Progress in surface modification of NiTi shape memory alloy

The near-equiatomic NiTi shape memory alloy was a functional material with unique shape memory effect, superelasticity and good corrosion resistance. However, Ni⁺ released from NiTi during the long-term corrosion in human body liquids can cause the risks of allergy, inflammatory and cancerogenic reactions. The research progresses on surface modification of NiTi shape memory alloy by oxidation, plasma and coatings in recent years were reviewed. The aim of the modification was to modify the naturally generated oxide on the surface of NiTi alloy and form a new stable surface with enhancing corrosion resistance, suppressing the release of Ni⁺ and thus improving the long-term biocompatibility. The advantages and disadvantages of these surface modification methods were summarized. Finally, the main research directions in the future of surface modification on NiTi were proposed.