Based on molecular dynamics(MD)simulation,the mechanisms of plastic anisotropy in nanotwinned polycrystalline copper with{111}texture during tensile deformation were systematically studied from the aspects of Schmid f...Based on molecular dynamics(MD)simulation,the mechanisms of plastic anisotropy in nanotwinned polycrystalline copper with{111}texture during tensile deformation were systematically studied from the aspects of Schmid factor of the dominant slip system and the dislocation mechanism.The results show that the Schmid factor of dominated slip system is altered by changing the inclining angle of the twin boundaries(TBs),while the yield stress or flow stress does not strictly follow the Schmid law.There exist hard and soft orientations involving different dislocation mechanisms during the tensile deformation.The strengthening mechanism of hard orientation lies in the fact that there exist interactions between the dislocations and the TBs during plastic deformation,which leads to the dislocation blocking and reactions.The softening mechanism of soft orientation lies in the fact that there is no interaction between the dislocations and the TBs because only the slip systems parallel to the TBs are activated and the dislocations slip on the planes parallel to the TBs.It is concluded that the plastic anisotropy in the nanotwinned polycrystalline copper with{111}texture is aroused by the combination effect of the Schmid factor of dominated slip system and the dislocation mechanism.展开更多
Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis ba...Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data.Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale.Statistically stored dislocation(SSD)density and geometrically necessary dislocation(GND)density were further used in order to illuminate the microstructure evolution during uniaxial compression.SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain.GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains,namely,a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.展开更多
Three different NiTi-based alloys,whose nominal compositions were Ni50Ti50,Ni49Ti49Fe2,Ni45Ti51.8Fe3.2(molefraction,%),respectively,were used in the current research to understand the influence of Fe addition on phase...Three different NiTi-based alloys,whose nominal compositions were Ni50Ti50,Ni49Ti49Fe2,Ni45Ti51.8Fe3.2(molefraction,%),respectively,were used in the current research to understand the influence of Fe addition on phase transformationbehavior in NiTi shape memory alloy(SMA).The microstructure and phase transformation behavior of the alloys were investigatedby optical microscopy(OM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and differential scanningcalorimetry(DSC)analysis.The results show that the matrix of the Ni50Ti50alloy consists of both B19′(martensite)phase and B2(austenite)phase.Moreover,the substructures of twins could be observed in the B19′phase.However,the ternary alloys of NiTiFeexhibit B2phase in the microstructures.Such microstructures were also characterized by large presence of Ti2Ni precipitatesdispersed homogenously in the matrix of the two kinds of alloys.The addition of Fe to the NiTi SMA results in the decrease in phasetransformation temperatures in the ternary alloys.Based on mechanism analysis,it can be concluded that this phenomenon isprimarily attributed to atom relaxation of the distorted lattice induced by Ni-antisite defects and Fe substitutions during phasetransformation,which enables stabilization of B2phase during phase transformation.展开更多
In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were d...In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were developed by hot compression tests at temperatures ranging from 500 to 1100 °C and strain rates ranging from 0.0005 to 0.5 s?1. The results show that the instability region of the hot processing map increases with the increase of deformation extent. The instability occurs in the low and high temperature regions. The instability region presents the adiabatic shear bands at low temperatures, but it exhibits the abnormal growth of the grains at high temperatures. Consequently, it is necessary to avoid processing the equiatomic NiTi SMA in these regions. It is preferable to process the NiTi SMA at the temperatures ranging from 750 to 900 °C.展开更多
Based on the channel die compression, NiTiFe shape memory alloy(SMA) was subjected to plane strain compression. Mechanically-induced martensite transformation, nanocrystalline and amorphous phase can be observed in th...Based on the channel die compression, NiTiFe shape memory alloy(SMA) was subjected to plane strain compression. Mechanically-induced martensite transformation, nanocrystalline and amorphous phase can be observed in the case of large plastic strain. Mechanically-induced martensite transformation is obviously different from the conventional stress-induced martensite transformation. The former generally occurs after dislocation slip, whereas the latter arises prior to dislocation slip. The occurrence of B19’ martensite phase contributes to accommodating subsequent plastic deformation of NiTiFe SMA. Mechanically-induced B19’ martensite is partially stabilized due to the existence of local high stress field and consequently it is unable to be reverted to B2 austenite phase during unloading.展开更多
Fe66Mn15Si5Cr9Ni5(wt.%)shape memory alloy(SMA)withγaustenite andεmartensite was subjected to mechanical vibrating polishing and consequently its surface suffered from plastic deformation in the case of compressive s...Fe66Mn15Si5Cr9Ni5(wt.%)shape memory alloy(SMA)withγaustenite andεmartensite was subjected to mechanical vibrating polishing and consequently its surface suffered from plastic deformation in the case of compressive stress.Almost completeεmartensite transformation is found to occur in FeMnSiCrNi sample subjected to mechanical vibrating polishing,where stress-induced martensite transformation plays a predominant role.Stressinduced martensite transformation of FeMnSiCrNi SMA is closely related to the orientation of external stress.The complicated compressive stress which results from the mechanical vibrating polishing contributes toεmartensite transformation fromγaustenite of FeMnSiCrNi SMA.Mechanical vibrating polishing has a certain influence on the surface texture ofεmartensite of FeMnSiCrNi SMA,where■<0001>texture appears in the polished FeMnSiCrNi SMA.展开更多
基金the National Natural Science Foundation of China(No.51871070).
文摘Based on molecular dynamics(MD)simulation,the mechanisms of plastic anisotropy in nanotwinned polycrystalline copper with{111}texture during tensile deformation were systematically studied from the aspects of Schmid factor of the dominant slip system and the dislocation mechanism.The results show that the Schmid factor of dominated slip system is altered by changing the inclining angle of the twin boundaries(TBs),while the yield stress or flow stress does not strictly follow the Schmid law.There exist hard and soft orientations involving different dislocation mechanisms during the tensile deformation.The strengthening mechanism of hard orientation lies in the fact that there exist interactions between the dislocations and the TBs during plastic deformation,which leads to the dislocation blocking and reactions.The softening mechanism of soft orientation lies in the fact that there is no interaction between the dislocations and the TBs because only the slip systems parallel to the TBs are activated and the dislocations slip on the planes parallel to the TBs.It is concluded that the plastic anisotropy in the nanotwinned polycrystalline copper with{111}texture is aroused by the combination effect of the Schmid factor of dominated slip system and the dislocation mechanism.
基金Projects(51475101,51305091,51305092)supported by the National Natural Science Foundation of China
文摘Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data.Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale.Statistically stored dislocation(SSD)density and geometrically necessary dislocation(GND)density were further used in order to illuminate the microstructure evolution during uniaxial compression.SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain.GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains,namely,a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.
基金Projects(51305091,51305092,51475101)supported by the National Natural Science Foundation of ChinaProject(20132304120025)supported by Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘Three different NiTi-based alloys,whose nominal compositions were Ni50Ti50,Ni49Ti49Fe2,Ni45Ti51.8Fe3.2(molefraction,%),respectively,were used in the current research to understand the influence of Fe addition on phase transformationbehavior in NiTi shape memory alloy(SMA).The microstructure and phase transformation behavior of the alloys were investigatedby optical microscopy(OM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and differential scanningcalorimetry(DSC)analysis.The results show that the matrix of the Ni50Ti50alloy consists of both B19′(martensite)phase and B2(austenite)phase.Moreover,the substructures of twins could be observed in the B19′phase.However,the ternary alloys of NiTiFeexhibit B2phase in the microstructures.Such microstructures were also characterized by large presence of Ti2Ni precipitatesdispersed homogenously in the matrix of the two kinds of alloys.The addition of Fe to the NiTi SMA results in the decrease in phasetransformation temperatures in the ternary alloys.Based on mechanism analysis,it can be concluded that this phenomenon isprimarily attributed to atom relaxation of the distorted lattice induced by Ni-antisite defects and Fe substitutions during phasetransformation,which enables stabilization of B2phase during phase transformation.
基金Projects(51305091,51305092,51475101)supported by the National Natural Science Foundation of ChinaProject(20132304120025)supported by the Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘In order to describe the deformation behavior and the hot workability of equiatomic NiTi shape memory alloy (SMA) during hot deformation, Arrhenius-type constitutive equation and hot processing map of the alloy were developed by hot compression tests at temperatures ranging from 500 to 1100 °C and strain rates ranging from 0.0005 to 0.5 s?1. The results show that the instability region of the hot processing map increases with the increase of deformation extent. The instability occurs in the low and high temperature regions. The instability region presents the adiabatic shear bands at low temperatures, but it exhibits the abnormal growth of the grains at high temperatures. Consequently, it is necessary to avoid processing the equiatomic NiTi SMA in these regions. It is preferable to process the NiTi SMA at the temperatures ranging from 750 to 900 °C.
基金Projects(51475101,51871070)supported by the National Natural Science Foundation of China。
文摘Based on the channel die compression, NiTiFe shape memory alloy(SMA) was subjected to plane strain compression. Mechanically-induced martensite transformation, nanocrystalline and amorphous phase can be observed in the case of large plastic strain. Mechanically-induced martensite transformation is obviously different from the conventional stress-induced martensite transformation. The former generally occurs after dislocation slip, whereas the latter arises prior to dislocation slip. The occurrence of B19’ martensite phase contributes to accommodating subsequent plastic deformation of NiTiFe SMA. Mechanically-induced B19’ martensite is partially stabilized due to the existence of local high stress field and consequently it is unable to be reverted to B2 austenite phase during unloading.
基金Projects (51475101, 51871070) supported by the National Natural Science Foundation of China。
文摘Fe66Mn15Si5Cr9Ni5(wt.%)shape memory alloy(SMA)withγaustenite andεmartensite was subjected to mechanical vibrating polishing and consequently its surface suffered from plastic deformation in the case of compressive stress.Almost completeεmartensite transformation is found to occur in FeMnSiCrNi sample subjected to mechanical vibrating polishing,where stress-induced martensite transformation plays a predominant role.Stressinduced martensite transformation of FeMnSiCrNi SMA is closely related to the orientation of external stress.The complicated compressive stress which results from the mechanical vibrating polishing contributes toεmartensite transformation fromγaustenite of FeMnSiCrNi SMA.Mechanical vibrating polishing has a certain influence on the surface texture ofεmartensite of FeMnSiCrNi SMA,where■<0001>texture appears in the polished FeMnSiCrNi SMA.