The Study Of Shape Memory Properties And Physical Mechanical Properties Of TiNiNb Shape Memory Alloys

This paper aims at the requirement of the engineering application of TiNiNb SMA, and the requirement of computer simulation technology in phase transformation processing of SMA pipe-connector. It unfolds these studies about several aspects thereinafter:1. Metallic thermal physics properties of SMA are measured in different temperature range. It includes specific heat, thermal diffusivity, thermal conductivity and so on in need of computer simulation study.2. The study of influencing mechanism on the relationships among phase transformation of SMA, temperature, stress and time.3. The affection of heat treatment to shape memory properties and mechanical properties of alloys.We make use of these advanced testing technology including laser flash method, DSC method, SEM and X-Ray diffracting technology, and make over controlling temperature system that have very good controlling temperature precision for measuring recovery stress between high temperature and low temperature, and design liquefied nitrogen refrigeration system and so on examination arms.Through measuring thermo physical properties, experiment indicates that thermal diffusivity, specific heat, and thermal conductivity increase with temperature increasing from 30℃ to 300℃. average linear swell factor of Ni-Ti-Nb alloy is about 11.43 X 10~-6 per centigrade.We proposed the equation to calculate the recovery stress during heating under constraints. Experiment indicates that the recovery stress σrmof alloys is decreasing with pre-strain increasing, and The movement tide of the recovery stress σrmof alloys is rising initially and declining finally with temperature of pre-strain increasing from-90 ℃ to-30℃.We find that the change of two heat treatment methods between non-vacuum heat treatment and vacuum heat treatment do not affect the recovery stress σrm, but the recovery stress σrm of cold-drawing alloys is the highest than the other two. The recovery stress σrm is increasing with recovery temperature increasing in different recovery temperature ranges. Experiment indicates that the higher the pre-strain is, the greater the influence of deformation temperature on the shape recovery ratio is, the higher martensitic anti-transformation As' temperature is.The shape recovery ratio of alloys with non-vacuum heat treatment is the same as the one with vacuum heat treatment. The shape recovery ratio of cold-drawing alloys is the highest than the other two. Based stress relaxation's curves, we analyzed that the phenomena on stress relaxation of alloys may not happen from 10T? to 50°C, resist- stress relaxing properties is excellent, and it has good engineering applicative foreground.Experiment indicates that, through measuring mechanical properties, the stress curves of alloys of restricting recover haven't the evident yield band, and the stress o02of alloys of restricting recover is higher than the ones of alloys of non-restricting recover, but the stress ab of alloys of restricting recover is lower than the ones of alloys of non-restricting recover. We find that the stress ob and o02 of cold-drawing alloys are the highest than the other two (non-vacuum heat treatment and vacuum heat treatment), but its stretch ratio is lowest than the other two. With cold-drawing treatment or non-vacuum heat treatment, its stretch ratio that is about 15% to 17% can't satisfy the require of engineering application, but the method of vacuum heat treatment can prevent oxidation effectively, its stretch ratio arrive at 36% around and is perfect.The yield stress of the recovery samples after pre-strain are higher than the ones of these original samples at 20°C,100°C and 200°C, and the stress curves of these recovery samples haven't the evident yield band. With temperature increasing the stress ob of these samples under different states are increasing. The critical yield stress is increasing with increasing temperature and that the range of transformation hystersis is wide makes for engineering application. Above Mss temperature (Mss ^60°C ), the critical yield stress is decreasing with increasing temperature, and shape memory properties is decreasing with increasing temperature.