In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electro...In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and tensile tests. The results showed that Ti can decrease the secondary dendrite arm spacing(SDAS). The tensile strength of the Mg-8Sn-1Zn-Ti alloys is initially increased by increasing the Ti content up to 0.09 wt.%, but subsequently decreased for further increase of Ti content. The improved tensile properties are attributed to the decreased SDAS and refi ned Mg_2Sn phases, as well as the increased fraction of tin(Sn) segregated regions. The tensile fracture surface of the studied alloys shows mixed characteristics of cleavage and quasi-cleavage fracture. Adding Ti does not significantly change the fracture mode of the studied alloys.展开更多
The corrosion behavior of Mg-8Li-3Zn-Al alloy was investigated in neutral 3.5%NaCl aqueous solution by morphology observation and electrochemical tests.The weight loss method was to measure the corrosion rate.The elec...The corrosion behavior of Mg-8Li-3Zn-Al alloy was investigated in neutral 3.5%NaCl aqueous solution by morphology observation and electrochemical tests.The weight loss method was to measure the corrosion rate.The electrochemical results indicated that the corrosion resistance of Mg-8Li-3Zn-Al alloy in 3.5%NaCl solution is poorer than that in distilled water.The Cl-anion leads to the initiation and development of the corrosion pits.And the corrosion products are mainly Mg(OH)_(2).展开更多
Mg-8Li-3Al-xCe(x=0, 1.0, 3.0) alloys were prepared. And the effects of cerium content on the microstructure and mechanical properties were studied. Results show that the as-cast alloy is composed of α(Mg), β(Li) and...Mg-8Li-3Al-xCe(x=0, 1.0, 3.0) alloys were prepared. And the effects of cerium content on the microstructure and mechanical properties were studied. Results show that the as-cast alloy is composed of α(Mg), β(Li) and Al2Ce. Cerium has obvious refining effect on α(Mg). And the strength and elongation of alloys were improved.展开更多
The ageing behavior of the mechanically alloyed Cu-15Ni-8Sn alloy has been studied. Compared with the alloys prepared by casting and rapid solidification, the modulation structure developed during ageing process of th...The ageing behavior of the mechanically alloyed Cu-15Ni-8Sn alloy has been studied. Compared with the alloys prepared by casting and rapid solidification, the modulation structure developed during ageing process of those prepared by mechanical alloying is finer and much more uniform, which leads to a higher peak hardness. However, their spinodal decomposition temperature are almost the same. Cold deformation prior to ageing not only accelerates the ageing process but also increases the peak hardness of the alloy.展开更多
Aiming at the problems of poor plastic forming ability,narrow forging temperature range,and strain rate sensitivity of rare earth magnesium alloys,a study on the microstructure and mechanical properties of Mg-8Gd-3Y-0...Aiming at the problems of poor plastic forming ability,narrow forging temperature range,and strain rate sensitivity of rare earth magnesium alloys,a study on the microstructure and mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with different isothermal forging processes is carried out.The microstructure and properties of the alloy in the as-cast,isothermal forged,and post-aging states after forging are studied with optical microscope(OM),scanning electron microscope(SEM),and tensile testing.The results show that significant dynamic recrystallization occurs during the isothermal forging process,a fine equiaxed grain structure is formed,and the mechanical properties of the alloy are greatly improved.When the isothermal forging temperature is 460℃ and the strain rate is 0.02 s^(-1),the alloy structure performance is the best,the room temperature tensile yield strength(TYS)is 218 MPa,the ultimate tensile strength(UTS)is 299 MPa,and the fracture elongation(FE)is 19.2%.When the alloy is post-forging artificial aged,theα-Mg matrix is dispersed,the Mg_5(Gd,Y)phase is precipitated,the UTS of the alloy is increased to 392 MPa,and the FE is reduced to 12.0%.展开更多
Microstructure and mechanical behavior of the squeeze-casting and squeeze-casting plus T6 heat-treated Mg-8 Gd-2 Y-0.4 Zr magnesium alloys at room and elevated temperatures were investigated. The experimental results ...Microstructure and mechanical behavior of the squeeze-casting and squeeze-casting plus T6 heat-treated Mg-8 Gd-2 Y-0.4 Zr magnesium alloys at room and elevated temperatures were investigated. The experimental results showed that the T6 treated alloy aged at slightly high temperature exhibited good comprehensive strength and ductility. However, the strength of the tested alloys was not sensitive to the change of tensile temperature, i e, the yield strength and ultimate tensile strength did not decrease significantly with increasing tensile temperature, while the ductility increased greatly. In addition, the squeeze-casting alloy exhibited predominant intergranular fracture accompanied by minor transgranular rupture, and the tensile fracture mode for the T6 treated alloy had typical transgranular cleavage fracture.展开更多
Corrosion resistance of laser powder bed fusion(LPBF)Cu-15Ni-8Sn alloys is crucial towards its practical application in marine engineering.In this work,corrosion behavior of LPBF Cu-15Ni-8Sn alloy was com-prehensively...Corrosion resistance of laser powder bed fusion(LPBF)Cu-15Ni-8Sn alloys is crucial towards its practical application in marine engineering.In this work,corrosion behavior of LPBF Cu-15Ni-8Sn alloy was com-prehensively investigated.The results suggest that LPBF Cu-15Ni-8Sn alloy exhibits superior corrosion re-sistance than the conventional casting counterpart and their corrosion behavior is highly associated with Sn segregation.Generally,a triple-layer film will be formed on the surface of LPBF Cu-15Ni-8Sn alloy when being exposed to 3.5 wt%NaCl solution.To be more detailed,the abundance of nanoscale Sn-rich precipitates at the molten pool boundaries promotes the initial formation of a thick inner layer,where Ni and Sn tend to be distributed at inner and outer positions of the layer,respectively.In contrast,the inner layer on molten pools is much thinner ascribed to a lower Sn content,facilitating the earlier nucleation and growth of a compact middle layer that is mainly composed of numerous Cu-rich nanoparticles.At the outmost position,CuO,Cu(OH)_(2) and Ni(OH)_(2) constitute the major composition of the loose layer.The results of this study could contribute to the optimal design and processing of additively manufactured Cu-Ni-Sn alloys.展开更多
The microstructures and mechanical properties of the directionally solidified Cu-15Ni-8Sn alloy were investigated at solidification rates ranging from 100 to 3000μm/s.The results showed that the solidification rate s...The microstructures and mechanical properties of the directionally solidified Cu-15Ni-8Sn alloy were investigated at solidification rates ranging from 100 to 3000μm/s.The results showed that the solidification rate significantly affects the phase distribution of the as-cast Cu-15Ni-8Sn alloy.The primary and secondary dendritic spacing reduces and eventually becomes stable as the solidification rate increases.Meanwhile,the size of the primary phase decreases,and its distribution becomes more uniform.The most severe segregation problem of this alloy has been greatly improved.Upon solidification at 100μm/s,the as-cast Cu-15Ni-8Sn alloy consists of the α-Cu matrix,γ-CuNi_(2)Sn phase,discontinuous precipitation structure,modulated structure,and DO_(22) ordered phases.However,as the solidification rate increases,the discontinuous precipitation structure,modulated structures,and DO_(22) ordered phases decrease and even disappear,reducing hardness.As the solidification rate increases,after homogenization treatment,the composition and microhardness distributions of Cu-15Ni-8Sn alloy become more uniform.The time for homogenization is also shortened.It reduces production energy usage and facilitates further mechanical processing.展开更多
The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS). And, compression...The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS). And, compression deformation behavior at room-temperature was studied. The results showed that the microstructure of Mg-8Zn-1Y alloy solidified under ambient pressure and super-high pressure was both mainly composed of ■-Mg and quasicrystal I-Mg3Zn6 Y. Solidification under super-high pressure contributed to refining solidified microstructure and changing morphology of the intergranular second phase. The morphology of intergranular second phase(quasicrystal I-Mg3Zn6Y) was transformed from continuous network(ambient pressure) to long island(high pressure) and finally to granular(super-high pressure) with the increase in pressure. The compressive strength, yield strength and rupture strain of the samples solidified under ambient pressure were significantly improved from 262.6 MPa, 244.4 MPa and 13.3% to 437.3 MPa, 368.9 MPa and 24.7% under the pressure of 6 GPa, respectively. Under ambient pressure, cleavage plane on compressive fracture was large and smooth. When it was solidified under the pressure ranging from 4 to 6 GPa, cleavage plane on compressive fracture was small and coarse. In addition, dimple, tear ridge and lobate patterns existed.展开更多
Double-pass hot compression tests were carried out over a wide range of holding time(0–180 s) and Zener-Hollomon parameter(1.6 E15–1.3 E20) to study the deformation behavior of cast Mg-8 Gd-3 Y alloy.The flow cu...Double-pass hot compression tests were carried out over a wide range of holding time(0–180 s) and Zener-Hollomon parameter(1.6 E15–1.3 E20) to study the deformation behavior of cast Mg-8 Gd-3 Y alloy.The flow curves show obvious work hardening and strain softening stages, leading to the peak stress of double-pass hot compression. Holding time and Zener-Hollomon parameter can significantly affect the second pass peak stress. It is found that increasing the holding time can cause a higher peak stress in the second pass deformation. The second pass stress reaches the peak stress of 71 MPa at ZenerHollomom parameter of 1.6 E15. When the parameter rises to 1.3 E20, the second pass peak goes up to237 MPa. In addition, the second pass peak stress is significantly higher than the unloading stress, which is opposite to the flow behavior of aluminum alloys. Residual stored deformation energy caused by the first pass deformation could be consumed by metadynamic recrystallization. Therefore, more strain energy is required for subsequent dynamic recrystallization, resulting in hardening behavior. A hardening fraction is defined to describe the deformation behavior quantitatively, which shows a positive correlation with the metadynamic recrystallization fraction. The metadynamic recrystallization leads to grain growth at the inter pass holding stage, diminishing dynamic recrystallization nucleation positions in the second pass deformation.展开更多
Sheet samples of Mg-8Li,Mg-8Li-3Al,Mg-8Li-3AlSi and Mg-8Li-5AlSi alloys were obtained by hot rolling.Optical microscope,microhardness tester,nanoindentor,X-ray diffractometer and electrochemical analyzer were adopted ...Sheet samples of Mg-8Li,Mg-8Li-3Al,Mg-8Li-3AlSi and Mg-8Li-5AlSi alloys were obtained by hot rolling.Optical microscope,microhardness tester,nanoindentor,X-ray diffractometer and electrochemical analyzer were adopted to investigate the microstructures,micro-mechanical properties and corrosion resistance.Roller was preheated to 150°C before rolling process,and rolling reduction designed was about20% per pass with a total rolling reduction of 84%.The rolled plates were annealed at 200°C for 120 min.The tensile tests were performed at room temperature.Experimental results showed that both the strength and corrosion resistance of theα+βdual-phase of Mg-Li alloy were significantly improved with adding Al-Si elements.The strength enhancement was attributed to the solid solution of Al into theα-Mg matrix and into theβ-Li matrix as well as to the precipitation strengthening of Mg2 Si particles.Besides,the dendrite grains ofα-Mg transformed to equiaxed ones with addition of Al into alloy Mg-Li.展开更多
Alloys used as bearings in aircraft landing gear are required to reduce friction and wear as well as improve the load‐carrying capability due to the increased aircraft weights.Cu–15Ni–8Sn–0.8Nb alloy is well known...Alloys used as bearings in aircraft landing gear are required to reduce friction and wear as well as improve the load‐carrying capability due to the increased aircraft weights.Cu–15Ni–8Sn–0.8Nb alloy is well known for possessing good mechanical and wear properties that satisfy such requirements.In this study,the microstructure,mechanical properties,and grease‐lubricated sliding wear behavior of Cu–15Ni–8Sn–0.8Nb alloy with 0.8 wt%Nb are investigated.The nanoscale NbNi3 and NbNi2Sn compounds can strengthen the alloy through the Orowan strengthening mechanism.A Stribeck‐like curve is plotted to illustrate the relationship among friction coefficient,normal load,and sliding velocity and to analyze the grease‐lubricated mechanism.The wear rate increases with normal load and decreases with sliding velocity,except at 2.58 m/s.A wear mechanism map has been developed to exhibit the dominant wear mechanisms under various friction conditions.When the normal load is 700 N and the sliding velocity is 2.58 m/s,a chemical reaction between the lubricating grease and friction pairs occurs,resulting in the failure of lubricating grease and an increase in wear.展开更多
Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjec...Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjected to dynamic loading. In the present work, stress–strain curves at strain rate from 1.5 9 103to 5.0 9 103s-1were analyzed, and optical microscope(OM) was used to reveal adiabatic shearing behavior of recovered samples. Results show that both the two alloys manifest significant strain hardening effects. Critical damage strain rate of the two alloys is about 4.3 9 103s-1, under which the impact absorbs energy of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V are 560 and 470 MJ m-3, respectively. Both of them fracture along the maximum shearing strength orientation, an angle of 45° to the compression axis. No adiabatic shear band(ASB) is found in Ti–5Al–2.5Sn ELI alloy, whereas several ASBs with different widths exist without regular direction in Ti–8Al–1Mo–1V alloy.展开更多
基金supported by the National Natural Science Foundation of China(Grant no.51404166)Shanxi Province Science Foundation for Youths(2013021013-4)+2 种基金Research Project Supported by Shanxi Scholarship Council of China(2014-023)Technological Innovation Programs of Higher Education Institutions Shanxi(Grant no.2014120)the Advanced Programs of Department of Human Resources and Social Security of Shanxi Province for Returned Scholars(2013101)
文摘In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and tensile tests. The results showed that Ti can decrease the secondary dendrite arm spacing(SDAS). The tensile strength of the Mg-8Sn-1Zn-Ti alloys is initially increased by increasing the Ti content up to 0.09 wt.%, but subsequently decreased for further increase of Ti content. The improved tensile properties are attributed to the decreased SDAS and refi ned Mg_2Sn phases, as well as the increased fraction of tin(Sn) segregated regions. The tensile fracture surface of the studied alloys shows mixed characteristics of cleavage and quasi-cleavage fracture. Adding Ti does not significantly change the fracture mode of the studied alloys.
基金This work was supported by the financial support of the National Natural Science Foundation of China(No.41276074)National Research Program of China(No.2014CB643304).
文摘The corrosion behavior of Mg-8Li-3Zn-Al alloy was investigated in neutral 3.5%NaCl aqueous solution by morphology observation and electrochemical tests.The weight loss method was to measure the corrosion rate.The electrochemical results indicated that the corrosion resistance of Mg-8Li-3Zn-Al alloy in 3.5%NaCl solution is poorer than that in distilled water.The Cl-anion leads to the initiation and development of the corrosion pits.And the corrosion products are mainly Mg(OH)_(2).
基金Project supported by Heilongjiang Province Key Technologies R&D Project (GC06A212)
文摘Mg-8Li-3Al-xCe(x=0, 1.0, 3.0) alloys were prepared. And the effects of cerium content on the microstructure and mechanical properties were studied. Results show that the as-cast alloy is composed of α(Mg), β(Li) and Al2Ce. Cerium has obvious refining effect on α(Mg). And the strength and elongation of alloys were improved.
文摘The ageing behavior of the mechanically alloyed Cu-15Ni-8Sn alloy has been studied. Compared with the alloys prepared by casting and rapid solidification, the modulation structure developed during ageing process of those prepared by mechanical alloying is finer and much more uniform, which leads to a higher peak hardness. However, their spinodal decomposition temperature are almost the same. Cold deformation prior to ageing not only accelerates the ageing process but also increases the peak hardness of the alloy.
文摘Aiming at the problems of poor plastic forming ability,narrow forging temperature range,and strain rate sensitivity of rare earth magnesium alloys,a study on the microstructure and mechanical properties of Mg-8Gd-3Y-0.5Zr alloy with different isothermal forging processes is carried out.The microstructure and properties of the alloy in the as-cast,isothermal forged,and post-aging states after forging are studied with optical microscope(OM),scanning electron microscope(SEM),and tensile testing.The results show that significant dynamic recrystallization occurs during the isothermal forging process,a fine equiaxed grain structure is formed,and the mechanical properties of the alloy are greatly improved.When the isothermal forging temperature is 460℃ and the strain rate is 0.02 s^(-1),the alloy structure performance is the best,the room temperature tensile yield strength(TYS)is 218 MPa,the ultimate tensile strength(UTS)is 299 MPa,and the fracture elongation(FE)is 19.2%.When the alloy is post-forging artificial aged,theα-Mg matrix is dispersed,the Mg_5(Gd,Y)phase is precipitated,the UTS of the alloy is increased to 392 MPa,and the FE is reduced to 12.0%.
基金Funded by the Major State Basic Research Development Program of China(2016YFB0701405)the National Natural Science Foundation of China(51705314)
文摘Microstructure and mechanical behavior of the squeeze-casting and squeeze-casting plus T6 heat-treated Mg-8 Gd-2 Y-0.4 Zr magnesium alloys at room and elevated temperatures were investigated. The experimental results showed that the T6 treated alloy aged at slightly high temperature exhibited good comprehensive strength and ductility. However, the strength of the tested alloys was not sensitive to the change of tensile temperature, i e, the yield strength and ultimate tensile strength did not decrease significantly with increasing tensile temperature, while the ductility increased greatly. In addition, the squeeze-casting alloy exhibited predominant intergranular fracture accompanied by minor transgranular rupture, and the tensile fracture mode for the T6 treated alloy had typical transgranular cleavage fracture.
基金financially supported by the National Natural Science Foundation of China(No.51901018)Young Elite Scientists Sponsorship Program by China Association for Science and Tech-nology(YESS,No.2019QNRC001)+3 种基金the Fundamental Research Funds for the Central Universities(No.FRF-AT-20-07,06500119)the Nat-ural Science Foundation of Beijing Municipality(No.2212037)the National Science and Technology Resources Investigation Program of China(No.2019FY101400)the National Natural Science Foundation of China(No.52104368).
文摘Corrosion resistance of laser powder bed fusion(LPBF)Cu-15Ni-8Sn alloys is crucial towards its practical application in marine engineering.In this work,corrosion behavior of LPBF Cu-15Ni-8Sn alloy was com-prehensively investigated.The results suggest that LPBF Cu-15Ni-8Sn alloy exhibits superior corrosion re-sistance than the conventional casting counterpart and their corrosion behavior is highly associated with Sn segregation.Generally,a triple-layer film will be formed on the surface of LPBF Cu-15Ni-8Sn alloy when being exposed to 3.5 wt%NaCl solution.To be more detailed,the abundance of nanoscale Sn-rich precipitates at the molten pool boundaries promotes the initial formation of a thick inner layer,where Ni and Sn tend to be distributed at inner and outer positions of the layer,respectively.In contrast,the inner layer on molten pools is much thinner ascribed to a lower Sn content,facilitating the earlier nucleation and growth of a compact middle layer that is mainly composed of numerous Cu-rich nanoparticles.At the outmost position,CuO,Cu(OH)_(2) and Ni(OH)_(2) constitute the major composition of the loose layer.The results of this study could contribute to the optimal design and processing of additively manufactured Cu-Ni-Sn alloys.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFA0714400)Science and Technology Projects of Jiangxi Provincial Department of Education(Grant Nos.GJ210843 and GJJ200873)+2 种基金Scientific Research Starting Foundation for Advanced Talents of Jiangxi University of Science and Technology(Grant No.205200100570)the Project of the Key Scientific and Technological of Jiangxi Province(Grant No.20181BCB19003)Ningbo Enterprise Innovation Consortium Special Project(Grant No.2021H003).
文摘The microstructures and mechanical properties of the directionally solidified Cu-15Ni-8Sn alloy were investigated at solidification rates ranging from 100 to 3000μm/s.The results showed that the solidification rate significantly affects the phase distribution of the as-cast Cu-15Ni-8Sn alloy.The primary and secondary dendritic spacing reduces and eventually becomes stable as the solidification rate increases.Meanwhile,the size of the primary phase decreases,and its distribution becomes more uniform.The most severe segregation problem of this alloy has been greatly improved.Upon solidification at 100μm/s,the as-cast Cu-15Ni-8Sn alloy consists of the α-Cu matrix,γ-CuNi_(2)Sn phase,discontinuous precipitation structure,modulated structure,and DO_(22) ordered phases.However,as the solidification rate increases,the discontinuous precipitation structure,modulated structures,and DO_(22) ordered phases decrease and even disappear,reducing hardness.As the solidification rate increases,after homogenization treatment,the composition and microhardness distributions of Cu-15Ni-8Sn alloy become more uniform.The time for homogenization is also shortened.It reduces production energy usage and facilitates further mechanical processing.
基金Project supported by National Natural Science Foundation of China(51475486)Natural Science Foundation of Hebei Province(E2013501096)
文摘The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS). And, compression deformation behavior at room-temperature was studied. The results showed that the microstructure of Mg-8Zn-1Y alloy solidified under ambient pressure and super-high pressure was both mainly composed of ■-Mg and quasicrystal I-Mg3Zn6 Y. Solidification under super-high pressure contributed to refining solidified microstructure and changing morphology of the intergranular second phase. The morphology of intergranular second phase(quasicrystal I-Mg3Zn6Y) was transformed from continuous network(ambient pressure) to long island(high pressure) and finally to granular(super-high pressure) with the increase in pressure. The compressive strength, yield strength and rupture strain of the samples solidified under ambient pressure were significantly improved from 262.6 MPa, 244.4 MPa and 13.3% to 437.3 MPa, 368.9 MPa and 24.7% under the pressure of 6 GPa, respectively. Under ambient pressure, cleavage plane on compressive fracture was large and smooth. When it was solidified under the pressure ranging from 4 to 6 GPa, cleavage plane on compressive fracture was small and coarse. In addition, dimple, tear ridge and lobate patterns existed.
基金support of the National Key Research and Development Program of China (Grant No. 2016YFB0301103 and No. 2016YFB0101604)the National Natural Science Foundation of China (Grant No. 51601112)the Shanghai Rising-Star Program (Grant No. 17QB1403000)
文摘Double-pass hot compression tests were carried out over a wide range of holding time(0–180 s) and Zener-Hollomon parameter(1.6 E15–1.3 E20) to study the deformation behavior of cast Mg-8 Gd-3 Y alloy.The flow curves show obvious work hardening and strain softening stages, leading to the peak stress of double-pass hot compression. Holding time and Zener-Hollomon parameter can significantly affect the second pass peak stress. It is found that increasing the holding time can cause a higher peak stress in the second pass deformation. The second pass stress reaches the peak stress of 71 MPa at ZenerHollomom parameter of 1.6 E15. When the parameter rises to 1.3 E20, the second pass peak goes up to237 MPa. In addition, the second pass peak stress is significantly higher than the unloading stress, which is opposite to the flow behavior of aluminum alloys. Residual stored deformation energy caused by the first pass deformation could be consumed by metadynamic recrystallization. Therefore, more strain energy is required for subsequent dynamic recrystallization, resulting in hardening behavior. A hardening fraction is defined to describe the deformation behavior quantitatively, which shows a positive correlation with the metadynamic recrystallization fraction. The metadynamic recrystallization leads to grain growth at the inter pass holding stage, diminishing dynamic recrystallization nucleation positions in the second pass deformation.
基金supported by National Natural Science Foundation of China(51274149,51401143)Shanxi Scholarship Council of China(No.2014-029)
文摘Sheet samples of Mg-8Li,Mg-8Li-3Al,Mg-8Li-3AlSi and Mg-8Li-5AlSi alloys were obtained by hot rolling.Optical microscope,microhardness tester,nanoindentor,X-ray diffractometer and electrochemical analyzer were adopted to investigate the microstructures,micro-mechanical properties and corrosion resistance.Roller was preheated to 150°C before rolling process,and rolling reduction designed was about20% per pass with a total rolling reduction of 84%.The rolled plates were annealed at 200°C for 120 min.The tensile tests were performed at room temperature.Experimental results showed that both the strength and corrosion resistance of theα+βdual-phase of Mg-Li alloy were significantly improved with adding Al-Si elements.The strength enhancement was attributed to the solid solution of Al into theα-Mg matrix and into theβ-Li matrix as well as to the precipitation strengthening of Mg2 Si particles.Besides,the dendrite grains ofα-Mg transformed to equiaxed ones with addition of Al into alloy Mg-Li.
基金The authors would like to express their gratitude for the financial support provided by the National Key Research and Development Program of China(Grant Nos.2017YFB0306105 and 2018YFE0306100).
文摘Alloys used as bearings in aircraft landing gear are required to reduce friction and wear as well as improve the load‐carrying capability due to the increased aircraft weights.Cu–15Ni–8Sn–0.8Nb alloy is well known for possessing good mechanical and wear properties that satisfy such requirements.In this study,the microstructure,mechanical properties,and grease‐lubricated sliding wear behavior of Cu–15Ni–8Sn–0.8Nb alloy with 0.8 wt%Nb are investigated.The nanoscale NbNi3 and NbNi2Sn compounds can strengthen the alloy through the Orowan strengthening mechanism.A Stribeck‐like curve is plotted to illustrate the relationship among friction coefficient,normal load,and sliding velocity and to analyze the grease‐lubricated mechanism.The wear rate increases with normal load and decreases with sliding velocity,except at 2.58 m/s.A wear mechanism map has been developed to exhibit the dominant wear mechanisms under various friction conditions.When the normal load is 700 N and the sliding velocity is 2.58 m/s,a chemical reaction between the lubricating grease and friction pairs occurs,resulting in the failure of lubricating grease and an increase in wear.
基金financially supported by the Ministry of Science and Technology of China (No. 2012DFG51540)
文摘Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjected to dynamic loading. In the present work, stress–strain curves at strain rate from 1.5 9 103to 5.0 9 103s-1were analyzed, and optical microscope(OM) was used to reveal adiabatic shearing behavior of recovered samples. Results show that both the two alloys manifest significant strain hardening effects. Critical damage strain rate of the two alloys is about 4.3 9 103s-1, under which the impact absorbs energy of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V are 560 and 470 MJ m-3, respectively. Both of them fracture along the maximum shearing strength orientation, an angle of 45° to the compression axis. No adiabatic shear band(ASB) is found in Ti–5Al–2.5Sn ELI alloy, whereas several ASBs with different widths exist without regular direction in Ti–8Al–1Mo–1V alloy.