The Study On The Effect Of Cold-deformation And Heat-treatment On The Phase Transformation And Super-elastic Of TiNiCr Shape Memory Alloys

This article focuses on the effect of pre-deformation,mid-temperature treatment and aging treatment on the transformation of TiNiCr shape memory alloys,and the effect of tensile strength-deformation cycle on the super-elastic of TiNiCr shape memory alloys.Through testing of the DSC and observation of metallographic microstructure photographs,the test researches the effect of different pre-deformation and mid-temperature treatment on the DSC curve and phase-change point of TiNiCr shape memory alloys.From the DSC curve,we can see that the heating and cooling are in the process of a peak,which is in the process of heating only to create B19'phase(M)→B2 phase(P) while in the cooling process when took place with B2(P)→B19'phase(M). The whole changing process have not been observed R-phase.Tests showed that martensitic transition temperature—Ms was in the first rise as the increase of the cold deformation,but when the pre-deformation was up to more than 15%,as the increase of the cold deformation Ms was in reduce.As,Af were the highest when the pre-deformation was up to 15%.Heat treatment can significantly improve the martensitic transformation temperature,which made changes easily.Mid-temperature treatment in 460℃can make Ms increase largely.At 400℃of aging treatment,the longer the holding time was,the lower temperature Ms and Mf were.The thermal hysteresis As-Ms are not affected dy the time of mid-temperature treatment.Through testing of the DSC and the D/max2500PC automatic X-ray diffraction equipment(XRD),the effect of aging treatment on DSC curves as well as the phase transition point have been studied.The study shows that two-stage transformation of B2-R-B19'has turned out during the cooling process,as the result of the nucleation and grown-up of Ti3Ni4 precipitant which stimulating uneven constituents and stress field inducing R phase transformation.When aging treatment in 730℃,R phase transformation is ample,up to 750℃,Rs,Rf lower.We recorded various phase-change points of TiNiCr shape memory alloy unde the different cold deformation,heat treatment of different temperatures and different holding time,so as that we have to determine the appropriate technology to provide a reference.By the tensile test,we have also studied the sample curves of the tensile strength-deformation cycle under the different conditions of cold deformation and heat treatment in order to study the effect of super-elastic of TiNiCr shape memory alloy. Test shows that the different cold deformation wire through the same annealing temperature,the greater the amount of cold deformation is,the less impact non-linear tensile strength-deformation circulating has on super-elastic properties.With the same amount of deformation of the wire,the higher the heat treatment temperature is,the more impact non-linear tensile strength-deformation circulating has on super-elastic properties.After heat treatment procession of the sample,the process of the tensile strength-deformation circulating will have a certain amount of residual deformation,at the same time,the area of the hysteresis curve surrounded gradually reduced the size and appeared to have stabilized.In short,alloy wire processing the cold deformation and annealing,which have been gone through a certain number of times of tensile strength-deformation circulating in order to obtain complete non-linear super-elastic.