Abstract
In this research, the influences of applied strain during repeated heat-treatment under constrained strain on critical stress for inducing martensite (σ_M), recovery stress (σ_A) and plastic strain of Ti-Ni shape memory alloy (SMA) (deliverability, conformability and scalability of SMA stent) was investigated by tensile tests with constant strain condition and amplitude tests. The chemical composition of the alloy is Ti-50.4at%Ni. The condition of repeated heat-treatment under constrained strain was in the following; the heat-treatment condition is 773K for 181ks, the applied strain in each heat-treatment is varied from 8 to 13.3%, and the total applied strain is 40%. From the results of tensile tests, the σ_M increases with increasing applied strain. On the other hands, the plastic strain has a minimum at 13.3%. Therefore, the deliverability decreases with increasing applied strain. However the scalability is improved by the increasing applied strain. In the case of amplitude tests, σ_M and σ_A shows a maximum at 13.3%. However regardless of applied strain, σ_M almost becomes constant (200MPa) when the number of cycle is above 500. Meanwhile, variation of σ_A of each sample is a little during amplitude tests.
