Volume 47,Issue 8,2018 Table of Contents
2018, 47(8):2290-2297.
Abstract:
Microstructure and mechanical properties of transient liquid phase (TLP) bonded joints and the post bonding heat treatment (PBHT) for CB2 heat resistant steel using BNi-2 insert alloy were investigated. The Cr-rich borides (CrB, CrB2, Cr2B3, Cr3B4 and Cr5B3) and Cr-Mo borides generate in the transition region (TZ) and diffusion-affected zone (DAZ) reach the peak values in size and quantity when the isothermal is completed. Subsequent elevation in bonding temperature and increment in bonding time result in gradual disappearance of such Cr-rich and Cr-Mo borides, increased percent of BN precipitates. After PBHT the Cr-rich borides almost disappear while the size and amount of BN precipitates rise. The maximum tensile strength reach to 934 MPa for the joint bonded at 1150 °C for 1800 s with elongation of 5.3%. PBHT result in significant improvement in ductility of the joint as elongation of 20% is achieved with a decreased strength of 720 MPa, the fracture takes place at base materials.
Microstructure and mechanical properties of transient liquid phase (TLP) bonded joints and the post bonding heat treatment (PBHT) for CB2 heat resistant steel using BNi-2 insert alloy were investigated. The Cr-rich borides (CrB, CrB2, Cr2B3, Cr3B4 and Cr5B3) and Cr-Mo borides generate in the transition region (TZ) and diffusion-affected zone (DAZ) reach the peak values in size and quantity when the isothermal is completed. Subsequent elevation in bonding temperature and increment in bonding time result in gradual disappearance of such Cr-rich and Cr-Mo borides, increased percent of BN precipitates. After PBHT the Cr-rich borides almost disappear while the size and amount of BN precipitates rise. The maximum tensile strength reach to 934 MPa for the joint bonded at 1150 °C for 1800 s with elongation of 5.3%. PBHT result in significant improvement in ductility of the joint as elongation of 20% is achieved with a decreased strength of 720 MPa, the fracture takes place at base materials.
2018, 47(8):2275-2282.
Abstract:
During the machining of powder metallurgy (PM) superalloy parts, the machined surface undergoes severe plastic deformation which appears to be in the form of microstructure and mechanical properties transformation. White layer which is belong to the microstructure and mechanical properties transformation, usually generated on the machined surface during hard machining of PM superalloy, it has significant effect on the machined surface quality. The effect of cutting speed on the white layer formation has been successfully investigated in order to illustrate the microstructure and mechanical properties transformation in the machined surface of PM superalloy FGH95. White layer thickness on the machined surface increased with the increasing of cutting speed. The investigation results showed that machined surface exhibited densification with no obvious structural features characteristics. FGH95 superalloy bulk material existed in the form of Ni-based solid solution, while the microstructure of white layer was observed significantly different from bulk materials. It’s because of the transformation of microstructure presented in the form of Ni-based solid solution in FGH95 during the cutting process. The higher the cutting speeds more severe grain refinement, which will leads to higher values of hardness in white layer. Residual stresses in the machined surface of FGH95 were seems to be observed tensile in all cutting conditions and it was observed an increasing trend with respect to the increment of cutting speed. The microstructure and mechanical properties transformation in the machined surface of PM superalloy was revealed in order to identify the mechanism of machined surface integrity, it can be provide the theoretical basis for the controlling of machined surface quality.
During the machining of powder metallurgy (PM) superalloy parts, the machined surface undergoes severe plastic deformation which appears to be in the form of microstructure and mechanical properties transformation. White layer which is belong to the microstructure and mechanical properties transformation, usually generated on the machined surface during hard machining of PM superalloy, it has significant effect on the machined surface quality. The effect of cutting speed on the white layer formation has been successfully investigated in order to illustrate the microstructure and mechanical properties transformation in the machined surface of PM superalloy FGH95. White layer thickness on the machined surface increased with the increasing of cutting speed. The investigation results showed that machined surface exhibited densification with no obvious structural features characteristics. FGH95 superalloy bulk material existed in the form of Ni-based solid solution, while the microstructure of white layer was observed significantly different from bulk materials. It’s because of the transformation of microstructure presented in the form of Ni-based solid solution in FGH95 during the cutting process. The higher the cutting speeds more severe grain refinement, which will leads to higher values of hardness in white layer. Residual stresses in the machined surface of FGH95 were seems to be observed tensile in all cutting conditions and it was observed an increasing trend with respect to the increment of cutting speed. The microstructure and mechanical properties transformation in the machined surface of PM superalloy was revealed in order to identify the mechanism of machined surface integrity, it can be provide the theoretical basis for the controlling of machined surface quality.
2018, 47(8):2283-2289.
Abstract:
CrN films were deposited on 304 stainless steel by DC reactive magnetron sputtering. The effects of nitrogen flow on the microstructure, mechanical and tribological properties were characterized by X-ray diffraction, scanning electron microscopy, atom force microscope, microhardness, wear tester and Nanomap 500LS profile. The results showed that with the increase of nitrogen flow, the CrN films exhibited a preferential orientation in the (200) direction. The deposition rate of CrN films decrease with the increase of nitrogen flow. Besides, the surface roughness exhibited the tendency of decrease first and then increase with further increase of nitrogen flow. As nitrogen flow increased from 15 to 30 sccm, microhardness was improved from 527.34 HV to 1042.26 HV, and then decrease to 918 HV when the nitrogen flow further increase to 35 sccm. Wear test showed that the CrN films deposited at nitrogen flow of 30 sccm was achieved lowest friction coefficient with 0.93 and wear rate with 2.02×10-15m3·(N·m)-1, which presented best wear resistance performance.
CrN films were deposited on 304 stainless steel by DC reactive magnetron sputtering. The effects of nitrogen flow on the microstructure, mechanical and tribological properties were characterized by X-ray diffraction, scanning electron microscopy, atom force microscope, microhardness, wear tester and Nanomap 500LS profile. The results showed that with the increase of nitrogen flow, the CrN films exhibited a preferential orientation in the (200) direction. The deposition rate of CrN films decrease with the increase of nitrogen flow. Besides, the surface roughness exhibited the tendency of decrease first and then increase with further increase of nitrogen flow. As nitrogen flow increased from 15 to 30 sccm, microhardness was improved from 527.34 HV to 1042.26 HV, and then decrease to 918 HV when the nitrogen flow further increase to 35 sccm. Wear test showed that the CrN films deposited at nitrogen flow of 30 sccm was achieved lowest friction coefficient with 0.93 and wear rate with 2.02×10-15m3·(N·m)-1, which presented best wear resistance performance.
2018, 47(8):2298-2304.
Abstract:
Cu/Ti3SiC2/C/MWCNTs/Graphene/La nanocomposites were fabricated by vacuum hot-pressing sintering and hot isostatic pressing. Effect of lanthanum (La) content on tribological behavior of Cu/Ti3SiC2/C/MWCNTs/Graphene/La nanocomposites against GCr15 was evaluated using a wear and abrasion tester. Effect of La content, normal force and rotational speed on tribological behavior of the nanocomposite was investigated to analyze their interaction mechanism. The mutual influence of La content, normal force and rotational speed was analyzed by orthogonality analysis, variance analysis and range analysis. The morphologies of worn surfaces have been observed and analyzed by means of scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). Results demonstrate that La content plays a primary role in the influence of friction and wear performance results. The wear mechanism of nanocomposites with 0.05 wt.% La is abrasive wear, delamination wear and oxidation wear. And wear mechanism of nanocomposites with 0.1 wt.% and 0.3 wt.% La is adhesive wear and oxidation wear.
Cu/Ti3SiC2/C/MWCNTs/Graphene/La nanocomposites were fabricated by vacuum hot-pressing sintering and hot isostatic pressing. Effect of lanthanum (La) content on tribological behavior of Cu/Ti3SiC2/C/MWCNTs/Graphene/La nanocomposites against GCr15 was evaluated using a wear and abrasion tester. Effect of La content, normal force and rotational speed on tribological behavior of the nanocomposite was investigated to analyze their interaction mechanism. The mutual influence of La content, normal force and rotational speed was analyzed by orthogonality analysis, variance analysis and range analysis. The morphologies of worn surfaces have been observed and analyzed by means of scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDS). Results demonstrate that La content plays a primary role in the influence of friction and wear performance results. The wear mechanism of nanocomposites with 0.05 wt.% La is abrasive wear, delamination wear and oxidation wear. And wear mechanism of nanocomposites with 0.1 wt.% and 0.3 wt.% La is adhesive wear and oxidation wear.
2018, 47(8):2305-2311.
Abstract:
This paper presented a fundamental investigation of the formation mechanism and compatibility of microstructure/mechanical property of Fe-Cr-Ni-B steel samples, these samples were built by the divided-area forming and integral connection methods. The stress at the edge of the specimen produced in additive manufacturing could be reduced by the divided-area forming and integral connection methods. According to the microstructure analysis using stereology microscopy/optical microscopy/scanning electron microscope/X-ray diffractometer/Schaeffler diagram, the macrostructure distributed in strip band geometry and the microstructures consisted of dendrites with the intermetallic phases containing austenite phase, boride/matrix eutectic phase. Additionally, the macrostructure strips near the bonding line bent to the building direction and was discontinuous because of unique forming method. However, the microstructures and compositions of the samples were homogeneous. Due to the existence of boride and the finer microstructures, mechanical properties analysis showed that the alloy had high hardness, high ultimate strength and bad deformability. The hardness distribution was homogeneous apart from some positions of the re-melting zone and the heat-affected zone near the bonding line, which had a limited lower hardness because of difference in microstructure.
This paper presented a fundamental investigation of the formation mechanism and compatibility of microstructure/mechanical property of Fe-Cr-Ni-B steel samples, these samples were built by the divided-area forming and integral connection methods. The stress at the edge of the specimen produced in additive manufacturing could be reduced by the divided-area forming and integral connection methods. According to the microstructure analysis using stereology microscopy/optical microscopy/scanning electron microscope/X-ray diffractometer/Schaeffler diagram, the macrostructure distributed in strip band geometry and the microstructures consisted of dendrites with the intermetallic phases containing austenite phase, boride/matrix eutectic phase. Additionally, the macrostructure strips near the bonding line bent to the building direction and was discontinuous because of unique forming method. However, the microstructures and compositions of the samples were homogeneous. Due to the existence of boride and the finer microstructures, mechanical properties analysis showed that the alloy had high hardness, high ultimate strength and bad deformability. The hardness distribution was homogeneous apart from some positions of the re-melting zone and the heat-affected zone near the bonding line, which had a limited lower hardness because of difference in microstructure.
6 Effects of Hot-rolling Reduction on Microstructure and Mechanical Properties of GNPs/Ti Composites
2018, 47(8):2312-2317.
Abstract:
Graphene nanoplatelets (GNPs)/Ti composites were fabricated by spark plasma sintering (SPS) and hot-rolling. This work was focused on the effects of rolling reduction on microstructure and mechanical properties of GNPs/Ti composites. The SEM microstructure results showed that matrix grains were gradually elongated and the amount of GNPs which were along the rolling direction rose with the increase of rolling reduction. The tensile test results show that the ultimate tensile strength and fracture elongation of the GNPs/Ti composites increase with the increase of rolling reduction. The ultimate tensile strength of the composites with 60% rolling reduction is 680MPa, which is increased by 33% compared with pure Ti. Hot-rolling process can relieve defects and lead to GNPs aligned along the rolling direction, which contribute to the improvement of the tensile property.
Graphene nanoplatelets (GNPs)/Ti composites were fabricated by spark plasma sintering (SPS) and hot-rolling. This work was focused on the effects of rolling reduction on microstructure and mechanical properties of GNPs/Ti composites. The SEM microstructure results showed that matrix grains were gradually elongated and the amount of GNPs which were along the rolling direction rose with the increase of rolling reduction. The tensile test results show that the ultimate tensile strength and fracture elongation of the GNPs/Ti composites increase with the increase of rolling reduction. The ultimate tensile strength of the composites with 60% rolling reduction is 680MPa, which is increased by 33% compared with pure Ti. Hot-rolling process can relieve defects and lead to GNPs aligned along the rolling direction, which contribute to the improvement of the tensile property.
2018, 47(8):2318-2321.
Abstract:
Hastelloy C-276 was subjected to 10% deformation and annealed at 1100°C for different times. The fractions of Σ3n(n=1,2,3) boundaries and the connectivity of random boundary networks were characterized by electron back-scatter diffraction (EBSD). The results showed that the Σ3 boundary fraction is hardly increasing during annealing time. Instead, the fractions of Σ9 and Σ27 boundaries have a dramatic change with annealing times, whose peaks are arisen at annealed 15min. Meanwhile, the corresponding connectivity of random boundary network is effectively disrupted. This can be attributed to the incoherent Σ3 boundary producing more Σ9 and Σ27 boundaries and incorporating those boundaries into the random boundary networks. Actually, the connectivity of random boundary networks can be definitely identified by Σ(9+27)/Σ3 radio.
Hastelloy C-276 was subjected to 10% deformation and annealed at 1100°C for different times. The fractions of Σ3n(n=1,2,3) boundaries and the connectivity of random boundary networks were characterized by electron back-scatter diffraction (EBSD). The results showed that the Σ3 boundary fraction is hardly increasing during annealing time. Instead, the fractions of Σ9 and Σ27 boundaries have a dramatic change with annealing times, whose peaks are arisen at annealed 15min. Meanwhile, the corresponding connectivity of random boundary network is effectively disrupted. This can be attributed to the incoherent Σ3 boundary producing more Σ9 and Σ27 boundaries and incorporating those boundaries into the random boundary networks. Actually, the connectivity of random boundary networks can be definitely identified by Σ(9+27)/Σ3 radio.
2018, 47(8):2322-2327.
Abstract:
Ultra-low-density bulk nanoporous gold (NPG) is required in inertial confined fusion (ICF) experiments. Existing bulk NPG has some limitations in ICF application due to non-uniformity structure or residues of C elements originated from organic template. Here, combined with dealloying, NPG with submicron cavities and nanopores was prepared by nano-SiO2 templates. However, the smaller templates bring greater challenges for the volume shrinkage control during drying as gold content on each shell is extremely low for ultra-low density. Therefore, the influence of drying method on volume shrinkage was investigated. The results show that volume shrinkage was up to 86.41% during conventional drying, but it was controlled below 4% by supercritical CO2 drying. Finally, NPG with ultra-low-density of 0.35g/cm3 was successfully fabricated. Compared to NPG prepared by micro templates, the NPG with 500nm spherical cavities and 2-70nm nanopores reduces the size difference between large cavities and nanopores and significantly improves the uniformity of its structure.
Ultra-low-density bulk nanoporous gold (NPG) is required in inertial confined fusion (ICF) experiments. Existing bulk NPG has some limitations in ICF application due to non-uniformity structure or residues of C elements originated from organic template. Here, combined with dealloying, NPG with submicron cavities and nanopores was prepared by nano-SiO2 templates. However, the smaller templates bring greater challenges for the volume shrinkage control during drying as gold content on each shell is extremely low for ultra-low density. Therefore, the influence of drying method on volume shrinkage was investigated. The results show that volume shrinkage was up to 86.41% during conventional drying, but it was controlled below 4% by supercritical CO2 drying. Finally, NPG with ultra-low-density of 0.35g/cm3 was successfully fabricated. Compared to NPG prepared by micro templates, the NPG with 500nm spherical cavities and 2-70nm nanopores reduces the size difference between large cavities and nanopores and significantly improves the uniformity of its structure.
Di Wang
,
Shibiao Wu
,
Fan Fu
,
Guangzhao Ye
,
Shuzhen Mai
,
Zeyu Qian
,
Changhui Song
,
Yongqiang Yang
2018, 47(8):2328-2334.
Abstract:
In order to investigate the influential mechanism of grinding and sand blasting pretreatment of CoCr alloy manufactured by SLM (selective laser melting) process on the metal-porcelain bonding of the restorations, and then provide references for SLM manufacturing CoCr alloy dental crown and bridge restorations with good mechanical properties. Three groups of CoCr alloy substrates were manufactured by SLM process with optimal parameters. The samples were subjected to different grinding and sand blasting pretreatment respectively, and the porcelain sintering was carried out with the same parameters. The samples of different groups were analyzed by three-point bending test, roughness test, SEM and EDS. Results show that the metal-porcelain bonding strength of samples in group a grinded and sand blasted is 36.79 ± 0.49MPa, which is obviously higher than that of group b with non-grinding but sand blasting and group c with only grinding. The average metal-porcelain bonding strength of the three group samples was higher than the ISO9693: 1999 standard minimum 25MPa.The metal-porcelain bonding effect of group a and c is better than that of group b, and the element diffusion on metal-porcelain interface was observed in all three groups. The results also showed that there were significant differences among the three groups on residues and element distribution of metal-porcelain peeling surface. The final conclusion is that the surface roughness obtained by the pretreatment of sand blasting and grinding can ensure the strong chemical combination of metal and porcelain and considerable mechanical properties combination, which can improve the performance of metal-porcelain restorations manufactured by SLM.
In order to investigate the influential mechanism of grinding and sand blasting pretreatment of CoCr alloy manufactured by SLM (selective laser melting) process on the metal-porcelain bonding of the restorations, and then provide references for SLM manufacturing CoCr alloy dental crown and bridge restorations with good mechanical properties. Three groups of CoCr alloy substrates were manufactured by SLM process with optimal parameters. The samples were subjected to different grinding and sand blasting pretreatment respectively, and the porcelain sintering was carried out with the same parameters. The samples of different groups were analyzed by three-point bending test, roughness test, SEM and EDS. Results show that the metal-porcelain bonding strength of samples in group a grinded and sand blasted is 36.79 ± 0.49MPa, which is obviously higher than that of group b with non-grinding but sand blasting and group c with only grinding. The average metal-porcelain bonding strength of the three group samples was higher than the ISO9693: 1999 standard minimum 25MPa.The metal-porcelain bonding effect of group a and c is better than that of group b, and the element diffusion on metal-porcelain interface was observed in all three groups. The results also showed that there were significant differences among the three groups on residues and element distribution of metal-porcelain peeling surface. The final conclusion is that the surface roughness obtained by the pretreatment of sand blasting and grinding can ensure the strong chemical combination of metal and porcelain and considerable mechanical properties combination, which can improve the performance of metal-porcelain restorations manufactured by SLM.
2018, 47(8):2335-2340.
Abstract:
The welding of 15mm TC18 titanium alloy thick plate is realized by electron beam welding. The effect of different welding speeds (10 mm / s, 20 mm / s, 30mm / s) on the fatigue properties of the electron beam welded joints for TC18 titanium alloy was investigated. The macroscopic morphology, microstructure and fracture characteristics of the joints were analyzed by optical microscope, scanning electron microscopy and transmission electron microscopy, and the fatigue properties of welded joints were studied and tested by an electronic universal testing machine. The results showed that the weld fusion zone was mainly composed of columnar β phase and acicular α martensite phase. The upper melting width, the middle melting width and the lower melting width were obviously reduced, and the grain size gradually decreased with the increased of welding speed, which resulted in the increase of fatigue properties of welded joints. At Nf =107, the fatigue limit of the weld was increased by nearly 29% with the welding speed from 10mm/s to 30mm/s. The fatigue fracture of the joints can be divided into three typical regions of fatigue crack source zone, expansion zone and instantaneous zone, and the fatigue cracks all originated from the surface of the specimen. With the increased of welding speed, the proportion of instantaneous area decreased and the fatigue performance increased.
The welding of 15mm TC18 titanium alloy thick plate is realized by electron beam welding. The effect of different welding speeds (10 mm / s, 20 mm / s, 30mm / s) on the fatigue properties of the electron beam welded joints for TC18 titanium alloy was investigated. The macroscopic morphology, microstructure and fracture characteristics of the joints were analyzed by optical microscope, scanning electron microscopy and transmission electron microscopy, and the fatigue properties of welded joints were studied and tested by an electronic universal testing machine. The results showed that the weld fusion zone was mainly composed of columnar β phase and acicular α martensite phase. The upper melting width, the middle melting width and the lower melting width were obviously reduced, and the grain size gradually decreased with the increased of welding speed, which resulted in the increase of fatigue properties of welded joints. At Nf =107, the fatigue limit of the weld was increased by nearly 29% with the welding speed from 10mm/s to 30mm/s. The fatigue fracture of the joints can be divided into three typical regions of fatigue crack source zone, expansion zone and instantaneous zone, and the fatigue cracks all originated from the surface of the specimen. With the increased of welding speed, the proportion of instantaneous area decreased and the fatigue performance increased.
2018, 47(8):2341-2346.
Abstract:
In this study, isothermal compression tests at the temperature range of 1123 - 1273K and the strain rate range of 0.001 - 1s-1 were conducted to analyze the elevated temperature deformation behavior of TA7 titanium alloy for the purpose of acquiring the optimum processing parameters. Besides, a modified parallel constitutive model was put forward to illustrate the high temperature flow stress as the function of the strain rate, the deformation temperature and the true strain. Thereafter, the processing map which was on the basis of dynamic materials model was established. Thereafter, the investigation was made from the microstructure of compressed TA7 titanium alloy specimens to validate processing map. According to the result, deformation temperature of 1223K and strain rate of 0.001s-1 were the best processing parameters for the TA7 alloy. In addition, the instability regions located at relatively lower temperature-higher strain rate region.
In this study, isothermal compression tests at the temperature range of 1123 - 1273K and the strain rate range of 0.001 - 1s-1 were conducted to analyze the elevated temperature deformation behavior of TA7 titanium alloy for the purpose of acquiring the optimum processing parameters. Besides, a modified parallel constitutive model was put forward to illustrate the high temperature flow stress as the function of the strain rate, the deformation temperature and the true strain. Thereafter, the processing map which was on the basis of dynamic materials model was established. Thereafter, the investigation was made from the microstructure of compressed TA7 titanium alloy specimens to validate processing map. According to the result, deformation temperature of 1223K and strain rate of 0.001s-1 were the best processing parameters for the TA7 alloy. In addition, the instability regions located at relatively lower temperature-higher strain rate region.
2018, 47(8):2347-2352.
Abstract:
Section flattening is an inevitable physical phenomenon in the forming process of tube bending, and severe section flattening will affect the reasonable assembly of the tube fittings, and therefore restricts its wide application. Finite element (FE) model for numerical control (NC) bending of titanium tube considering the variation law of contractile strain ratio (CSR) and the Young"s modulus (E) is established in this paper. The section flattening behaviors of TA18 tube under different geometric conditions and different process conditions have been investigated. The results show that considering the variation law of CSR-E can make the cross-section change, which has no remarkable influence on the change law. The reasonable range of geometric and process parameters are obtained, which provides a basis for studying the forming prediction and controlling the final precision for the NC bending of TA18 tube.
Section flattening is an inevitable physical phenomenon in the forming process of tube bending, and severe section flattening will affect the reasonable assembly of the tube fittings, and therefore restricts its wide application. Finite element (FE) model for numerical control (NC) bending of titanium tube considering the variation law of contractile strain ratio (CSR) and the Young"s modulus (E) is established in this paper. The section flattening behaviors of TA18 tube under different geometric conditions and different process conditions have been investigated. The results show that considering the variation law of CSR-E can make the cross-section change, which has no remarkable influence on the change law. The reasonable range of geometric and process parameters are obtained, which provides a basis for studying the forming prediction and controlling the final precision for the NC bending of TA18 tube.
2018, 47(8):2353-2359.
Abstract:
The evolution of metal flow, microstructure and corrosion properties of 5A06 alloy after friction stir welding has been studied in present paper. It was observed that metal on the advancing side is curled directly into the threads and then is extruded down into the weld nugget zone by complex motions of torsion and swirl. However, the material on the retreating side encounters chaotic flow patterns. The electro backscattering diffraction results indicated that the grains in stir zone were pronouncedly refined by dynamic recrystallization, the average grain size is about 6μm. The scanning electron microscope analysis displayed that β-phase (Al3Mg2) and Al6(Mn, Fe) dispersedly distribute in the stir zone and the size of the Al6(Mn, Fe) is smaller than that in base material. The hardness profile is characterized by material softening along the cross-section and the minimum hardness value of 72HV is located in the interface between stirring zone and thermo-mechanically affected zone. It was evident that the stir zone exhibits better corrosion resistance than the base material. The corrosion potential of stir zone is 35mV larger than that in base material (-0.725V).
The evolution of metal flow, microstructure and corrosion properties of 5A06 alloy after friction stir welding has been studied in present paper. It was observed that metal on the advancing side is curled directly into the threads and then is extruded down into the weld nugget zone by complex motions of torsion and swirl. However, the material on the retreating side encounters chaotic flow patterns. The electro backscattering diffraction results indicated that the grains in stir zone were pronouncedly refined by dynamic recrystallization, the average grain size is about 6μm. The scanning electron microscope analysis displayed that β-phase (Al3Mg2) and Al6(Mn, Fe) dispersedly distribute in the stir zone and the size of the Al6(Mn, Fe) is smaller than that in base material. The hardness profile is characterized by material softening along the cross-section and the minimum hardness value of 72HV is located in the interface between stirring zone and thermo-mechanically affected zone. It was evident that the stir zone exhibits better corrosion resistance than the base material. The corrosion potential of stir zone is 35mV larger than that in base material (-0.725V).
2018, 47(8):2360-2364.
Abstract:
Specimens of as-cast Mg-1Ag-Zn, Mg-3Ag-Zn and Mg-5Ag-Zn alloys were fabricated, and then the specimens’ thermal conductivity was calculated. With the increase of Ag content, the thermal conductivity decreased significantly of as-cast alloys. After that, directional solidified specimens of the above mentioned as-cast Mg-Ag-Zn alloys were made at three different pulling velocities: V=25μm/s, V=50μm/s, V=75μm/s, and then again calculated their thermal conductivity. The result showed that with the increase of the pulling velocity, the thermal conductivity of alloys decreased significantly. Variations in the solute content and the pulling velocities are believed to play important roles on the thermal conductivity of Mg- Ag-Zn alloys. Since those two circumstances can strengthen the electron’s scattering process, reduce their free path, and thereby reduce the alloys’ thermal conductivity.
Specimens of as-cast Mg-1Ag-Zn, Mg-3Ag-Zn and Mg-5Ag-Zn alloys were fabricated, and then the specimens’ thermal conductivity was calculated. With the increase of Ag content, the thermal conductivity decreased significantly of as-cast alloys. After that, directional solidified specimens of the above mentioned as-cast Mg-Ag-Zn alloys were made at three different pulling velocities: V=25μm/s, V=50μm/s, V=75μm/s, and then again calculated their thermal conductivity. The result showed that with the increase of the pulling velocity, the thermal conductivity of alloys decreased significantly. Variations in the solute content and the pulling velocities are believed to play important roles on the thermal conductivity of Mg- Ag-Zn alloys. Since those two circumstances can strengthen the electron’s scattering process, reduce their free path, and thereby reduce the alloys’ thermal conductivity.
2018, 47(8):2365-2370.
Abstract:
The mechanical state at the crack tip is one of the major factors affecting the stress corrosion cracking (SCC) growth rate in structural materials of the nuclear power plant. To understand the crack growth driving forces and their effects on SCC growth rate in the whole process of SCC, a finite element model of the growth process of SCC was built by using a commercial software ABAQUS, sequentially the working load, residual stress, and the film induced stress produced by the oxide film formationin front of the crack tip during SCC initial stage were discussed in this paper. The results indicate that the film induced stress produced by the formation of oxide film is the main crack growth driving force during the initial stage of SCC. While the working load and residual stress gradually become the main crack growth driving force as SCC crack advances.
The mechanical state at the crack tip is one of the major factors affecting the stress corrosion cracking (SCC) growth rate in structural materials of the nuclear power plant. To understand the crack growth driving forces and their effects on SCC growth rate in the whole process of SCC, a finite element model of the growth process of SCC was built by using a commercial software ABAQUS, sequentially the working load, residual stress, and the film induced stress produced by the oxide film formationin front of the crack tip during SCC initial stage were discussed in this paper. The results indicate that the film induced stress produced by the formation of oxide film is the main crack growth driving force during the initial stage of SCC. While the working load and residual stress gradually become the main crack growth driving force as SCC crack advances.
2018, 47(8):2371-2380.
Abstract:
Biodegradable magnesium (Mg)-based biomaterials have draw extensively attention, due to the high strength-to-weight ratio, low elastic modulus and good biocompatibility. However, the high corrosion rate is still the major obstacle for the potential clinical applications. Therefore, the highly biocompatible hydroxyapatite (HA) coatings are usually introduced to restrain the interactions between Mg-based substrate and the body fluid environment. HA and strontium (Sr)-doped HA coatings were prepared on Mg-4Zn substrates by electrochemical deposition. The surface properties of the samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), three-dimensional laser scanning microscopy (3D LSM) and a contact angle video system. The dynamic ion release, protein adsorption, cell adhesion, proliferation and differentiation behavior of the samples were also evaluated. The results reveal that the incorporation of Sr in the HA coatings leads to lattice distortion and decreased crystallinity. The lower amount of Mg ion release of the Sr-doped HA coated samples suggests a better corrosion resistance. The improved protein adsorption and initial adhesion of mesenchymal stem cells (MSCs) of the Sr-doped samples should be due to their higher surface roughness and wettability. The introduction of Sr leads to comparable cell proliferation behavior, but significantly improved osteogenic differentiation. It is concluded that the Sr-doped HA coatings are promising candidates for the protective biocompatible coating on Mg-based implants.
Biodegradable magnesium (Mg)-based biomaterials have draw extensively attention, due to the high strength-to-weight ratio, low elastic modulus and good biocompatibility. However, the high corrosion rate is still the major obstacle for the potential clinical applications. Therefore, the highly biocompatible hydroxyapatite (HA) coatings are usually introduced to restrain the interactions between Mg-based substrate and the body fluid environment. HA and strontium (Sr)-doped HA coatings were prepared on Mg-4Zn substrates by electrochemical deposition. The surface properties of the samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), three-dimensional laser scanning microscopy (3D LSM) and a contact angle video system. The dynamic ion release, protein adsorption, cell adhesion, proliferation and differentiation behavior of the samples were also evaluated. The results reveal that the incorporation of Sr in the HA coatings leads to lattice distortion and decreased crystallinity. The lower amount of Mg ion release of the Sr-doped HA coated samples suggests a better corrosion resistance. The improved protein adsorption and initial adhesion of mesenchymal stem cells (MSCs) of the Sr-doped samples should be due to their higher surface roughness and wettability. The introduction of Sr leads to comparable cell proliferation behavior, but significantly improved osteogenic differentiation. It is concluded that the Sr-doped HA coatings are promising candidates for the protective biocompatible coating on Mg-based implants.
2018, 47(8):2381-2385.
Abstract:
The electroless nickel plating on AZ31 magnesium alloy was studied, basing on the pretreatment process of H3PO4+HNO3 pickling and NH4HF2+H3PO4 activation. The morphology, composition distribution, phase structure and elemental analysis of electroless nickel plating coating were investigated through scanning electron microscope (SEM), energy dispersive analysis of X-ray(EDS), X-ray diffractometer (XRD), x ray photoelectron spectroscope(XPS). The results indicate that the surface of the electroless nickel plating coating is smooth and bright, the structure of deposits is amorphous with high content of phosphorous. The occurrence mode of nickel on the surface of deposits is pure nickel(26.7%), NiO(32.96%)and Ni(OH)2(40.29%), and occurrence mode of phosphorus is pure P(20.17%), PO42- (17.37%)and PO43-(62.46%). Furthermore, the occurrence mode of nickel in the intermediate layers of the coating is almost 100% pure nickel, and occurrence mode of phosphorus is pure P (74.11%) and PO42-(25.89%).
The electroless nickel plating on AZ31 magnesium alloy was studied, basing on the pretreatment process of H3PO4+HNO3 pickling and NH4HF2+H3PO4 activation. The morphology, composition distribution, phase structure and elemental analysis of electroless nickel plating coating were investigated through scanning electron microscope (SEM), energy dispersive analysis of X-ray(EDS), X-ray diffractometer (XRD), x ray photoelectron spectroscope(XPS). The results indicate that the surface of the electroless nickel plating coating is smooth and bright, the structure of deposits is amorphous with high content of phosphorous. The occurrence mode of nickel on the surface of deposits is pure nickel(26.7%), NiO(32.96%)and Ni(OH)2(40.29%), and occurrence mode of phosphorus is pure P(20.17%), PO42- (17.37%)and PO43-(62.46%). Furthermore, the occurrence mode of nickel in the intermediate layers of the coating is almost 100% pure nickel, and occurrence mode of phosphorus is pure P (74.11%) and PO42-(25.89%).
2018, 47(8):2386-2391.
Abstract:
Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li, one of the most important turbine disk materials, at an elevated temperature of 650°C with different grain sizes, to investigate the mechanism of grain size on the creep-fatigue life of GH720Li. Experimental results shows that the creep-fatigue life of GH720Li superalloy will decrease with the decrease of grain size. SEM fracture analysis indicates that the oxidation and cracking is the main mechanism of GH720Li in the process of creep-fatigue under high temperature, and the smaller of grain size will result in the longer length of grain boundary. Finally, two methods including the damage function based on hysteresis energy and the applied mechanical work density (AMWD) are modified to predict the creep-fatigue life of GH720Li, which match well with experimental data.
Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li, one of the most important turbine disk materials, at an elevated temperature of 650°C with different grain sizes, to investigate the mechanism of grain size on the creep-fatigue life of GH720Li. Experimental results shows that the creep-fatigue life of GH720Li superalloy will decrease with the decrease of grain size. SEM fracture analysis indicates that the oxidation and cracking is the main mechanism of GH720Li in the process of creep-fatigue under high temperature, and the smaller of grain size will result in the longer length of grain boundary. Finally, two methods including the damage function based on hysteresis energy and the applied mechanical work density (AMWD) are modified to predict the creep-fatigue life of GH720Li, which match well with experimental data.
2018, 47(8):2392-2403.
Abstract:
Specimens of AZ91-1.5Si-0.4Ca and AZ91 with different section thicknesses were prepared by HPDC(high pressure die-casting). The solidification rate of the HPDC specimens was numerically simulated. The microstructure, tensile properties and the fracture morphologySat the ambient temperature and 180oC of the specimens were investigated. The results show that: 1) Si and Mg form Mg2Si phase and Ca mainlySdissolves in the matrix. Besides, Si and Ca have some effect of grain refinement on the Mg matrix. 2) The increase of solidification rate causes that the Mg2Si phase in AZ91-1.5Si-0.4Ca turn from bulky polygons and Chinese script type to fine polygons and short rod. 3)The mechanical properties of AZ91-1.5Si-0.4Ca and AZ91 at ambient temperature and 180oC increase with the increase of solidification rate. The influence of section thickness on tensile strength of AZ91-1.5Si-0.4Ca is greater than that of AZ91, but the influence on elongation is less than that of AZ91. Furthermore, the tensile strength of AZ91-1.5Si-0.4Ca at 180oC is higher than that of AZ91 when the section thickness is less than 2.5mm, and the tensile strength of AZ91-1.5Si-0.4Ca at ambient temperature is higher than that of AZ91 when the section thickness is less than 3mm.
Specimens of AZ91-1.5Si-0.4Ca and AZ91 with different section thicknesses were prepared by HPDC(high pressure die-casting). The solidification rate of the HPDC specimens was numerically simulated. The microstructure, tensile properties and the fracture morphologySat the ambient temperature and 180oC of the specimens were investigated. The results show that: 1) Si and Mg form Mg2Si phase and Ca mainlySdissolves in the matrix. Besides, Si and Ca have some effect of grain refinement on the Mg matrix. 2) The increase of solidification rate causes that the Mg2Si phase in AZ91-1.5Si-0.4Ca turn from bulky polygons and Chinese script type to fine polygons and short rod. 3)The mechanical properties of AZ91-1.5Si-0.4Ca and AZ91 at ambient temperature and 180oC increase with the increase of solidification rate. The influence of section thickness on tensile strength of AZ91-1.5Si-0.4Ca is greater than that of AZ91, but the influence on elongation is less than that of AZ91. Furthermore, the tensile strength of AZ91-1.5Si-0.4Ca at 180oC is higher than that of AZ91 when the section thickness is less than 2.5mm, and the tensile strength of AZ91-1.5Si-0.4Ca at ambient temperature is higher than that of AZ91 when the section thickness is less than 3mm.
2018, 47(8):2404-2410.
Abstract:
A new B-Al-rich steel with high-strength and plasticity was developed and its RSW performance was studied when used as the structure materials of automobiles. The hybrid orthogonal experiments of complex welding conditions were implemented under the ISO14327-2004 standard and the main factors that can influence the spattering of nuggets were found. The boundary curves of nugget-spatter lobe diagram that could effectively predicate the expulsion rate of the developed steel were also drawn. The relationships among the nugget size, spatter, welding process and environments were further understood. A moment balance function of nugget was developed and the function-based numerical simulation for the coefficient of swelling stress was conducted. Therefore, the further understood spatter mechanism promoted the engineering application of the developed hot-stamped steels.
A new B-Al-rich steel with high-strength and plasticity was developed and its RSW performance was studied when used as the structure materials of automobiles. The hybrid orthogonal experiments of complex welding conditions were implemented under the ISO14327-2004 standard and the main factors that can influence the spattering of nuggets were found. The boundary curves of nugget-spatter lobe diagram that could effectively predicate the expulsion rate of the developed steel were also drawn. The relationships among the nugget size, spatter, welding process and environments were further understood. A moment balance function of nugget was developed and the function-based numerical simulation for the coefficient of swelling stress was conducted. Therefore, the further understood spatter mechanism promoted the engineering application of the developed hot-stamped steels.
2018, 47(8):2411-2416.
Abstract:
With the help of self-designed magnetic field generator,beryllium bronze as the substrate, Fe-Ga-Al-Y MF samples were prepared under different static magnetic field environments by ion beam sputter deposition, its composition is Fe74.34-79.33Ga11.45-13.73Al5.33-6.95Y3.27-4.36 .The surface morphology of Fe-Ga-Al-Y MF was observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Deflection of cantilever and hysteresis loop of films were measured by laser micro-displacement sensor and alternating gradient magnetometer, respectively. The surface morphology of Fe-Ga-Al-Y MF and the effect of the direction and size of the static magnetic field applied during deposition on magnetic properties of the films were studied．The results showed that the thin film samples prepared by IBSD method have smooth surface, no obvious defects, and the structure of the thin film is uniform and compact.The easy magnetization axis direction of films can be regulated by static magnetic field applied during film formation. The easy magnetization axis direction of Fe-Ga-Al-Y MF was the same to the direction of the static magnetic field applied during film formation. When the direction of static magnetic field applied during film formation was parallel to the minor axis direction of the substrate, it can significantly improve the saturation magnetostrictive properties of the Fe-Ga-Al-Y MF. With the increase of magnetic field, the saturation magnetostriction coefficient of film has been continuously improved and the saturation magnetization , coercive force of the films within the film plane (along the x-axis direction, y-axis direction) gradually increased .
With the help of self-designed magnetic field generator,beryllium bronze as the substrate, Fe-Ga-Al-Y MF samples were prepared under different static magnetic field environments by ion beam sputter deposition, its composition is Fe74.34-79.33Ga11.45-13.73Al5.33-6.95Y3.27-4.36 .The surface morphology of Fe-Ga-Al-Y MF was observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Deflection of cantilever and hysteresis loop of films were measured by laser micro-displacement sensor and alternating gradient magnetometer, respectively. The surface morphology of Fe-Ga-Al-Y MF and the effect of the direction and size of the static magnetic field applied during deposition on magnetic properties of the films were studied．The results showed that the thin film samples prepared by IBSD method have smooth surface, no obvious defects, and the structure of the thin film is uniform and compact.The easy magnetization axis direction of films can be regulated by static magnetic field applied during film formation. The easy magnetization axis direction of Fe-Ga-Al-Y MF was the same to the direction of the static magnetic field applied during film formation. When the direction of static magnetic field applied during film formation was parallel to the minor axis direction of the substrate, it can significantly improve the saturation magnetostrictive properties of the Fe-Ga-Al-Y MF. With the increase of magnetic field, the saturation magnetostriction coefficient of film has been continuously improved and the saturation magnetization , coercive force of the films within the film plane (along the x-axis direction, y-axis direction) gradually increased .
2018, 47(8):2417-2421.
Abstract:
Y and Mn co-doped BaTiO3 ceramics were prepared by the conventional solid state reaction. The phases, microstructures and compositions of the prepared samples were characterized by X-ray diffractometer, scanning electron microscope and energy dispersive spectrometer, respectively, and the electrical parameters were measured. Results showed that the room temperature resistance of BaTiO3 could be effectively decreased by Y doping. However, the excessive Y would segregate at the grain boundary, which weakened the PTC effect of BaTiO3 ceramic, combined with Mn at the grain boundary. Through the coordinating behavior between grain and grain boundary, the PTC effect of BaTiO3 ceramic could be efficiently tailored.
Y and Mn co-doped BaTiO3 ceramics were prepared by the conventional solid state reaction. The phases, microstructures and compositions of the prepared samples were characterized by X-ray diffractometer, scanning electron microscope and energy dispersive spectrometer, respectively, and the electrical parameters were measured. Results showed that the room temperature resistance of BaTiO3 could be effectively decreased by Y doping. However, the excessive Y would segregate at the grain boundary, which weakened the PTC effect of BaTiO3 ceramic, combined with Mn at the grain boundary. Through the coordinating behavior between grain and grain boundary, the PTC effect of BaTiO3 ceramic could be efficiently tailored.
Gou Yujun
,
Shuang Yuanhua
,
Zhou Yan
,
Cai Wei
,
Dai Jia
,
Mao Feilong
,
Ding Xiaofeng
,
Zhao Chunjiang
2018, 47(8):2422-2428.
Abstract:
Based on the tube bending forming mechanism and Johnson-Cook damage theory, the influence of initial bending temperature、aid-push speed and aid-push mode of magnesium alloy tube bending process , with large curvature and no-mandrel , on the damage and wall thickness variation was analyzed by the Deform-3D finite element method. The results showed that: when the aid-push die and pressure die exerted a certain effect on the tube, the initial bending temperature was too high or too low, which was detrimental to the bending of the magnesium alloy tube, and the optimum initial bending temperature was 350℃. Under the optimum initial bending temperature , when the aid-push die moved synchronously with the pressure die, the unilateral wall thickness variations degree can only be improved, and the overall wall thickness variations can not be improved simultaneously, so the wall thickness non-uniformity of the tube was remarkable. When the aid-push die and pressure die were not synchronized, the axial tension or compression deformation degree of the tube-bending can be changed with reasonably matching the axial velocity between the aid-push die and the pressure die in the feed stage, thus the wall thickness uniformity can be achieved a rather good effect. When the external aid-push die moved synchronously with the pressure die, and the internal aid-push die moved at a velocity of the same magnitude but in opposite direction with the above two dies, the wall thickness uniformity was optimal, thus the bending quality of magnesium alloy tube with good comprehensive properties was obtained.
Based on the tube bending forming mechanism and Johnson-Cook damage theory, the influence of initial bending temperature、aid-push speed and aid-push mode of magnesium alloy tube bending process , with large curvature and no-mandrel , on the damage and wall thickness variation was analyzed by the Deform-3D finite element method. The results showed that: when the aid-push die and pressure die exerted a certain effect on the tube, the initial bending temperature was too high or too low, which was detrimental to the bending of the magnesium alloy tube, and the optimum initial bending temperature was 350℃. Under the optimum initial bending temperature , when the aid-push die moved synchronously with the pressure die, the unilateral wall thickness variations degree can only be improved, and the overall wall thickness variations can not be improved simultaneously, so the wall thickness non-uniformity of the tube was remarkable. When the aid-push die and pressure die were not synchronized, the axial tension or compression deformation degree of the tube-bending can be changed with reasonably matching the axial velocity between the aid-push die and the pressure die in the feed stage, thus the wall thickness uniformity can be achieved a rather good effect. When the external aid-push die moved synchronously with the pressure die, and the internal aid-push die moved at a velocity of the same magnitude but in opposite direction with the above two dies, the wall thickness uniformity was optimal, thus the bending quality of magnesium alloy tube with good comprehensive properties was obtained.
2018, 47(8):2429-2424.
Abstract:
Laser seal welding of 0.4mm thickness pure titanium with holes was achieved by N d: YAG pulse laser. The effect of laser spot size on the weld geometry of the sealed joint was studied. The results show that full seal welded joint can be achieved when the spot diameter is no more than 0.4mm. The effective thickness of sealing area increases at first then decreases with the increasing of spot diameter. The maximum effective sealing thickness is about 352μm.The sealing joint was consisted of alpha grains with different shapes, and there was a large HAZ in the joint. Besides, with the increase of the spot diameter, the surface melting area of the sealed joint is basically unchanged, but the sealing mode is changed from the keyhole to the heat-conduction type, and the heat-conduction model is more suitable for the hole sealing. Further, calculated laser energy of sealing area shown that there was a positive proportion between the theoretical energy value and laser spot size, but the theoretical analysis does not match with the actual situation. The reason may be that the molten metal beside the hole flow into the hole under the effect of gravity and other forces, which cause the increasing of actual absorption of laser energy.
Laser seal welding of 0.4mm thickness pure titanium with holes was achieved by N d: YAG pulse laser. The effect of laser spot size on the weld geometry of the sealed joint was studied. The results show that full seal welded joint can be achieved when the spot diameter is no more than 0.4mm. The effective thickness of sealing area increases at first then decreases with the increasing of spot diameter. The maximum effective sealing thickness is about 352μm.The sealing joint was consisted of alpha grains with different shapes, and there was a large HAZ in the joint. Besides, with the increase of the spot diameter, the surface melting area of the sealed joint is basically unchanged, but the sealing mode is changed from the keyhole to the heat-conduction type, and the heat-conduction model is more suitable for the hole sealing. Further, calculated laser energy of sealing area shown that there was a positive proportion between the theoretical energy value and laser spot size, but the theoretical analysis does not match with the actual situation. The reason may be that the molten metal beside the hole flow into the hole under the effect of gravity and other forces, which cause the increasing of actual absorption of laser energy.
2018, 47(8):2435-2439.
Abstract:
In this article,two layer and three layer TBCs were deposited by electron beam physical vapor deposition(EB-PVD) on the Ni-based superalloy (N5) . Thermal shocktest of the coatings was carried out by heating the coating from room temperature to 1100℃ for 5 min, followed by water quenching. After the microstructural characterization was analysed by SEM, EDS and XRD, the result showed that the mixture layer, composite by NiCrAlY and YSZ, can retard the growth of TGO layer and reduce the inter-stress between bond coating and top coating. Both of them improved the thermal math performance of three layers TBCs.
In this article,two layer and three layer TBCs were deposited by electron beam physical vapor deposition(EB-PVD) on the Ni-based superalloy (N5) . Thermal shocktest of the coatings was carried out by heating the coating from room temperature to 1100℃ for 5 min, followed by water quenching. After the microstructural characterization was analysed by SEM, EDS and XRD, the result showed that the mixture layer, composite by NiCrAlY and YSZ, can retard the growth of TGO layer and reduce the inter-stress between bond coating and top coating. Both of them improved the thermal math performance of three layers TBCs.
2018, 47(8):2440-2445.
Abstract:
In order to study the modification mechanism of Lanthanum doping on SnO2 catalytic electrodethe. In this paper, La doped Ti/Sb-SnO2 electrode was prepared by sol-gel method. Taking phenol as a target organics, the electrochemical performance of the electrode was investigated. Polarization curves and Mott-Schottky curve of the prepared electrodes were tested, the analysis results showed that the oxygen evolution potential of lanthanum modified Ti/Sb-SnO2 electrode is first increased and then decreased. And the exchange current density of Sn:Sb:La 100:10:1.5 electrode is maximum under 2.0V potential. The La doping promotes the negative shift of flat band potential and the slope of fitting straight-line of Mott-Schottky curve has fallen from 2.96 to 1.66, enhances the active surface area, improve carrier concentration correspondingly. Cyclic voltammetry and electrochemical impedance spectroscopy of prepared electrodes were performed, the results showed that the electrochemical reaction resistance of the doped electrode is decreased, the active charge can be increased from 14.1μF to 322μF. At the same time, the peak current of the direct oxidation of phenol is enhanced, the peak potential is decreased. The above results explain the intrinsic reason for the improvement of the electrocatalytic activity.
In order to study the modification mechanism of Lanthanum doping on SnO2 catalytic electrodethe. In this paper, La doped Ti/Sb-SnO2 electrode was prepared by sol-gel method. Taking phenol as a target organics, the electrochemical performance of the electrode was investigated. Polarization curves and Mott-Schottky curve of the prepared electrodes were tested, the analysis results showed that the oxygen evolution potential of lanthanum modified Ti/Sb-SnO2 electrode is first increased and then decreased. And the exchange current density of Sn:Sb:La 100:10:1.5 electrode is maximum under 2.0V potential. The La doping promotes the negative shift of flat band potential and the slope of fitting straight-line of Mott-Schottky curve has fallen from 2.96 to 1.66, enhances the active surface area, improve carrier concentration correspondingly. Cyclic voltammetry and electrochemical impedance spectroscopy of prepared electrodes were performed, the results showed that the electrochemical reaction resistance of the doped electrode is decreased, the active charge can be increased from 14.1μF to 322μF. At the same time, the peak current of the direct oxidation of phenol is enhanced, the peak potential is decreased. The above results explain the intrinsic reason for the improvement of the electrocatalytic activity.
2018, 47(8):2446-2452.
Abstract:
the corrosion behavior of cobalt-based alloy powder with different Te content that was sintered under non-vacuum environment is researched high temperature molten salt in a static 800±5℃75% Na2SO4+25% NaCl high temperature molten salt. Making use of OM, SEM and XRD diffraction analyze the alloy microstructure, corrosion product morphology and phase composition, and the results show that: with the increase of Te mass fraction in cobalt-based alloy, high-temperature molten salt corrosion rate decreased gradually; when the Te content is about 1.6wt%, the alloy substrate surface form a kind of homogeneous and dense Cr2O3 protection oxide film and the new phase (CoTeO3, Fe2TeO5) dispersed in the matrix to inhibit Co atoms diffusing to grain boundaries, which retard alloy matrix element dissolution and improve the performance of the alloy hot corrosion. Corrosion rate of cobalt-based alloy decreases from free Te 4.0483mg/(cm2*h) to 0.216mg/(cm2*h).
the corrosion behavior of cobalt-based alloy powder with different Te content that was sintered under non-vacuum environment is researched high temperature molten salt in a static 800±5℃75% Na2SO4+25% NaCl high temperature molten salt. Making use of OM, SEM and XRD diffraction analyze the alloy microstructure, corrosion product morphology and phase composition, and the results show that: with the increase of Te mass fraction in cobalt-based alloy, high-temperature molten salt corrosion rate decreased gradually; when the Te content is about 1.6wt%, the alloy substrate surface form a kind of homogeneous and dense Cr2O3 protection oxide film and the new phase (CoTeO3, Fe2TeO5) dispersed in the matrix to inhibit Co atoms diffusing to grain boundaries, which retard alloy matrix element dissolution and improve the performance of the alloy hot corrosion. Corrosion rate of cobalt-based alloy decreases from free Te 4.0483mg/(cm2*h) to 0.216mg/(cm2*h).
2018, 47(8):2453-2457.
Abstract:
Uni-axial compression test was used to analyze characteristics of stress-strain curves and effects of porosity on mechanical properties and deformations of the Fe-40at%Al intermetallic compound porous material, which was prepared by the element mixture partial diffusion - reactive synthesis – sintering method. Its microscopic fracture mechanism were revealed by scanning electron microscope test. Research results show that the compressive stress-strain curves of the FeAl porous material with different porosities can be divided into four stages: elasticity, yielding, strengthening and failure, where the larger the porosity (i.e., the lower the relative density), the more obvious the nonlinear elasticity. As the porosity is increased, the yield strength is almost unchanged, while the compressive strength and elastic modulus are decrease greatly. Its characteristic of the fracture surface is of brittle fracture in macroscopy and of intergranular fracture in microscopy. Compared with the theoretical values and experimental values of the elastic modulus of FeAl porous material,the micromechanics model of heterogeneous Plateau porous structure is more accurate for predicting the effective elastic modulus of the medium-density porous material but not for high-density porous materials.
Uni-axial compression test was used to analyze characteristics of stress-strain curves and effects of porosity on mechanical properties and deformations of the Fe-40at%Al intermetallic compound porous material, which was prepared by the element mixture partial diffusion - reactive synthesis – sintering method. Its microscopic fracture mechanism were revealed by scanning electron microscope test. Research results show that the compressive stress-strain curves of the FeAl porous material with different porosities can be divided into four stages: elasticity, yielding, strengthening and failure, where the larger the porosity (i.e., the lower the relative density), the more obvious the nonlinear elasticity. As the porosity is increased, the yield strength is almost unchanged, while the compressive strength and elastic modulus are decrease greatly. Its characteristic of the fracture surface is of brittle fracture in macroscopy and of intergranular fracture in microscopy. Compared with the theoretical values and experimental values of the elastic modulus of FeAl porous material,the micromechanics model of heterogeneous Plateau porous structure is more accurate for predicting the effective elastic modulus of the medium-density porous material but not for high-density porous materials.
2018, 47(8):2458-2464.
Abstract:
The 304 stainless steel/Q245 carbon steel explosive welding interface was taken as the research object to systematically detect the structure heterogeneity and its effect on the shear behavior in engineering application. First, characters on the transverse section and longitudinal section of the welding interface were detected. And based on the non-equilibrium theory, the mechanism of the heterogeneity on the welding interface has been explained. Furthermore, taking into account the wavy structure and its undulance along the detonation direction, shear performances varied with orientation angles were measured according to the national standard (GB/T 6396-2008). Finally, the morphologies of fracture surface were observed by SEM to recognize the influence of welding interface structure on the failure mode. Results show out that the explosive detonation pressure fluctuation is the fundamental cause of the inhomogeneity on the welding interface, the failure mode and cracks developments were determined by the undulation characters of wavy interface. Besides, an optimal orientation angle, on which samples have the maximum shear strength, was revealed. All of them can be used to guide the engineering application for explosive welding plates.
The 304 stainless steel/Q245 carbon steel explosive welding interface was taken as the research object to systematically detect the structure heterogeneity and its effect on the shear behavior in engineering application. First, characters on the transverse section and longitudinal section of the welding interface were detected. And based on the non-equilibrium theory, the mechanism of the heterogeneity on the welding interface has been explained. Furthermore, taking into account the wavy structure and its undulance along the detonation direction, shear performances varied with orientation angles were measured according to the national standard (GB/T 6396-2008). Finally, the morphologies of fracture surface were observed by SEM to recognize the influence of welding interface structure on the failure mode. Results show out that the explosive detonation pressure fluctuation is the fundamental cause of the inhomogeneity on the welding interface, the failure mode and cracks developments were determined by the undulation characters of wavy interface. Besides, an optimal orientation angle, on which samples have the maximum shear strength, was revealed. All of them can be used to guide the engineering application for explosive welding plates.
2018, 47(8):2465-2471.
Abstract:
Different added proportion of ZrO2 in TC4/ZrO2 composite thin-wall samples were produced by laser engineered net shaping. Influence of scanning speed on thermal stress in forming process was studied. X-ray diffractometer analysis(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) were carried out for the sample phase composition, microstructure and elements distribution respectively. The research indicates that lower scanning speed can reduce the residual stress of thin-wall samples and the tendency to cracking. The result of XRD shows that when the proportion of ZrO2 is higher than 30%, nonstoichiometric compound ,TiO.325, is formed; The grain morphology of TC4 matrix changed from acicular, lamellar to bulk grain with the increasing of proportion of ZrO2; The result of EDS shows a segregation of ZrO2 at lamellar Ti grain boundaries; The content of Zr in Ti solid solution increases with the content of ZrO2increasing.A reliable technical support is provided by this study to finally form TC4/ZrO2 graded materials.
Different added proportion of ZrO2 in TC4/ZrO2 composite thin-wall samples were produced by laser engineered net shaping. Influence of scanning speed on thermal stress in forming process was studied. X-ray diffractometer analysis(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) were carried out for the sample phase composition, microstructure and elements distribution respectively. The research indicates that lower scanning speed can reduce the residual stress of thin-wall samples and the tendency to cracking. The result of XRD shows that when the proportion of ZrO2 is higher than 30%, nonstoichiometric compound ,TiO.325, is formed; The grain morphology of TC4 matrix changed from acicular, lamellar to bulk grain with the increasing of proportion of ZrO2; The result of EDS shows a segregation of ZrO2 at lamellar Ti grain boundaries; The content of Zr in Ti solid solution increases with the content of ZrO2increasing.A reliable technical support is provided by this study to finally form TC4/ZrO2 graded materials.
2018, 47(8):2472-2476.
Abstract:
The performance of niobium superconducting radiofrequency (SRF) accelerator cavities strongly depends on its interior surface state. This paper describes the experimental characteristics of chemical polishing technology for niobium metal, namely polishing rate, surface topography, chemical composition and grain orientation, which have been conducted to optimize process parameters. The mixed solution of hydrofluoric acid, Nitric acid and prthoposphoric acid, 1: 1: 2 in parts by volume is proposed as appropriate polishing reagents with rate equation h = 29.359 × t 0.9247. Polishing for 6 ~ 15 min can remove 154 ~ 360 μm of material using this solution, corresponding roughness Ra and Nb2O5 layer thickness of polished surface is less than 0.65 μm and 10 nm respectively. Meanwhile, we discussed the polishing mechanism using electron back scatter diffration (EBSD) and laser scanning confocal microscope (LSCM), found that the outmost surface of over-polishing sample consists of many fine high-index planes which intersects each other to form sharp egdes in grains or at boundaries.
The performance of niobium superconducting radiofrequency (SRF) accelerator cavities strongly depends on its interior surface state. This paper describes the experimental characteristics of chemical polishing technology for niobium metal, namely polishing rate, surface topography, chemical composition and grain orientation, which have been conducted to optimize process parameters. The mixed solution of hydrofluoric acid, Nitric acid and prthoposphoric acid, 1: 1: 2 in parts by volume is proposed as appropriate polishing reagents with rate equation h = 29.359 × t 0.9247. Polishing for 6 ~ 15 min can remove 154 ~ 360 μm of material using this solution, corresponding roughness Ra and Nb2O5 layer thickness of polished surface is less than 0.65 μm and 10 nm respectively. Meanwhile, we discussed the polishing mechanism using electron back scatter diffration (EBSD) and laser scanning confocal microscope (LSCM), found that the outmost surface of over-polishing sample consists of many fine high-index planes which intersects each other to form sharp egdes in grains or at boundaries.
2018, 47(8):2477-2482.
Abstract:
In order to reveal the mechanism of the high-frequency vibratory stress relief, the effect of the evolution of the dislocation density with the help of high-frequency vibration on the residual stress relaxation. The Williamson-Hall (WH) method and the hole-drilling method were used to evaluate the dislocation densities and the residual stresses in the Cr12MoV steel quenched specimen before and after high-frequency vibration. Based on the experimental results, the multi-freedom system of the crystal grain was developed based on the microscopic dynamics theory in order to analyze the mechanism of high-frequency vibration activated dislocation motion. In addition, the governing equation of the dislocation density evolution with the aid of high-frequency vibration was proposed in order to reveal the microcosmic mechanism of the high-frequency vibratory stress relief. The results show that the dislocations inside the materials were activated with the help of high-frequency vibration. The dislocation density evolution process mainly consists of the dislocation accumulation process and the dislocation annihilation process. And the dislocation annihilation process has a dominant process with the help of high-frequency vibration, which results in that the dislocation density inside the materials can be reduced. The degree of the lattice distortion can be reduced due to the decrease of the dislocation density. As a result, the residual stress inside the materials can be relieved by the high-frequency vibratory stress relief.
In order to reveal the mechanism of the high-frequency vibratory stress relief, the effect of the evolution of the dislocation density with the help of high-frequency vibration on the residual stress relaxation. The Williamson-Hall (WH) method and the hole-drilling method were used to evaluate the dislocation densities and the residual stresses in the Cr12MoV steel quenched specimen before and after high-frequency vibration. Based on the experimental results, the multi-freedom system of the crystal grain was developed based on the microscopic dynamics theory in order to analyze the mechanism of high-frequency vibration activated dislocation motion. In addition, the governing equation of the dislocation density evolution with the aid of high-frequency vibration was proposed in order to reveal the microcosmic mechanism of the high-frequency vibratory stress relief. The results show that the dislocations inside the materials were activated with the help of high-frequency vibration. The dislocation density evolution process mainly consists of the dislocation accumulation process and the dislocation annihilation process. And the dislocation annihilation process has a dominant process with the help of high-frequency vibration, which results in that the dislocation density inside the materials can be reduced. The degree of the lattice distortion can be reduced due to the decrease of the dislocation density. As a result, the residual stress inside the materials can be relieved by the high-frequency vibratory stress relief.
2018, 47(8):2483-2488.
Abstract:
In order to study the effect of the over-temperature on the microstructures and high cycle fatigue properties of DD6 single crystal superalloy, the alloy after standard heat treatment was hold at 1200℃ and 1200℃/50MPa for 1h respectively, which simulated different over-temperature process, and was then air cooled. The microstructures and high cycle fatigue properties of DD6 alloy with standard heat treatment, 1200℃/1h, 1200℃/50MPa/1h at 800℃ were investigated by SEM and rotary benging fatigue testing machine. The results show that after heat-treatment at 1200℃ for 1h, the size of γ′ particles becomes larger slightly and quite nonuniform, serrated γ/γ′ interface appeares and a small number of fine secondary γ′-particles precipitate in the γ matrix channels. After heat-treatment at 1200℃/50MPa for 1h, the size of γ′ particles also becomes larger while also quite nonuniform; a large number of fine secondary γ′ particles precipitate in the γ matrix channels which have become wider significantly and the directional coarsening of γ′ particles occurs. In addition, the rafting of the sheet-like morphology of γ′ particles is formed along the [100] and [010] directions after fatigue test. The high cycle fatigue properties of DD6 alloy by standard heat treatment are higher than that of the alloy by 1200℃/1h, but are similar to the alloy by 1200℃/50MPa/1h. Analysis on fracture surfaces of three heat treatment process at 800℃ demonstrates that quasi-cleavage mode is observed.
In order to study the effect of the over-temperature on the microstructures and high cycle fatigue properties of DD6 single crystal superalloy, the alloy after standard heat treatment was hold at 1200℃ and 1200℃/50MPa for 1h respectively, which simulated different over-temperature process, and was then air cooled. The microstructures and high cycle fatigue properties of DD6 alloy with standard heat treatment, 1200℃/1h, 1200℃/50MPa/1h at 800℃ were investigated by SEM and rotary benging fatigue testing machine. The results show that after heat-treatment at 1200℃ for 1h, the size of γ′ particles becomes larger slightly and quite nonuniform, serrated γ/γ′ interface appeares and a small number of fine secondary γ′-particles precipitate in the γ matrix channels. After heat-treatment at 1200℃/50MPa for 1h, the size of γ′ particles also becomes larger while also quite nonuniform; a large number of fine secondary γ′ particles precipitate in the γ matrix channels which have become wider significantly and the directional coarsening of γ′ particles occurs. In addition, the rafting of the sheet-like morphology of γ′ particles is formed along the [100] and [010] directions after fatigue test. The high cycle fatigue properties of DD6 alloy by standard heat treatment are higher than that of the alloy by 1200℃/1h, but are similar to the alloy by 1200℃/50MPa/1h. Analysis on fracture surfaces of three heat treatment process at 800℃ demonstrates that quasi-cleavage mode is observed.
2018, 47(8):2489-2499.
Abstract:
At present, the roll temperature control method of the magnesium alloy sheet rolling process is simple and accurate, which has a serious influence on the shape, thickness and crack. So adopting the method for fluid circulation to control temperature, using fluent software to simulate the fluid-solid coupled heat transfer process and verifying by experiment, then giving the heat transfer trends and laws. The results showed that heating the roll by this method, the surface temperature distribution is more uniform, the maximum temperature difference between the edge and the middle is 6℃, and fluid temperature and velocity have little effect on it; At different fluid temperature and velocities, the temperature of the roll rises with trend of decreasing rate, and when the fluid temperature rises and the velocity increases, the temperature rise of the roll becomes faster, the effect of the fluid temperature on the roll temperature rise is greater than the fluid velocity; The relationship between the temperature of the roll surface and the time is obtained under different heating conditions; The roll surface temperature drop has a period of extension when the roll is stopped heating, the higher the temperature, the longer the extension; There is an error between the simulation results and the experimental results in the roll temperature rise stage, fluid temperature increases, the error becomes larger, the roll temperature increases, the error also becomes larger, the maximum error is 16.16%, the results are consistent, indicating that the model can correctly represent the heat transfer process of the fluid heating roll.
At present, the roll temperature control method of the magnesium alloy sheet rolling process is simple and accurate, which has a serious influence on the shape, thickness and crack. So adopting the method for fluid circulation to control temperature, using fluent software to simulate the fluid-solid coupled heat transfer process and verifying by experiment, then giving the heat transfer trends and laws. The results showed that heating the roll by this method, the surface temperature distribution is more uniform, the maximum temperature difference between the edge and the middle is 6℃, and fluid temperature and velocity have little effect on it; At different fluid temperature and velocities, the temperature of the roll rises with trend of decreasing rate, and when the fluid temperature rises and the velocity increases, the temperature rise of the roll becomes faster, the effect of the fluid temperature on the roll temperature rise is greater than the fluid velocity; The relationship between the temperature of the roll surface and the time is obtained under different heating conditions; The roll surface temperature drop has a period of extension when the roll is stopped heating, the higher the temperature, the longer the extension; There is an error between the simulation results and the experimental results in the roll temperature rise stage, fluid temperature increases, the error becomes larger, the roll temperature increases, the error also becomes larger, the maximum error is 16.16%, the results are consistent, indicating that the model can correctly represent the heat transfer process of the fluid heating roll.
2018, 47(8):2500-2505.
Abstract:
High entropy alloys (HEAs) formed with simple crystal structures such as FCC and BCC have been reported exhibiting superior tensile or compressive properties, resistance to wear, high thermal stability. However, few works were carried out on the wettability of the molten metals on HEAs substrate. And the general objective of this work is to better understand the wettability of the molten metals on the HEAs substrate. Bi-Sn alloy with the low melting point and the AlCoFeNiCr HEA and the CuCoFeNiCr HEA were selected as experiential materials. By the sessile drop method, the wetting behavior and the interfacial characteristics of the molten Bi-Sn on the AlCoFeNiCr HEA and the CuCoFeNiCr HEA substrate were investigated. The scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) was used to analyze the microstructure the Bi-Sn/AlCoFeNiCr HEA and Bi-Sn/CuCoFeNiCr HEA interface. The results show that the AlCoFeNiCr HEA and the CuCoFeNiCrHEA form with a single solid solution structure. However, Bi-Sn molten alloy on CuCoFeNiCr HEA substrate has better wetting characteristics than Bi-Sn molten alloy on AlCoFeNiCr HEA substrate. With increasing wetting temperature, a number of intermetallic compounds existed at the interface between the molten Bi-Sn and the CuCoFeNiCr HEA substrate, and the diffusion of Sn atom along the Cu-rich solid-solution phase in CuCoFeNiCr HEA is much more intense. On the contrary, interface of the Bi-Sn/AlCoFeNiCr HEA system is still the straight interface, and there are new intermetallic compounds on the Bi-Sn/AlCoFeNiCr HEA interface with increasing wetting temperature. It is found that the Cu-rich phase in CuCoFeNiCrHEA provides a “wetting channel” for the wetting process between the molten Sn and CuCoNiFeCr HEA substrate, which result in the two wetting systems with different wetting mechanism.
High entropy alloys (HEAs) formed with simple crystal structures such as FCC and BCC have been reported exhibiting superior tensile or compressive properties, resistance to wear, high thermal stability. However, few works were carried out on the wettability of the molten metals on HEAs substrate. And the general objective of this work is to better understand the wettability of the molten metals on the HEAs substrate. Bi-Sn alloy with the low melting point and the AlCoFeNiCr HEA and the CuCoFeNiCr HEA were selected as experiential materials. By the sessile drop method, the wetting behavior and the interfacial characteristics of the molten Bi-Sn on the AlCoFeNiCr HEA and the CuCoFeNiCr HEA substrate were investigated. The scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) was used to analyze the microstructure the Bi-Sn/AlCoFeNiCr HEA and Bi-Sn/CuCoFeNiCr HEA interface. The results show that the AlCoFeNiCr HEA and the CuCoFeNiCrHEA form with a single solid solution structure. However, Bi-Sn molten alloy on CuCoFeNiCr HEA substrate has better wetting characteristics than Bi-Sn molten alloy on AlCoFeNiCr HEA substrate. With increasing wetting temperature, a number of intermetallic compounds existed at the interface between the molten Bi-Sn and the CuCoFeNiCr HEA substrate, and the diffusion of Sn atom along the Cu-rich solid-solution phase in CuCoFeNiCr HEA is much more intense. On the contrary, interface of the Bi-Sn/AlCoFeNiCr HEA system is still the straight interface, and there are new intermetallic compounds on the Bi-Sn/AlCoFeNiCr HEA interface with increasing wetting temperature. It is found that the Cu-rich phase in CuCoFeNiCrHEA provides a “wetting channel” for the wetting process between the molten Sn and CuCoNiFeCr HEA substrate, which result in the two wetting systems with different wetting mechanism.
2018, 47(8):2506-2510.
Abstract:
In order to study the effect of pulsed laser nitriding on uranium, the crystal structure and oxidation kinetics of nitride layer were investigated using X-ray diffraction and in situ reactor chamber. The experimental results indicate that the crystal structure of nitride is affected by the scanning speed of pulsed laser remarkably. The UN is the sole nitride at lower scanning speed; the mix structure of UN and U2N3 will achieve at higher scanning speed. The oxidation kinetics of uranium is slow in the extreme when the surface is covered with a layer of UN. The oxidation kinetics and oxidation mechanism of nitride are analyzed and discussed in this paper.
In order to study the effect of pulsed laser nitriding on uranium, the crystal structure and oxidation kinetics of nitride layer were investigated using X-ray diffraction and in situ reactor chamber. The experimental results indicate that the crystal structure of nitride is affected by the scanning speed of pulsed laser remarkably. The UN is the sole nitride at lower scanning speed; the mix structure of UN and U2N3 will achieve at higher scanning speed. The oxidation kinetics of uranium is slow in the extreme when the surface is covered with a layer of UN. The oxidation kinetics and oxidation mechanism of nitride are analyzed and discussed in this paper.
37 Effect of Thermal Exposure on Mechanical Properties in Welding Seam of TC11/Ti-22Al-25Nb Dual Alloy
2018, 47(8):2511-2517.
Abstract:
The microstructures and fracture morphologies at the fracture position of electron beam welding and near isothermally forged TC11/Ti-22Al-25Nb dual alloy simulation disc underwent thermal exposure at 550℃ and 600℃ for 300 h, 500h respectively, were investigated through tensile and stress-rupture experiments and observed by SEM and TEM. The results indicate that: after the thermal exposure of the samples at room temperature tensile, fracture at the weld position. After 550℃ thermal exposure, the fracture of tensile samples belong to ductile fracture while tensile samples belong to brittle cleavage fracture when it experienced 600 ℃ thermal exposure, and crack source always starts in surface of the sample. As the thermal exposure temperature increasing and time extend, an overall improvement in room temperature tensile strength, ductility decreases, lasting time is reduced, and the element of the welding connection area distributes more uniform, the composition curve becomes more smooth.
The microstructures and fracture morphologies at the fracture position of electron beam welding and near isothermally forged TC11/Ti-22Al-25Nb dual alloy simulation disc underwent thermal exposure at 550℃ and 600℃ for 300 h, 500h respectively, were investigated through tensile and stress-rupture experiments and observed by SEM and TEM. The results indicate that: after the thermal exposure of the samples at room temperature tensile, fracture at the weld position. After 550℃ thermal exposure, the fracture of tensile samples belong to ductile fracture while tensile samples belong to brittle cleavage fracture when it experienced 600 ℃ thermal exposure, and crack source always starts in surface of the sample. As the thermal exposure temperature increasing and time extend, an overall improvement in room temperature tensile strength, ductility decreases, lasting time is reduced, and the element of the welding connection area distributes more uniform, the composition curve becomes more smooth.
2018, 47(8):2518-2524.
Abstract:
The microstructure and mechanical properties of as-cast, solution-treated and as-extruded Mg-8Li-4Al-0.3Y alloys were studied by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction analysis (XRD) and tensile tests machines, etc. The results show that as-cast Mg-8Li-4Al-0.3Y alloys are composed of ɑ-Mg, β-Li, Al2Y, AlLi and MgAlLi2 phases. MgAlLi2 compound and most of AlLi phase decomposes and dissolves into the matrix, only part of larger AlLi particles are left during the solution treatment. The micro-hardness of solution-treated alloy is much higher than that of as-cast one due to solution strengthening. The mechanical properties of Mg-8Li-4Al-0.3Y alloys are improved a lot by extrusion and the ultimate strength and elongation of the extrude alloy reaches to 208 MPa and 25.1% respectively.
The microstructure and mechanical properties of as-cast, solution-treated and as-extruded Mg-8Li-4Al-0.3Y alloys were studied by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction analysis (XRD) and tensile tests machines, etc. The results show that as-cast Mg-8Li-4Al-0.3Y alloys are composed of ɑ-Mg, β-Li, Al2Y, AlLi and MgAlLi2 phases. MgAlLi2 compound and most of AlLi phase decomposes and dissolves into the matrix, only part of larger AlLi particles are left during the solution treatment. The micro-hardness of solution-treated alloy is much higher than that of as-cast one due to solution strengthening. The mechanical properties of Mg-8Li-4Al-0.3Y alloys are improved a lot by extrusion and the ultimate strength and elongation of the extrude alloy reaches to 208 MPa and 25.1% respectively.
2018, 47(8):2525-2530.
Abstract:
Based on die casting AZ81 alloy, this article focuses on the effects of adding alloying elements (0.5%Pb, 0.5%Pb+0.5%Sn、0.5%Pb+1.0%Sn) on its microstructure and mechanical properties at room temperature and 180℃. 1) In the alloy of AZ81-0.5%Pb-1.0%Sn, there was polygon Mg2Sn phase at grain boundary. In the meantime, Pb and Sn suppressed the formation of precipitation Mg17Al12 at grain boundary to a certain extent, which contributed to the medium temperature resistance. 2) At room temperature, the tensile strength and yield strength of the alloys increased with the increase of Sn. The tensile strength and yeild strength of die casting AZ81-0.5Pb-1.0Sn at room temperature were 211 MPa and 150.5 MPa, respectively. 3) At 180℃,the tensile and yeild strength increased with the increase of Sn as well. The tensile strength and yeild strength of die casting AZ81-0.5Pb-1.0Sn alloy at 180℃ were 200.5 MPa and 145.2 MPa, respectively. 4) The Pb-Sn made the fracture mechanism transferred from plasticity to brittleness.
Based on die casting AZ81 alloy, this article focuses on the effects of adding alloying elements (0.5%Pb, 0.5%Pb+0.5%Sn、0.5%Pb+1.0%Sn) on its microstructure and mechanical properties at room temperature and 180℃. 1) In the alloy of AZ81-0.5%Pb-1.0%Sn, there was polygon Mg2Sn phase at grain boundary. In the meantime, Pb and Sn suppressed the formation of precipitation Mg17Al12 at grain boundary to a certain extent, which contributed to the medium temperature resistance. 2) At room temperature, the tensile strength and yield strength of the alloys increased with the increase of Sn. The tensile strength and yeild strength of die casting AZ81-0.5Pb-1.0Sn at room temperature were 211 MPa and 150.5 MPa, respectively. 3) At 180℃,the tensile and yeild strength increased with the increase of Sn as well. The tensile strength and yeild strength of die casting AZ81-0.5Pb-1.0Sn alloy at 180℃ were 200.5 MPa and 145.2 MPa, respectively. 4) The Pb-Sn made the fracture mechanism transferred from plasticity to brittleness.
40 Investigation on the microstructure and corrosion behavior of the as-cast Mg-xAl(x=9, 12, 15) alloys
2018, 47(8):2531-2536.
Abstract:
The Mg-xAl(x=9, 12, 15) alloys were prepared by meaning of semi-continuous casting. The effects of Al contents on evolution of microstructure of Mg-Al alloy were investigated used X-ray diffraction(XRD), optical microscopy(OM) and scanning electron microscopy(SEM). Meanwhile, the corrosion behaviors of Mg-xAl(x=9, 12, 15) alloys were studied by both hydrogen evolution and Potentiodynamic polarization curves. Moreover, the corrosion mechanism of Mg-xAl(x=9, 12, 15) alloys was also discussed in details based on the SEM corrosion morphologies of as-cast Mg-Al alloys after hydrogen evolution testing for 72 h in 3.5 wt.% NaCl without corrosion products. The results indicated that the microstructure of three alloys is composed of α-Mg phase and β-Mg17Al12 phase. Moreover, the content of beta phase increases with the increase of Al content. As a result, the corrosion resistance of the three alloys was enhanced with the increase of the β phase. The Mg-15%Al alloy has the best corrosion resistance, and Mg-9%Al is the worst. The oxide film formed on the all as cast Mg-Al alloys surface after hydrogen evolution testing for 72 h in 3.5 wt.% NaCl. Furthermore, the stability of the film increased with the increase of Al content.
The Mg-xAl(x=9, 12, 15) alloys were prepared by meaning of semi-continuous casting. The effects of Al contents on evolution of microstructure of Mg-Al alloy were investigated used X-ray diffraction(XRD), optical microscopy(OM) and scanning electron microscopy(SEM). Meanwhile, the corrosion behaviors of Mg-xAl(x=9, 12, 15) alloys were studied by both hydrogen evolution and Potentiodynamic polarization curves. Moreover, the corrosion mechanism of Mg-xAl(x=9, 12, 15) alloys was also discussed in details based on the SEM corrosion morphologies of as-cast Mg-Al alloys after hydrogen evolution testing for 72 h in 3.5 wt.% NaCl without corrosion products. The results indicated that the microstructure of three alloys is composed of α-Mg phase and β-Mg17Al12 phase. Moreover, the content of beta phase increases with the increase of Al content. As a result, the corrosion resistance of the three alloys was enhanced with the increase of the β phase. The Mg-15%Al alloy has the best corrosion resistance, and Mg-9%Al is the worst. The oxide film formed on the all as cast Mg-Al alloys surface after hydrogen evolution testing for 72 h in 3.5 wt.% NaCl. Furthermore, the stability of the film increased with the increase of Al content.
2018, 47(8):2537-2543.
Abstract:
The microstructure of V-Ti-Ni alloy affects not only the hydrogen separation performance, but also the mechanical properties and formability. The microstructure, hardness and tensile properties of multiphase V100-2x-Tix-Nix (X=10, 15, 20) alloys for hydrogen separation were investigated. The microstructure of V100-2x-Tix-Nix alloys ingot consists of dendritic phase (V base solid solution) and interdendritic phase (NiTi and NiTi2). With the increase of the content of Ti and Ni in the alloy, the volume ratio of interdendritic phase in the alloy increases, and blocks the connection of dendrite arm due to forming a continuous network. At room temperature, the bulk hardness, tensile strength, elongation and reduction of area of the alloy increase with the increase of Ti and Ni content. V based solid solution and NiTi2 phase are the main factors affecting the bulk hardness of the three alloys. The three alloys are brittle materials at room temperature. The content of NiTi in the alloy has a great influence on the elongation of the alloy.
The microstructure of V-Ti-Ni alloy affects not only the hydrogen separation performance, but also the mechanical properties and formability. The microstructure, hardness and tensile properties of multiphase V100-2x-Tix-Nix (X=10, 15, 20) alloys for hydrogen separation were investigated. The microstructure of V100-2x-Tix-Nix alloys ingot consists of dendritic phase (V base solid solution) and interdendritic phase (NiTi and NiTi2). With the increase of the content of Ti and Ni in the alloy, the volume ratio of interdendritic phase in the alloy increases, and blocks the connection of dendrite arm due to forming a continuous network. At room temperature, the bulk hardness, tensile strength, elongation and reduction of area of the alloy increase with the increase of Ti and Ni content. V based solid solution and NiTi2 phase are the main factors affecting the bulk hardness of the three alloys. The three alloys are brittle materials at room temperature. The content of NiTi in the alloy has a great influence on the elongation of the alloy.
2018, 47(8):2544-2548.
Abstract:
Bimetal composite materials having multifunction and more performance are one of the research focuses, at present. And then, the 7075/6061 cladding bimetal composite ingots with “semi-solid microstructure / dendrite microstructure” distribution characteristic were prepared by the solid / liquid metals compound casting. Interfacial morphology and mechanical properties of the ingots with different melt temperatures were analyzed and tested. At last, the interface bonding mechanism of the ingot was discussed. The results show that the 7075/6061 cladding bimetal composite ingot has a advantageous microstructure distribution and morphology, and has the best compressive strength, while the parameters are the outside melt temperature 760 ℃, the billet pre-temperature 300 ℃, holding time 40 min and air cooling. With the increasing of the outside melt temperature, the near-spheroidal α-Al solid particles of the semi-solid billets of the inner layer 7075 alloy are more coarsening and more non-spherical, the remelted area of the semi-solid billet at the bonding interface also increase. Otherwise, as the outside melt temperature increasing, an evolution rule of the semi-solid microstructures nearby the bonding interface is occurred following: near-spheroidal solid particles merging and growing, non-spherical crystal, dendritic crystal. During the compression mechanical property test at ambient temperature, the samples fracture along 45° angle direction to axis, and not along the bonding interface.
Bimetal composite materials having multifunction and more performance are one of the research focuses, at present. And then, the 7075/6061 cladding bimetal composite ingots with “semi-solid microstructure / dendrite microstructure” distribution characteristic were prepared by the solid / liquid metals compound casting. Interfacial morphology and mechanical properties of the ingots with different melt temperatures were analyzed and tested. At last, the interface bonding mechanism of the ingot was discussed. The results show that the 7075/6061 cladding bimetal composite ingot has a advantageous microstructure distribution and morphology, and has the best compressive strength, while the parameters are the outside melt temperature 760 ℃, the billet pre-temperature 300 ℃, holding time 40 min and air cooling. With the increasing of the outside melt temperature, the near-spheroidal α-Al solid particles of the semi-solid billets of the inner layer 7075 alloy are more coarsening and more non-spherical, the remelted area of the semi-solid billet at the bonding interface also increase. Otherwise, as the outside melt temperature increasing, an evolution rule of the semi-solid microstructures nearby the bonding interface is occurred following: near-spheroidal solid particles merging and growing, non-spherical crystal, dendritic crystal. During the compression mechanical property test at ambient temperature, the samples fracture along 45° angle direction to axis, and not along the bonding interface.
2018, 47(8):2549-2554.
Abstract:
In the magnesium air battery, the polarization and corrosion of the magnesium anode is an important index to measure the magnesium air battery. In this paper, by means of dynamic potential polarization method and electrochemical impedance spectroscopy (NaCl), the effect of six hydrated cerium (CeN3O9.6H2O) on the corrosion resistance of AZ31 cathode was studied. The results showed that CeN3O9.6H2O were added into the electrolyte to form Ce(OH)3 protective film on the surface of AZ31 magnesium alloy to improve the corrosion resistance of the magnesium alloy. With the increase of the concentration of CeN3O9.6H2O, the Ce(OH)3 protective film became denser, and the corrosion rate of AZ magnesium alloy was decreased. When the concentration of CeN3O9.6H2O reached 1.0g/L, the corrosion rate of the magnesium alloy was the lowest, and the corrosion inhibition rate was 70.4%. However, when the concentration of CeN3O9.6H2O is greater than 1.0g/L, the corrosion rate of magnesium alloy is increased due to the dissolution of Ce(OH)3 protective film. Ce(HO)3 protective film formed on the surface of magnesium alloy CeN3O9.6H2O was found by the SEM diagram of AZ alloy, which was found in the of 50h after immersion. The Mg2+ charge transfer resistance is increased by 69.5Ω from the equivalent circuit diagram, which improves the corrosion resistance of the magnesium alloy. The discharge performance of CeN3O9.6H2O was improved by the discharge test, and the discharge time was prolonged by nearly 1h.
In the magnesium air battery, the polarization and corrosion of the magnesium anode is an important index to measure the magnesium air battery. In this paper, by means of dynamic potential polarization method and electrochemical impedance spectroscopy (NaCl), the effect of six hydrated cerium (CeN3O9.6H2O) on the corrosion resistance of AZ31 cathode was studied. The results showed that CeN3O9.6H2O were added into the electrolyte to form Ce(OH)3 protective film on the surface of AZ31 magnesium alloy to improve the corrosion resistance of the magnesium alloy. With the increase of the concentration of CeN3O9.6H2O, the Ce(OH)3 protective film became denser, and the corrosion rate of AZ magnesium alloy was decreased. When the concentration of CeN3O9.6H2O reached 1.0g/L, the corrosion rate of the magnesium alloy was the lowest, and the corrosion inhibition rate was 70.4%. However, when the concentration of CeN3O9.6H2O is greater than 1.0g/L, the corrosion rate of magnesium alloy is increased due to the dissolution of Ce(OH)3 protective film. Ce(HO)3 protective film formed on the surface of magnesium alloy CeN3O9.6H2O was found by the SEM diagram of AZ alloy, which was found in the of 50h after immersion. The Mg2+ charge transfer resistance is increased by 69.5Ω from the equivalent circuit diagram, which improves the corrosion resistance of the magnesium alloy. The discharge performance of CeN3O9.6H2O was improved by the discharge test, and the discharge time was prolonged by nearly 1h.
2018, 47(8):2555-2560.
Abstract:
SP700 titanium alloy has excellent superplasticity at low temperature, the paper used fiber laser welding SP700 titanium alloy to study the superplastic forming ability, microstructure evolution and RT tensile property after SPF. Result indicates that the welding direction parallel to the rolling direction of base material could have better superplasticity to form a cone part at 800℃, the max. pressure and cone height is 0.8MPa and 75mm, respectively, which is 20mm higher than base material"s. With the increase of deformation, the coarse columnar grains and weld undercut were eliminated and the grains was comparably fine. With about 33% deformation reduction, the tensile strength of materials with two welding directions were all decreased, and tensile strength of specimen with welding direction parallel to the rolling direction and formed at 775℃ only decreased by 2.2%. The fracture position all were on the base material for the cone part and tensile specimen.
SP700 titanium alloy has excellent superplasticity at low temperature, the paper used fiber laser welding SP700 titanium alloy to study the superplastic forming ability, microstructure evolution and RT tensile property after SPF. Result indicates that the welding direction parallel to the rolling direction of base material could have better superplasticity to form a cone part at 800℃, the max. pressure and cone height is 0.8MPa and 75mm, respectively, which is 20mm higher than base material"s. With the increase of deformation, the coarse columnar grains and weld undercut were eliminated and the grains was comparably fine. With about 33% deformation reduction, the tensile strength of materials with two welding directions were all decreased, and tensile strength of specimen with welding direction parallel to the rolling direction and formed at 775℃ only decreased by 2.2%. The fracture position all were on the base material for the cone part and tensile specimen.
2018, 47(8):2561-2566.
Abstract:
Porous ceramic coating were prepared on AZ91 magnesium alloy by micro-arc oxidation (MAO), and the duplex coating were prepared by magnetic sputtering copper. The surface phase?composition, surface roughness, surface and cross-sectional morphology, surface wettability, and electrochemical characteristics of MAO and duplex coatings were studied. The results indicate that the surface of AZ91 magnesium alloy treated by MAO shows hydrophilic due to its micro-nano coarse porous structure, and its phase?consists of MgO, Mg and Mg2SiO4. However, the surface of MAO coating turns into relatively compact copper with hydrophobic property after magnetic sputtering copper, at the same time the surface roughness decreases a little. Four-point probe measurement indicates that the duplex coating exhibits well electrical conductivity,the sheet resistance is 16.2mΩ?□-1. Meanwhile, potentiodynamic polarization curves reveal that the corrosion current density of duplex coating reduces to 10%, and the corrosion?potential increases 0.36V, while the polarization resistance increases around 80?times compared with bare magnesium alloy. Compared with the MAO coating, the corrosion?potential of the duplex coating increases 0.24V, suggesting that the corrosion trend decreases. Nevertheless, the corrosion current density and polarization resistance of the duplex coating all decrease to some extent. These?survey?results?indicate that the duplex treatment by MAO and magnetic sputtering copper on surface of the magnesium alloy improve its electrical conductivity greatly?without?losing corrosion resistance of magnesium alloy.
Porous ceramic coating were prepared on AZ91 magnesium alloy by micro-arc oxidation (MAO), and the duplex coating were prepared by magnetic sputtering copper. The surface phase?composition, surface roughness, surface and cross-sectional morphology, surface wettability, and electrochemical characteristics of MAO and duplex coatings were studied. The results indicate that the surface of AZ91 magnesium alloy treated by MAO shows hydrophilic due to its micro-nano coarse porous structure, and its phase?consists of MgO, Mg and Mg2SiO4. However, the surface of MAO coating turns into relatively compact copper with hydrophobic property after magnetic sputtering copper, at the same time the surface roughness decreases a little. Four-point probe measurement indicates that the duplex coating exhibits well electrical conductivity,the sheet resistance is 16.2mΩ?□-1. Meanwhile, potentiodynamic polarization curves reveal that the corrosion current density of duplex coating reduces to 10%, and the corrosion?potential increases 0.36V, while the polarization resistance increases around 80?times compared with bare magnesium alloy. Compared with the MAO coating, the corrosion?potential of the duplex coating increases 0.24V, suggesting that the corrosion trend decreases. Nevertheless, the corrosion current density and polarization resistance of the duplex coating all decrease to some extent. These?survey?results?indicate that the duplex treatment by MAO and magnetic sputtering copper on surface of the magnesium alloy improve its electrical conductivity greatly?without?losing corrosion resistance of magnesium alloy.
46 Study on the electrochemical property of NiO - ZnO nano-fibers fabricated by Electrostatic spinning
2018, 47(8):2567-2572.
Abstract:
By Electrostatic spinning method，it was prepared NiO - ZnO oxide nanofibers with different mass ratios. Their structure, composition and morphology were characterized by XRD, XPS, BET, SEM and TEM respectively and their electrochemical properties were also investigated by electrochemical workstation. The results showed that when the nickel and zinc ratio was 10:1, the obtained nanofibers possessed large surface area of 71.425m2/g and were porous with mesoporous diameter of 13.37nm. Electrochemical tests showed that the 10:1 sample had clearer redox peak and more large discharge capacity than the pure NiO fibers, in which the value of the capacity had risen from 331F/g to 441F/g under the current density of 1A/g. Eespecially, it still remained 81.2% of starting value after 1000 cycles, and its maximum capacitance was 461F/g at 0.5A/g, which showed the excellent electrochemical performance of the sample.The process of the nanofiber synthesis was also introduced.
By Electrostatic spinning method，it was prepared NiO - ZnO oxide nanofibers with different mass ratios. Their structure, composition and morphology were characterized by XRD, XPS, BET, SEM and TEM respectively and their electrochemical properties were also investigated by electrochemical workstation. The results showed that when the nickel and zinc ratio was 10:1, the obtained nanofibers possessed large surface area of 71.425m2/g and were porous with mesoporous diameter of 13.37nm. Electrochemical tests showed that the 10:1 sample had clearer redox peak and more large discharge capacity than the pure NiO fibers, in which the value of the capacity had risen from 331F/g to 441F/g under the current density of 1A/g. Eespecially, it still remained 81.2% of starting value after 1000 cycles, and its maximum capacitance was 461F/g at 0.5A/g, which showed the excellent electrochemical performance of the sample.The process of the nanofiber synthesis was also introduced.
47 Fabrication of Palladium-Free Nickel-Coated Carbon Fiber Reinforced Sn-3.0Ag-0.5Cu Composite Solder
2018, 47(8):2573-2577.
Abstract:
Palladium-free Nickel coating was deposited on the surface of carbon fibers by electroless plating method. Nickel coated carbon fibers reinforced Sn-3.0Ag-0.5Cu composite solder was made using the powder metallurgy technique. Microstructure of composite solder was observed and analyzed with the help of SEM, EDS and OM. The effect of Nickel coated carbon fibers contents on the microstructure and properties of composites solder was studied. The results showed that nickel plated carbon fiber was mainly distributed in the grain boundary of the composite solder. The dispersity of coated carbon fiber decreased with its content increasing, while the melting point of composite solder changed little. When the coated carbon fiber content was greater than 1wt%, the reinforced phase appeared obvious agglomeration, which led to the higher electrical resistivity. The added 1wt% coated carbon fiber will be helpful to decrease the surface tension of liquid composite solder between the flux and Copper substrate, which caused the excellent wetting effect. At the same time, the current density of solder matrix was decreased, which resulted in the lower electrical resistivity of composite solder.
Palladium-free Nickel coating was deposited on the surface of carbon fibers by electroless plating method. Nickel coated carbon fibers reinforced Sn-3.0Ag-0.5Cu composite solder was made using the powder metallurgy technique. Microstructure of composite solder was observed and analyzed with the help of SEM, EDS and OM. The effect of Nickel coated carbon fibers contents on the microstructure and properties of composites solder was studied. The results showed that nickel plated carbon fiber was mainly distributed in the grain boundary of the composite solder. The dispersity of coated carbon fiber decreased with its content increasing, while the melting point of composite solder changed little. When the coated carbon fiber content was greater than 1wt%, the reinforced phase appeared obvious agglomeration, which led to the higher electrical resistivity. The added 1wt% coated carbon fiber will be helpful to decrease the surface tension of liquid composite solder between the flux and Copper substrate, which caused the excellent wetting effect. At the same time, the current density of solder matrix was decreased, which resulted in the lower electrical resistivity of composite solder.
2018, 47(8):2578-2584.
Abstract:
High power pulsed magnetron sputtering (HiPIMS) technology can be used to prepare high quality coatings with smooth surface and dense structure due to its high ionization rate and high ion energy. And the deposition temperature will determine the kinetic energy and diffusion ability of the deposited particles, which has a significant impact on the growth process and performance. In this paper, Al-Cr-Si-N coating is prepared by HiPIMS technology at different deposition temperatures. The effects of deposition temperature on the structure, composition, microstructure, mechanical properties and tribological properties of the coatings were systematically studied. The results show that as the deposition temperature rises from 100°C to 350°C, the interior of the coating begins to convert from amorphous to nanocrystals, and the FCC-AlN phase appears at 300°C. The smoothness and compactness of the coatings are progressively improved. The adhesion strength increase gradually, reached the maximum value of 83N at 300 °C and decreases to 18N at 350 °C due to the serious glow etching effect .The hardness of the coating increases gradually and reaches a maximum of 19 GPa at 350°C. No columnar crystals are found and the residual stress is low, and the inverse Hallpez effect occurs, due to the increase in kinetic energy of the deposited particles and the densification of the structure.
High power pulsed magnetron sputtering (HiPIMS) technology can be used to prepare high quality coatings with smooth surface and dense structure due to its high ionization rate and high ion energy. And the deposition temperature will determine the kinetic energy and diffusion ability of the deposited particles, which has a significant impact on the growth process and performance. In this paper, Al-Cr-Si-N coating is prepared by HiPIMS technology at different deposition temperatures. The effects of deposition temperature on the structure, composition, microstructure, mechanical properties and tribological properties of the coatings were systematically studied. The results show that as the deposition temperature rises from 100°C to 350°C, the interior of the coating begins to convert from amorphous to nanocrystals, and the FCC-AlN phase appears at 300°C. The smoothness and compactness of the coatings are progressively improved. The adhesion strength increase gradually, reached the maximum value of 83N at 300 °C and decreases to 18N at 350 °C due to the serious glow etching effect .The hardness of the coating increases gradually and reaches a maximum of 19 GPa at 350°C. No columnar crystals are found and the residual stress is low, and the inverse Hallpez effect occurs, due to the increase in kinetic energy of the deposited particles and the densification of the structure.
2018, 47(8):2585-2591.
Abstract:
The Zr70Al8Cu22-xNix（x=8.5,9,9.5,10,10.5,11）bulk amorphous alloy rods with 2mm diameters were prepared by copper mold casting technique,and the effect of Ni/Cu content ratio on thermal stability and mechanical properties of Zr-based amorphous alloys were investigated by differential scanning calorimeter（DSC）and uniaxial compression test methods.The results show that the value of supercooled liquid regionΔTx change from 80K to 81Kwith the Ni/Cu content ratio increase,but theΔTx have a bigger value than other alloys when Ni/Cu content ratio arrive 0.63 and 0.76,when Ni/Cu content ratio arrive 0.76,which has a better thermal stability because of itsΔTx value is 89K.And the plastic strain exhabit a downward tend with the Ni/Cu content ratio increase,but there exists a unnormal larger value when Ni/Cu content ratio arrive 0.76,which has good plastic strain,and the compressive strength has a downward tend over all with wave and changeless nature.And the young modulus value arrives the maximum value 80 GPa when Ni/Cu content ratio is 0.63,but other alloys change from 58 GPa to 65 GPa.In totally, the plastic strain,compressive strength and young modulus also arrive the maximum value when Ni/Cu content ratio is 0.63.
The Zr70Al8Cu22-xNix（x=8.5,9,9.5,10,10.5,11）bulk amorphous alloy rods with 2mm diameters were prepared by copper mold casting technique,and the effect of Ni/Cu content ratio on thermal stability and mechanical properties of Zr-based amorphous alloys were investigated by differential scanning calorimeter（DSC）and uniaxial compression test methods.The results show that the value of supercooled liquid regionΔTx change from 80K to 81Kwith the Ni/Cu content ratio increase,but theΔTx have a bigger value than other alloys when Ni/Cu content ratio arrive 0.63 and 0.76,when Ni/Cu content ratio arrive 0.76,which has a better thermal stability because of itsΔTx value is 89K.And the plastic strain exhabit a downward tend with the Ni/Cu content ratio increase,but there exists a unnormal larger value when Ni/Cu content ratio arrive 0.76,which has good plastic strain,and the compressive strength has a downward tend over all with wave and changeless nature.And the young modulus value arrives the maximum value 80 GPa when Ni/Cu content ratio is 0.63,but other alloys change from 58 GPa to 65 GPa.In totally, the plastic strain,compressive strength and young modulus also arrive the maximum value when Ni/Cu content ratio is 0.63.
2018, 47(8):2592-2599.
Abstract:
Inspired by non-smooth surfaces in nature, surface texture which can play positive roles in tribology such as capturing debris, storing lubricant and reducing the contact area during service has been regarded as an effective approach to improve the tribological behaviors of materials. Some beneficial results in enhancing tribological properties of titanium alloys have been obtained. This review focused on the studies of design and processing of surface texture, mechanisms of friction reduction and wear-resistant, duplex treatments with surface technology that applied on titanium alloys. Research progress on surface texture for improving tribological properties of titanium alloys were summarized. The prospect of surface texture related research ideas and methods of titanium alloys were suggested
Inspired by non-smooth surfaces in nature, surface texture which can play positive roles in tribology such as capturing debris, storing lubricant and reducing the contact area during service has been regarded as an effective approach to improve the tribological behaviors of materials. Some beneficial results in enhancing tribological properties of titanium alloys have been obtained. This review focused on the studies of design and processing of surface texture, mechanisms of friction reduction and wear-resistant, duplex treatments with surface technology that applied on titanium alloys. Research progress on surface texture for improving tribological properties of titanium alloys were summarized. The prospect of surface texture related research ideas and methods of titanium alloys were suggested
2018, 47(8):2600-2606.
Abstract:
Silicon, one of the most promising high-capacity anode materials of lithium ion batteries, has high theoretical specific capacity, moderate insertion / removal potential for lithium and low reactivity with electrolyte. However, it suffers from the huge volume effect, which leads to its poor electrochemical performance. In this paper, some investigations and the preparation methods about overcoming the shortcomings of silicon based materials in recent years are reviewed, including silicon nanoparticles, silicon composites, and other related materials for lithium ion battery. The development trend and the prospect of silicon based anode materials for lithium ion batteries are also analyzed.
Silicon, one of the most promising high-capacity anode materials of lithium ion batteries, has high theoretical specific capacity, moderate insertion / removal potential for lithium and low reactivity with electrolyte. However, it suffers from the huge volume effect, which leads to its poor electrochemical performance. In this paper, some investigations and the preparation methods about overcoming the shortcomings of silicon based materials in recent years are reviewed, including silicon nanoparticles, silicon composites, and other related materials for lithium ion battery. The development trend and the prospect of silicon based anode materials for lithium ion batteries are also analyzed.
