Volume 47,Issue 5,2018 Table of Contents
2018, 47(5):1325-1332.
Abstract:
The influence of structural, elastic properties, thermodynamics and electronic properties Al-Y alloy were investigated by using first-principles. The equilibrium lattice constant, elastic constants, and elastic modulus as calculated here agree with results of previous studies. Calculated results of bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio v and Debye temperature all increase as pressure increase, but the opposite is true for heat capacity cp. In addition, the Debye temperature for the phases reduces gradually as follows: Al2Y > Al3Y> AlY. Additionally, the G/B ratio indicates that AlY and Al3Y are ductile materials, while Al2Y is a brittle material, and that the ductility of AlY and Al3Y can be improved with increased pressure, while the brittleness of Al2Y does not improve with increased pressure. Finally, the paper presents and discusses calculations of density of states and charge populations as they are affected by pressure.
The influence of structural, elastic properties, thermodynamics and electronic properties Al-Y alloy were investigated by using first-principles. The equilibrium lattice constant, elastic constants, and elastic modulus as calculated here agree with results of previous studies. Calculated results of bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio v and Debye temperature all increase as pressure increase, but the opposite is true for heat capacity cp. In addition, the Debye temperature for the phases reduces gradually as follows: Al2Y > Al3Y> AlY. Additionally, the G/B ratio indicates that AlY and Al3Y are ductile materials, while Al2Y is a brittle material, and that the ductility of AlY and Al3Y can be improved with increased pressure, while the brittleness of Al2Y does not improve with increased pressure. Finally, the paper presents and discusses calculations of density of states and charge populations as they are affected by pressure.
2 Effect of hot-rolling temperature on microstructure and dynamic mechanical properties of Ti–6Al–4V
2018, 47(5):1333-1340.
Abstract:
The equiaxed Ti-6Al-4V alloys were rolled with an overall reduction ratio of 0.78 at 840℃, 870℃, 900℃ and 930℃, respectively. The microstructure, texture and anisotropy of dynamic mechanical properties of the rolled alloy were investigated. Results have shown that, recrystallization and phase transformation did not occur until the rolling was performed at a temperature higher than 900℃, and then the microstructure of the rolled alloy turned into bimodal, while the amount of lamellar αs+β structure and recrystallized α grains showed an increasing tendency with the increased rolling temperature. Moreover, it was interesting to find that although the texture was varying with the rolling temperature, the <0001> direction of α phase kept parallel to the normal direction (ND) during the hot-rolling process at various temperatures. Based on the analyses of dynamic mechanical properties, Ti-6Al-4V alloy was observed to exhibit anisotropy of dynamic mechanical properties after hot-rolling at different temperature. However, resulting from the rolling-temperature-depended texture and distribution of dislocation, the anisotropic tendency of dynamic mechanical properties varied with the rolling temperature. Moreover, with the increased rolling temperature, the dynamic flow stress loaded along ND decreased, while the adiabatic shearing failure strain slightly increased. The dynamic flow stress loaded along RD remained constant, while the adiabatic shearing failure strain exhibited an obviously decreasing tendency with the increased rolling temperature. The dynamic mechanical properties loaded along Transverse Direction (TD) remained constant when the rolling temperature was in the range of 840℃ to 900℃, while the dynamic flow stress loaded along TD increased evidently when the rolling temperature reaches 930℃, but the adiabatic shearing failure strain decreased greatly.
The equiaxed Ti-6Al-4V alloys were rolled with an overall reduction ratio of 0.78 at 840℃, 870℃, 900℃ and 930℃, respectively. The microstructure, texture and anisotropy of dynamic mechanical properties of the rolled alloy were investigated. Results have shown that, recrystallization and phase transformation did not occur until the rolling was performed at a temperature higher than 900℃, and then the microstructure of the rolled alloy turned into bimodal, while the amount of lamellar αs+β structure and recrystallized α grains showed an increasing tendency with the increased rolling temperature. Moreover, it was interesting to find that although the texture was varying with the rolling temperature, the <0001> direction of α phase kept parallel to the normal direction (ND) during the hot-rolling process at various temperatures. Based on the analyses of dynamic mechanical properties, Ti-6Al-4V alloy was observed to exhibit anisotropy of dynamic mechanical properties after hot-rolling at different temperature. However, resulting from the rolling-temperature-depended texture and distribution of dislocation, the anisotropic tendency of dynamic mechanical properties varied with the rolling temperature. Moreover, with the increased rolling temperature, the dynamic flow stress loaded along ND decreased, while the adiabatic shearing failure strain slightly increased. The dynamic flow stress loaded along RD remained constant, while the adiabatic shearing failure strain exhibited an obviously decreasing tendency with the increased rolling temperature. The dynamic mechanical properties loaded along Transverse Direction (TD) remained constant when the rolling temperature was in the range of 840℃ to 900℃, while the dynamic flow stress loaded along TD increased evidently when the rolling temperature reaches 930℃, but the adiabatic shearing failure strain decreased greatly.
2018, 47(5):1341-1346.
Abstract:
In present work, the impact of hot extrusion on the microstructure and texture, as well as mechanical properties of the Mg?1Gd?1Nd (wt.%) alloy were investigated. The results demonstrated that the as-cast alloy displayed a typical eutectic microstructure consisting α-Mg solid solution and semi-continuous eutectic compounds. After solution treatment, the eutectic compounds were mostly dissolved in the α-Mg matrix. The microstructure and texture of the extruded alloy were analyzed by electron backscatter diffraction (EBSD) technique. It was demonstrated that the extruded alloy exhibited fully recrystallized microstructure and weak basal texture. In details, the basal planes of the grains majority were spread both towards extrusion direction and transverse direction of the extruded alloy sheet. Especially in the extrusion direction, the orientation distribution was significantly dispersive. The broad spread in orientations resulted in effective activation of the basal slip and allows the alloy to accommodate higher strains prior to failure. On the other hand, the texture was responsible for the planar anisotropies of the extruded alloy sheet.
In present work, the impact of hot extrusion on the microstructure and texture, as well as mechanical properties of the Mg?1Gd?1Nd (wt.%) alloy were investigated. The results demonstrated that the as-cast alloy displayed a typical eutectic microstructure consisting α-Mg solid solution and semi-continuous eutectic compounds. After solution treatment, the eutectic compounds were mostly dissolved in the α-Mg matrix. The microstructure and texture of the extruded alloy were analyzed by electron backscatter diffraction (EBSD) technique. It was demonstrated that the extruded alloy exhibited fully recrystallized microstructure and weak basal texture. In details, the basal planes of the grains majority were spread both towards extrusion direction and transverse direction of the extruded alloy sheet. Especially in the extrusion direction, the orientation distribution was significantly dispersive. The broad spread in orientations resulted in effective activation of the basal slip and allows the alloy to accommodate higher strains prior to failure. On the other hand, the texture was responsible for the planar anisotropies of the extruded alloy sheet.
2018, 47(5):1347-1351.
Abstract:
Pure Mg was subjected to high pressure torsion (HPT) at room temperature, and the structural and hardness evolutions were studied. In addition, the grain size evolution during the hardness steady state was systematically investigated. The results indicated that the hardness initially increases with increasing the equivalent strain, reaches a maximum value of ~53 Hv, and then decreases to a steady-state level at large strains. However, although the hardness reaches the steady state, the average grain size does not reach a steady state. The evolution of the grain size is different from the evolution of the hardness during the HPT processing. The continuously decreased grain size during harness steady state may be caused by the annihilation of the dislocations during dynamic recovery or dynamic recrystallization, resulted from the temperature rising during the continuous HPT processing and the low melting temperature of Mg.
Pure Mg was subjected to high pressure torsion (HPT) at room temperature, and the structural and hardness evolutions were studied. In addition, the grain size evolution during the hardness steady state was systematically investigated. The results indicated that the hardness initially increases with increasing the equivalent strain, reaches a maximum value of ~53 Hv, and then decreases to a steady-state level at large strains. However, although the hardness reaches the steady state, the average grain size does not reach a steady state. The evolution of the grain size is different from the evolution of the hardness during the HPT processing. The continuously decreased grain size during harness steady state may be caused by the annihilation of the dislocations during dynamic recovery or dynamic recrystallization, resulted from the temperature rising during the continuous HPT processing and the low melting temperature of Mg.
2018, 47(5):1352-1358.
Abstract:
Cu-Ag particles with different molar ratio have been prepared in the hyperbranched polyester matrix by using ascorbic acid as a reducing agent. The third generation hyperbranched polyester has been synthesized by step by step polymerization using the first generation hyperbranched polyester as core molecular and 2, 2-dimethylol propionic acid as branched monomer. The synthesized hyperbranched polyester and Cu-Ag alloy were characterized by different analytical techniques such as FT-IR, 1H-NMR, UV-vis spectra, X-ray diffraction (XRD), SEM, Energy Dispersive X-ray (EDX), Laser particle size measurement, TEM, etc. The XRD and EDX studies confirm the formation of Cu-Ag alloy. The Laser particle size measurement, SEM and TEM studies show that the Cu-Ag alloy is well-dispersed particles with average size of 120 nm. The thermal properties of the Cu-Ag alloy have been studied by thermogravimetric Analysis (TGA). The results showed that the measurement values are close to the theoretical ones.
Cu-Ag particles with different molar ratio have been prepared in the hyperbranched polyester matrix by using ascorbic acid as a reducing agent. The third generation hyperbranched polyester has been synthesized by step by step polymerization using the first generation hyperbranched polyester as core molecular and 2, 2-dimethylol propionic acid as branched monomer. The synthesized hyperbranched polyester and Cu-Ag alloy were characterized by different analytical techniques such as FT-IR, 1H-NMR, UV-vis spectra, X-ray diffraction (XRD), SEM, Energy Dispersive X-ray (EDX), Laser particle size measurement, TEM, etc. The XRD and EDX studies confirm the formation of Cu-Ag alloy. The Laser particle size measurement, SEM and TEM studies show that the Cu-Ag alloy is well-dispersed particles with average size of 120 nm. The thermal properties of the Cu-Ag alloy have been studied by thermogravimetric Analysis (TGA). The results showed that the measurement values are close to the theoretical ones.
Peng Sun
,
Ji-Cai Liang
,
Guang-Yi Chen
,
Yu-Hui Li
,
Kai-Yuan Zhou
,
Jia-Ang Liu
,
Wen-Zhuo Zhang
,
Fu Niu
,
Wan-Xi Zhang
2018, 47(5):1359-1364.
Abstract:
Freestanding porous Co9S8 nanoneedle bundles arrays on Ni foam were in-situ synthesized by a facile ion exchange reaction and were directly used as the electrode for supercapacitors. The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) were adopted to evaluate the electrochemical property of the porous Co9S8 nanoneedle bundles arrays electrode in 3M KOH solution. The specific capacitance of the porous Co9S8 nanoneedle bundles arrays was 1400 F g-1 at a current density of 4 A g-1 and exhibited good cycling stability. The excellent electrochemical performance can be ascribed to the porous nanostructure of Co9S8 nanoneedle bundles arrays and the 3D conductive nickel foam, which can increase the contact areas between electrode and electrolyte and improve the conductivity of the whole electrode.
Freestanding porous Co9S8 nanoneedle bundles arrays on Ni foam were in-situ synthesized by a facile ion exchange reaction and were directly used as the electrode for supercapacitors. The structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) were adopted to evaluate the electrochemical property of the porous Co9S8 nanoneedle bundles arrays electrode in 3M KOH solution. The specific capacitance of the porous Co9S8 nanoneedle bundles arrays was 1400 F g-1 at a current density of 4 A g-1 and exhibited good cycling stability. The excellent electrochemical performance can be ascribed to the porous nanostructure of Co9S8 nanoneedle bundles arrays and the 3D conductive nickel foam, which can increase the contact areas between electrode and electrolyte and improve the conductivity of the whole electrode.
2018, 47(5):1365-1369.
Abstract:
In this paper, two sample groups, N5/(ZrB2+ZrO2)/NiCrAl and N5/ZrO2/NiCrAl, were prepared on Ni-based single crystal alloy (Rene N5) substrate by electron beam physical vapor deposition (EB-PVD). Both sample groups were exposed to isothermal oxidation at 900 °C for 5 h and at 1000 °C, for 250 h, 300 h or 350 h. The microstructural evolution and deterioration failure behavior was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results suggest that the introduction of ZrB2 decelerates the interfacial reaction rate of the active diffusion barrier of Al2O3 but did not affect the final formation of the Al2O3 diffusion barrier with anti-diffusion properties. Moreover, the introduction of ZrB2 prolongs the service life of active diffusion barrier structure and changes its failure mode.
In this paper, two sample groups, N5/(ZrB2+ZrO2)/NiCrAl and N5/ZrO2/NiCrAl, were prepared on Ni-based single crystal alloy (Rene N5) substrate by electron beam physical vapor deposition (EB-PVD). Both sample groups were exposed to isothermal oxidation at 900 °C for 5 h and at 1000 °C, for 250 h, 300 h or 350 h. The microstructural evolution and deterioration failure behavior was investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results suggest that the introduction of ZrB2 decelerates the interfacial reaction rate of the active diffusion barrier of Al2O3 but did not affect the final formation of the Al2O3 diffusion barrier with anti-diffusion properties. Moreover, the introduction of ZrB2 prolongs the service life of active diffusion barrier structure and changes its failure mode.
8 Crack propagation and microstructural evolution of Ni-based single crystal alloy under shear loads
2018, 47(5):1370-1376.
Abstract:
Under shear load, crack propagation and microstructural evolution of Ni-based single crystal alloy have been investigated by molecular dynamics simulations. Stress-strain, potential energy and crack growth rates have been explored. Moreover, the influences of temperatures and strain rates have been verified. Simulation results show that the critical stress value increases with the decreasing temperature and increasing strain rate, respectively. As the temperature increases, the crack propagation is accelerated by severe thermal vibrations. Then, dislocations pile-up and twinning emerge resulting in significantly work hardening at a higher strain rate.
Under shear load, crack propagation and microstructural evolution of Ni-based single crystal alloy have been investigated by molecular dynamics simulations. Stress-strain, potential energy and crack growth rates have been explored. Moreover, the influences of temperatures and strain rates have been verified. Simulation results show that the critical stress value increases with the decreasing temperature and increasing strain rate, respectively. As the temperature increases, the crack propagation is accelerated by severe thermal vibrations. Then, dislocations pile-up and twinning emerge resulting in significantly work hardening at a higher strain rate.
2018, 47(5):1377-1384.
Abstract:
The Mg–5Al–2Ca alloys reinforced by 2 vol.%, 5 vol.% and 10 vol.% 5μm SiCp were fabricated by stir casting. The cast composites were subject to hot extrusion. In the cast composites, addition of SiCp disturbs the network distribution of Al2Ca phase along grain boundaries. After extrusion, grains of the matrix are refined further and the Al2Ca phase broke into particulates. Moreover, the Al2Ca phase and grain size can be further refined by the addition of SiCp. As compared with monolithic Mg–5Al–2Ca alloy, the addition of SiCp conduces to obvious improvement of TYS and work hardening rate, however, at the expense of elongation. Unlike the TYS, the UTS of SiCp/Mg-5Al-2Ca composite does not change monotonously with increasing SiCp’s content, the highest UTS appears when the SiCp’s volume fraction is 5%. The interfacial debonding between SiCp and Al2Ca phase and cracked particles are considered as the main crack source for SiCp/Mg–5Al–2Ca composite.
The Mg–5Al–2Ca alloys reinforced by 2 vol.%, 5 vol.% and 10 vol.% 5μm SiCp were fabricated by stir casting. The cast composites were subject to hot extrusion. In the cast composites, addition of SiCp disturbs the network distribution of Al2Ca phase along grain boundaries. After extrusion, grains of the matrix are refined further and the Al2Ca phase broke into particulates. Moreover, the Al2Ca phase and grain size can be further refined by the addition of SiCp. As compared with monolithic Mg–5Al–2Ca alloy, the addition of SiCp conduces to obvious improvement of TYS and work hardening rate, however, at the expense of elongation. Unlike the TYS, the UTS of SiCp/Mg-5Al-2Ca composite does not change monotonously with increasing SiCp’s content, the highest UTS appears when the SiCp’s volume fraction is 5%. The interfacial debonding between SiCp and Al2Ca phase and cracked particles are considered as the main crack source for SiCp/Mg–5Al–2Ca composite.
2018, 47(5):1385-1392.
Abstract:
The phase, microstructure and properties of mulit-core cermets based on (Ti,W,Ta)CN and TiCN powders were investigated in sintering process. According the analyses of X-Ray diffraction (XRD) and scanning electron microscope (SEM), it indicated that the sintering behavior of the multi-core cermet in sintering process could be divided into three stages: (I) pre-densification stage (the sintering temperature < 1200 °C); (II) rapid densification stage (the sintering temperature between 1200 °C and 1350 °C); (III) final densification stage (the sintering temperature > 1350 °C). Meanwhile, the evolution of η-phase in multi-core cermet was discussed as well. Furthermore, the microstructural and chemical information of η-phase were studied by Transmission Electron Microscopy (TEM) using X-ray energy dispersive spectrometry (XEDS) and selected area electron diffraction (SAED). The thickness of the rim structure would increase with the rise of sintering temperature, while the mechanical properties of the material would firstly increase then decrease with the rise of sintering temperature, and achieve the highest transverse rupture strength at 1450°C, the highest hardness at 1390°C.
The phase, microstructure and properties of mulit-core cermets based on (Ti,W,Ta)CN and TiCN powders were investigated in sintering process. According the analyses of X-Ray diffraction (XRD) and scanning electron microscope (SEM), it indicated that the sintering behavior of the multi-core cermet in sintering process could be divided into three stages: (I) pre-densification stage (the sintering temperature < 1200 °C); (II) rapid densification stage (the sintering temperature between 1200 °C and 1350 °C); (III) final densification stage (the sintering temperature > 1350 °C). Meanwhile, the evolution of η-phase in multi-core cermet was discussed as well. Furthermore, the microstructural and chemical information of η-phase were studied by Transmission Electron Microscopy (TEM) using X-ray energy dispersive spectrometry (XEDS) and selected area electron diffraction (SAED). The thickness of the rim structure would increase with the rise of sintering temperature, while the mechanical properties of the material would firstly increase then decrease with the rise of sintering temperature, and achieve the highest transverse rupture strength at 1450°C, the highest hardness at 1390°C.
2018, 47(5):1393-1398.
Abstract:
The microstructure evolution of Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy during homogenization was investigated by differential thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-Ray diffraction. Also, the Vikers hardness was measured. It was found that the microstructure of as-cast Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy consists of α-Mg, and Mg3(Y,Nd)2Zn3 phases．The alloy has an endothermic peak at 510 ℃ before homogenization. The endothermic peak disappears in the alloy homogenized at 500 °C for 16 h. A small quantity of Mg3(Y,Nd)2Zn3 phases dissolve at 470 ℃ and 490 ℃．However, after homogenization at 500 ℃ for 16 h, there are only a small number of rich-Y and rich-Nd fine particles (Mg3(Y,Nd)2Zn3) dispersing at grain boundary, and dendritic segregation is almost eliminated. Therefore, the optimum homogenization parameter is 500 ℃ for 16 h. Homogenization can effectively decrease the hardness of the as-cast Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy from 185.2 HV to 144.2 HV.
The microstructure evolution of Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy during homogenization was investigated by differential thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-Ray diffraction. Also, the Vikers hardness was measured. It was found that the microstructure of as-cast Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy consists of α-Mg, and Mg3(Y,Nd)2Zn3 phases．The alloy has an endothermic peak at 510 ℃ before homogenization. The endothermic peak disappears in the alloy homogenized at 500 °C for 16 h. A small quantity of Mg3(Y,Nd)2Zn3 phases dissolve at 470 ℃ and 490 ℃．However, after homogenization at 500 ℃ for 16 h, there are only a small number of rich-Y and rich-Nd fine particles (Mg3(Y,Nd)2Zn3) dispersing at grain boundary, and dendritic segregation is almost eliminated. Therefore, the optimum homogenization parameter is 500 ℃ for 16 h. Homogenization can effectively decrease the hardness of the as-cast Mg-5.9Zn-1.6Zr-1.6Nd-0.9Y alloy from 185.2 HV to 144.2 HV.
2018, 47(5):1399-1405.
Abstract:
Nickel-based alloys are commonly used to fabricate transfer tubes of pressurized water vapor generators. However, the stress corrosion cracking (SCC) induced by surface pits and scratches of the tubes is more sudden and has great influence on the safety and reliability of nuclear power plant. To understand the effects of the oxide morphology on the crack tip of scratched surface on SCC behavior of nickel-based alloy, the local stress-strain field at scratched crack tip in the presence of film-induced stress is simulated. Results show that wedge force is the major crack driving force that causes the SCC growth. Greater oxide thickness of scratch crack will give rise to wedge force and lead to an increase in SCC crack growth rate (CGR). The formation of oxide at crack tip will induce compressive stress, compressive strain and negative strain gradient, and thus retard the SCC propagation in the upper and lower part of the semi-ellipticalScrack front.
Nickel-based alloys are commonly used to fabricate transfer tubes of pressurized water vapor generators. However, the stress corrosion cracking (SCC) induced by surface pits and scratches of the tubes is more sudden and has great influence on the safety and reliability of nuclear power plant. To understand the effects of the oxide morphology on the crack tip of scratched surface on SCC behavior of nickel-based alloy, the local stress-strain field at scratched crack tip in the presence of film-induced stress is simulated. Results show that wedge force is the major crack driving force that causes the SCC growth. Greater oxide thickness of scratch crack will give rise to wedge force and lead to an increase in SCC crack growth rate (CGR). The formation of oxide at crack tip will induce compressive stress, compressive strain and negative strain gradient, and thus retard the SCC propagation in the upper and lower part of the semi-ellipticalScrack front.
2018, 47(5):1406-1410.
Abstract:
MgB2 bulks with a density, 1.95g/cm3, have been successfully prepared by an improved Mg-diffusion method. The effects of different heat treatment conditions on superconducting transitions temperature, Tc and critical current density, Jc of MgB2 have been discussed. The MgB2 synthesized by optimal heat treatment conditions has the Tc, 38.1K and Jc at 10K, self-field, 0.53MA/cm2. In order to improve poor high field properties in diffusion method, nano-Pr6O11 and C doping effects on Jc and the irreversible field, Hirr of MgB2 have also been studied. The results show that at 10K and 6T the Jc for 15 at.% C-doped MgB2 reaches 104 A/cm2, which is almost two orders of magnitude higher than the undoped one, and better than the nano-C doped MgB2 prepared by solid-state reaction. For the nano-Pr6O11-doped MgB2, the Jc also increases by a factor of 9.4 than the pure sample at 10K and 2T. According to a great of experimental results and theoretic analyses, we propose that the combination of the improved Mg-diffusion method and chemical doing, nanoparticles or C doping, may be an efficient approach to make the MgB2 have excellent Jc and Hirr capability in whole magnetic field.
MgB2 bulks with a density, 1.95g/cm3, have been successfully prepared by an improved Mg-diffusion method. The effects of different heat treatment conditions on superconducting transitions temperature, Tc and critical current density, Jc of MgB2 have been discussed. The MgB2 synthesized by optimal heat treatment conditions has the Tc, 38.1K and Jc at 10K, self-field, 0.53MA/cm2. In order to improve poor high field properties in diffusion method, nano-Pr6O11 and C doping effects on Jc and the irreversible field, Hirr of MgB2 have also been studied. The results show that at 10K and 6T the Jc for 15 at.% C-doped MgB2 reaches 104 A/cm2, which is almost two orders of magnitude higher than the undoped one, and better than the nano-C doped MgB2 prepared by solid-state reaction. For the nano-Pr6O11-doped MgB2, the Jc also increases by a factor of 9.4 than the pure sample at 10K and 2T. According to a great of experimental results and theoretic analyses, we propose that the combination of the improved Mg-diffusion method and chemical doing, nanoparticles or C doping, may be an efficient approach to make the MgB2 have excellent Jc and Hirr capability in whole magnetic field.
2018, 47(5):1411-1421.
Abstract:
The aluminothermic reduction of high Ti containing acid soluble Ti bearing slag (ASTS) was carried out to prepare the multicomponents TiAl based alloy. In order to control and understand the preparation of TiAl alloy, the effects of the addition of Al and CaO, and temperature were discussed. By considering materials proportioning calculations it could successfully make TiAl alloy with sound slag-alloy separation. The recovery rates of most reduced elements are mostly shown high value and it is about 95% in the all experimental conditions. The Al addition can mainly affect the composition of TiAl alloy, while CaO addition affects the slag-metal separation by varying composition of slag system. Besides, the temperature of system can increase the recovery rate and distribution ratio for the most of reduced elements.
The aluminothermic reduction of high Ti containing acid soluble Ti bearing slag (ASTS) was carried out to prepare the multicomponents TiAl based alloy. In order to control and understand the preparation of TiAl alloy, the effects of the addition of Al and CaO, and temperature were discussed. By considering materials proportioning calculations it could successfully make TiAl alloy with sound slag-alloy separation. The recovery rates of most reduced elements are mostly shown high value and it is about 95% in the all experimental conditions. The Al addition can mainly affect the composition of TiAl alloy, while CaO addition affects the slag-metal separation by varying composition of slag system. Besides, the temperature of system can increase the recovery rate and distribution ratio for the most of reduced elements.
2018, 47(5):1422-1428.
Abstract:
A homogenized Mg-13Gd-4Y-2Zn-0.5Zr (wt.%) alloy was subjected to repetitive upsetting-extrusion (RUE) process at decreasing temperature from 480 to 370℃. The microstructure and texture development of the alloy during the RUE process was investigated in current study. The results showed that average grain size decreased with increasing cumulative strain and decreasing temperature. Uniform ultrafine-grain structure with an average grain size of 3.4 μm was achieved after 6 passes, i.e., cumulative strain of 8.4. Results revealed that grain refinement was induced by a complicated combination of discontinuous dynamic recrystallization and continuous dynamic recrystallization. Kink of lamellar long period stacking order (LPSO) phases played an important role in the grain refinement through subdividing the coarse grains by inducing recrystallization evolved in the kink bands. After 1 pass of RUE, a strong basal texture was obtained. With increasing RUE passes, the texture was gradually weakened, which resulted from cooperative effect of DRX and the alternative change of loading directions (axial and radial) during RUE processing.
A homogenized Mg-13Gd-4Y-2Zn-0.5Zr (wt.%) alloy was subjected to repetitive upsetting-extrusion (RUE) process at decreasing temperature from 480 to 370℃. The microstructure and texture development of the alloy during the RUE process was investigated in current study. The results showed that average grain size decreased with increasing cumulative strain and decreasing temperature. Uniform ultrafine-grain structure with an average grain size of 3.4 μm was achieved after 6 passes, i.e., cumulative strain of 8.4. Results revealed that grain refinement was induced by a complicated combination of discontinuous dynamic recrystallization and continuous dynamic recrystallization. Kink of lamellar long period stacking order (LPSO) phases played an important role in the grain refinement through subdividing the coarse grains by inducing recrystallization evolved in the kink bands. After 1 pass of RUE, a strong basal texture was obtained. With increasing RUE passes, the texture was gradually weakened, which resulted from cooperative effect of DRX and the alternative change of loading directions (axial and radial) during RUE processing.
2018, 47(5):1429-1436.
Abstract:
Microstructure and the corrosion behavior of ZK60-1Nd magnesium alloy in 3.5 wt % NaCl aqueous solution was studied by scanning electron microscope (SEM) , electrochemical workstation and brine weight loss method. The results indicate that the as-cast microstructure of ZK60-1Nd alloy is mainly composed of matrixα-Mg, a coarse network eutectic phase containing rare earth Nd distribute along the grain boundaries and the distribution of fine MgZn2 phase in the matrix. The corrosion rate of ZK60-1Nd magnesium alloy in 3.5 wt % NaCl aqueous solution was 0.2 mg ? cm-2 ? h-1 in NaCl solution. After homogenization at 300 ℃ for 8.0 h , the microstructure was improved;after annealing at 400 ℃ for 96 h, A portion of the eutectic phase is fused to a particle with a maximum size of 1.5 μm and the corrosion rate is reduced to 0.1 mg.cm-2.h-1; After annealing at 500 ℃ for 8.0 h , fishbone eutectic phase composition of patchy, the MgZn2 phase is dissolvedSintoSmatrix , the contents of Nd, Zn and Zr were increased and the distribution was uniform in the matrix , corrosion rate reached a minimum of 0.03 mg.cm-2.h-1. The main reason for the improvement of corrosion resistance is that the increase of the content of solid solution Nd in matrix α-Mg lead to the improvement of corrosion potential and the decrease in the number of micro galvanic corrosion.
Microstructure and the corrosion behavior of ZK60-1Nd magnesium alloy in 3.5 wt % NaCl aqueous solution was studied by scanning electron microscope (SEM) , electrochemical workstation and brine weight loss method. The results indicate that the as-cast microstructure of ZK60-1Nd alloy is mainly composed of matrixα-Mg, a coarse network eutectic phase containing rare earth Nd distribute along the grain boundaries and the distribution of fine MgZn2 phase in the matrix. The corrosion rate of ZK60-1Nd magnesium alloy in 3.5 wt % NaCl aqueous solution was 0.2 mg ? cm-2 ? h-1 in NaCl solution. After homogenization at 300 ℃ for 8.0 h , the microstructure was improved;after annealing at 400 ℃ for 96 h, A portion of the eutectic phase is fused to a particle with a maximum size of 1.5 μm and the corrosion rate is reduced to 0.1 mg.cm-2.h-1; After annealing at 500 ℃ for 8.0 h , fishbone eutectic phase composition of patchy, the MgZn2 phase is dissolvedSintoSmatrix , the contents of Nd, Zn and Zr were increased and the distribution was uniform in the matrix , corrosion rate reached a minimum of 0.03 mg.cm-2.h-1. The main reason for the improvement of corrosion resistance is that the increase of the content of solid solution Nd in matrix α-Mg lead to the improvement of corrosion potential and the decrease in the number of micro galvanic corrosion.
2018, 47(5):1437-1444.
Abstract:
High niobium (Nb) Ti-Al intermetallic compound composite coating was fabricated on BT3-1 titanium alloy surface by laser cladding process. According to differential thermal analysis (DTA) and thermogravimetry (TG) curves, the laser in situ synthesis reaction mechanism of Ti, Al, Nb three kinds of elements mixed powder under the argon and nitrogen protection was discussed. The phase composition and microstructure of composite cladding coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show the composite coating is mainly composed of Nb elemental and γ-TiAl intermetallic compounds, α2-Ti3Al and Ti3Al2, and Nb is only part of the in situ reaction happened in coating. N2 can reduce the reaction temperature and increase the reaction rate between Ti and Al, and also can promote the reaction between Ti and Al. The laser cladding composite coating does not appear columnar crystal having a laser cladding epitaxial growth characteristics, but produce the fine equiaxed grain structure.
High niobium (Nb) Ti-Al intermetallic compound composite coating was fabricated on BT3-1 titanium alloy surface by laser cladding process. According to differential thermal analysis (DTA) and thermogravimetry (TG) curves, the laser in situ synthesis reaction mechanism of Ti, Al, Nb three kinds of elements mixed powder under the argon and nitrogen protection was discussed. The phase composition and microstructure of composite cladding coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show the composite coating is mainly composed of Nb elemental and γ-TiAl intermetallic compounds, α2-Ti3Al and Ti3Al2, and Nb is only part of the in situ reaction happened in coating. N2 can reduce the reaction temperature and increase the reaction rate between Ti and Al, and also can promote the reaction between Ti and Al. The laser cladding composite coating does not appear columnar crystal having a laser cladding epitaxial growth characteristics, but produce the fine equiaxed grain structure.
2018, 47(5):1445-1450.
Abstract:
Influence of 1wt% and 2wt% Li addition on the electrochemical corrosion behavior of pure Al was studied in 0.1MNaCl+0.01MH2SO4 acidic solution. Corrosion resistance was tested by free corrosion potential and electrochemical impedance spectrum (EIS). The composition and semiconducting properti of corrosion product films for pure Al, Al-1Li alloy and Al-2Li alloy formed at free corrosion potential were respectively analyzed by X-ray photoelectron spectroscopy (XPS) and Mott-Schottky (M-S) approach. The results showed that free corrosion potential of pure Al shifted in more active direction by Li addition, while its corrosion resistance was improved. Li, with high chemical activity, could participate in the film formation process and Li2O together with Al2O3 were existed in the product films. M-S plots revealed that Li addition did not change n-type semiconductor of corrosion product film on pure Al. But, the increasing of corrosion resistance was attributed to the decreasing of oxygen vacancy concentration in corrosion product films by Li addition to pure Al.
Influence of 1wt% and 2wt% Li addition on the electrochemical corrosion behavior of pure Al was studied in 0.1MNaCl+0.01MH2SO4 acidic solution. Corrosion resistance was tested by free corrosion potential and electrochemical impedance spectrum (EIS). The composition and semiconducting properti of corrosion product films for pure Al, Al-1Li alloy and Al-2Li alloy formed at free corrosion potential were respectively analyzed by X-ray photoelectron spectroscopy (XPS) and Mott-Schottky (M-S) approach. The results showed that free corrosion potential of pure Al shifted in more active direction by Li addition, while its corrosion resistance was improved. Li, with high chemical activity, could participate in the film formation process and Li2O together with Al2O3 were existed in the product films. M-S plots revealed that Li addition did not change n-type semiconductor of corrosion product film on pure Al. But, the increasing of corrosion resistance was attributed to the decreasing of oxygen vacancy concentration in corrosion product films by Li addition to pure Al.
2018, 47(5):1451-1458.
Abstract:
The corrosion behavior of Nd-Fe-B magnets was studied through immersion test in 3.5 wt.% NaCl solution. The morphology and composition of corrosion product were characterized by scanning electron microscope (SEM) and Raman spectroscopy. The corrosion behavior of the specimens were investigated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The electrochemical equivalent circuits were used for fitting the EIS data. Results are as follows: Pitting corrosion, intergranularScorrosion and StotalScorrosion occurred in sequence during the immersion period. However, the corrosion product layer ofSlooseSstructure could only temporarily slow down the corrosion rate. At the initial stage, the Nd-rich phase atStheSgrain boundary preferentially dissolved into the media. Later the main phase particles were exposed to the corrosive solution and quicklyScorroded, causing a damage to the magnets. The corrosion products were mainly iron and neodymium oxides or hydroxides which was evolving with the immersion period.
The corrosion behavior of Nd-Fe-B magnets was studied through immersion test in 3.5 wt.% NaCl solution. The morphology and composition of corrosion product were characterized by scanning electron microscope (SEM) and Raman spectroscopy. The corrosion behavior of the specimens were investigated by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The electrochemical equivalent circuits were used for fitting the EIS data. Results are as follows: Pitting corrosion, intergranularScorrosion and StotalScorrosion occurred in sequence during the immersion period. However, the corrosion product layer ofSlooseSstructure could only temporarily slow down the corrosion rate. At the initial stage, the Nd-rich phase atStheSgrain boundary preferentially dissolved into the media. Later the main phase particles were exposed to the corrosive solution and quicklyScorroded, causing a damage to the magnets. The corrosion products were mainly iron and neodymium oxides or hydroxides which was evolving with the immersion period.
2018, 47(5):1459-1465.
Abstract:
The formation and evolution of adiabatic shear bands in U-5.7Nb alloy deformed at a strain rate of 8 000 s-1 were investigated in this paper．Dynamic deformation at different strain values of U-5.7Nb alloy were obtained by means of the strain stopping rings and the controlled strain rate．The experimental results show that two types adiabatic shear bands in U-5.7Nb alloy under dynamic deformation were distinguished as the strain increasing．The critical strain value for the deformed band formation was adjacent to the 0.33,and the corresponding critical strain value for the transformed band formation was close to 0.39．Microstructural observation shows that the deformed bands were composed of the severe deformed and elongated grains,and the transformed bands mainly composed of the ultrafine and equiaxed grains were confirmed. Based on characterization of adiabatic shear bands at different strains, the plastic deformation and fracture process of U-5.7Nb alloy subjected to dynamic loading were speculated.
The formation and evolution of adiabatic shear bands in U-5.7Nb alloy deformed at a strain rate of 8 000 s-1 were investigated in this paper．Dynamic deformation at different strain values of U-5.7Nb alloy were obtained by means of the strain stopping rings and the controlled strain rate．The experimental results show that two types adiabatic shear bands in U-5.7Nb alloy under dynamic deformation were distinguished as the strain increasing．The critical strain value for the deformed band formation was adjacent to the 0.33,and the corresponding critical strain value for the transformed band formation was close to 0.39．Microstructural observation shows that the deformed bands were composed of the severe deformed and elongated grains,and the transformed bands mainly composed of the ultrafine and equiaxed grains were confirmed. Based on characterization of adiabatic shear bands at different strains, the plastic deformation and fracture process of U-5.7Nb alloy subjected to dynamic loading were speculated.
2018, 47(5):1466-1470.
Abstract:
The ω phase transformation of Ti-1300 alloy during continuous heating was investigated using dilatometric method. Results show the βM→ω+β phase transformation happenes in low temperature zone, but the βM→α+β phase transformation happenes in high temperature zone during continuous heating. The temperature region of the β→ω phase transformation in the Ti-1300 alloy increased with increasing heating rate. The curves of ω phase transformed volume fraction and temperature at different heating rates exhibited a typical ‘S’ pattern. The activation energy of non-thermal ω phase transformation increased as increasing of ω phase transforming volume fraction, which added to precipitating resistance of ω phase. The average activation energy of the non-thermal ω phase transformation of the alloy was 55 kJ/mol.
The ω phase transformation of Ti-1300 alloy during continuous heating was investigated using dilatometric method. Results show the βM→ω+β phase transformation happenes in low temperature zone, but the βM→α+β phase transformation happenes in high temperature zone during continuous heating. The temperature region of the β→ω phase transformation in the Ti-1300 alloy increased with increasing heating rate. The curves of ω phase transformed volume fraction and temperature at different heating rates exhibited a typical ‘S’ pattern. The activation energy of non-thermal ω phase transformation increased as increasing of ω phase transforming volume fraction, which added to precipitating resistance of ω phase. The average activation energy of the non-thermal ω phase transformation of the alloy was 55 kJ/mol.
Che Jinda
,
Jiang Beibei
,
Wang Qing
,
Dong Chuang
,
Chen Guoqing
,
Zhang Ruiqian
,
Tang Rui
,
Xu Fen
,
Sun Lixian
2018, 47(5):1471-1477.
Abstract:
The present work intevatigated the composition rule of the near-? Ti alloy Ti1100 using a cluster-plus-glue-atom model for solid-solution alloys, and its cluster formula could be expressed as [Al-(Ti13.7Zr0.3)](Al0.69Sn0.18Mo0.03Si0.12). A new series of alloys by adding minor Hf, Ta and Nb with similar elements substititution in equimolar ratio were then designed, being [Al-(Ti13.7Zr0.15Hf0.15)](Al0.69Sn0.18Si0.1(Mo/Ta/Nb)0.03). These alloys were solid-solution-treated at 950 ℃ for 1 h followed by water-quenching, and then aged at 560 ℃ for 6 h. The microstructures, microhardness, oxidation- and corrosion-resistant properties of alloys were measured. The experimental results showed that the alloy with Hf0.15 substitution for Zr0.15 in Ti1100 still exhibits a ?-transformed lamellar microstructure, while the further combinations of Ta and Nb induce a large amount of equiaxed ??grains to form a duplex microstructure. The change of microstructure doesn’t affect the microhardness of alloys, within a range of 330-370 HV. All the designed alloys, as well as the reference Ti1100, possess excellent oxidation-resistant property at 650 ℃, in which all the oxidation weight gains are less than 1.0 mg/cm2. But the results are obviously different at 800 ℃ in comparison with that of Ti1100, which the oxidation weight gains of the designed alloys with Hf, Ta and Nb co-alloying after 100 h are far less than Ti1100, and the widths of the dense oxidation layers are among 25-27??m. The [Al-(Ti13.7Zr0.15Hf0.15)](Al0.69Sn0.18Si0.1Ta0.015Nb0.015) alloy has the best oxidation resistance with a lowest oxidation weight gain of 2.6 mg/cm2. In addition, this series of alloys also have good corrosion resistance in 3.5 %NaCl.
The present work intevatigated the composition rule of the near-? Ti alloy Ti1100 using a cluster-plus-glue-atom model for solid-solution alloys, and its cluster formula could be expressed as [Al-(Ti13.7Zr0.3)](Al0.69Sn0.18Mo0.03Si0.12). A new series of alloys by adding minor Hf, Ta and Nb with similar elements substititution in equimolar ratio were then designed, being [Al-(Ti13.7Zr0.15Hf0.15)](Al0.69Sn0.18Si0.1(Mo/Ta/Nb)0.03). These alloys were solid-solution-treated at 950 ℃ for 1 h followed by water-quenching, and then aged at 560 ℃ for 6 h. The microstructures, microhardness, oxidation- and corrosion-resistant properties of alloys were measured. The experimental results showed that the alloy with Hf0.15 substitution for Zr0.15 in Ti1100 still exhibits a ?-transformed lamellar microstructure, while the further combinations of Ta and Nb induce a large amount of equiaxed ??grains to form a duplex microstructure. The change of microstructure doesn’t affect the microhardness of alloys, within a range of 330-370 HV. All the designed alloys, as well as the reference Ti1100, possess excellent oxidation-resistant property at 650 ℃, in which all the oxidation weight gains are less than 1.0 mg/cm2. But the results are obviously different at 800 ℃ in comparison with that of Ti1100, which the oxidation weight gains of the designed alloys with Hf, Ta and Nb co-alloying after 100 h are far less than Ti1100, and the widths of the dense oxidation layers are among 25-27??m. The [Al-(Ti13.7Zr0.15Hf0.15)](Al0.69Sn0.18Si0.1Ta0.015Nb0.015) alloy has the best oxidation resistance with a lowest oxidation weight gain of 2.6 mg/cm2. In addition, this series of alloys also have good corrosion resistance in 3.5 %NaCl.
2018, 47(5):1478-1484.
Abstract:
Bimodal nanocrystalline (nc) Cu-Ag and nc Cu were prepared by high pressure sintering method in argon atmosphere. The microscopic structures of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The thermal conductivity of the samples with average grain sizes ranging from 50 to 270nm were measured. The test results showed that the thermal conductivity of nc Cu-Ag and nc Cu were reduced significantly from 243.84 W/m.K to 163.45 W/m.K and 259.93 W/m.K to 180.36 W/m.K at 300K, respectively. In addition, the thermal conductivity increases with the increasing of grain size. For a better understanding of the effects of grain boundary and size on the thermal conductivity of nc material, a modified model, with special emphasis on the contributions of electron conduction, is presented by incorporating the concept of the Kapitza resistance into an effective medium approach. The theoretical calculations are in good agreement with our experimental results.
Bimodal nanocrystalline (nc) Cu-Ag and nc Cu were prepared by high pressure sintering method in argon atmosphere. The microscopic structures of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The thermal conductivity of the samples with average grain sizes ranging from 50 to 270nm were measured. The test results showed that the thermal conductivity of nc Cu-Ag and nc Cu were reduced significantly from 243.84 W/m.K to 163.45 W/m.K and 259.93 W/m.K to 180.36 W/m.K at 300K, respectively. In addition, the thermal conductivity increases with the increasing of grain size. For a better understanding of the effects of grain boundary and size on the thermal conductivity of nc material, a modified model, with special emphasis on the contributions of electron conduction, is presented by incorporating the concept of the Kapitza resistance into an effective medium approach. The theoretical calculations are in good agreement with our experimental results.
2018, 47(5):1485-1491.
Abstract:
Isothermal constant strain rate compression tests of TA15 titanium alloy with basket-weave and Widmannstatten two types of beta transformed microstructurehave been carried out in the temperature range of 750℃-950℃ and strain rate of 0.001s-1-10s-1. The results show that there is a wide range of plastic flow instabilitySof the two beta transformed microstructure at low temperature and high strain rate region (750℃-880℃,0.0032s-1-10s-1).The instability range of Widmannstatten microstructure is larger than that of basket-weave. In the range of 750℃-775℃,0.001s-1-0.0032s-1 and 880℃-950℃,0.56s-1-10s-1 the Widmannstatten microstructure also have plastic flow instability defects.The instability defects of Widmannstatten microstructure have 45° macro shear crack, flow localization band and microcrack. The basket-weave microstructure has 45° macro shear crack and flow localization defects. The plastic flow instability is more likely to happen in Widmannstatten than basket-weave microstructure is primary cause of the difference of the initial alpha lamellar thickness in two beta transformed microstructure.
Isothermal constant strain rate compression tests of TA15 titanium alloy with basket-weave and Widmannstatten two types of beta transformed microstructurehave been carried out in the temperature range of 750℃-950℃ and strain rate of 0.001s-1-10s-1. The results show that there is a wide range of plastic flow instabilitySof the two beta transformed microstructure at low temperature and high strain rate region (750℃-880℃,0.0032s-1-10s-1).The instability range of Widmannstatten microstructure is larger than that of basket-weave. In the range of 750℃-775℃,0.001s-1-0.0032s-1 and 880℃-950℃,0.56s-1-10s-1 the Widmannstatten microstructure also have plastic flow instability defects.The instability defects of Widmannstatten microstructure have 45° macro shear crack, flow localization band and microcrack. The basket-weave microstructure has 45° macro shear crack and flow localization defects. The plastic flow instability is more likely to happen in Widmannstatten than basket-weave microstructure is primary cause of the difference of the initial alpha lamellar thickness in two beta transformed microstructure.
2018, 47(5):1492-1496.
Abstract:
Ti-8Si, Ti-8Si-0.7Zr, Ti-8Si-1.4Zr and Ti-8Si-1.4Zr-0.1Y2O3(wt%) alloys were preparation by high-energy ball milling, cold-pressure sintering using Ti, Si, Zr and Y2O3 powders. Morphologies and phase composition of sintered samples were analyzing by means of SEM and EDS, and the hardness, friction coefficient and wear resistance of friction/wear properties were investigated. The results show that four kinds of formula samples are mainly containing of Ti5Si3 phase, Ti(Si) solid solution and Ti(Si、Zr) solid solution. Functioned as dispersion strengthening or solid solution strengthening element, the microhardness of the formulas adding Zr and Y2O3 were improved by changing the content of Ti5Si3 and other phases and the proportion of solid solution. The formula of Ti-8Si-1.4Zr-0.1Y2O3 has the highest microhardness(1377 HV), improved by 35% than Ti-8Si(1020 HV). The friction coefficient of Ti-8Si alloy (about 0.365) was minimum, and the friction coefficient of Ti-8Si-1.4Zr-0.1Y2O3 (about 0.375) decreased by 26% than Ti-8Si-1.4Zr(0.504). Zr element decreased the wear width and improved the wear properties, while Zr element increased the friction coefficient. Ti-8Si-1.4Zr-0.1Y2O3 alloy has the best wear resistance with minimum wear width, and significantly improved the wear properties. The wear mechanism of four alloys were mainly fatigue wear, accompanied by adhesive wear, abrasive wear and oxidation wear.
Ti-8Si, Ti-8Si-0.7Zr, Ti-8Si-1.4Zr and Ti-8Si-1.4Zr-0.1Y2O3(wt%) alloys were preparation by high-energy ball milling, cold-pressure sintering using Ti, Si, Zr and Y2O3 powders. Morphologies and phase composition of sintered samples were analyzing by means of SEM and EDS, and the hardness, friction coefficient and wear resistance of friction/wear properties were investigated. The results show that four kinds of formula samples are mainly containing of Ti5Si3 phase, Ti(Si) solid solution and Ti(Si、Zr) solid solution. Functioned as dispersion strengthening or solid solution strengthening element, the microhardness of the formulas adding Zr and Y2O3 were improved by changing the content of Ti5Si3 and other phases and the proportion of solid solution. The formula of Ti-8Si-1.4Zr-0.1Y2O3 has the highest microhardness(1377 HV), improved by 35% than Ti-8Si(1020 HV). The friction coefficient of Ti-8Si alloy (about 0.365) was minimum, and the friction coefficient of Ti-8Si-1.4Zr-0.1Y2O3 (about 0.375) decreased by 26% than Ti-8Si-1.4Zr(0.504). Zr element decreased the wear width and improved the wear properties, while Zr element increased the friction coefficient. Ti-8Si-1.4Zr-0.1Y2O3 alloy has the best wear resistance with minimum wear width, and significantly improved the wear properties. The wear mechanism of four alloys were mainly fatigue wear, accompanied by adhesive wear, abrasive wear and oxidation wear.
2018, 47(5):1497-1502.
Abstract:
The influences of small dose B doping and heat treatment on the phase structure and magnetocaloric properties of La-Fe-Si melt spun ribbons were investigated. The results showed that the doping of B promoted the formation of the La(Fe,Si)13 phase. And La-Fe-Si-B alloys have already acquired more La(Fe,Si)13 phase before heat treatment compared to La-Fe-Si alloys. During the solidification process, it has the most content of the phase of La(Fe,Si)13 when the doping content is 0.08. B doping is beneficial for the refining of microstructure during rapid solidification which shortens the element diffusion path of peritectoid reaction in the following process of heat treatment(α-Fe + LaFeSi → La(Fe, Si)13)and is in favor of the formation of La(Fe,Si)13 phase. In the process of heat treatment, the microstructures of La-Fe-Si alloys were optimized by B doping compared to La-Fe-Si alloys. B doping refines the heat treatment structure of La-Fe-Si alloys and its Curie temperature and magnetocaloric effect has been improved. The Curie temperature of the ribbons changes from 210 K to 233 K，the maximum isothermal magnet entropy change promotes from 5.47 J/kg?K to 9.40 J/kg?K.
The influences of small dose B doping and heat treatment on the phase structure and magnetocaloric properties of La-Fe-Si melt spun ribbons were investigated. The results showed that the doping of B promoted the formation of the La(Fe,Si)13 phase. And La-Fe-Si-B alloys have already acquired more La(Fe,Si)13 phase before heat treatment compared to La-Fe-Si alloys. During the solidification process, it has the most content of the phase of La(Fe,Si)13 when the doping content is 0.08. B doping is beneficial for the refining of microstructure during rapid solidification which shortens the element diffusion path of peritectoid reaction in the following process of heat treatment(α-Fe + LaFeSi → La(Fe, Si)13)and is in favor of the formation of La(Fe,Si)13 phase. In the process of heat treatment, the microstructures of La-Fe-Si alloys were optimized by B doping compared to La-Fe-Si alloys. B doping refines the heat treatment structure of La-Fe-Si alloys and its Curie temperature and magnetocaloric effect has been improved. The Curie temperature of the ribbons changes from 210 K to 233 K，the maximum isothermal magnet entropy change promotes from 5.47 J/kg?K to 9.40 J/kg?K.
2018, 47(5):1503-1508.
Abstract:
The lattice constants, cohesive energy, mechanical property and electronic structure of δ-Pu at ground state and high pressure are calculated by a plane wave pseudo-potential method within the framework of density function theory. It shows that δ-Pu is unstable under high pressure and the phase transition happens at about 10GPa, besides, its structural stability decreases with the increase of pressure. The calculated electronic structures indicate that the bonding abilities of 5f and 6d electrons enhance, while the sp hybridization weakens with the increase of pressure. The change of bonding effect caused by the increase of pressure reveals the electronic mechanism of pressure-induced phase transition of δ-Pu.
The lattice constants, cohesive energy, mechanical property and electronic structure of δ-Pu at ground state and high pressure are calculated by a plane wave pseudo-potential method within the framework of density function theory. It shows that δ-Pu is unstable under high pressure and the phase transition happens at about 10GPa, besides, its structural stability decreases with the increase of pressure. The calculated electronic structures indicate that the bonding abilities of 5f and 6d electrons enhance, while the sp hybridization weakens with the increase of pressure. The change of bonding effect caused by the increase of pressure reveals the electronic mechanism of pressure-induced phase transition of δ-Pu.
2018, 47(5):1509-1516.
Abstract:
In this paper, the effects of SiC nanoparticles on the structure and morphology of Ni-Co coating were investigated by scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X ray diffraction (XRD). The influences of SiC nanoparticles on Ni-Co composite electrodeposition process and the electrochemical corrosion properties of Ni-Co/SiC composite coatings were studied by EIS and Tafel methods. The results show that the addition of Co2+ ions will refine the grain size of the Ni coating, reduce the porosity, transform some structure to amorphous and improve the corrosion resistance. SiC nanoparticles can promote the nucleation and growth of Ni-Co alloy and improve the hardness of the alloys. Compared with Ni-Co alloys, Ni-Co/SiC coatings have excellent corrosion and wear resistance which have the more positive Ecorr, the lower icorr and the larger Rc. Ni-Co/SiC composite coatings have the better stability of service performance, while the corrosion resistance of Ni-Co alloy decreased fast in 3.5 wt.% NaCl solution. The process of corrosion experienced three stages, namely the wetting stage, diffusion control stage which electrolyte transport in the coating and electrochemical control stage in which diffusion process is larger than that of electrochemical’s after electrolytes reach the substrate surface. Ni-Co/SiC alloys can provide long-term protection of marine engineering machinery under the influence of multifactors interaction in seawater environment.
In this paper, the effects of SiC nanoparticles on the structure and morphology of Ni-Co coating were investigated by scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X ray diffraction (XRD). The influences of SiC nanoparticles on Ni-Co composite electrodeposition process and the electrochemical corrosion properties of Ni-Co/SiC composite coatings were studied by EIS and Tafel methods. The results show that the addition of Co2+ ions will refine the grain size of the Ni coating, reduce the porosity, transform some structure to amorphous and improve the corrosion resistance. SiC nanoparticles can promote the nucleation and growth of Ni-Co alloy and improve the hardness of the alloys. Compared with Ni-Co alloys, Ni-Co/SiC coatings have excellent corrosion and wear resistance which have the more positive Ecorr, the lower icorr and the larger Rc. Ni-Co/SiC composite coatings have the better stability of service performance, while the corrosion resistance of Ni-Co alloy decreased fast in 3.5 wt.% NaCl solution. The process of corrosion experienced three stages, namely the wetting stage, diffusion control stage which electrolyte transport in the coating and electrochemical control stage in which diffusion process is larger than that of electrochemical’s after electrolytes reach the substrate surface. Ni-Co/SiC alloys can provide long-term protection of marine engineering machinery under the influence of multifactors interaction in seawater environment.
Zhang Chunhua
,
Wu SHIqi
,
He Siwen
,
Zhang Song
,
WuChenliang
,
Guan Meng
,
Tan Junzhe
,
Cui Wendong
2018, 47(5):1517-1522.
Abstract:
Ni-base RE cladding layer was prepared on Monel 400 alloy by Laser cladding technology. The microstructure, chemical composition, phase identification, hardness distribution, cavitation erosion resistance and failure mechanisms of the modified layer were examined by using SEM, EDS, XRD, microhardness tester and ultrasonic cavitation erosion tester, respectively. The results show that the Y2O3 can refine the grain. The cladding layer was mainly composed of γ-Ni solid solution, Ni3B and the high-hardness carbides (Cr23C6 and Cr7C3). The average hardness of the modified layer can reach 886 HV. The cavitation erosion resistance of Ni-based RE cladding layer was increased by 8 times compared to the Monel 400 alloy. The failure mechanism of the cladding layers is the erosion peeling of the dendrite. Grain refinement strengthening and the net structure blocking grain boundary are the key to improving the cavitation corrosion resistance of the cladding layer.
Ni-base RE cladding layer was prepared on Monel 400 alloy by Laser cladding technology. The microstructure, chemical composition, phase identification, hardness distribution, cavitation erosion resistance and failure mechanisms of the modified layer were examined by using SEM, EDS, XRD, microhardness tester and ultrasonic cavitation erosion tester, respectively. The results show that the Y2O3 can refine the grain. The cladding layer was mainly composed of γ-Ni solid solution, Ni3B and the high-hardness carbides (Cr23C6 and Cr7C3). The average hardness of the modified layer can reach 886 HV. The cavitation erosion resistance of Ni-based RE cladding layer was increased by 8 times compared to the Monel 400 alloy. The failure mechanism of the cladding layers is the erosion peeling of the dendrite. Grain refinement strengthening and the net structure blocking grain boundary are the key to improving the cavitation corrosion resistance of the cladding layer.
2018, 47(5):1523-1528.
Abstract:
Electrodeposition of molybdenum in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP]Tf2N) ionic liquid was investigated. MoCl5-[BMP]Tf2N was used for the electrolyte of electrodeposition and cyclic voltammetry curves was tested at various temperature ranging from 25℃ to 120℃. Electrodeposition was carried out using potentiostatic method. Deposits was observed and characterized by SEM, EDS, TEM and XPS. The results showed that some reduction peaks disappeared when the temperature above 100℃. The metallic molybdenum can be obtained potentiostatially at -2.2V and -2.7V on platinum electrode at 120℃. Deposit obtained at -2.2V was flat without cracked, while deposit obtained at -2.7V contained crystalline molybdenum though it was cracked.
Electrodeposition of molybdenum in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP]Tf2N) ionic liquid was investigated. MoCl5-[BMP]Tf2N was used for the electrolyte of electrodeposition and cyclic voltammetry curves was tested at various temperature ranging from 25℃ to 120℃. Electrodeposition was carried out using potentiostatic method. Deposits was observed and characterized by SEM, EDS, TEM and XPS. The results showed that some reduction peaks disappeared when the temperature above 100℃. The metallic molybdenum can be obtained potentiostatially at -2.2V and -2.7V on platinum electrode at 120℃. Deposit obtained at -2.2V was flat without cracked, while deposit obtained at -2.7V contained crystalline molybdenum though it was cracked.
2018, 47(5):1529-1536.
Abstract:
Multi-phases Mo-Si-B alloy prepared using mechanical alloying (MA) followed by hot pressing is the composite material which consists of a ductile α-Mo solid solution and the high-strengthed Mo3Si and Mo5SiB2 intermetallics. The microstructure exhibits that the spherical Mo3Si and Mo5SiB2 particles distribute within the grain and along with the grain boundary of the continuous and uniform α-Mo matrix. Some nanoscale La2O3 particles also are mainly dispersed in the α-Mo grain and partially in the Mo3Si and Mo5SiB2 intermetallic particles. These La2O3 particles can refine the grain sizes or particle sizes of α-Mo matrix and intermetallic, which promotes the alloy to obtain a fine-grained microstructure. The average grain sizes or particle sizes of α-Mo, Mo3Si and Mo5SiB2 phases are only sub-microns in size. The strengthening mechanisms include fine grain strengthening, solution strengthening and particles strengthening are quantitatively analyzed, which combines the microstructure and the mechanical test results.
Multi-phases Mo-Si-B alloy prepared using mechanical alloying (MA) followed by hot pressing is the composite material which consists of a ductile α-Mo solid solution and the high-strengthed Mo3Si and Mo5SiB2 intermetallics. The microstructure exhibits that the spherical Mo3Si and Mo5SiB2 particles distribute within the grain and along with the grain boundary of the continuous and uniform α-Mo matrix. Some nanoscale La2O3 particles also are mainly dispersed in the α-Mo grain and partially in the Mo3Si and Mo5SiB2 intermetallic particles. These La2O3 particles can refine the grain sizes or particle sizes of α-Mo matrix and intermetallic, which promotes the alloy to obtain a fine-grained microstructure. The average grain sizes or particle sizes of α-Mo, Mo3Si and Mo5SiB2 phases are only sub-microns in size. The strengthening mechanisms include fine grain strengthening, solution strengthening and particles strengthening are quantitatively analyzed, which combines the microstructure and the mechanical test results.
32 Study on the Interface Microstructure and Bonding Strength of V-4Cr-4Ti/Ti Diffusion Bonding Joint
2018, 47(5):1537-1542.
Abstract:
The diffusion bonding of V-4Cr-4Ti alloy and pure titanium was achieved by the hot forging process. The interface microstructure and bonding strength of the diffusion joint were analyzed by OM, SEM, EDS, and shear test, respectively. The diffusion joint is about 100 μm wide in total, and can be divided into two zones with different width and microstructure. The SEM analysis across the diffusion interface presents a smooth diffusion interface without any defects. According to the Vickers hardness distribution across the substrates and the diffusion joint, it can be divided into six regions (A, B, C, D, E and F). The boundary zone of region C close to Ti substrate possesses the highest hardness of 332 HV, and the zone of region E close to region D has the lowest hardness(182 HV), while the average hardness of Ti substrate and V-4Cr-4Ti alloy are 190 HV and 258 HV, respectively. The result of shear test shows that the actual shear strength is higher than 165.2 MPa, and the fracture occurred at the boundary zone of titanium substrate close to the diffusion joint, which is mainly ascribed to the stress concentration due to the phase trasition for Ti substrate during cooling process.
The diffusion bonding of V-4Cr-4Ti alloy and pure titanium was achieved by the hot forging process. The interface microstructure and bonding strength of the diffusion joint were analyzed by OM, SEM, EDS, and shear test, respectively. The diffusion joint is about 100 μm wide in total, and can be divided into two zones with different width and microstructure. The SEM analysis across the diffusion interface presents a smooth diffusion interface without any defects. According to the Vickers hardness distribution across the substrates and the diffusion joint, it can be divided into six regions (A, B, C, D, E and F). The boundary zone of region C close to Ti substrate possesses the highest hardness of 332 HV, and the zone of region E close to region D has the lowest hardness(182 HV), while the average hardness of Ti substrate and V-4Cr-4Ti alloy are 190 HV and 258 HV, respectively. The result of shear test shows that the actual shear strength is higher than 165.2 MPa, and the fracture occurred at the boundary zone of titanium substrate close to the diffusion joint, which is mainly ascribed to the stress concentration due to the phase trasition for Ti substrate during cooling process.
2018, 47(5):1543-1549.
Abstract:
Effect of cryogenic treatement temperature to corrosion behavior of AZ31 magnesium cold metal transfer(CMT) weld joint was studied by adopting electrochemical method.Result was that compared to non-cryogenic joint,the corrosion resistance of joints that were cryogenic treated under -100℃/4h,-140℃/4h,-180℃/4h were increased to a different extent.With the temperature decrease,the corrosion resistances show a downward curve after the initial raise.Critical cause of this trend are the change of the size,quantity and distribution of the second phase caused by cryogenic treatment. The weld zone that was cryogenic treated under -140℃/4h shows the best corrosion resistance because the charge transfer resistance and corrosion product film resistance of that reaches maximum and the corrosion current of that reaches minimum.
Effect of cryogenic treatement temperature to corrosion behavior of AZ31 magnesium cold metal transfer(CMT) weld joint was studied by adopting electrochemical method.Result was that compared to non-cryogenic joint,the corrosion resistance of joints that were cryogenic treated under -100℃/4h,-140℃/4h,-180℃/4h were increased to a different extent.With the temperature decrease,the corrosion resistances show a downward curve after the initial raise.Critical cause of this trend are the change of the size,quantity and distribution of the second phase caused by cryogenic treatment. The weld zone that was cryogenic treated under -140℃/4h shows the best corrosion resistance because the charge transfer resistance and corrosion product film resistance of that reaches maximum and the corrosion current of that reaches minimum.
2018, 47(5):1550-1554.
Abstract:
:Ti55.5Cu18.5Ni17.5Al8.5amorphous powders were produced by mechanical alloying process. The microstructure, amorphization behavior and hardness were studied by X-ray diffraction, differential scanning calorimetry, scanning electronic microscopy and transmission electron microscopy, et al. The results show that the microstructure changed significantly with increasing milling time. Firstly grain size decreased and nanometric intermetallic appeared. Secondly long range disordered structure occured inside the nanometric intermetallics with further milling. Finally the intermetalics were separated into many smaller parts by the disordered structure and then amorphization. The amorphization mechaniam was stuied at atomic scale and shows that the major reason is the server plastic deformation occurred during high energy ball milling, leading to high density of dislocation and large lattice distortaion, which results into long range disordered structure and amorphous structure. The alloy’s hardness increases significantly with milling owing to the work hardening and amorphization during ball milling.
:Ti55.5Cu18.5Ni17.5Al8.5amorphous powders were produced by mechanical alloying process. The microstructure, amorphization behavior and hardness were studied by X-ray diffraction, differential scanning calorimetry, scanning electronic microscopy and transmission electron microscopy, et al. The results show that the microstructure changed significantly with increasing milling time. Firstly grain size decreased and nanometric intermetallic appeared. Secondly long range disordered structure occured inside the nanometric intermetallics with further milling. Finally the intermetalics were separated into many smaller parts by the disordered structure and then amorphization. The amorphization mechaniam was stuied at atomic scale and shows that the major reason is the server plastic deformation occurred during high energy ball milling, leading to high density of dislocation and large lattice distortaion, which results into long range disordered structure and amorphous structure. The alloy’s hardness increases significantly with milling owing to the work hardening and amorphization during ball milling.
2018, 47(5):1555-1561.
Abstract:
The AZ31B magnesium alloy sheet was subjected to a hot rolling test at a temperature of 250℃ to 400℃ at a rate of 0.5 m/s, and four different cross rolling paths were selected to reduce the edge cracks during the deformation. The hot rolling structures and textures were modified for controlling the edge crack generation. The macroscopic morphology, microstructure and texture of the magnesium alloy plate obtained by different rolling processes were analyzed by scanning electron microscopy (SEM) and electron backscattering (EBSD). The results show that, the edge crack of the magnesium plate decreases with the increase of the temperature, and there was almost no crack appearance in the magnesium alloy plate obtained by the RII rolling path at 400℃. The angles between Edge crack and rolling direction were approximately 45 degrees, and the edge of the magnesium plate formed a “O” with the widest part of 129μm under rolling path II, which meant that It will difficult to further expand to both sides. After the multi-cross rolling, the grains were obviously refined, and most of the grains had a completely dynamic recrystallization. The number of low-angle-grain-boundaries decreased with the changes of different rolling path, and the intensity of the base texture was reduced from 23.68 to 7.62. More fine grains can not only produce a larger grain boundary, but also weaken the base texture, and obviously inhibit the expansion of the crack, control the formation of edge crack.
The AZ31B magnesium alloy sheet was subjected to a hot rolling test at a temperature of 250℃ to 400℃ at a rate of 0.5 m/s, and four different cross rolling paths were selected to reduce the edge cracks during the deformation. The hot rolling structures and textures were modified for controlling the edge crack generation. The macroscopic morphology, microstructure and texture of the magnesium alloy plate obtained by different rolling processes were analyzed by scanning electron microscopy (SEM) and electron backscattering (EBSD). The results show that, the edge crack of the magnesium plate decreases with the increase of the temperature, and there was almost no crack appearance in the magnesium alloy plate obtained by the RII rolling path at 400℃. The angles between Edge crack and rolling direction were approximately 45 degrees, and the edge of the magnesium plate formed a “O” with the widest part of 129μm under rolling path II, which meant that It will difficult to further expand to both sides. After the multi-cross rolling, the grains were obviously refined, and most of the grains had a completely dynamic recrystallization. The number of low-angle-grain-boundaries decreased with the changes of different rolling path, and the intensity of the base texture was reduced from 23.68 to 7.62. More fine grains can not only produce a larger grain boundary, but also weaken the base texture, and obviously inhibit the expansion of the crack, control the formation of edge crack.
2018, 47(5):1562-1566.
Abstract:
Partial NO is oxidized to NO2 during the emission gas through diesel oxidation catalysts (DOC). Proper NO2 /NOx ratio increases the low-temperature soot oxidation rate of diesel particulate filter (DPF) and the NOx conversion efficiency of selective catalytic reduction (SCR). In order to study the degreening effect of DOC, in-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRFTS), H2 temperature-programmed reduction (H2-TPR) and High-revolution transmission electron microscope (HR-TEM) were performed to characterize the Pt/Al2O3 catalyst. A larger amount of nitrate and nitrite species was observed in the fresh Pt/Al2O3 catalysts blow 300 oC. It is shown that PtOx species that interacted strongly with support are the main cause of degreening effect. The particle size of Pt has no significant change after 3-cycles temperature-programmed reaction.
Partial NO is oxidized to NO2 during the emission gas through diesel oxidation catalysts (DOC). Proper NO2 /NOx ratio increases the low-temperature soot oxidation rate of diesel particulate filter (DPF) and the NOx conversion efficiency of selective catalytic reduction (SCR). In order to study the degreening effect of DOC, in-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRFTS), H2 temperature-programmed reduction (H2-TPR) and High-revolution transmission electron microscope (HR-TEM) were performed to characterize the Pt/Al2O3 catalyst. A larger amount of nitrate and nitrite species was observed in the fresh Pt/Al2O3 catalysts blow 300 oC. It is shown that PtOx species that interacted strongly with support are the main cause of degreening effect. The particle size of Pt has no significant change after 3-cycles temperature-programmed reaction.
2018, 47(5):1567-1572.
Abstract:
In this paper, (TiC+TiB2)/Cu composites are successfully prepared by mixing and hot-press sintering of Cu powder with mechanical alloyed Ti-B4C powder mixture. Results show that, mechanical alloying can ensure the decomposition and solution of B4C in to Ti powder, and thus form a solution of ternary Ti-C-B system. As a result, on-set temperature of Ti-B4C in-situ reaction is decreased and reaction products are TiC+TiB2, because that the formation of TiB2 has lower Gibbs free energy change than that of TiB. When the content is low, reinforcements presents to be small and well-dispersed particles in Cu matrix, and the reinforcements and matrix is well combined, resulting in significant improvements on hardness of composites. With the content increases, reinforcements aggregate seriously, and the interface transfers to be simple mechamical package. When the designed content of reinforcements is 15vol.%, the electrical conductivity of prepared (TiC+TiB2)/Cu composites is 47.1%IACS, much higher than composites prepared from non-milled Cu-Ti-B4C mixture (12.46%IACS), suggesting that mechanical alloying can accelerate reaction between Ti-B4C while prevent solution of Ti into Cu matrix.
In this paper, (TiC+TiB2)/Cu composites are successfully prepared by mixing and hot-press sintering of Cu powder with mechanical alloyed Ti-B4C powder mixture. Results show that, mechanical alloying can ensure the decomposition and solution of B4C in to Ti powder, and thus form a solution of ternary Ti-C-B system. As a result, on-set temperature of Ti-B4C in-situ reaction is decreased and reaction products are TiC+TiB2, because that the formation of TiB2 has lower Gibbs free energy change than that of TiB. When the content is low, reinforcements presents to be small and well-dispersed particles in Cu matrix, and the reinforcements and matrix is well combined, resulting in significant improvements on hardness of composites. With the content increases, reinforcements aggregate seriously, and the interface transfers to be simple mechamical package. When the designed content of reinforcements is 15vol.%, the electrical conductivity of prepared (TiC+TiB2)/Cu composites is 47.1%IACS, much higher than composites prepared from non-milled Cu-Ti-B4C mixture (12.46%IACS), suggesting that mechanical alloying can accelerate reaction between Ti-B4C while prevent solution of Ti into Cu matrix.
2018, 47(5):1573-1577.
Abstract:
In this paper, as the example of AZ31 magnesium alloy, the process of magnesium alloy spun tube with the sixth spinning passes has been studied, and the microstructue evolution and the micro/nan mechanical properties of the tube billet has been analyzed. The magnesium alloy tube with the wall thickness of 1 mm from the wall thickness of 10 mm has a good forming and no bulge defects, such as bump by power spinning testing. The microstructure of the tube samples with several spinning passes was analysed by optical microsco. The results show that the grain distribution from original coarse and uneven grain transform to main twin, even and fine grain characteristic. The nanoindentor properties were tested by G200 Micro-nano mechanics test system. The results present that the hardness increased with the spinning passes, and the hardness were 0.377 GPaand 1.053 GPa, respectively. The modulus of original and after power spinning magnesium alloy tube samples were with features of plastic fracture. However, The fracture original magnesium alloy tube was dimple fracture with larger and deeper. On the contrary, the fracture after power spinning was dimple fracture with small and shallow.
In this paper, as the example of AZ31 magnesium alloy, the process of magnesium alloy spun tube with the sixth spinning passes has been studied, and the microstructue evolution and the micro/nan mechanical properties of the tube billet has been analyzed. The magnesium alloy tube with the wall thickness of 1 mm from the wall thickness of 10 mm has a good forming and no bulge defects, such as bump by power spinning testing. The microstructure of the tube samples with several spinning passes was analysed by optical microsco. The results show that the grain distribution from original coarse and uneven grain transform to main twin, even and fine grain characteristic. The nanoindentor properties were tested by G200 Micro-nano mechanics test system. The results present that the hardness increased with the spinning passes, and the hardness were 0.377 GPaand 1.053 GPa, respectively. The modulus of original and after power spinning magnesium alloy tube samples were with features of plastic fracture. However, The fracture original magnesium alloy tube was dimple fracture with larger and deeper. On the contrary, the fracture after power spinning was dimple fracture with small and shallow.
39 Preparation and Microstructure of FeCrNiMoCu high-entropy alloy coatings by magnetron co-sputtering
2018, 47(5):1578-1582.
Abstract:
The FeCrNiMoCu high-entropy alloy coatings were prepared in 304 stainless steel by five- targets co-sputtering. Nano-indentation hardness, microstructure and morphology of the as-deposited coating were investigated using Nano indentation, X-ray diffraction ( XRD), atom force microscopy(AFM) and scanning electron microscopy ( SEM). The obtained results indicate that the coatings have simple FCC solid solution and high hardness, and coating surface hardness increase with Fe content.
The FeCrNiMoCu high-entropy alloy coatings were prepared in 304 stainless steel by five- targets co-sputtering. Nano-indentation hardness, microstructure and morphology of the as-deposited coating were investigated using Nano indentation, X-ray diffraction ( XRD), atom force microscopy(AFM) and scanning electron microscopy ( SEM). The obtained results indicate that the coatings have simple FCC solid solution and high hardness, and coating surface hardness increase with Fe content.
2018, 47(5):1583-1588.
Abstract:
The composite adsorbent graphene oxide-chitosan (GO-CTS) was prepared successfully and characterized by FTIR spectra and SEM. The products were used to study the adsorption of uranium from aqueous solution. The solution pH, the adsorbent dosage, contact time and initial uranium concentration were investigated to estimate the adsorptive properties. The results show that for the uranium solution with initial concentration of 10 mg/L, the optimum adsorption conditions of GO and GO-CTS were pH of 4-7 and 5; the doses of 1.0 g/L and 1.0 g/L; adsorption balance time of <1 min and 70 min, and the maximum uranium removal rate of 99.5% and 97.5%, respectively.
The composite adsorbent graphene oxide-chitosan (GO-CTS) was prepared successfully and characterized by FTIR spectra and SEM. The products were used to study the adsorption of uranium from aqueous solution. The solution pH, the adsorbent dosage, contact time and initial uranium concentration were investigated to estimate the adsorptive properties. The results show that for the uranium solution with initial concentration of 10 mg/L, the optimum adsorption conditions of GO and GO-CTS were pH of 4-7 and 5; the doses of 1.0 g/L and 1.0 g/L; adsorption balance time of <1 min and 70 min, and the maximum uranium removal rate of 99.5% and 97.5%, respectively.
2018, 47(5):1589-1595.
Abstract:
The one-step aging behavior of 7A52 aluminum alloy laser welding joint were characterized by mechanical properties, electrical conductivity test, EDS and TEM. It was found that the base metal and the weld joint of 7A52 aluminum alloy need almost same time to reach peak hardness under different temperatures. When the aging temperature was increased from 120℃ to 160℃, The age hardening rate of contact joint was noticeably accelerated and the time to reach peak hardness was significantly reduced. After aging 16h at 140℃, the tensile strength of joint, loss of weight and the conductivity were 351 MPa, 0.0070 g/min and 21.2 MS/m. Compared with the data after aging 24h at 120℃, the result shows 1.13% tensile strength of joint decrease, 2.94% loss of weight decrease and 12.2% conductivity increase. Thus aging 24h at 120℃ is considered as a reasonable one-step aging process. The precipitate phase of the welding joint and the base metal was MgZn2. At 140℃, the precipitate phase got an amount increase and coarsening with the aging time extending. And the main strengthening phase were η， phase (MgZn2) and GP zone at peak aging state.
The one-step aging behavior of 7A52 aluminum alloy laser welding joint were characterized by mechanical properties, electrical conductivity test, EDS and TEM. It was found that the base metal and the weld joint of 7A52 aluminum alloy need almost same time to reach peak hardness under different temperatures. When the aging temperature was increased from 120℃ to 160℃, The age hardening rate of contact joint was noticeably accelerated and the time to reach peak hardness was significantly reduced. After aging 16h at 140℃, the tensile strength of joint, loss of weight and the conductivity were 351 MPa, 0.0070 g/min and 21.2 MS/m. Compared with the data after aging 24h at 120℃, the result shows 1.13% tensile strength of joint decrease, 2.94% loss of weight decrease and 12.2% conductivity increase. Thus aging 24h at 120℃ is considered as a reasonable one-step aging process. The precipitate phase of the welding joint and the base metal was MgZn2. At 140℃, the precipitate phase got an amount increase and coarsening with the aging time extending. And the main strengthening phase were η， phase (MgZn2) and GP zone at peak aging state.
2018, 47(5):1596-1600.
Abstract:
The microstructure and mechanical properties of nano-crystalline Ti films were studied with different pulse duration,which were deposited by the High Power Pulsed ion plating. The results shows that when the average current kept in low value, the larger peak current can be obtained by adjusting the pulse duration (duty ratio), which has a significant effect on the microstructure of the thin film. The surface morphologies showed gradually appeared apparent porosity of the particles and the growth dimensions of the spherical agglomeration significantly increases with the single pulses duration prolonged. The cross section of the growth showed that the morphology transition from the columnar to the dendritic with the extension of the duration of the pulse, while a large number of pores and defects occurred and the density of the films decreased obviously. The hardness and modulus of the films are showing increased first and the substantially reduced trend with the prolonged of the pulse duration. The value of the hardness and modulus exist the maximum when the single pulse duration reached about 4ms.
The microstructure and mechanical properties of nano-crystalline Ti films were studied with different pulse duration,which were deposited by the High Power Pulsed ion plating. The results shows that when the average current kept in low value, the larger peak current can be obtained by adjusting the pulse duration (duty ratio), which has a significant effect on the microstructure of the thin film. The surface morphologies showed gradually appeared apparent porosity of the particles and the growth dimensions of the spherical agglomeration significantly increases with the single pulses duration prolonged. The cross section of the growth showed that the morphology transition from the columnar to the dendritic with the extension of the duration of the pulse, while a large number of pores and defects occurred and the density of the films decreased obviously. The hardness and modulus of the films are showing increased first and the substantially reduced trend with the prolonged of the pulse duration. The value of the hardness and modulus exist the maximum when the single pulse duration reached about 4ms.
2018, 47(5):1601-1606.
Abstract:
The FeBSiNb amorphous coating was prepared by flame spraying using the alloy powders were fabricated by gas atomization. The morphology, microstructure, phase composition and thermal stability were investigated by XRD, SEM, TEM and DSC. The FeBSiNb alloy powder is composed of Fe2B crystalline phase and α-Fe(Si) solid solution. The morphology of particle is spherical or elliptical. The FeBSiNb amorphous coating is consisted of amorphous (~85 vol%), Fe2B crystalline phase and α-Fe(Si) nanocrystalline phase. The crystallization of FeBSiNb amorphous coating occurs around 531~605℃.The glass transition top temperature Tg is about 513℃ and the onset top temperature of first crystallization event Tx is about 531℃. The critical cooling rate for glass formation of FeBSiNb alloy is calculated of about 2.0×106 K/s. Under the dry friction condition of 5N, 5Hz, 30min, the friction coefficient of FeBSiNb amorphous coating is only 0.2. The relative wear resistance of amorphous coating was more than 10 times compared with the 45# steel substrate.
The FeBSiNb amorphous coating was prepared by flame spraying using the alloy powders were fabricated by gas atomization. The morphology, microstructure, phase composition and thermal stability were investigated by XRD, SEM, TEM and DSC. The FeBSiNb alloy powder is composed of Fe2B crystalline phase and α-Fe(Si) solid solution. The morphology of particle is spherical or elliptical. The FeBSiNb amorphous coating is consisted of amorphous (~85 vol%), Fe2B crystalline phase and α-Fe(Si) nanocrystalline phase. The crystallization of FeBSiNb amorphous coating occurs around 531~605℃.The glass transition top temperature Tg is about 513℃ and the onset top temperature of first crystallization event Tx is about 531℃. The critical cooling rate for glass formation of FeBSiNb alloy is calculated of about 2.0×106 K/s. Under the dry friction condition of 5N, 5Hz, 30min, the friction coefficient of FeBSiNb amorphous coating is only 0.2. The relative wear resistance of amorphous coating was more than 10 times compared with the 45# steel substrate.
44 Effect of severe plastic deformation on the microstructure evolution of bulk AZ31 Mgmgnesium alloys
2018, 47(5):1607-1612.
Abstract:
Equal channel angular pressing (ECAP) processes have the capability to produce bulk nonstructural materials without loose holes. Using commercial metal forming finite element code, ECAP process is analyzed numerically in this paper. It is combining through node reflection method and three-dimensional model switching to realize multi-pressing process of Routs A, Ba, Bc and C by using finite element method, the distribution of accumulated effective strain and the influence rules of deformation uniformity in round billets are obtained, and the grain refine mechanism of equal channel angular multi-pressing for different processing Routes are obtained. The microstructure evolution of the workpiece can be changed via different processing routes. With increase of passes pressing, the grain microstructure in the workpiece is gradually refined for different processing routes. It is found that route Bc can get a high angle grain boundaries distribution in the workpiece than other routes. In addition, the experimental microstructure results are also consistent with FE analysis results. The microstructure evolutions of grain refinement mechanisms for different multi-pass ECAE processing routes are accord with the accumulated effective strain rules in the workpiece. Those results can offer better process planning and guidelines for ECAP experiments.
Equal channel angular pressing (ECAP) processes have the capability to produce bulk nonstructural materials without loose holes. Using commercial metal forming finite element code, ECAP process is analyzed numerically in this paper. It is combining through node reflection method and three-dimensional model switching to realize multi-pressing process of Routs A, Ba, Bc and C by using finite element method, the distribution of accumulated effective strain and the influence rules of deformation uniformity in round billets are obtained, and the grain refine mechanism of equal channel angular multi-pressing for different processing Routes are obtained. The microstructure evolution of the workpiece can be changed via different processing routes. With increase of passes pressing, the grain microstructure in the workpiece is gradually refined for different processing routes. It is found that route Bc can get a high angle grain boundaries distribution in the workpiece than other routes. In addition, the experimental microstructure results are also consistent with FE analysis results. The microstructure evolutions of grain refinement mechanisms for different multi-pass ECAE processing routes are accord with the accumulated effective strain rules in the workpiece. Those results can offer better process planning and guidelines for ECAP experiments.
2018, 47(5):1613-1619.
Abstract:
By controlling the sintering temperature of Gd211 solid pellet, a series of Gd211 precursors with different microstructures were obtained. On this basis, Single domain GdBCO bulk superconductors have been successfully fabricated by the top-seeding melt infiltration growth process. Through observing the macro morphology and microstructure of the GdBCO bulk and the Gd211 precursors, as well as measuring the magnetic levitation force of GdBCO superconductor, the results show that It was only when the microstructure of the precursors block meet conditions: Gd211 particles are spherical or ellipsoidal and the average size is smaller. The gaps between Gd211 particles are appropriate. The size of Gd211 particles in the single domain GdBCO bulk superconductor is the smallest, The magnetic flux pinning and levitation force of the sample is the largest(The maximum force is 38.7N, The sample diameter is 20mm, The test temperature is 77K, The permanent magnet diameter is 20mm,The surface magnetic field is 0.5T). The results provide scientific basis and ideas to improve the superconducting properties of HTS.
By controlling the sintering temperature of Gd211 solid pellet, a series of Gd211 precursors with different microstructures were obtained. On this basis, Single domain GdBCO bulk superconductors have been successfully fabricated by the top-seeding melt infiltration growth process. Through observing the macro morphology and microstructure of the GdBCO bulk and the Gd211 precursors, as well as measuring the magnetic levitation force of GdBCO superconductor, the results show that It was only when the microstructure of the precursors block meet conditions: Gd211 particles are spherical or ellipsoidal and the average size is smaller. The gaps between Gd211 particles are appropriate. The size of Gd211 particles in the single domain GdBCO bulk superconductor is the smallest, The magnetic flux pinning and levitation force of the sample is the largest(The maximum force is 38.7N, The sample diameter is 20mm, The test temperature is 77K, The permanent magnet diameter is 20mm,The surface magnetic field is 0.5T). The results provide scientific basis and ideas to improve the superconducting properties of HTS.
2018, 47(5):1620-1624.
Abstract:
Laser butt welding of DD407 and GH1140 commonly used for aeroengine blisk was conducted in this paper. The effects of beam displacement on mechanical properties, microstructure characteristics, and microhardness of laser joints were comprehensive analyzed. The results showed that the tensile strength of the joint reached 466.3MPa, which was NOT resulted from beam displacements, while determined by the performance of base metal GH1140. The morphology of joint cross section shaped like "wine-cup", and the microstructure of weld mainly consisted of columnar grains growth from both sides of weld and equiaxed grains in weld centre. The gradually increased distribution of micro-hardness along horizontal line located upper side of joint cross-section from base metal of GH1140, weld, to base metal of DD407 in different laser beam displacements was considered as the results from the solution strengthening of W and Co elements,the increased content of γ" strengthening phase, and the coarsened grains in weld.
Laser butt welding of DD407 and GH1140 commonly used for aeroengine blisk was conducted in this paper. The effects of beam displacement on mechanical properties, microstructure characteristics, and microhardness of laser joints were comprehensive analyzed. The results showed that the tensile strength of the joint reached 466.3MPa, which was NOT resulted from beam displacements, while determined by the performance of base metal GH1140. The morphology of joint cross section shaped like "wine-cup", and the microstructure of weld mainly consisted of columnar grains growth from both sides of weld and equiaxed grains in weld centre. The gradually increased distribution of micro-hardness along horizontal line located upper side of joint cross-section from base metal of GH1140, weld, to base metal of DD407 in different laser beam displacements was considered as the results from the solution strengthening of W and Co elements,the increased content of γ" strengthening phase, and the coarsened grains in weld.
2018, 47(5):1625-1630.
Abstract:
Through the in-situ synthesizing the doping of zirconium dioxide and graphite, the ZrC particles reinforced NiCrBSi composite coating was produced onto the mild steel by laser cladding. Microstructure, phase constitution of NiCrBSi+Zr composite coating were characterized by scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and X-ray diffractometer(XRD). And the morphology, formation and growth mechanism and distribution of ZrC reinforcements were studied and discussed, and the hardness of coating was investigated as well. The results showed that ZrC reinforcements were uniformly distributed in the upper and middle coating, only little was in the bottom of coating. The morphology of ZrC were mainly consist of triangle, quadrilateral similar to rhombus and long-bar shape, which contributes to obstruction from the interdendritic growth, the collision and sintering caused by high convection and repulsion between solid-liquid interface in the molten pool. Hardness of composite coating was improved by ZrC reinforcements and carbide such as M23C6, which contribute to its high hardness. Finally, the hardness of composite coating can reach to HV0.2 720.
Through the in-situ synthesizing the doping of zirconium dioxide and graphite, the ZrC particles reinforced NiCrBSi composite coating was produced onto the mild steel by laser cladding. Microstructure, phase constitution of NiCrBSi+Zr composite coating were characterized by scanning electron microscope(SEM), energy dispersive spectrometer(EDS) and X-ray diffractometer(XRD). And the morphology, formation and growth mechanism and distribution of ZrC reinforcements were studied and discussed, and the hardness of coating was investigated as well. The results showed that ZrC reinforcements were uniformly distributed in the upper and middle coating, only little was in the bottom of coating. The morphology of ZrC were mainly consist of triangle, quadrilateral similar to rhombus and long-bar shape, which contributes to obstruction from the interdendritic growth, the collision and sintering caused by high convection and repulsion between solid-liquid interface in the molten pool. Hardness of composite coating was improved by ZrC reinforcements and carbide such as M23C6, which contribute to its high hardness. Finally, the hardness of composite coating can reach to HV0.2 720.
2018, 47(5):1631-1636.
Abstract:
This paper aims to explore the generation mechanism of blowhole defects in TiAl based alloys exhaust valve in the process of vacuum suction casting. By comparing the morphology and distribution of void defects in TiAl based alloys exhaust valve fabricated by different process parameters, the type of void defects is identified as blowhole. Combining with numerical simulation of calculating the fluid state of the alloy melt in the suction casting process, the reason of blowhole formation is determined. By optimizing the casting parameters in the process, blowhole is eliminated ultimately.
This paper aims to explore the generation mechanism of blowhole defects in TiAl based alloys exhaust valve in the process of vacuum suction casting. By comparing the morphology and distribution of void defects in TiAl based alloys exhaust valve fabricated by different process parameters, the type of void defects is identified as blowhole. Combining with numerical simulation of calculating the fluid state of the alloy melt in the suction casting process, the reason of blowhole formation is determined. By optimizing the casting parameters in the process, blowhole is eliminated ultimately.
2018, 47(5):1637-1642.
Abstract:
Pd/C catalysts were prepared by introducing complexone (nitrilotriacetic acid trisodium salt, NTA) into Pd precursor solutions, Pd particles were stabilized by the coordination of Pd2+ and NTA. Catalysts were characterized by XRD, XPS, TEM and H2-TPR, and we found that compared with Pd/C catalyst prepared by impregnation method, the average particle size of Pd could by effectively reduced by introducing NTA during preparation. Furthermore, Pd particles could be size-controlled by adjusting the amount of NTA, the average particle size of Pd was decreased from 5.7 to 2.1 nm by increase NTA from 0.5 to 2 times of Pd (molar ratio), but Pd particle size did not continue to decrease by continue increasing the amount of NTA. The best catalytic performance was achieved when the average particle size was 4nm (NTA: Pd=1: 1), conversion was 100% and selectivity of 2,3-dichloropyridine was up to 76.86% after 6 hours of reaction.
Pd/C catalysts were prepared by introducing complexone (nitrilotriacetic acid trisodium salt, NTA) into Pd precursor solutions, Pd particles were stabilized by the coordination of Pd2+ and NTA. Catalysts were characterized by XRD, XPS, TEM and H2-TPR, and we found that compared with Pd/C catalyst prepared by impregnation method, the average particle size of Pd could by effectively reduced by introducing NTA during preparation. Furthermore, Pd particles could be size-controlled by adjusting the amount of NTA, the average particle size of Pd was decreased from 5.7 to 2.1 nm by increase NTA from 0.5 to 2 times of Pd (molar ratio), but Pd particle size did not continue to decrease by continue increasing the amount of NTA. The best catalytic performance was achieved when the average particle size was 4nm (NTA: Pd=1: 1), conversion was 100% and selectivity of 2,3-dichloropyridine was up to 76.86% after 6 hours of reaction.
2018, 47(5):1643-1647.
Abstract:
The NdFeB magnetic powder with main phase Nd2Fe14B was successfully prepared by using the chemical method to prepare NdFeB intermediates and then through two-step reduction annealing. Phase, microstructure, phase transformation of different temperatures and magnetic properties of the samples were analyzed with XRD、TEM、DSC、VSM and so on. The formation mechanism of Nd2Fe14B phase was discussed. The results show that the nano-sized NdFeB intermediates with good dispersion, including spherical Fe3O4 particle and flocculent organic ligands consisting of Nd and B elements, can be synthesized by chemical method. In order to obtain NdFeB magnetic powder, the intermediate should be performed two-step reduction annealing. In the first-step reduction annealing process, NdFeB intermediates were converted into NdFeO3, B2O3, Nd2O3 and α-Fe phases. During the second-step annealing was carried out by CaH2, the reaction experiences following processes: firstly, B2O3 is reduced at 501 ℃.Then, Nd2O3 and NdFeO3 are reduced into NdH2 and α-Fe phases at 678 ℃. Finally, B、NdH2 and α-Fe are alloying reaction to formed Nd2Fe14B magnetic powder at 895 ℃.
The NdFeB magnetic powder with main phase Nd2Fe14B was successfully prepared by using the chemical method to prepare NdFeB intermediates and then through two-step reduction annealing. Phase, microstructure, phase transformation of different temperatures and magnetic properties of the samples were analyzed with XRD、TEM、DSC、VSM and so on. The formation mechanism of Nd2Fe14B phase was discussed. The results show that the nano-sized NdFeB intermediates with good dispersion, including spherical Fe3O4 particle and flocculent organic ligands consisting of Nd and B elements, can be synthesized by chemical method. In order to obtain NdFeB magnetic powder, the intermediate should be performed two-step reduction annealing. In the first-step reduction annealing process, NdFeB intermediates were converted into NdFeO3, B2O3, Nd2O3 and α-Fe phases. During the second-step annealing was carried out by CaH2, the reaction experiences following processes: firstly, B2O3 is reduced at 501 ℃.Then, Nd2O3 and NdFeO3 are reduced into NdH2 and α-Fe phases at 678 ℃. Finally, B、NdH2 and α-Fe are alloying reaction to formed Nd2Fe14B magnetic powder at 895 ℃.
2018, 47(5):1648-1654.
Abstract:
Along with the development of rare earth materials, the preparation of novel rare earth function materials needed higher purity of rare earth metals. The methods for purifying rare earth metal mainly included vacuum melting, electrolytic refining, vacuum distillation/sublimation, fused-salt extraction, zone refining, solid-state electrotransport, electrochemical deoxidation, external getter method, plasma arc melting (Ar or Ar+H2), etc. The purification mechanism of rare earths metals was briefly explained, and the research progress and purification effects are summarized. Combining multiple means for removing impurities and promoting the level of equipment, in order to improve the effects of purification, and reduce the cost, shorten production cycle.
Along with the development of rare earth materials, the preparation of novel rare earth function materials needed higher purity of rare earth metals. The methods for purifying rare earth metal mainly included vacuum melting, electrolytic refining, vacuum distillation/sublimation, fused-salt extraction, zone refining, solid-state electrotransport, electrochemical deoxidation, external getter method, plasma arc melting (Ar or Ar+H2), etc. The purification mechanism of rare earths metals was briefly explained, and the research progress and purification effects are summarized. Combining multiple means for removing impurities and promoting the level of equipment, in order to improve the effects of purification, and reduce the cost, shorten production cycle.
