Abstract
In this research, the influences of applied strain during repeated heat-treatment under constrained strain on fatigue characteristics of Ti-Ni shape memory alloy (SMA) for stent was investigated. 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 18ks, the applied strain in each heat-treatment is varied from 8 to 13.3%, and the total applied strain is 40%. The fatigue test for the specimens is rotary bending test and carried out at the 310K (bodily temperature). The bending strain range during fatigue test is varied from 1.0 to 5.0%. The fatigue life of the specimen heat-treatment under constrained strain is slightly lower than that of initial state. In addition, the differential of the fatigue limit between the specimen heat-treatment under constrained strain and the specimen of initial state is little. Meanwhile, the fatigue limit of each specimen is improved by the surface preparation, and the differential of fatigue curve between the specimen heat-treatment under constrained strain and the specimen of initial state is disappeared by the surface preparation. However, the effect of the surface preparation decreases with increasing of bending strain. This tendency is caused by the differential of crack initiation, which is caused by the variation of bending strain.
