Selective surface oxidation and nitridation of NiTi shape memory alloys by reduction annealing

The current investigation aims in understanding the effect of short-term (300 s) annealing of NiTi shape memory alloys (SMAs) in a reducing atmosphere of N2–10% H2. The influence of temperature on the resulting surface morphology and chemistry is elucidated. On annealing at 600 °C, the surface is covered with a thin layer of titanium oxide, which is 7.5 nm thick, while at 800 °C, the surface is covered with a golden-yellow layer of TiN of thickness more than 100 nm. The surface analysis carried out by XPS on the specimen annealed at 800 °C confirms the formation of TiN and more notably, the surface is devoid of Ni.