Electrical discharge machining characteristics of nickel-titanium shape memory alloy based on full factorial design

Among many shape memory alloys, nickel-titanium (NiTi) alloys are popular due to their superior properties in shape memory effect and superelasticity. They are presently often used in microengineering and medical technology especially in orthopedic and orthodontic implants due to their specific properties. In this study, the electric discharge machine characteristics of NiTi shape memory alloys have been fully investigated by full factorial design. Analysis of mean showed that the material removal rate of NiTi in the electric discharge machine process significantly related to the electrodischarge energy, involving the pulse current and pulse duration. Many electrodischarge craters and recast layers were observed on the electric discharge machine surface of NiTi samples. In addition, there was no significant difference between copper (Cu) and tungsten-copper (W-Cu) electrodes in material removal rate but work stability of W-Cu electrode was longer. On the contrary, quantity of impurity on the surface of the Cu electrode was lower. The specimen's hardness near the outer surface could reach 1200 Hv, which originated from the hardening effect of the recast layer. Here, the microstructure, composition, and hardness of electric discharge machine surfaces are also discussed.