of high pressure on mechanical properties and electronic structures of Ni-Mo binary compounds (Ni4Mo、Ni3Mo(DOa)、Ni3Mo(DO22)、Ni2Mo) have been studied by first-principles calculation based on density functional theory method.Studies have shown that：The values of V/V0 decrease with pressure and the rates of change decrease gradually. The formation enthalpy are negative, and decrease with pressure.Thus high pressure can improve the ability of alloying.The calculated results of bulk modulus B、shear modulus G、Young"s modulus E、Lama constant λ and Hardness H illustrate that pressure can improve the resistance to deformation、compression resistance and hardness of four compounds. In addition,ratio of bulk modulus to shear modulus B/G and poisson"s ratio ν shows that all the considered compounds are ductile materials.The state density are also analyzed to explain the physical origin of the pressure effect on four compounds.Thus suggests that increasing pressure can improve?the stability and hardness of all compounds.
2018, 47(3):853-859.
Abstract:
The propagation form of the preset edge crack in The nano Single crystal gamma-TiAl under different strain rate were simulated by the method of molecular dynamics in this paper, velocity loading way was used to obtain dynamic uniaxial tensile for preset edge crack in the single crystal gamma-TiAl within 5.0*107S-1~7.5*109 S-1. The results showed that the crack propagation form varies with the range of strain rate. In the non-sensitive region(≤4*108 S-1), the crack propagates in a brittle cleavage manner. In the sensitive region(4.0*108 S-1＜the strain≤1.0*109 S-1), it was cleavage extension features Early,the slip dislocation was emitted from the crack tip, and the void defect initiates the place where dislocation piled up and then growed to the child crack later,the child crack linked the main crack when it biased 45-degree under the strain≤5.0*108 S-1,but it connected the main crack at the same direction under 5.0*108 S-1＜the strain≤1.0*109 S-1,thus leaded to the fracture both finally； In the sharp-change region(≥1.0*109 S-1), the crack didn、t craze in the maximum stress for the reinforcement of strain,and the Stress decreased for it continues to increase some time. The non-crystallizing of the atom structure occurs near the crack tip because of high strain rate, and then the micro crack initiates in area of structure disordered, the micro crack growth leads to the “test specimen” fracture eventually.
The propagation form of the preset edge crack in The nano Single crystal gamma-TiAl under different strain rate were simulated by the method of molecular dynamics in this paper, velocity loading way was used to obtain dynamic uniaxial tensile for preset edge crack in the single crystal gamma-TiAl within 5.0*107S-1~7.5*109 S-1. The results showed that the crack propagation form varies with the range of strain rate. In the non-sensitive region(≤4*108 S-1), the crack propagates in a brittle cleavage manner. In the sensitive region(4.0*108 S-1＜the strain≤1.0*109 S-1), it was cleavage extension features Early,the slip dislocation was emitted from the crack tip, and the void defect initiates the place where dislocation piled up and then growed to the child crack later,the child crack linked the main crack when it biased 45-degree under the strain≤5.0*108 S-1,but it connected the main crack at the same direction under 5.0*108 S-1＜the strain≤1.0*109 S-1,thus leaded to the fracture both finally； In the sharp-change region(≥1.0*109 S-1), the crack didn、t craze in the maximum stress for the reinforcement of strain,and the Stress decreased for it continues to increase some time. The non-crystallizing of the atom structure occurs near the crack tip because of high strain rate, and then the micro crack initiates in area of structure disordered, the micro crack growth leads to the “test specimen” fracture eventually.
2018, 47(3):860-866.
Abstract:
In this work, the effect of varying Al and Ti contents of Incoloy825 alloy on the phase transformations that might occur in the material was simulated using a thermodynamic modelling tool. Employ optical microscope (OM), scanning electron microscope (SEM) to observe the microstructure as well as the corrosion morphology of the tested alloy. Potentiodynamic polarization curves, electrochemical impedance spectroscopy and corrosion rate of the tested alloy were investigated by electrochemical workstation and static weight-loss method in 1mol/L, 3mol/L HCl solutions. The results indicate that the microstructure of as-forged Incoloy825 is composed of γ substrate and a small quantity of Ti(C,N) at final forging temperature. With the improvement of Al, Ti contents, precipitation volume of blocky Ti(C,N) increased gradually, grain is refined; corrosion current density increased gradually, corrosion resistance decreased significantly, tendency to pitting of the tested alloy is increased. Large, faceted Ti(C,N) particles in Incoloy825 alloy provide preferred sites for pit initiation in the chloride environments. With the improvement of Al, Ti contents, corrosion products on the tested alloy surface became more porous, the protection to matrix is decreased.
In this work, the effect of varying Al and Ti contents of Incoloy825 alloy on the phase transformations that might occur in the material was simulated using a thermodynamic modelling tool. Employ optical microscope (OM), scanning electron microscope (SEM) to observe the microstructure as well as the corrosion morphology of the tested alloy. Potentiodynamic polarization curves, electrochemical impedance spectroscopy and corrosion rate of the tested alloy were investigated by electrochemical workstation and static weight-loss method in 1mol/L, 3mol/L HCl solutions. The results indicate that the microstructure of as-forged Incoloy825 is composed of γ substrate and a small quantity of Ti(C,N) at final forging temperature. With the improvement of Al, Ti contents, precipitation volume of blocky Ti(C,N) increased gradually, grain is refined; corrosion current density increased gradually, corrosion resistance decreased significantly, tendency to pitting of the tested alloy is increased. Large, faceted Ti(C,N) particles in Incoloy825 alloy provide preferred sites for pit initiation in the chloride environments. With the improvement of Al, Ti contents, corrosion products on the tested alloy surface became more porous, the protection to matrix is decreased.
2018, 47(3):867-870.
Abstract:
The performance of thermal fatigue damage of crystalline tungsten variation at different cycles was studied in power of 141.5 MW/m2，by electron beam thermal fatigue test system which was built independently in laboratory. Changes in surface topography after thermal shock in many cycles were observed by scanning electron microscopy (SEM). Changes of three-dimensional morphology and surface roughness were detected by Atomic force microscope (AFM).and the surface hardness was tested after thermal fatigue. Results show that: with the increase of the cyclic number, thermal fatigue damage intensifies. The surface roughness measured with changes linearly with the cyclic number; the surface hardness increased firstly then decreased because of the performance of fatigue hardening.
The performance of thermal fatigue damage of crystalline tungsten variation at different cycles was studied in power of 141.5 MW/m2，by electron beam thermal fatigue test system which was built independently in laboratory. Changes in surface topography after thermal shock in many cycles were observed by scanning electron microscopy (SEM). Changes of three-dimensional morphology and surface roughness were detected by Atomic force microscope (AFM).and the surface hardness was tested after thermal fatigue. Results show that: with the increase of the cyclic number, thermal fatigue damage intensifies. The surface roughness measured with changes linearly with the cyclic number; the surface hardness increased firstly then decreased because of the performance of fatigue hardening.
2018, 47(3):871-877.
Abstract:
The effects of trace Mn addition on microstructure and mechanical properties of 2297 Al-Li alloy were investigated by optical microscopy, tensile test, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and scanning transmission electron microscopy(STEM), fitted with high-angle annular dark field detector(HAADF). The results show that Mn exists in the form of AlCuMn rod-like dispersed particle and Al(CuMnFe) coarse phase in 2297 alloy. In addition, the Al(CuMnFe) phases in 2297 alloy are uniformly distributed and the size of the coarse particles is smaller than that in Mn-free alloy. As a result, the tensile strength of 2297 alloy was enhanced. The study indicates that the addition of Mn has no influence on the precipitation behavior of Al3Zr. And the level of recrystallization in 2297 alloy has not been changed, though the AlCuMn rod-like dispersed phases are precipitated.
The effects of trace Mn addition on microstructure and mechanical properties of 2297 Al-Li alloy were investigated by optical microscopy, tensile test, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and scanning transmission electron microscopy(STEM), fitted with high-angle annular dark field detector(HAADF). The results show that Mn exists in the form of AlCuMn rod-like dispersed particle and Al(CuMnFe) coarse phase in 2297 alloy. In addition, the Al(CuMnFe) phases in 2297 alloy are uniformly distributed and the size of the coarse particles is smaller than that in Mn-free alloy. As a result, the tensile strength of 2297 alloy was enhanced. The study indicates that the addition of Mn has no influence on the precipitation behavior of Al3Zr. And the level of recrystallization in 2297 alloy has not been changed, though the AlCuMn rod-like dispersed phases are precipitated.
2018, 47(3):878-883.
Abstract:
The hot flow behaviors and deformation model of spray formed superalloy GH738 were investigated using Gleeble-3500TM simulator at the temperature range of 950~1200℃, strain rate range of 0.13~6.5s-1 and reduction of 50%. The evolution of microstructure was studied by microscope and image analysis system. The results show that the flow stress decrease with increasing deformation temperature or decreasing strain rate. The hot deformation activation energy Q is 580.81kjmol-1. As the temperature increase, the necklace structures are obtained along the boundaries which are protuberated by the new recrystallized grains in the high dislocation-density serrated grain boundary zones. The structures show fully dynamic recrystallization characteristic at the temperature of 1100℃ while the higher temperature and the low strain rate forced the structure grown.
The hot flow behaviors and deformation model of spray formed superalloy GH738 were investigated using Gleeble-3500TM simulator at the temperature range of 950~1200℃, strain rate range of 0.13~6.5s-1 and reduction of 50%. The evolution of microstructure was studied by microscope and image analysis system. The results show that the flow stress decrease with increasing deformation temperature or decreasing strain rate. The hot deformation activation energy Q is 580.81kjmol-1. As the temperature increase, the necklace structures are obtained along the boundaries which are protuberated by the new recrystallized grains in the high dislocation-density serrated grain boundary zones. The structures show fully dynamic recrystallization characteristic at the temperature of 1100℃ while the higher temperature and the low strain rate forced the structure grown.
2018, 47(3):884-894.
Abstract:
Based on the microstructure evolution of AZ31 magnesium alloy during hot compression, a recrystallization grain size model and dynamic recrystallization percentage model were established by the cellular automaton model. The dislocation density model, critical dislocation density model, nucleation rate model and grain growth model of magnesium alloy AZ31 were deduced by thermal compression experiments under different deformation conditions. Combining the specific evolution rules of cellular automata, cellular automata model was established. The simulation results and accury of cellular automata were verified by stress-strain curves and grain size. Based on the experimental data and the JMAK theory, the recrystallization grain size model and dynamic recrystallization percentage model were deduced. With DEFORM-3D analysis software, the change of grain size distribution and dynamic recrystallization percentage distribution in deformation were obtained.
Based on the microstructure evolution of AZ31 magnesium alloy during hot compression, a recrystallization grain size model and dynamic recrystallization percentage model were established by the cellular automaton model. The dislocation density model, critical dislocation density model, nucleation rate model and grain growth model of magnesium alloy AZ31 were deduced by thermal compression experiments under different deformation conditions. Combining the specific evolution rules of cellular automata, cellular automata model was established. The simulation results and accury of cellular automata were verified by stress-strain curves and grain size. Based on the experimental data and the JMAK theory, the recrystallization grain size model and dynamic recrystallization percentage model were deduced. With DEFORM-3D analysis software, the change of grain size distribution and dynamic recrystallization percentage distribution in deformation were obtained.
2018, 47(3):895-903.
Abstract:
Typical grade 654SMo and C-276 were selected to investigate the precipitated phases of high Mo super austenictic stainless steel and Ni-Cr-Mo Nickel-base alloy. Microstructure observation, EDS and phase analysis was taken for 654SMo and C-276 samples at different aging conditions.The results showed that the types and morphology of the precipitated phase in 654SMo and C-276 were different due to their different alloy system athough they both contained high content of Cr, Mo element. About eight kinds of second phases were precipitated in 654SMo, which included σ phase,Cr2N,μ phase,χphase,Laves phase,M23C6,M6C and M3C. σ phase and Cr2N were the main harmful phases of 654SMo and the peak precipitating temperature is 900℃. For C-276 alloy, M6C and μ phase were the main precipitated phases and σ phase wasn’t found under the aging condition of this aticle.
Typical grade 654SMo and C-276 were selected to investigate the precipitated phases of high Mo super austenictic stainless steel and Ni-Cr-Mo Nickel-base alloy. Microstructure observation, EDS and phase analysis was taken for 654SMo and C-276 samples at different aging conditions.The results showed that the types and morphology of the precipitated phase in 654SMo and C-276 were different due to their different alloy system athough they both contained high content of Cr, Mo element. About eight kinds of second phases were precipitated in 654SMo, which included σ phase,Cr2N,μ phase,χphase,Laves phase,M23C6,M6C and M3C. σ phase and Cr2N were the main harmful phases of 654SMo and the peak precipitating temperature is 900℃. For C-276 alloy, M6C and μ phase were the main precipitated phases and σ phase wasn’t found under the aging condition of this aticle.
2018, 47(3):904-909.
Abstract:
Stess corrosion behavior and cracking mechanism of 2205 duplex stainless steel (DSS) in saturated H2S environment were studied by using C-rings Stress Corrosion Cracking Test. The results showed that 2205 DSS has good resistance to stress corrosion in Test Solution A of NACE Standard. Through OM, SEM, EDS and electrochemical analysis, stress corrosion cracking in 2205 DSS undergoes the following procedures: pitting corrosion on surface, formation of corrosion hole, dissociation of H2S, absorption of H atoms and their diffusion from corrosion hole to inner metal, then gathering at some place in matix, finally initiation of cracks by hydrogen induced cracking mechanism and their gradual propagation.
Stess corrosion behavior and cracking mechanism of 2205 duplex stainless steel (DSS) in saturated H2S environment were studied by using C-rings Stress Corrosion Cracking Test. The results showed that 2205 DSS has good resistance to stress corrosion in Test Solution A of NACE Standard. Through OM, SEM, EDS and electrochemical analysis, stress corrosion cracking in 2205 DSS undergoes the following procedures: pitting corrosion on surface, formation of corrosion hole, dissociation of H2S, absorption of H atoms and their diffusion from corrosion hole to inner metal, then gathering at some place in matix, finally initiation of cracks by hydrogen induced cracking mechanism and their gradual propagation.
2018, 47(3):976-981.
Abstract:
The mechanical properties and environmental embrittlement of ordered (Fe,Co)3V alloys doping with various boron content have been investigated when tensile tested in vacuum and 1 kPa H2. The results show that the grain size of the ordered (Fe,Co)3V alloy doped with 0.02 wt.%B decreased by 27.5 % compared with boron-free (Fe,Co)3V alloy, while the tensile strength and elongation reached the maximum. However, as the boron content in the ordered (Fe,Co)3V alloy exceeds 0.02 wt.%, the grain size and mechanical properties remain unchanged when tensile tested in vacuum and hydrogen gas. The ordered boron-free (Fe,Co)3V alloy exhibits severe brittleness in hydrogen gas. By adding 0.02 wt. %B the hydrogen embrittlement factor of the ordered (Fe,Co)3V alloy decrease by 34.4 % and the fracture mode changes from full intergranular to mixed fracture of intergranular and transgranular. But when boron content increases continuously in the ordered (Fe,Co)3V alloy, the hydrogen embrittlement factor keeps about 50 %, indicating boron cannot completely suppress the environmental embrittlement of the ordered (Fe,Co)3V alloy in hydrogen.
The mechanical properties and environmental embrittlement of ordered (Fe,Co)3V alloys doping with various boron content have been investigated when tensile tested in vacuum and 1 kPa H2. The results show that the grain size of the ordered (Fe,Co)3V alloy doped with 0.02 wt.%B decreased by 27.5 % compared with boron-free (Fe,Co)3V alloy, while the tensile strength and elongation reached the maximum. However, as the boron content in the ordered (Fe,Co)3V alloy exceeds 0.02 wt.%, the grain size and mechanical properties remain unchanged when tensile tested in vacuum and hydrogen gas. The ordered boron-free (Fe,Co)3V alloy exhibits severe brittleness in hydrogen gas. By adding 0.02 wt. %B the hydrogen embrittlement factor of the ordered (Fe,Co)3V alloy decrease by 34.4 % and the fracture mode changes from full intergranular to mixed fracture of intergranular and transgranular. But when boron content increases continuously in the ordered (Fe,Co)3V alloy, the hydrogen embrittlement factor keeps about 50 %, indicating boron cannot completely suppress the environmental embrittlement of the ordered (Fe,Co)3V alloy in hydrogen.
2018, 47(3):910-914.
Abstract:
The Ni-based wear resistance coating on pure titanium TA1 substrate by plasma spray-welding method has been prepared. The interface morphology, microstructure, the microhardness of the coating and its tribological properties have been studied. The results show that the coating is composed of transition layer and strengthening layer, and a metallurgical bonding interface based on atomic diffusion and a transition layer mainly composed of dentrite are formed between the coating and substrate. The phases of the coating mainly compose of γ-Ni andγ-Ni(Ti) and hard particles such as TiC、Cr7C3、Ni3B and TiB2 and so on. Strengthening layer is characterized by a wear resistance microstructure composed of tough Ni matrix and hard particles, the micro-hardness is between 830~907HV, which is 700HV higher than that of the substrate. The element distribution and the microstructure, micro-hardness of coating in the cross section change continuously and gradually along depth direction. Compared with TA1 substrate, the friction coefficient of Ni-based spray-welding coating decreases, the wear resistance has been obviously enhanced and spray-welding coating appears a slightly abrasive wear characteristics.
The Ni-based wear resistance coating on pure titanium TA1 substrate by plasma spray-welding method has been prepared. The interface morphology, microstructure, the microhardness of the coating and its tribological properties have been studied. The results show that the coating is composed of transition layer and strengthening layer, and a metallurgical bonding interface based on atomic diffusion and a transition layer mainly composed of dentrite are formed between the coating and substrate. The phases of the coating mainly compose of γ-Ni andγ-Ni(Ti) and hard particles such as TiC、Cr7C3、Ni3B and TiB2 and so on. Strengthening layer is characterized by a wear resistance microstructure composed of tough Ni matrix and hard particles, the micro-hardness is between 830~907HV, which is 700HV higher than that of the substrate. The element distribution and the microstructure, micro-hardness of coating in the cross section change continuously and gradually along depth direction. Compared with TA1 substrate, the friction coefficient of Ni-based spray-welding coating decreases, the wear resistance has been obviously enhanced and spray-welding coating appears a slightly abrasive wear characteristics.
2018, 47(3):915-919.
Abstract:
The morphology, distribution and crystallographic orientation of TiB in situ formed in TiB/Ti-6Al-4V composite coating by laser was observed and analyzed by TEM, EBSD systematically, in order to explore the formation mechanism of tubular TiB. The results show that, TiB showed two morphologies: rod and needle. And the morphology of TiB crystals is controlled by growth time and element concentration. Rod-like TiB nucleated in the hypereutectic region, and needle-like TiB nucleated in the eutectic and hypoeutectic region. The growth of (010)B27 and (001)BF planes will no longer be stable, when the the product of diameter and the growth rate of TiB exceed the critical value. The growth rate in the edge region of TiB is faster than the center due to the concentration of B. TiB eventually forms a tubular structure because B element is consumed by the growth of edges that further inhibits the growth of the central region.With the increase of diameter of TiB, the tubular structure appears more frequently.
The morphology, distribution and crystallographic orientation of TiB in situ formed in TiB/Ti-6Al-4V composite coating by laser was observed and analyzed by TEM, EBSD systematically, in order to explore the formation mechanism of tubular TiB. The results show that, TiB showed two morphologies: rod and needle. And the morphology of TiB crystals is controlled by growth time and element concentration. Rod-like TiB nucleated in the hypereutectic region, and needle-like TiB nucleated in the eutectic and hypoeutectic region. The growth of (010)B27 and (001)BF planes will no longer be stable, when the the product of diameter and the growth rate of TiB exceed the critical value. The growth rate in the edge region of TiB is faster than the center due to the concentration of B. TiB eventually forms a tubular structure because B element is consumed by the growth of edges that further inhibits the growth of the central region.With the increase of diameter of TiB, the tubular structure appears more frequently.
2018, 47(3):920-926.
Abstract:
A Ti-6Al-4V wall was fabricated by WAAM on the basis of substrate alloy. Residual stress in the WAAM-substrate wall was measured by using contour method. There were considerable residual stresses in the WAAM-substrate wall. A finite element model was developed to simulate stress release in the cutting processing of the compact tension (C(T)) specimen from the wall. The calculated residual stress retained in the C(T) specimen was in good agreement with the measurement result obtained by contour method. Residual stress evolution and its effects on the crack propagation behavior at the WAAM/substrate interface were estimated by the developed finite element model. Following observations are revealed by experimental and numerical analysis. Residual stress distributions are quite different in the Type A and C specimen. For Type A specimen (notch located in the substrate), the compression residual stress area is closed to the notch, whereas for the Type C specimen (notch located in the WAAM alloy), the compression residual stress area is far away from the notch. Residual stresses has a little effect on the fatigue crack growth life of Type A specimen since most of them are released after the crack quickly entered and went through the compression area. However, residual stresses decrease a little with the crack growth at a long period for Type C specimen, which results a considerable stress intensity factor and shortens the fatigue crack growth life.
A Ti-6Al-4V wall was fabricated by WAAM on the basis of substrate alloy. Residual stress in the WAAM-substrate wall was measured by using contour method. There were considerable residual stresses in the WAAM-substrate wall. A finite element model was developed to simulate stress release in the cutting processing of the compact tension (C(T)) specimen from the wall. The calculated residual stress retained in the C(T) specimen was in good agreement with the measurement result obtained by contour method. Residual stress evolution and its effects on the crack propagation behavior at the WAAM/substrate interface were estimated by the developed finite element model. Following observations are revealed by experimental and numerical analysis. Residual stress distributions are quite different in the Type A and C specimen. For Type A specimen (notch located in the substrate), the compression residual stress area is closed to the notch, whereas for the Type C specimen (notch located in the WAAM alloy), the compression residual stress area is far away from the notch. Residual stresses has a little effect on the fatigue crack growth life of Type A specimen since most of them are released after the crack quickly entered and went through the compression area. However, residual stresses decrease a little with the crack growth at a long period for Type C specimen, which results a considerable stress intensity factor and shortens the fatigue crack growth life.
2018, 47(3):927-931.
Abstract:
TZM alloy was successfully brazed using Ti-28Ni as filler metal at 1040℃. The effect of holding time on interfacial microstructure and mechanical properties of brazed joints was studied and the typical microstructure of joint was detected using SEM, EDS. As a result, the typical interfacial microstructure was: TZM/Tiss/δ-Ti2Ni/Tiss/TZM. As increased the holding time, the width of the braze seam decreased, the continuous width of Tiss basically did not change, and the width of central δ-Ti2Ni layer decreased to some extent. Meanwhile, the diffusion of TZM into base materials enhanced. When the holding time was relatively short, there was undissolved TZM block in the weld joints, and the base metal could dissolve thoroughly while extending the holding time. The highest average shear strength of 92.6 MPa was achieved when the holding time was 10 min, and the fracture happened at δ-Ti2Ni layer, which was intergranular brittle fracture.
TZM alloy was successfully brazed using Ti-28Ni as filler metal at 1040℃. The effect of holding time on interfacial microstructure and mechanical properties of brazed joints was studied and the typical microstructure of joint was detected using SEM, EDS. As a result, the typical interfacial microstructure was: TZM/Tiss/δ-Ti2Ni/Tiss/TZM. As increased the holding time, the width of the braze seam decreased, the continuous width of Tiss basically did not change, and the width of central δ-Ti2Ni layer decreased to some extent. Meanwhile, the diffusion of TZM into base materials enhanced. When the holding time was relatively short, there was undissolved TZM block in the weld joints, and the base metal could dissolve thoroughly while extending the holding time. The highest average shear strength of 92.6 MPa was achieved when the holding time was 10 min, and the fracture happened at δ-Ti2Ni layer, which was intergranular brittle fracture.
2018, 47(3):932-936.
Abstract:
The Ti6Al4V-xB(wt.%,x=0,0.05,0.1,0.15)alloys were prepared at 900 ℃ for 2h by non-consumable melting and suction casting. In this study, the effect of Ti6Al4V-xB alloys with doping different B proportion on as-cast microstructures and mechanical properties is analyzed. The results show that the addition of boron impacts the solidification process of titanium alloy. The enriched B in solid-liquid frontier retarded the growth of initial β-Ti and was effective to promote grain refining. When the boron proportion was more than 0.1%, TiB phases precipitated from liquid. The ultimate strength of Ti6Al4V-xB alloys increased with the proportion of B (893 Mpa to 966 Mpa), which are attributed to grain-refinement and precipitation strengthening. The change of alloy plasticity is first increases and then decreases, about increasing 15% of Ti6Al4V-0.05B alloy and about decreasing 50% of Ti6Al4V-0.1B and Ti6Al4V-0.5B. This is because the fragile precipitated-phase of TiB is formed , which can cause the crack-sensitive zone.
The Ti6Al4V-xB(wt.%,x=0,0.05,0.1,0.15)alloys were prepared at 900 ℃ for 2h by non-consumable melting and suction casting. In this study, the effect of Ti6Al4V-xB alloys with doping different B proportion on as-cast microstructures and mechanical properties is analyzed. The results show that the addition of boron impacts the solidification process of titanium alloy. The enriched B in solid-liquid frontier retarded the growth of initial β-Ti and was effective to promote grain refining. When the boron proportion was more than 0.1%, TiB phases precipitated from liquid. The ultimate strength of Ti6Al4V-xB alloys increased with the proportion of B (893 Mpa to 966 Mpa), which are attributed to grain-refinement and precipitation strengthening. The change of alloy plasticity is first increases and then decreases, about increasing 15% of Ti6Al4V-0.05B alloy and about decreasing 50% of Ti6Al4V-0.1B and Ti6Al4V-0.5B. This is because the fragile precipitated-phase of TiB is formed , which can cause the crack-sensitive zone.
2018, 47(3):937-942.
Abstract:
Microstructure evolution and deformation stored energy change of sintered pure tungsten during multi-directional forging was investigated by OM and DSC. The source of deformation stored energy and dynamic recrystallization behavior of pure tungsten were studied with XRD and EBSD. The results indicate that dynamic recrystallization during hot deformation leads to remarkably grain refining with porosity significantly reduced. High-density dislocation structure retained in the grain and subgrain result in an increase in deformation stored energy after deformation. There are quantities of recrystallized grains distributed along the higher energy zone in grain boundaries and grain boundary Intersection. The mechanism of dynamic recrystallization is the mixture of deformation induced grain boundary migration mechanism with subgrain coarsening and grain mechanical fragmentation. The recrystallization temperature of pure tungsten unchanged substantially with thermal stability increased after multiple direction forging.
Microstructure evolution and deformation stored energy change of sintered pure tungsten during multi-directional forging was investigated by OM and DSC. The source of deformation stored energy and dynamic recrystallization behavior of pure tungsten were studied with XRD and EBSD. The results indicate that dynamic recrystallization during hot deformation leads to remarkably grain refining with porosity significantly reduced. High-density dislocation structure retained in the grain and subgrain result in an increase in deformation stored energy after deformation. There are quantities of recrystallized grains distributed along the higher energy zone in grain boundaries and grain boundary Intersection. The mechanism of dynamic recrystallization is the mixture of deformation induced grain boundary migration mechanism with subgrain coarsening and grain mechanical fragmentation. The recrystallization temperature of pure tungsten unchanged substantially with thermal stability increased after multiple direction forging.
2018, 47(3):943-948.
Abstract:
The (Cu-50Mo)-0.5%LaCl3 and (Cu-50Mo)-5%WC-0.5%LaCl3 composites were prepared by spark plasma sintering (SPS) process. The density, hardness, electrical conductivity and microstructure of the composites were investigated respectively. The electrical contact test was carried out for both composites. The materials transfer direction and the anode, cathode mass change and the contact ends total mass change of the composites were studied under the condition of different DC and resistance load respectively. The morphologies after arc erosion were investigated by means of scanning electronic microscopy (SEM). The electrical erosive characteristics of the composites were analyzed. The results show that the composites have better comprehensive properties prepared by SPS method. The transfer mass increases with increase of electrical current density. The contact surface of the composites present the appearance characteristics with pores、molten pool and pits after arc erosion test. The surface arc erosion characteristics are much more obvious with increasing of current density. The contact resistance decreases with increasing of current. The contact resistance with the current changes has no obvious fluctuation, while the welding force increases with increase of current.
The (Cu-50Mo)-0.5%LaCl3 and (Cu-50Mo)-5%WC-0.5%LaCl3 composites were prepared by spark plasma sintering (SPS) process. The density, hardness, electrical conductivity and microstructure of the composites were investigated respectively. The electrical contact test was carried out for both composites. The materials transfer direction and the anode, cathode mass change and the contact ends total mass change of the composites were studied under the condition of different DC and resistance load respectively. The morphologies after arc erosion were investigated by means of scanning electronic microscopy (SEM). The electrical erosive characteristics of the composites were analyzed. The results show that the composites have better comprehensive properties prepared by SPS method. The transfer mass increases with increase of electrical current density. The contact surface of the composites present the appearance characteristics with pores、molten pool and pits after arc erosion test. The surface arc erosion characteristics are much more obvious with increasing of current density. The contact resistance decreases with increasing of current. The contact resistance with the current changes has no obvious fluctuation, while the welding force increases with increase of current.
2018, 47(3):949-953.
Abstract:
In this paper, the CrTiAlN coating was prepared by physical deposition technology on M2 high speed steel. The tribological behavior and surface morphology of the coatings were studied by means of emission scanning electron microscopy, energy dispersive spectroscopy, confocal scanning microscopy and ball-disc friction and wear testing machine. The results show that the friction coefficient of the coating increases with the increase of ambient temperature. At room temperature, the friction coefficient of the coating is about 0.24 and is gentle with time. At 200℃, the friction coefficient is greatly changed with time at beginning of Friction and then is stably about 0.53 at stable friction stage after half an hour. The wear rate of the CrTiAlN coating also increases with the increase of ambient temperature. The time variation curve of friction fluctuates greatly at high temperature and the wear degree of the grinding ball is gradually increased with the increase of temperature. The wear mechanism of the coating is mainly coordination role of oxidation wear, adhesive wear and abrasive wear.
In this paper, the CrTiAlN coating was prepared by physical deposition technology on M2 high speed steel. The tribological behavior and surface morphology of the coatings were studied by means of emission scanning electron microscopy, energy dispersive spectroscopy, confocal scanning microscopy and ball-disc friction and wear testing machine. The results show that the friction coefficient of the coating increases with the increase of ambient temperature. At room temperature, the friction coefficient of the coating is about 0.24 and is gentle with time. At 200℃, the friction coefficient is greatly changed with time at beginning of Friction and then is stably about 0.53 at stable friction stage after half an hour. The wear rate of the CrTiAlN coating also increases with the increase of ambient temperature. The time variation curve of friction fluctuates greatly at high temperature and the wear degree of the grinding ball is gradually increased with the increase of temperature. The wear mechanism of the coating is mainly coordination role of oxidation wear, adhesive wear and abrasive wear.
2018, 47(3):954-960.
Abstract:
La(Fe,Si)13 hydride is regarded as one of the most promising room-temperature magnetic refrigerants. A typical active magnetic refrigerator machine requires thin plate-shaped refrigerants. In this work, plate-shaped LaFe11.44Si1.56 hydrides with different particle sizes were prepared by sintering in a high-pressure H2 atmosphere of 40MPa. Effect of particle size and sintering duration on the structure and magnetocaloric effect was investigated. Compared to the parent alloy, α-Fe contents of the sintered samples are increased and different particle sizes and sintering duration do not remarkably influence the precipitation of α-Fe. Upon increasing of particle size, Curie temperatures of sintered samples slightly increase and are shifted to above room temperature. Hysteresis of plate-shaped LaFe11.44Si1.56 hydrides has been almost eliminated due to the existence of micropores with a large size of distribution and small particle size, which reduces the internal strain during the process of the phase transitions. Compared with the sintered sample with particle size from 110 to 150μm, the hysteresis loss of the sintered sample with particle size smaller than 40μm is decreased by 35%, while the large magnetic-entropy ΔSm maintains. LaFe11.44Si1.56 thin plate-shaped hydride with particle size smaller than 40μm exhibits a large change ΔSm of 8.5J/kg.K(53mJ/cm3.K) for a field change of 1.5T at 345K.
La(Fe,Si)13 hydride is regarded as one of the most promising room-temperature magnetic refrigerants. A typical active magnetic refrigerator machine requires thin plate-shaped refrigerants. In this work, plate-shaped LaFe11.44Si1.56 hydrides with different particle sizes were prepared by sintering in a high-pressure H2 atmosphere of 40MPa. Effect of particle size and sintering duration on the structure and magnetocaloric effect was investigated. Compared to the parent alloy, α-Fe contents of the sintered samples are increased and different particle sizes and sintering duration do not remarkably influence the precipitation of α-Fe. Upon increasing of particle size, Curie temperatures of sintered samples slightly increase and are shifted to above room temperature. Hysteresis of plate-shaped LaFe11.44Si1.56 hydrides has been almost eliminated due to the existence of micropores with a large size of distribution and small particle size, which reduces the internal strain during the process of the phase transitions. Compared with the sintered sample with particle size from 110 to 150μm, the hysteresis loss of the sintered sample with particle size smaller than 40μm is decreased by 35%, while the large magnetic-entropy ΔSm maintains. LaFe11.44Si1.56 thin plate-shaped hydride with particle size smaller than 40μm exhibits a large change ΔSm of 8.5J/kg.K(53mJ/cm3.K) for a field change of 1.5T at 345K.
2018, 47(3):961-967.
Abstract:
It was investigated that the microstructure and mechanical property evolution of a supperalloy USC 141 under aging 10000h at 700oC in this paper. The results show that both of the strengths of the alloy tested at room temperature and 700oC were maintained at high level during long-term aging, while the coarsening behavior of carbides along grain boundary, which transformed in a shape of chain generally, leads to decrease plasticity and toughness. During the process of long-term aging，the precipitation of M23C6 showed a trend of slow increasing. Whereas the evolution of M6C type carbide in this alloy consists of three stages. The first stage could be marked as the continuum transformation of M6C to M12C, which was induced by the diffusion of Mo and Ni. At the second stage, the carbide type and the precipitation of carbides changed little. At the third stage, M12C carbides further coarsened afterwards by the diffusion of Mo, and M12C inside grains shows a shape of plate. The microstructure evolution of γ′ precipitates could be divided into three stages as well. The formation and initial grow up fastly of γ′ was resulted from the diffusion of Cr, and the γ′ particles were distributed finely during the first stage. At the second stage, the means size and precipitation of γ′ increase slowly. The last stage was marked by the coarsening behavior of γ′, mainly resulting from the coalescence of adjacent γ′ particles, and finally exhibited higher dispersion level of particle size distribution.
It was investigated that the microstructure and mechanical property evolution of a supperalloy USC 141 under aging 10000h at 700oC in this paper. The results show that both of the strengths of the alloy tested at room temperature and 700oC were maintained at high level during long-term aging, while the coarsening behavior of carbides along grain boundary, which transformed in a shape of chain generally, leads to decrease plasticity and toughness. During the process of long-term aging，the precipitation of M23C6 showed a trend of slow increasing. Whereas the evolution of M6C type carbide in this alloy consists of three stages. The first stage could be marked as the continuum transformation of M6C to M12C, which was induced by the diffusion of Mo and Ni. At the second stage, the carbide type and the precipitation of carbides changed little. At the third stage, M12C carbides further coarsened afterwards by the diffusion of Mo, and M12C inside grains shows a shape of plate. The microstructure evolution of γ′ precipitates could be divided into three stages as well. The formation and initial grow up fastly of γ′ was resulted from the diffusion of Cr, and the γ′ particles were distributed finely during the first stage. At the second stage, the means size and precipitation of γ′ increase slowly. The last stage was marked by the coarsening behavior of γ′, mainly resulting from the coalescence of adjacent γ′ particles, and finally exhibited higher dispersion level of particle size distribution.
2018, 47(3):968-971.
Abstract:
This paper proposes a method to sintering tungsten-copper alloy coating layer to copper plate surface. Sintering in the hydrogen after pre-compacted tungsten-copper alloy powder to the surface of the copper plate, then compacte the powder by explosive sintering,diffusion sintering after explosive compaction.The compressing process of explosive compaction was simulated using the commercially available package AUTODYN.Numerical simulation indicates deformation of the coating layer and pressure distribution during the compressing process,ensure the parameters of experiment is well.Use these parameters we mke the coating layer up to 99.3% of the theoretical density.Microstructure characteristics indicate that tungsten copper powder well mixed.The size of the tungsten particles is larger than copper particles.The SEM fracture surface analysis is different from traditional fracture. Tungsten copper joint surface,analyzed by SEM,indicates that tungsten copper alloy sintered on the surface of the copper.
This paper proposes a method to sintering tungsten-copper alloy coating layer to copper plate surface. Sintering in the hydrogen after pre-compacted tungsten-copper alloy powder to the surface of the copper plate, then compacte the powder by explosive sintering,diffusion sintering after explosive compaction.The compressing process of explosive compaction was simulated using the commercially available package AUTODYN.Numerical simulation indicates deformation of the coating layer and pressure distribution during the compressing process,ensure the parameters of experiment is well.Use these parameters we mke the coating layer up to 99.3% of the theoretical density.Microstructure characteristics indicate that tungsten copper powder well mixed.The size of the tungsten particles is larger than copper particles.The SEM fracture surface analysis is different from traditional fracture. Tungsten copper joint surface,analyzed by SEM,indicates that tungsten copper alloy sintered on the surface of the copper.
2018, 47(3):972-975.
Abstract:
The effect of nitrogen–oxygen ratio on composition, micro–structure and optical properties of AlOxNy films deposited by ion beam assisted deposition (IBAD) was investigated by using XPS, XRD and spectroscopic ellipsometry. As the ratio of nitrogen to oxygen decreases, the content of nitrogen in the films decreases, whereas, the content of oxygen in the films increases; at the same time, the amorphous phase in the films transfer to AlON phase. The zero value for extinction coefficient of the films indicates the deposited films are dielectric materials. And the refractive index of films within the whole wavelength range decreases with decreasing the ratio of nitrogen to oxygen.
The effect of nitrogen–oxygen ratio on composition, micro–structure and optical properties of AlOxNy films deposited by ion beam assisted deposition (IBAD) was investigated by using XPS, XRD and spectroscopic ellipsometry. As the ratio of nitrogen to oxygen decreases, the content of nitrogen in the films decreases, whereas, the content of oxygen in the films increases; at the same time, the amorphous phase in the films transfer to AlON phase. The zero value for extinction coefficient of the films indicates the deposited films are dielectric materials. And the refractive index of films within the whole wavelength range decreases with decreasing the ratio of nitrogen to oxygen.
2018, 47(3):982-989.
Abstract:
3D fabric reinforced Cf/Al composites were fabricated by the vacuum assisted pressure infiltration method. The microstructure and interfacial reaction of the composites prepared at different temperature levels was investigated. The uniaxial tensile property of the composites was tested at room temperature and elevated temperature and the corresponding tensile fracture surface was analyzed. The results indicated that the relative density increased and the fiber segregation in partial region decreased with fabrication temperature increasing. Meanwhile the content of Al4C3 compound at interface increased obviously. At room temperature, the ultimate tensile strength of the composites from 570℃ to 600℃ degenerated dramatically with interfacial reaction aggravated. When the composites were tested at elevated temperature, however, the ultimate tensile strength increased with fabrication temperature increasing. The improvement of interfacial strength is beneficial to the high temperature mechanical property. The matrix alloy softening and interface weakening due to elevated temperature can promote the fiber pull out and interface sliding during the fracture process.
3D fabric reinforced Cf/Al composites were fabricated by the vacuum assisted pressure infiltration method. The microstructure and interfacial reaction of the composites prepared at different temperature levels was investigated. The uniaxial tensile property of the composites was tested at room temperature and elevated temperature and the corresponding tensile fracture surface was analyzed. The results indicated that the relative density increased and the fiber segregation in partial region decreased with fabrication temperature increasing. Meanwhile the content of Al4C3 compound at interface increased obviously. At room temperature, the ultimate tensile strength of the composites from 570℃ to 600℃ degenerated dramatically with interfacial reaction aggravated. When the composites were tested at elevated temperature, however, the ultimate tensile strength increased with fabrication temperature increasing. The improvement of interfacial strength is beneficial to the high temperature mechanical property. The matrix alloy softening and interface weakening due to elevated temperature can promote the fiber pull out and interface sliding during the fracture process.
2018, 47(3):990-994.
Abstract:
Minor alloying is a useful approach for promoting glass forming ability (GFA) of metallic glasses. U-Co metallic glasses can be achieved in a wide composition range, but their GFAs are very poor. This study is aimed to increase the GFA in U-Co system by minor alloying. Sn, Si, Be, Cu, Pd, Y and Zr were selected as different-typed minor alloying elements in U69.2Co30.8 alloy. The glassy U69Co30M1 (M=Sn, Si, Be, Cu, Pd, Y, Zr) ribbon samples were prepared by melt-spinning with a copper roller, and their phase formation and thermodynamics were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. The results indicate that, Sn element significantly improves the GFA, Si displays the second improvement, Be and Cu are slightly effective while Pd, Y and Zr deteriorate the GFA. Based on the combination of the melting behavior change reflected by the DSC result, and the relationship between the GFA and the melting temperatures, electro-negativities, atomic sizes of M elements as well as mixing-enthalpies of M-C, the effect of the minor alloying on the GFA in U-Co system should be attributed to the variation of both metallic liquid stability and the crystallization driving force.
Minor alloying is a useful approach for promoting glass forming ability (GFA) of metallic glasses. U-Co metallic glasses can be achieved in a wide composition range, but their GFAs are very poor. This study is aimed to increase the GFA in U-Co system by minor alloying. Sn, Si, Be, Cu, Pd, Y and Zr were selected as different-typed minor alloying elements in U69.2Co30.8 alloy. The glassy U69Co30M1 (M=Sn, Si, Be, Cu, Pd, Y, Zr) ribbon samples were prepared by melt-spinning with a copper roller, and their phase formation and thermodynamics were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. The results indicate that, Sn element significantly improves the GFA, Si displays the second improvement, Be and Cu are slightly effective while Pd, Y and Zr deteriorate the GFA. Based on the combination of the melting behavior change reflected by the DSC result, and the relationship between the GFA and the melting temperatures, electro-negativities, atomic sizes of M elements as well as mixing-enthalpies of M-C, the effect of the minor alloying on the GFA in U-Co system should be attributed to the variation of both metallic liquid stability and the crystallization driving force.
Li Jiajie
,
Guo Chengjun
,
Zhou Toujun
,
Liu Wujie
,
Chen Jinshui
,
Liu Renhui
,
Zhou Huijie
,
Yang Bin
2018, 47(3):995-1000.
Abstract:
The DyZn films on the sintered NdFeB magnet surface were prepared through DC magnetron sputtering. The magnetic properties, temperature stability and microstructure of the magnets before and after the thermal diffusion treatment were compared. Under the circumstances of keeping the remanence invariable, the magnet coercivity enhanced significantly from 963.68 kA/m to 1544.60 kA/m with an increasing of 63.31% after DyZn thermal diffusion. The magnet temperature stability could be improved by grain boundary diffusion. The temperature coefficient of the remanence kept constant while that of the coercivity reduced from -0.5533% /K to -0.4885% /K in the range of 293K~453K. Dy elements diffusing along the grain boundary phase mainly aggregated between the grain boundary phase and the grain epitaxial layer via SEM and EPMA with EDS observation.The optimization of microstructure and composition of the grain boundary phase and the formed transition layer (Nd,Dy)2Fe14B between them are the main reasons which causing the coercivity to upgrade dramatically.
The DyZn films on the sintered NdFeB magnet surface were prepared through DC magnetron sputtering. The magnetic properties, temperature stability and microstructure of the magnets before and after the thermal diffusion treatment were compared. Under the circumstances of keeping the remanence invariable, the magnet coercivity enhanced significantly from 963.68 kA/m to 1544.60 kA/m with an increasing of 63.31% after DyZn thermal diffusion. The magnet temperature stability could be improved by grain boundary diffusion. The temperature coefficient of the remanence kept constant while that of the coercivity reduced from -0.5533% /K to -0.4885% /K in the range of 293K~453K. Dy elements diffusing along the grain boundary phase mainly aggregated between the grain boundary phase and the grain epitaxial layer via SEM and EPMA with EDS observation.The optimization of microstructure and composition of the grain boundary phase and the formed transition layer (Nd,Dy)2Fe14B between them are the main reasons which causing the coercivity to upgrade dramatically.
2018, 47(3):1001-1006.
Abstract:
In this study, permanent magnetic nanocrystalline Sm5Co19Hf0.4 alloy and Sm5Co19Hf0. 4CNTs0. 4 alloy with high room-temperature coercivity were produced. The microstructure, crystal structure and magnetic were studied. The results show that the Hf elements and CNTs mixed added did not lead to phase decomposition of Ce5Co19 type structure, meanwhile the microstructure possess fine grain size and uniform distribution. Energy Dispersive X-ray Spectrometry (EDX) analysis confirmed that CNTs move into grain boundaries of the nanocrystalline Sm5Co19Hf0.4CNTs0.4alloy, which can improve the coercivity of the nanocrystalline Sm5Co19 alloy for the grain boundary pinning effect. Rietyeld refinement showed that Hf comes into the Sm vacancy decreasing the lattice parameters and increasing the axial ratio c/a , which furtherly enhance the magnetocrystalline anisotropy , thus strengthen the coercivity of nanocrystalline alloy. In this paper, the results of the study can promote the design of Sm-Co alloy with high magnetocrystalline anisotropy and intrinsic coercivity.
In this study, permanent magnetic nanocrystalline Sm5Co19Hf0.4 alloy and Sm5Co19Hf0. 4CNTs0. 4 alloy with high room-temperature coercivity were produced. The microstructure, crystal structure and magnetic were studied. The results show that the Hf elements and CNTs mixed added did not lead to phase decomposition of Ce5Co19 type structure, meanwhile the microstructure possess fine grain size and uniform distribution. Energy Dispersive X-ray Spectrometry (EDX) analysis confirmed that CNTs move into grain boundaries of the nanocrystalline Sm5Co19Hf0.4CNTs0.4alloy, which can improve the coercivity of the nanocrystalline Sm5Co19 alloy for the grain boundary pinning effect. Rietyeld refinement showed that Hf comes into the Sm vacancy decreasing the lattice parameters and increasing the axial ratio c/a , which furtherly enhance the magnetocrystalline anisotropy , thus strengthen the coercivity of nanocrystalline alloy. In this paper, the results of the study can promote the design of Sm-Co alloy with high magnetocrystalline anisotropy and intrinsic coercivity.
48 Research on the Process and Properties of Tin Bronze Alloy Manufactured by Laser Selective Melting
2018, 47(3):1007-1012.
Abstract:
In this paper, we choose QSn6.5-0.1 tin-bronze alloy that directly manufactured by SLM as material to study the influence of laser power,scan speed and scan space on the relative density of the tin-bronze alloy. An orthogonal process experiment with three factors and four levels on the basis of block forming experiment was designed to study the microstructure and the micro Vickers hardness of the forming parts. The results showed that high relative density of tin-bronze alloy could be got by increasing the laser power and choosing the appropriate scan speed and scan space. And with the optimized process parameters, the relative density of the samples is up to 98.71%. The microstructure is built up of obviously reticular dendrite structure with uniform distribution, mainly containing(α+δ)phase with rich tin and α phase with rich copper. The average micro vickers hardness of the top surface and the side face of the sample are respectively 133.87HV and 130.69HV, which are 45% higher than that of the traditional casting soft state of QSn6.5-0.1 tin-bronze alloy(70HB-90HB). so it had excellent mechanical properties. A three-dimensional wind-round model of tin bronze alloy was manufactured with optimized process parameter. Internal forming quality of wind-round model was researched by computer tomography (MicroCT) technology. And the Vickers hardness of top surface was also tested. The results showed that the internal relative density was high as well as the Vickers hardness of top surface. It is believed that QSn6.5-0.1 bronze alloy parts with fine quality can be manufactured by SLM technology.
In this paper, we choose QSn6.5-0.1 tin-bronze alloy that directly manufactured by SLM as material to study the influence of laser power,scan speed and scan space on the relative density of the tin-bronze alloy. An orthogonal process experiment with three factors and four levels on the basis of block forming experiment was designed to study the microstructure and the micro Vickers hardness of the forming parts. The results showed that high relative density of tin-bronze alloy could be got by increasing the laser power and choosing the appropriate scan speed and scan space. And with the optimized process parameters, the relative density of the samples is up to 98.71%. The microstructure is built up of obviously reticular dendrite structure with uniform distribution, mainly containing(α+δ)phase with rich tin and α phase with rich copper. The average micro vickers hardness of the top surface and the side face of the sample are respectively 133.87HV and 130.69HV, which are 45% higher than that of the traditional casting soft state of QSn6.5-0.1 tin-bronze alloy(70HB-90HB). so it had excellent mechanical properties. A three-dimensional wind-round model of tin bronze alloy was manufactured with optimized process parameter. Internal forming quality of wind-round model was researched by computer tomography (MicroCT) technology. And the Vickers hardness of top surface was also tested. The results showed that the internal relative density was high as well as the Vickers hardness of top surface. It is believed that QSn6.5-0.1 bronze alloy parts with fine quality can be manufactured by SLM technology.
2018, 47(3):1013-1019.
Abstract:
Thermoelectric material is a kind of key material for green energy conversion and thermoelectric thechnology application. It meets bottleneck for thermoelectric material due to mutual restriction among thermoelectric properties. It provides a clear idea for the next generation of thermoelectric materials development that the material designs about microstructure collaboratively adjust thermoelectric properties. The new concepts improving the thermoelectric properties are introduced in this paper, such as "multi-scale hierarchical architecture", "electronic crystals and ionic liquid ", "lattice defect engineering", "mosaic crystal" and "anharmonic vibration". The effect of some physic and chemical process ( such as energy band adjusting, weak bond, non harmonic vibration, Nano-domain scattering, spinal decomposition, energy filtering mechanism and phase transformation) on thermoelectric transport behave are adequately decribed. The effects of microstructure parameters (such as point defect, line defect, grain boundary, nano domain and second phase) adjusting on physical parameters (such as band structure, carrier free path and lattice vibration mode) are discussed in details. The development of the next generation high performance bulk thermoelectric materials is described on the basis of current status.
Thermoelectric material is a kind of key material for green energy conversion and thermoelectric thechnology application. It meets bottleneck for thermoelectric material due to mutual restriction among thermoelectric properties. It provides a clear idea for the next generation of thermoelectric materials development that the material designs about microstructure collaboratively adjust thermoelectric properties. The new concepts improving the thermoelectric properties are introduced in this paper, such as "multi-scale hierarchical architecture", "electronic crystals and ionic liquid ", "lattice defect engineering", "mosaic crystal" and "anharmonic vibration". The effect of some physic and chemical process ( such as energy band adjusting, weak bond, non harmonic vibration, Nano-domain scattering, spinal decomposition, energy filtering mechanism and phase transformation) on thermoelectric transport behave are adequately decribed. The effects of microstructure parameters (such as point defect, line defect, grain boundary, nano domain and second phase) adjusting on physical parameters (such as band structure, carrier free path and lattice vibration mode) are discussed in details. The development of the next generation high performance bulk thermoelectric materials is described on the basis of current status.
2018, 47(3):1020-1024.
Abstract:
The MgB2 wires and tapes have been well developeded during the past 15 years. MgB2 can be used in liquid hydrogen and low magnetic field, which has broad applicability in the future due to its cheap raw material. In this paper we review the traditional processing of MgB2 wires and set the stage for further. The method of internal magnesium diffusion is introduced in detail. A pure magnesium rod was placed at the center of copper shealth and niobium or tantalum barrier layer, and the space between magnesium rod and barrier layer was filled with boron powder. We can get the high density MgB2 layer after heat treatment. Finally, we discussed the key point of fabricating MgB2 tapes and wires in the future.
The MgB2 wires and tapes have been well developeded during the past 15 years. MgB2 can be used in liquid hydrogen and low magnetic field, which has broad applicability in the future due to its cheap raw material. In this paper we review the traditional processing of MgB2 wires and set the stage for further. The method of internal magnesium diffusion is introduced in detail. A pure magnesium rod was placed at the center of copper shealth and niobium or tantalum barrier layer, and the space between magnesium rod and barrier layer was filled with boron powder. We can get the high density MgB2 layer after heat treatment. Finally, we discussed the key point of fabricating MgB2 tapes and wires in the future.
