Formation of TiN films on biomedical NiTi shape memory alloy by PIIID

Abstract

TiN coatings with the characteristics of excellent corrosion and wear resistance, high hardness and good biocompatibility, have received much attention in biomedical applications. Plasma immersion ion implantation and deposition (PIIID) is a novel method that can not only ensure excellent bonding between the coating and underlying material, but also overcome the line-in-sight shortcoming. The aim of the present study is to deposit TiN coatings on the surface of Ti–50.6 at.% Ni alloy by the advanced PIIID method to improve the wear resistance and hardness of a NiTi alloy surface. Two process parameters, i.e. voltage, and flows of Ar and N 2 were varied in the present experiments. The chemical composition, mechanical and corrosion resistance properties of the samples were investigated using XPS, nanoindentation and electrochemical method. The XPS results showed that the flows of Ar and N 2 had a great influence on the composition of the TiN films. The hardness and elastic modulus of the TiN films increased with an increase of pulse bias voltage and reached a maximum value for films deposited at −20 kV when the flow rate ratio of Ar to N 2 was 2/1. The experimental results revealed that the film preparation parameters directly affected the microstructure of the TiN, and thus influenced the mechanical and corrosion properties of the NiTi alloy, open circuit potential (OCP) values of the specimens increased with the negative pulse bias voltage and reached its maximum value when the flow rate of Ar/N 2 was 2/1. Combined with the results of Tafel and anodic polarization curves, an excellent corrosion resistant TiN coating by PIIID technique could be obtained by varying the process parameters.