Shape setting of superelastic TiNi wire by deposition of protective TiN coating

The release of nickel ions into biological environment is still the main obstacle to the widespread medical application of TiNi-based shape memory alloys. The authors developed a method of ion-plasma deposition of the bioinert titanium nitride coating through formation a barrier layer on the TiNi alloy surface, depleted in nickel with simultaneous shape setting of the TiNi wire. It is shown that titanium nitride coatings are characterized by low friction coefficient values (µ= 0,2) and act as a barrier layer on the Ti-50,8 at.% Ni alloy surface. The influence of thermal deposition allowed us to obtain TiN coatings with the required elastic force and functional properties of the product. The reverse martensitic transformation temperature and the optimal operating voltage (from 160 till 200 MPa) are achieved due to an appropriate selection of the deposition parameters.