Volume 44,Issue 4,2015 Table of Contents
2015, 44(4):786-790.
Abstract:
Corrosion behaviors of sintered NdFeB magnets in H2SO4 solution, HCl solution and HNO3 solution of different concentrations were investigated by pickling, immersion test and electrochemical test. The results show that the corrosion mechanism of sintered NdFeB magnets in HNO3 solution is uniform corrosion, while the one in H2SO4 solution and HCl solution is selectively intergranular corrosion. The corrosion rate of NdFeB magnets increases with increasing of the concentrations of the three acid solutions, and the corrosion rate of NdFeB magnets in the HNO3 solution is the smallest among the three acid solutions both in immersion test and electrochemical test. Therefore, the HNO3 solution is more suitable to be used as the pickling solution for the surface pretreatment of sintered NdFeB magnets.
Corrosion behaviors of sintered NdFeB magnets in H2SO4 solution, HCl solution and HNO3 solution of different concentrations were investigated by pickling, immersion test and electrochemical test. The results show that the corrosion mechanism of sintered NdFeB magnets in HNO3 solution is uniform corrosion, while the one in H2SO4 solution and HCl solution is selectively intergranular corrosion. The corrosion rate of NdFeB magnets increases with increasing of the concentrations of the three acid solutions, and the corrosion rate of NdFeB magnets in the HNO3 solution is the smallest among the three acid solutions both in immersion test and electrochemical test. Therefore, the HNO3 solution is more suitable to be used as the pickling solution for the surface pretreatment of sintered NdFeB magnets.
2015, 44(4):813-816.
Abstract:
A series of bonded magnets of (Nd,Pr)10.5-xDyxFe83.5B6 (x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5) alloys were prepared by a melt-spun method. The effects of Dy substitution on the thermal stability of as-spun ribbons, the magnetic properties and microstructures of alloys were investigated. Dy addition will enhance the intrinsic coercivity Hcj greatly, but reduce the remanence Br, because Dy2Fe14B has a higher magnetocrystalline anisotropy field HA and a lower saturation magnetic polarization Js compared to those of Nd2Fe14B. The Dy substitution for Nd/Pr enhances the thermal stability and increases the crystallization annealing temperature. The higher annealing temperature leads the fine crystallites existing in as-spun ribbons to easily growing, resulting in appearance of some bigger grains and deterioration of the bonded magnet property. The bonded magnet of (Nd,Pr)9.5Dy1Fe83.5B6 alloy with 1.0at% Dy has optimal magnetic properties, i.e (BH)max=71.6 kJ/m3, Br=0.638 T, and Hcj= 611 kA/m
A series of bonded magnets of (Nd,Pr)10.5-xDyxFe83.5B6 (x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5) alloys were prepared by a melt-spun method. The effects of Dy substitution on the thermal stability of as-spun ribbons, the magnetic properties and microstructures of alloys were investigated. Dy addition will enhance the intrinsic coercivity Hcj greatly, but reduce the remanence Br, because Dy2Fe14B has a higher magnetocrystalline anisotropy field HA and a lower saturation magnetic polarization Js compared to those of Nd2Fe14B. The Dy substitution for Nd/Pr enhances the thermal stability and increases the crystallization annealing temperature. The higher annealing temperature leads the fine crystallites existing in as-spun ribbons to easily growing, resulting in appearance of some bigger grains and deterioration of the bonded magnet property. The bonded magnet of (Nd,Pr)9.5Dy1Fe83.5B6 alloy with 1.0at% Dy has optimal magnetic properties, i.e (BH)max=71.6 kJ/m3, Br=0.638 T, and Hcj= 611 kA/m
2015, 44(4):817-820.
Abstract:
Zr has become an indispensable trace element in the super-high strength aluminium alloy. In the present work, three Zr adding methods were adopted, that is adding aluminium zirconium master alloy, adding K2ZrF6 and adding composite zircon salt. The effects of melting temperature on the yield of Zr were studied, and the effects of different Zr element adding techniques on the existence form of Zr in aluminium alloy matrix were also researched. The results show that the yield of Zr is the highest and the grain refinement effect is the best upon adding composite zircon salt. The second phase containing Zr is coarse and the grain refinement effect is not good upon adding aluminium zirconium master alloy at 750 oC
Zr has become an indispensable trace element in the super-high strength aluminium alloy. In the present work, three Zr adding methods were adopted, that is adding aluminium zirconium master alloy, adding K2ZrF6 and adding composite zircon salt. The effects of melting temperature on the yield of Zr were studied, and the effects of different Zr element adding techniques on the existence form of Zr in aluminium alloy matrix were also researched. The results show that the yield of Zr is the highest and the grain refinement effect is the best upon adding composite zircon salt. The second phase containing Zr is coarse and the grain refinement effect is not good upon adding aluminium zirconium master alloy at 750 oC
2015, 44(4):826-825.
Abstract:
The products of self-healing phase BxC were examined as a function of temperature and initial gas molar ratios of BCl3:(BCl3+CH4) and H2:(BCl3+CH4) by complete thermodynamic equilibrium analysis. The results show that the composition of the condensed phase is quite sensitive to temperature and the molar ratios of BCl3:(BCl3+CH4) and H2:(BCl3+CH4). Based on our calculation, the ideal conditions for BxC deposition are as follows: the ratio of BCl3:(BCl3+CH4) is 0.8, the ratio of H2:(BCl3+CH4) ranges from 10 to 105.2, and the temperature is above 950 K. We found that the carbon-richment or boron-richment in materials are mainly adjusted by the ratios of BCl3:(BCl3+CH4) and H2:(BCl3+CH4)
The products of self-healing phase BxC were examined as a function of temperature and initial gas molar ratios of BCl3:(BCl3+CH4) and H2:(BCl3+CH4) by complete thermodynamic equilibrium analysis. The results show that the composition of the condensed phase is quite sensitive to temperature and the molar ratios of BCl3:(BCl3+CH4) and H2:(BCl3+CH4). Based on our calculation, the ideal conditions for BxC deposition are as follows: the ratio of BCl3:(BCl3+CH4) is 0.8, the ratio of H2:(BCl3+CH4) ranges from 10 to 105.2, and the temperature is above 950 K. We found that the carbon-richment or boron-richment in materials are mainly adjusted by the ratios of BCl3:(BCl3+CH4) and H2:(BCl3+CH4)
Zuo Jianhua
,
Yue Ming
,
Wang Yunqiao
,
Lu Qingmei
,
Liu Yanqin
,
Zhang Dongtao
,
Liu Weiqiang
,
Zhang Jiuxing
,
Guo Zhaohui
,
Li Wei
2015, 44(4):834-837.
Abstract:
The compounds of SmCo5 and Sm0.8Tm0.2Co5.2 have been studied via X-ray diffraction (XRD) and magnetic measurements, in order to clarify the effect of Tm doping on the crystal structure and intrinsic magnetic properties of the SmCo5 compound. XRD results show that both compounds have a single hexagonal CaCu5 type crystal structure, and the Tm doping leads to an expansion of the hexagonal unit cell in the direction of c axis and a contraction of a, b axes and the cell volume. The Curie temperatures (TC) of the SmCo5 and Sm0.8Tm0.2Co5.2 are 957 and 965 K, respectively. Magnetic measurements show that both the magnetic anisotropy field (HA) and the magnetization at an applied field of 7 T (M7T) of SmCo5 are higher than those of Sm0.8Tm0.2Co5.2 at room temperature (300 K). However, the HA and M7T of SmCo5 become lower than those of Sm0.8Tm0.2Co5.2 with the temperature increasing to 473 K. Therefore, it is concluded that Tm doping in SmCo5 can effectively improve the magnetic properties at elevated temperature
The compounds of SmCo5 and Sm0.8Tm0.2Co5.2 have been studied via X-ray diffraction (XRD) and magnetic measurements, in order to clarify the effect of Tm doping on the crystal structure and intrinsic magnetic properties of the SmCo5 compound. XRD results show that both compounds have a single hexagonal CaCu5 type crystal structure, and the Tm doping leads to an expansion of the hexagonal unit cell in the direction of c axis and a contraction of a, b axes and the cell volume. The Curie temperatures (TC) of the SmCo5 and Sm0.8Tm0.2Co5.2 are 957 and 965 K, respectively. Magnetic measurements show that both the magnetic anisotropy field (HA) and the magnetization at an applied field of 7 T (M7T) of SmCo5 are higher than those of Sm0.8Tm0.2Co5.2 at room temperature (300 K). However, the HA and M7T of SmCo5 become lower than those of Sm0.8Tm0.2Co5.2 with the temperature increasing to 473 K. Therefore, it is concluded that Tm doping in SmCo5 can effectively improve the magnetic properties at elevated temperature
2015, 44(4):848-853.
Abstract:
The phase transformation mechanism of near α titanium alloy Ti60 was investigated during the continuous cooling from β phase field, at the cooling rate from 80 oC?s-1 to 0.1 oC?s-1. The initial and final temperatures and kinetics of the β→α′ and β→α diffusion type transformations were analyzed by a dilatometric method. Over the cooling rate of 50 oC?s-1, the original β phase rapidly transformed to α′ martensite at 910 oC in the form of acicular platelets without any β phase left. A great amount of dislocations and stacking faults were found inside the marten site. Under cooling rate of 5 oC?s-1 , α phase nucleates along the grain boundary as well as inside the grain, while at the cooling rate below 1 oC?s-1, the nucleation occurred only along the grain boundary. A small amount of retained β phase was observed along the α platelet boundary under TEM, while the ordering transformation of α phase occurred inside the platelet, resulting in forming of α2 phase. Therefore, the cooling rate determines the alloy phase transformation mechanism and the inner structure of product phase
The phase transformation mechanism of near α titanium alloy Ti60 was investigated during the continuous cooling from β phase field, at the cooling rate from 80 oC?s-1 to 0.1 oC?s-1. The initial and final temperatures and kinetics of the β→α′ and β→α diffusion type transformations were analyzed by a dilatometric method. Over the cooling rate of 50 oC?s-1, the original β phase rapidly transformed to α′ martensite at 910 oC in the form of acicular platelets without any β phase left. A great amount of dislocations and stacking faults were found inside the marten site. Under cooling rate of 5 oC?s-1 , α phase nucleates along the grain boundary as well as inside the grain, while at the cooling rate below 1 oC?s-1, the nucleation occurred only along the grain boundary. A small amount of retained β phase was observed along the α platelet boundary under TEM, while the ordering transformation of α phase occurred inside the platelet, resulting in forming of α2 phase. Therefore, the cooling rate determines the alloy phase transformation mechanism and the inner structure of product phase
2015, 44(4):854-858.
Abstract:
The bulk amorphous alloy Mg60Ni23.6Y0.5La15.9 was prepared by copper-mold inject casting. Its microstructural transformation and electrochemical properties were investigated. The microstructures of Mg60Ni23.6Y0.5La15.9 amorphous alloy during charge and discharge cycling were characterized by XRD and SEM. The electrochemical performances of the alloy were tested by an automatic charge and discharge apparatus. The results show that the amorphous structure transforms into crystallized one step by step and Mg2NiH4, Mg2Ni and Mg(OH)2 phases are formed gradually during the process of hydrogenation and dehydrogenation. Furthermore, the result of electrochemical characteristics testing shows that the change process of discharge capacity for Mg60Ni23.6Y0.5La15.9 amorphous alloy can be divided into four stages and the highest discharge capacity reaches 410.5 mAh/g. It is found that the amorphous structure may be a critical factor to obtain the maximum discharge capacity.
The bulk amorphous alloy Mg60Ni23.6Y0.5La15.9 was prepared by copper-mold inject casting. Its microstructural transformation and electrochemical properties were investigated. The microstructures of Mg60Ni23.6Y0.5La15.9 amorphous alloy during charge and discharge cycling were characterized by XRD and SEM. The electrochemical performances of the alloy were tested by an automatic charge and discharge apparatus. The results show that the amorphous structure transforms into crystallized one step by step and Mg2NiH4, Mg2Ni and Mg(OH)2 phases are formed gradually during the process of hydrogenation and dehydrogenation. Furthermore, the result of electrochemical characteristics testing shows that the change process of discharge capacity for Mg60Ni23.6Y0.5La15.9 amorphous alloy can be divided into four stages and the highest discharge capacity reaches 410.5 mAh/g. It is found that the amorphous structure may be a critical factor to obtain the maximum discharge capacity.
2015, 44(4):859-865.
Abstract:
Jiangxi University of Science and Technology, Ganzhou 341000, China
Jiangxi University of Science and Technology, Ganzhou 341000, China
2015, 44(4):871-875.
Abstract:
The market prospect and industry management of metal catalytic converters in the automotive industry was analyzed. For the automotive metal catalytic converter samples, a determination method for precious metal Pt, Pd and Rh using ICP-MS was established. After soaked in 6 mol/L HCl solution, the sample turned into filtrate and insoluble, and then they were prepared into test solutions separately after tellurium co-precipitation. The method was co-verified by eight laboratories, and the results are as following: for Pt, Pd and Rh, the relative deviations between the determination results and the corresponding reference values are all less than 10%, and the reproducibility uncertainties are 6.6%, 6.5% and 5.8%, respectively. It is concluded that the method has low detection limits, high recoveries, good reproducibility and satisfactory feasibility
The market prospect and industry management of metal catalytic converters in the automotive industry was analyzed. For the automotive metal catalytic converter samples, a determination method for precious metal Pt, Pd and Rh using ICP-MS was established. After soaked in 6 mol/L HCl solution, the sample turned into filtrate and insoluble, and then they were prepared into test solutions separately after tellurium co-precipitation. The method was co-verified by eight laboratories, and the results are as following: for Pt, Pd and Rh, the relative deviations between the determination results and the corresponding reference values are all less than 10%, and the reproducibility uncertainties are 6.6%, 6.5% and 5.8%, respectively. It is concluded that the method has low detection limits, high recoveries, good reproducibility and satisfactory feasibility
2015, 44(4):875-880.
Abstract:
The high vacuum electron beam isolation welding (EBIW) was used to join vanadium alloy (V-5Cr-5Ti) to stainless-steel (HR-2) with different electroplated metal coatings. To investigate the effects of electroplated coating (Au, Ag, Cr and Ni) on the weldability, the weld appearance, the microstructure and the mechanical properties of the joints have been analyzed. The results show that the metallurgically bonded joints of V-5Cr-5Ti/Au(Ag, Cr, Ni)/HR-2 are achieved with EB off-set. The welds surface configuration are good and root reinforcement are full and smooth. The integration interface of V-5Cr-5Ti and fusion zone (FZ) is relatively flat, where an electroplated metal enrichment zone is found near V alloy side. The FZ consists of considerably smaller equiaxed dendritic structure in the center and columnar dendritic grained at the fusion line between FZ and HR-2. Au and Ag exhibit good isolation layer which helps increasing the weld quality. The maximal tensile strength of V-5Cr-5Ti/Au(Ag)/HR-2 of EBIW joint is over 400 MPa. There is no crack and detected porosity in the joints through X-ray inspection. In contrast, the tensile strength of V-5Cr-5Ti/Cr(Ni)/HR-2 of EBIW joints are lower than 100 MPa
The high vacuum electron beam isolation welding (EBIW) was used to join vanadium alloy (V-5Cr-5Ti) to stainless-steel (HR-2) with different electroplated metal coatings. To investigate the effects of electroplated coating (Au, Ag, Cr and Ni) on the weldability, the weld appearance, the microstructure and the mechanical properties of the joints have been analyzed. The results show that the metallurgically bonded joints of V-5Cr-5Ti/Au(Ag, Cr, Ni)/HR-2 are achieved with EB off-set. The welds surface configuration are good and root reinforcement are full and smooth. The integration interface of V-5Cr-5Ti and fusion zone (FZ) is relatively flat, where an electroplated metal enrichment zone is found near V alloy side. The FZ consists of considerably smaller equiaxed dendritic structure in the center and columnar dendritic grained at the fusion line between FZ and HR-2. Au and Ag exhibit good isolation layer which helps increasing the weld quality. The maximal tensile strength of V-5Cr-5Ti/Au(Ag)/HR-2 of EBIW joint is over 400 MPa. There is no crack and detected porosity in the joints through X-ray inspection. In contrast, the tensile strength of V-5Cr-5Ti/Cr(Ni)/HR-2 of EBIW joints are lower than 100 MPa
2015, 44(4):887-891.
Abstract:
PS@Au core-shell composite particles with excellent catalytic performance, high sphericity and no agglomeration were controllably synthesized by a suitable electroless plating process. The diameter of PS@Au composite particles could be adjusted continuously through tuning diameter of polystyrene microspheres. The influence of diameter on catalytic performance of PS@Au composite particles was investigated by SEM, XRD, UV-Vis spectrometer, and the detection of catalytic performance. The results indicate that the high specific surface area is responsible for the improvement of degradation rate of methylene blue chromophore and the excellent catalytic performance of PS@Au core-shell composite particles. Moreover, the diameter has a significant effect on both surface morphology and growth mode of Au nanoparticles, and the catalytic performance of the composite particles. When the diameter of core-shell structure is small, the curvature of the polystyrene microspheres is huge. Au nanoparticles exhibit isolated and granular structure because the orientation distribution of Au nanoparticles is diffused. In this case, PS@Au composite particles show the superior catalytic performance due to the higher specific surface area and surface energy. On the contrary, with the diameter of core-shell structure increasing, the curvature decreases. Au nanoparticles with close orientation merge and grow up rapidly, which is a film-like material. As a result, specific surface area and surface energy are decreased as the diameter rises and their catalytic performance also declines. In this study, the microstructure of Au nanoparticles begins to change from granular structure to continuous film-like structure, when the diameter of PS@Au core-shell composite particles is up to 400 nm
PS@Au core-shell composite particles with excellent catalytic performance, high sphericity and no agglomeration were controllably synthesized by a suitable electroless plating process. The diameter of PS@Au composite particles could be adjusted continuously through tuning diameter of polystyrene microspheres. The influence of diameter on catalytic performance of PS@Au composite particles was investigated by SEM, XRD, UV-Vis spectrometer, and the detection of catalytic performance. The results indicate that the high specific surface area is responsible for the improvement of degradation rate of methylene blue chromophore and the excellent catalytic performance of PS@Au core-shell composite particles. Moreover, the diameter has a significant effect on both surface morphology and growth mode of Au nanoparticles, and the catalytic performance of the composite particles. When the diameter of core-shell structure is small, the curvature of the polystyrene microspheres is huge. Au nanoparticles exhibit isolated and granular structure because the orientation distribution of Au nanoparticles is diffused. In this case, PS@Au composite particles show the superior catalytic performance due to the higher specific surface area and surface energy. On the contrary, with the diameter of core-shell structure increasing, the curvature decreases. Au nanoparticles with close orientation merge and grow up rapidly, which is a film-like material. As a result, specific surface area and surface energy are decreased as the diameter rises and their catalytic performance also declines. In this study, the microstructure of Au nanoparticles begins to change from granular structure to continuous film-like structure, when the diameter of PS@Au core-shell composite particles is up to 400 nm
2015, 44(4):912-917.
Abstract:
The ultrafine WC-0.5Co cemented carbide with a grain size smaller than 0.5 μm was prepared by high energy ball milling and HIP-sintering process. The raw materials were ultrafine WC and WC-0.5Co powder and the additives of grain growth inhibitor were VC/Cr3C2 and carbon. Microstructure and properties of the ultrafine WC-0.5Co cemented carbide with different VC/Cr3C2 and carbon contents were studied. The results show that there is a significant effect of VC/Cr3C2 on controlling WC particle size and hardness of ultrafine WC-0.5Co cemented carbide. Ultrafine WC-0.5Co cemented carbide has best Vickers hardness HV0.05 of 32 658 MPa with the VC/Cr3C2 content of 0.73% (mass fraction, similarly hereinafter). A certain amount of mixed carbon content is good for decarburization and properties of the ultrafine binderless cemented carbide. Ultrafine WC-0.5Co-073VC/Cr3C2 cemented carbide has best comprehensive mechanical properties with transverse rupture strength of 6.935 MPa·m1/2 and Vickers hardness HV0.05 of 32 216 MPa when the mixed content of carbon is 0.2%
The ultrafine WC-0.5Co cemented carbide with a grain size smaller than 0.5 μm was prepared by high energy ball milling and HIP-sintering process. The raw materials were ultrafine WC and WC-0.5Co powder and the additives of grain growth inhibitor were VC/Cr3C2 and carbon. Microstructure and properties of the ultrafine WC-0.5Co cemented carbide with different VC/Cr3C2 and carbon contents were studied. The results show that there is a significant effect of VC/Cr3C2 on controlling WC particle size and hardness of ultrafine WC-0.5Co cemented carbide. Ultrafine WC-0.5Co cemented carbide has best Vickers hardness HV0.05 of 32 658 MPa with the VC/Cr3C2 content of 0.73% (mass fraction, similarly hereinafter). A certain amount of mixed carbon content is good for decarburization and properties of the ultrafine binderless cemented carbide. Ultrafine WC-0.5Co-073VC/Cr3C2 cemented carbide has best comprehensive mechanical properties with transverse rupture strength of 6.935 MPa·m1/2 and Vickers hardness HV0.05 of 32 216 MPa when the mixed content of carbon is 0.2%
2015, 44(4):918-921.
Abstract:
The Cu-Nb multicore composite wires reinforced by high-strength and high-conductivity Nb tube were prepared by a bundling and drawing process. The composite wires with different sizes (Φ3.0 mm, Φ2.7 mm, Φ2.5 mm) were selected, and the core filament morphology as well as the microstructure of Cu-Nb interfaces with different sizes was characterized by SEM; then the evolution and the characteristics of the core filament and the microstructure of Cu-Nb interfaces under multi-size conditions were discussed. Finally, based on σ-ε and R-T curve, the evolution mechanism of property caused by size change was analyzed. Results show that when the diameter of the sample is Φ2.5 mm, the strength of composite wire approaches 1.1 GPa and the conductivity reaches 74%IACS
The Cu-Nb multicore composite wires reinforced by high-strength and high-conductivity Nb tube were prepared by a bundling and drawing process. The composite wires with different sizes (Φ3.0 mm, Φ2.7 mm, Φ2.5 mm) were selected, and the core filament morphology as well as the microstructure of Cu-Nb interfaces with different sizes was characterized by SEM; then the evolution and the characteristics of the core filament and the microstructure of Cu-Nb interfaces under multi-size conditions were discussed. Finally, based on σ-ε and R-T curve, the evolution mechanism of property caused by size change was analyzed. Results show that when the diameter of the sample is Φ2.5 mm, the strength of composite wire approaches 1.1 GPa and the conductivity reaches 74%IACS
2015, 44(4):922-926.
Abstract:
A nano-Al2O3 reinforced AgCu composite filler (named AgCuC) was developed by introducing nano-Al2O3 (2 wt%) into AgCu eutectic powder filler and then by high-energy ball milling. High-quality brazing of TC4 alloy to Al2O3 ceramic was achieved using the AgCuC filler. The typical interfacial microstructure of TC4/AgCuC/Al2O3 joint was TC4/α-Ti+Ti2Cu diffusion layer/Ti3Cu4 reaction layer/Ag(s,s)+Ti3Cu4+TiCu/Ti3Cu4 reaction layer/Ti3(Cu,Al)3O reaction layer/Al2O3. The addition of nano-Al2O3 in AgCuC filler could improve the interfacial microstructure by constraining the growth of continuous Ti-Cu intermetallic layers. Moreover, granular Ti-Cu phases reinforced Ag based composite is formed in brazed joint. Both the thickness of reaction layers and the size of granular Ti-Cu phases increase with an increasing brazing temperature, while the content of Ag based composite decreases. The highest shear strength of 67.8 MPa is achieved when brazed at 920 °C for 10 min. Typical fracture analyses show that the crack originates in the fillet, extends along the brazing seam and then transforms into Al2O3 ceramic, and finally fractures in the Al2O3 substrate side
A nano-Al2O3 reinforced AgCu composite filler (named AgCuC) was developed by introducing nano-Al2O3 (2 wt%) into AgCu eutectic powder filler and then by high-energy ball milling. High-quality brazing of TC4 alloy to Al2O3 ceramic was achieved using the AgCuC filler. The typical interfacial microstructure of TC4/AgCuC/Al2O3 joint was TC4/α-Ti+Ti2Cu diffusion layer/Ti3Cu4 reaction layer/Ag(s,s)+Ti3Cu4+TiCu/Ti3Cu4 reaction layer/Ti3(Cu,Al)3O reaction layer/Al2O3. The addition of nano-Al2O3 in AgCuC filler could improve the interfacial microstructure by constraining the growth of continuous Ti-Cu intermetallic layers. Moreover, granular Ti-Cu phases reinforced Ag based composite is formed in brazed joint. Both the thickness of reaction layers and the size of granular Ti-Cu phases increase with an increasing brazing temperature, while the content of Ag based composite decreases. The highest shear strength of 67.8 MPa is achieved when brazed at 920 °C for 10 min. Typical fracture analyses show that the crack originates in the fillet, extends along the brazing seam and then transforms into Al2O3 ceramic, and finally fractures in the Al2O3 substrate side
Chen Chuanming
,
Yao Meiyi
,
Zhou Jun
,
Zhou Bangxin
,
Zhang Jinlong
,
Li Qiang
,
Peng Jianchao
,
Liang Xue
2015, 44(4):933-938.
Abstract:
The corrosion resistance of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr-xBi (x=0.1, 0.3, 0.5, mass fraction, %) alloys was investigated in superheated stream at 400 oC/10.3 MPa by autoclave tests. SEM and TEM equipped with EDS were employed to investigate the microstructures of the alloys and fracture surface morphology of the oxide film. Results show that when the Bi content is below 0.3%, there exists Zr(Nb, Fe, Cr)2 second phase particles (SPPs) with a hexagonal crystal structure (hcp). And when the Bi content is up to 0.5%, besides many Zr(Nb, Fe, Cr)2 SPPs, there are also a few Zr(Bi, Fe, Sn)2 SPPs with an orthogonal structure and Zr-Nb-Bi-Fe-Cr-Sn SPPs with an unidentified structure. This indicates that the maximum concentration of Bi in α-Zr matrix of T5+xBi alloys is 0.3%￡CBi<0.5%. The addition of Bi promotes the precipitation of Sn as SPPs, which is originally in solid solution in the α-Zr matrix of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr alloy. When the Bi content is below 0.3%, the corrosion resistance of the alloys improves with the Bi content, but the addition of 0.5% Bi makes the corrosion resistance worse. It indicates that the solid solution of Bi in α-Zr matrix can improve the corrosion resistance, while the precipitation of the SPPs containing Bi and Sn is harmful to the corrosion resistance.
The corrosion resistance of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr-xBi (x=0.1, 0.3, 0.5, mass fraction, %) alloys was investigated in superheated stream at 400 oC/10.3 MPa by autoclave tests. SEM and TEM equipped with EDS were employed to investigate the microstructures of the alloys and fracture surface morphology of the oxide film. Results show that when the Bi content is below 0.3%, there exists Zr(Nb, Fe, Cr)2 second phase particles (SPPs) with a hexagonal crystal structure (hcp). And when the Bi content is up to 0.5%, besides many Zr(Nb, Fe, Cr)2 SPPs, there are also a few Zr(Bi, Fe, Sn)2 SPPs with an orthogonal structure and Zr-Nb-Bi-Fe-Cr-Sn SPPs with an unidentified structure. This indicates that the maximum concentration of Bi in α-Zr matrix of T5+xBi alloys is 0.3%￡CBi<0.5%. The addition of Bi promotes the precipitation of Sn as SPPs, which is originally in solid solution in the α-Zr matrix of Zr-0.7Sn-1.07Nb-0.32Fe-0.08Cr alloy. When the Bi content is below 0.3%, the corrosion resistance of the alloys improves with the Bi content, but the addition of 0.5% Bi makes the corrosion resistance worse. It indicates that the solid solution of Bi in α-Zr matrix can improve the corrosion resistance, while the precipitation of the SPPs containing Bi and Sn is harmful to the corrosion resistance.
2015, 44(4):939-944.
Abstract:
Based on the microscopic phase-field dynamic model and the micro-elasticity theory, the pre-precipitation process of Ni75Al14Mo11 alloy was simulated at 973 K. The investigation of the microscopic morphology evolution figures, the change of L10 volume fraction, order parameter and occupation probability indicate that the first precipitation is L10 structure which has two variants of L10(I) structure and L10(II) structure. With the increase of the elastic strain energy, the precipitation of two L10 structures are affected, and the elastic strain energy, obviously, inhibits the formation of the L10(I) structure. At last, the two L10 structures transform to precipitation of L12 order structure
Based on the microscopic phase-field dynamic model and the micro-elasticity theory, the pre-precipitation process of Ni75Al14Mo11 alloy was simulated at 973 K. The investigation of the microscopic morphology evolution figures, the change of L10 volume fraction, order parameter and occupation probability indicate that the first precipitation is L10 structure which has two variants of L10(I) structure and L10(II) structure. With the increase of the elastic strain energy, the precipitation of two L10 structures are affected, and the elastic strain energy, obviously, inhibits the formation of the L10(I) structure. At last, the two L10 structures transform to precipitation of L12 order structure
2015, 44(4):945-949.
Abstract:
The effects of Mg addition content and ball milling time on the hydrolysis kinetics of MgH2 prepared by hydriding combustion synthesis (HCS) in MgCl2 solution were investigated. When MgH2-60%Mg was milled for 3 h, hydrogen yield reached to 993 mL/g within 5 min (80% in conversion) and the hydrolysis was completed within 15 min with a single phase of Mg(OH)2 as the byproduct. Results indicate that the HCSed MgH2 with addition of Mg can serve as a low-cost on-board hydrogen source with some advantages such as excellent kinetics of hydrolysis and easy recycle of byproduct.
The effects of Mg addition content and ball milling time on the hydrolysis kinetics of MgH2 prepared by hydriding combustion synthesis (HCS) in MgCl2 solution were investigated. When MgH2-60%Mg was milled for 3 h, hydrogen yield reached to 993 mL/g within 5 min (80% in conversion) and the hydrolysis was completed within 15 min with a single phase of Mg(OH)2 as the byproduct. Results indicate that the HCSed MgH2 with addition of Mg can serve as a low-cost on-board hydrogen source with some advantages such as excellent kinetics of hydrolysis and easy recycle of byproduct.
2015, 44(4):956-960.
Abstract:
The effects of solution and aging treatments on the microstructures and mechanical properties of 7055 Al alloy bars were studied by transmission electron microscopy, optical microscopy and tensile mechanical property testing. The results show that an appropriate combination of solution and aging treatments plays an important role in controlling microstructure so as to obtain improved mechanical properties. Two-step solution of 470 oC/20 min+480~490 oC/20 min could further decrease the amount of undissolved particles and is helpful to enhance age-strengthening. When the 2nd-step solution temperature is increased to 490 oC, the volume fraction of undissolved particles decreases remarkably, from 2.5% in the case of one-step solution treatment to 2.0%. The grain size of the as-solutioned alloys under experimental conditions is in the range of 30~35 μm. Optimum combined mechanical properties are achieved under the regime of 470 oC/20 min+485 oC/20 min solution- treatment followed by 135 oC/16 h + 190 oC/10 min aging treatment, with the tensile strength and yield strength being 694 MPa and 660 MPa, respectively, in the meantime maintaining a high elongation to failure of 14%
The effects of solution and aging treatments on the microstructures and mechanical properties of 7055 Al alloy bars were studied by transmission electron microscopy, optical microscopy and tensile mechanical property testing. The results show that an appropriate combination of solution and aging treatments plays an important role in controlling microstructure so as to obtain improved mechanical properties. Two-step solution of 470 oC/20 min+480~490 oC/20 min could further decrease the amount of undissolved particles and is helpful to enhance age-strengthening. When the 2nd-step solution temperature is increased to 490 oC, the volume fraction of undissolved particles decreases remarkably, from 2.5% in the case of one-step solution treatment to 2.0%. The grain size of the as-solutioned alloys under experimental conditions is in the range of 30~35 μm. Optimum combined mechanical properties are achieved under the regime of 470 oC/20 min+485 oC/20 min solution- treatment followed by 135 oC/16 h + 190 oC/10 min aging treatment, with the tensile strength and yield strength being 694 MPa and 660 MPa, respectively, in the meantime maintaining a high elongation to failure of 14%
2015, 44(4):966-971.
Abstract:
The DSC curve characteristic and microstructure of 2524 aluminum alloy after stress coupled with electric field aging were investigated using Differential Scanning Calorimetry (DSC) and transmission electron microscopy (TEM), respectively. The results show that comparing to the alloy after aging at 190 oC/5 h without either external stress or electric field, the volume fraction of precipitated S phase increases in the sample after 25~130 MPa aging, the precipitation rate is increased by 30%, and the activation energy of S phase formation is decreased by 55 kJ/mol, while that of the alloy after aging under 130 MPa coupled with 16 kV/cm is decreased by only 38 kJ/mol
The DSC curve characteristic and microstructure of 2524 aluminum alloy after stress coupled with electric field aging were investigated using Differential Scanning Calorimetry (DSC) and transmission electron microscopy (TEM), respectively. The results show that comparing to the alloy after aging at 190 oC/5 h without either external stress or electric field, the volume fraction of precipitated S phase increases in the sample after 25~130 MPa aging, the precipitation rate is increased by 30%, and the activation energy of S phase formation is decreased by 55 kJ/mol, while that of the alloy after aging under 130 MPa coupled with 16 kV/cm is decreased by only 38 kJ/mol
2015, 44(4):972-976.
Abstract:
Effects of heat treatments on microstructure and mechanical properties of Ti-steel explosive clad plates were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), auger electronic spectrum (AES) and shear test. The Ti-steel explosive clad plates were subjected to a heat treatment process in the temperature range of 650~950 oC for 30~120 min. The results show that the heat treatment process leads to a great enhancement of diffusion and microstructural transformation. During the heat treatment process, a large amount of Ti-Fe intermetallics (Fe2Ti/FeTi) along with some TiC distributing continuously are formed at diffusion reaction layer. With the treatment temperature increasing, the thickness of diffusion layer increases and the shear strength decreases, whose functional relationship was proposed with the heat temperature as well as the holding time according to the experimental data
Effects of heat treatments on microstructure and mechanical properties of Ti-steel explosive clad plates were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), auger electronic spectrum (AES) and shear test. The Ti-steel explosive clad plates were subjected to a heat treatment process in the temperature range of 650~950 oC for 30~120 min. The results show that the heat treatment process leads to a great enhancement of diffusion and microstructural transformation. During the heat treatment process, a large amount of Ti-Fe intermetallics (Fe2Ti/FeTi) along with some TiC distributing continuously are formed at diffusion reaction layer. With the treatment temperature increasing, the thickness of diffusion layer increases and the shear strength decreases, whose functional relationship was proposed with the heat temperature as well as the holding time according to the experimental data
2015, 44(4):977-981.
Abstract:
AB5 hydrogen storage alloy electrodes have some disadvantages in the process of battery charge and discharge such as grave pulverization, short cycle life, and poor cycle stability. In this paper, we selected LaMg0.26Ni3.44Co0.66Al0.14Fe0.14 alloy as raw materials and offered a method to deal with the base hydrogen storage alloy. Based on the DSC test result, the hydrogenation-dehydrogenation condition was determined and a pre-treatment of hydrogenation and copper plating followed by hydrogen release was performed for the alloy. Then the battery properties were studied. The results show that the alloy with 0.7% hydrogen mass and copper plating followed by hydrogen release possesses the max discharge capacity 318.0 mAh·g-1, the decay ratio of discharge capacity is low, and the cycle stability is good. The effect of particle size indicates that 38~48 μm mesh alloy with 0.7% hydrogen mass and copper plating followed by hydrogen release has the max discharge capacity 327.3 mAh·g-1
AB5 hydrogen storage alloy electrodes have some disadvantages in the process of battery charge and discharge such as grave pulverization, short cycle life, and poor cycle stability. In this paper, we selected LaMg0.26Ni3.44Co0.66Al0.14Fe0.14 alloy as raw materials and offered a method to deal with the base hydrogen storage alloy. Based on the DSC test result, the hydrogenation-dehydrogenation condition was determined and a pre-treatment of hydrogenation and copper plating followed by hydrogen release was performed for the alloy. Then the battery properties were studied. The results show that the alloy with 0.7% hydrogen mass and copper plating followed by hydrogen release possesses the max discharge capacity 318.0 mAh·g-1, the decay ratio of discharge capacity is low, and the cycle stability is good. The effect of particle size indicates that 38~48 μm mesh alloy with 0.7% hydrogen mass and copper plating followed by hydrogen release has the max discharge capacity 327.3 mAh·g-1
2015, 44(4):982-988.
Abstract:
A new Al-Zn-Mg-Cu high strength aluminum alloy after solution and aging pre-treatments of 435 oC/2 h+200 oC/12 h was taken as the object and hot compressions at temperatures in the range of 350~400 oC, strain rates in the range of 0.01 to 1 s-1 and height reduction up to 60%~80% were carried out followed by subsequent annealing and solution treatments of 350 oC/0.5 h+470 oC/2 h. The influences of precipitated particles on grain evolution mechanisms and regulations during hot deformation and subsequent annealing and solution treatments were investigated by optical microscope (OM) and electronic microscope (EBSD, TEM). The conclusions can be drawn as following. (i) Continuous dynamic recrystallization occurs under deformation conditions of 400 ℃, 0.05 s-1, 60%, the value of lnZ is 24.33, and refined and uniform recrystallized grains appear. After subsequent annealing and solution treatments, recrystallized grains become more equiaxed and uniform, and the size of grains increases slightly. As a result, the refined, equiaxed and uniformly-distributed grain structure occurs. (ii) When hot compression is carried out under conditions of 380 oC, 0.1 s-1, 60%, the value of lnZ increases to 25 or so, grains are elongated along the deformation direction with some refined recrystallized grains at the grain-boundaries. After subsequent annealing and solution treatments, grain growth is not too much, and refined and recovered well sub-grains come forth evenly in the elongated grains. As a result, the elongated grain structure with refined and uniform sub-grains emerges. (iii) At other conditions of increased strain rates or decreased temperatures, the value of lnZ increases to about 26, and deformation increases to large values, dynamic recrystallization can not be observed obviously and the prior grains are elongated severely. After subsequent annealing and solution treatments, the grains grow rapidly. As a result, the coarse grain structure appears
A new Al-Zn-Mg-Cu high strength aluminum alloy after solution and aging pre-treatments of 435 oC/2 h+200 oC/12 h was taken as the object and hot compressions at temperatures in the range of 350~400 oC, strain rates in the range of 0.01 to 1 s-1 and height reduction up to 60%~80% were carried out followed by subsequent annealing and solution treatments of 350 oC/0.5 h+470 oC/2 h. The influences of precipitated particles on grain evolution mechanisms and regulations during hot deformation and subsequent annealing and solution treatments were investigated by optical microscope (OM) and electronic microscope (EBSD, TEM). The conclusions can be drawn as following. (i) Continuous dynamic recrystallization occurs under deformation conditions of 400 ℃, 0.05 s-1, 60%, the value of lnZ is 24.33, and refined and uniform recrystallized grains appear. After subsequent annealing and solution treatments, recrystallized grains become more equiaxed and uniform, and the size of grains increases slightly. As a result, the refined, equiaxed and uniformly-distributed grain structure occurs. (ii) When hot compression is carried out under conditions of 380 oC, 0.1 s-1, 60%, the value of lnZ increases to 25 or so, grains are elongated along the deformation direction with some refined recrystallized grains at the grain-boundaries. After subsequent annealing and solution treatments, grain growth is not too much, and refined and recovered well sub-grains come forth evenly in the elongated grains. As a result, the elongated grain structure with refined and uniform sub-grains emerges. (iii) At other conditions of increased strain rates or decreased temperatures, the value of lnZ increases to about 26, and deformation increases to large values, dynamic recrystallization can not be observed obviously and the prior grains are elongated severely. After subsequent annealing and solution treatments, the grains grow rapidly. As a result, the coarse grain structure appears
2015, 44(4):989-994.
Abstract:
AZ80 magnesium based composites strengthened by multi-walled carbon nanotubes (MWCNTs) of different volume fractions were fabricated by friction stir processing (FSP) and the effect of heat treatment on microstructure and mechanical property of MWCNTs/AZ80 were investigated. The results show that the Mg-based composites are dense with fine grains, in which MWCNTs distribute uniformly. A13Ni2 intermetallic compounds are formed on the interface between the MWCNTs and the magnesium matrix, leading to a sound bonding condition. The tensile strength of the composites increases with the increase of volume fraction of the MWCNTs, and it is also improved by the post heat treatment of solid solution and aging. The major factor affecting the mechanical property of the MWCNTs/AZ80 is the interface structure between the MWCNTs and the magnesium matrix
AZ80 magnesium based composites strengthened by multi-walled carbon nanotubes (MWCNTs) of different volume fractions were fabricated by friction stir processing (FSP) and the effect of heat treatment on microstructure and mechanical property of MWCNTs/AZ80 were investigated. The results show that the Mg-based composites are dense with fine grains, in which MWCNTs distribute uniformly. A13Ni2 intermetallic compounds are formed on the interface between the MWCNTs and the magnesium matrix, leading to a sound bonding condition. The tensile strength of the composites increases with the increase of volume fraction of the MWCNTs, and it is also improved by the post heat treatment of solid solution and aging. The major factor affecting the mechanical property of the MWCNTs/AZ80 is the interface structure between the MWCNTs and the magnesium matrix
2015, 44(4):995-999.
Abstract:
To study the forming quality during ring pipe hot push-expanding, the hot push-expanding experiments of β titanium alloy were carried out, and the process of hot push-expanding was analyzed by a mesh method and a finite element method. Moreover, the causes of quality defects, such as corrugate, cracking, wall unevenness, and ellipticity, were discussed. The results show that ram-horn mandrel, expanding radio, temperature and velocity are important parameters which influence the forming quality of ring pipe. They interact with each other and need a coordinated control. The coordinated control principle is that the ram-horn mandrel and the expanding ratio should be set, the temperature is a key factor, and the velocity is a coordination factor.
To study the forming quality during ring pipe hot push-expanding, the hot push-expanding experiments of β titanium alloy were carried out, and the process of hot push-expanding was analyzed by a mesh method and a finite element method. Moreover, the causes of quality defects, such as corrugate, cracking, wall unevenness, and ellipticity, were discussed. The results show that ram-horn mandrel, expanding radio, temperature and velocity are important parameters which influence the forming quality of ring pipe. They interact with each other and need a coordinated control. The coordinated control principle is that the ram-horn mandrel and the expanding ratio should be set, the temperature is a key factor, and the velocity is a coordination factor.
2015, 44(4):1012-1016.
Abstract:
The microstructure, micro-hardness and tensile behavior of bulk Sn-3.5Ag alloy were studied as a function of cooling rate. Sn-3.5Ag alloy samples with the controlled cooling rates of 101, 103 and 106 K/S of were obtained by cooling specimens in different media: air, water and rush cold. The microscopic analysis and mechanical properties test were conducted. Results show that the cooling rat has a significant effect on the secondary dendrite size and distribution of β-Sn phase. The β-Sn grain average size and the secondary dendrite arm space are gradually reduced with the increase of cooling rate, Ag3Sn grain also become smaller, and distribute more uniformly. Besides, the micro-hardness and tensile properties with increasing cooling rate improve. Finally, it is concluded that the microstructure and the distribution of Ag3Sn grains influence obviously the mechanical properties, and Ag3Sn grains play a dispersion strengthened role in the alloy
The microstructure, micro-hardness and tensile behavior of bulk Sn-3.5Ag alloy were studied as a function of cooling rate. Sn-3.5Ag alloy samples with the controlled cooling rates of 101, 103 and 106 K/S of were obtained by cooling specimens in different media: air, water and rush cold. The microscopic analysis and mechanical properties test were conducted. Results show that the cooling rat has a significant effect on the secondary dendrite size and distribution of β-Sn phase. The β-Sn grain average size and the secondary dendrite arm space are gradually reduced with the increase of cooling rate, Ag3Sn grain also become smaller, and distribute more uniformly. Besides, the micro-hardness and tensile properties with increasing cooling rate improve. Finally, it is concluded that the microstructure and the distribution of Ag3Sn grains influence obviously the mechanical properties, and Ag3Sn grains play a dispersion strengthened role in the alloy
2015, 44(4):1017-1023.
Abstract:
The nanocrystalline TiC solid solution strengthened tungsten matrix composites were prepared by selective laser melting (SLM). The influence of applied laser linear energy density (η) on densification level, microstructure, microhardness, and wear resistance of SLM-processed composite parts was studied. Results show that a low laser linear energy density leads to the formation of micropores. In contrast, a high laser linear energy density produces the microcracks, caused by the thermal stress. These two situations generally lower the SLM densification. However, at a reasonable η of 2.1 kJ/m, the SLM-processed composites part has a near-full 94.7 % theoretical density and a significantly increased microhardness (HV0.2) of 8062 MPa. The dry sliding wear tests reveal that a considerably low friction coefficient of 0.583 without any apparent fluctuation and a reduced wear rate of 0.69×10-15 m3/Nm are achieved. A uniform distribution of columnar crystals is obtained in SLM-processed tungsten matrix composites, with an average diameter of crystals of 0.73 μm.
The nanocrystalline TiC solid solution strengthened tungsten matrix composites were prepared by selective laser melting (SLM). The influence of applied laser linear energy density (η) on densification level, microstructure, microhardness, and wear resistance of SLM-processed composite parts was studied. Results show that a low laser linear energy density leads to the formation of micropores. In contrast, a high laser linear energy density produces the microcracks, caused by the thermal stress. These two situations generally lower the SLM densification. However, at a reasonable η of 2.1 kJ/m, the SLM-processed composites part has a near-full 94.7 % theoretical density and a significantly increased microhardness (HV0.2) of 8062 MPa. The dry sliding wear tests reveal that a considerably low friction coefficient of 0.583 without any apparent fluctuation and a reduced wear rate of 0.69×10-15 m3/Nm are achieved. A uniform distribution of columnar crystals is obtained in SLM-processed tungsten matrix composites, with an average diameter of crystals of 0.73 μm.
27 Mechanical Properties of Ti-35Nb-7Zr-XCPP Biomedical Composites Prepared by Spark Plasma Sintering
2015, 44(4):1030-1034.
Abstract:
Ti-35Nb-7Zr-XCPP biomedical composites were prepared by a spark plasma sintering (SPS) technique. The effects of the contents of the calcium pyrophosphate (CPP) on the relative density, microstructure and mechanical properties of the composites were investigated. The results show that the composites are consisted of β-Ti phase matrix, a little residual α-Ti phase and CPP phase. The α-Ti phase of the composites increases with the increasing of the content of the CPP. Furthermore, CPP would decompose due to its excessive content in the composites. The composites present a lower compressive elastic modulus in the range of 40~62 GPa and a higher compressive strength level more than 1000 MPa, and it exhibits a better mechanical compatibility. However, the compressive elastic modulus of the composites significantly increases when the CPP is excessive, and then it would do harm to the mechanical compatibility of the composites
Ti-35Nb-7Zr-XCPP biomedical composites were prepared by a spark plasma sintering (SPS) technique. The effects of the contents of the calcium pyrophosphate (CPP) on the relative density, microstructure and mechanical properties of the composites were investigated. The results show that the composites are consisted of β-Ti phase matrix, a little residual α-Ti phase and CPP phase. The α-Ti phase of the composites increases with the increasing of the content of the CPP. Furthermore, CPP would decompose due to its excessive content in the composites. The composites present a lower compressive elastic modulus in the range of 40~62 GPa and a higher compressive strength level more than 1000 MPa, and it exhibits a better mechanical compatibility. However, the compressive elastic modulus of the composites significantly increases when the CPP is excessive, and then it would do harm to the mechanical compatibility of the composites
