Work hardening influencing on shape memory effect of NiTi alloy by varying milling speeds

Nickel-titanium (NiTi) shape memory alloys (SMA) are widely being used as medical implants due to their excellent shape memory effect (SME) and super-elasticity (SE). The medical implants such as artificial knee joint are usually fabricated by mechanical milling operations. However, the work hardening generated during milling process affects the SME of NiTi alloy. There is requirement to study the effect of milling on the SME of NiTi alloy. The influence of milling parameters on SME of NiTi alloy is investigated by analyzing the effect of milling speed on work hardening in this research. It is found that work hardening decreases before 200 m min−1 cutting speed, but increases rapidly after 200 m min−1. And the change tendency of SME is contrary to that of work hardening. SME is reflected by the recovery rate of residual strain, and the difference of residual strain recovery rate is distinct under various milling speeds. Most of all the recovery rate of 200 m min−1 is obviously higher than those of other milling speeds. The plastic deformation in milling process is serious which weakens the SME when the work hardening becomes larger. Considering the comprehensive influence of milling speed on SME and work hardening induced by machining process, the 200 m min−1 milling speed should be selected.