Effect of N2 / Ar gas flow ratio on the deposition of TiN/Ti coatings on NiTi shape memory alloy by PIIID

TiN coating with a thin Ti intermediate layer was deposited on the NiTi shape memory alloy substrate using plasma immersion ion implantation and deposition technique. The effect of nitrogen to argon gas flow ratio on the surface characteristics, chemical composition and mechanical properties of the as-deposited samples were investigated. Atomic force microscopy analysis indicates that all the coatings exhibited island morphology and the average root mean square (RMS) values were determined to be 2.912, 4.152 and 4.227 nm for N2 / Ar ratios of 1 / 3, 1 / 2 and 2 / 3, respectively. The results of XPS and X-ray diffraction show that the chemical composition, phase composition and preferred orientation of the TiN coating varied significantly with the N2 / Ar gas ratio. Nanoindentation, scratch and wear tests results demonstrated that coatings deposited with N2 / Ar = 1 / 2 exhibited the highest hardness and elastic modulus, good adhesion strength and excellent wear resistance.