Improved in vitro corrosion resistance of a NiTi alloy by high current pulsed electron beam treatment

A coarse grained NiTi alloy was subjected to high current pulsed electron beam (HCPEB) irradiation. The treatment induces superfast melting, evaporation and solidification at the top surface layer. As a result of selective evaporation of Ni, the Ti content was increased in the melted layer. The surface melted layer resolidified into a 600 nm fine grain austenite (B2) structure. A martensitic phase transformation occurred in the subsurface zone due to the high thermal stress and shock waves induced by the HCPEB treatment. This transformation was avoided in the top surface melted layer due to the grain refinement which stabilized the austenite. Corrosion performance in the simulated body fluid was effectively improved after the HCPEB treatment under evaporation mode, which could be mainly attributed to the selective evaporation effect and the reduction of precipitates in the surface layer.