Study On Transformation Hysteresis And Deformation Behavior Of NiTi Shape Memory Alloy And NiTi Composites

NiTi shape memory alloy has super elasticity and shape memory effect,and the super elasticity of NiTi shape memory alloy is often accompanied with large stress hysteresis and has excellent mechanical damping characteristics,which has an important application in the large strain amplitude damping.Previous studies often tend to use the difference of upper platform and lower platform of super elastic NiTi shape memory alloy to character the stress hysteresis,the plastic deformation in process will greatly increase the transformation stress hysteresis.In order to reveal the intrinsic stress hysteresis of NiTi shape memory alloy,we use decreasing strain cyclic stretch(the second tensile strain is less than the first),focusing on the effect of annealing temperature and pre-deformation on the intrinsic transformation stress hysteresis,at the same time focusing on the elastic deformation behavior of W nanoribbons in NiTi shape memory alloy matrix,the main research and contents and conclusions are as follows.In this paper,researching the effect of annealing temperature,pre-deformation and cool drawing on the intrinsic transformation stress hysteresis of super elasticity NiTi shape memory alloy.We found as follows:(1)with the increase of annealing temperature,the stress hysteresis of the intrinsic phase transformation is larger;(2)the greater the stress hysteresis of the intrinsic phase change with the increase of pre strain;(3)cool drawing deformation can increase intrinsic stress hysteresis.This paper also research cool drawing deformation effect on the size of W nanoribbons in NiTi shaper memory alloy matrix,the thermal stability of W nanoribbons and elastic strain limit of W nanoribbons.We found as follows:(1)With the increase of amount of cold deformation,W nanoribbons thickness decreases;(2)W nano has a good thermal stability in the NiTi memory alloy matrix,the heating process is not easy to grow up.(3)In the process of stress induced martensitic transformation,the W nanoribbons can realize the super large elastic strain limit,and the maximum is 3.2%.(4)The elastic strain limit increases with the increase of the thickness of the W nanoribbons,but the elastic strain is almost constant when the thickness of W nanoribbons is greater than 200 nm.