Improving the wear resistance of NiTi shape memory alloy thin films by nitrogen and carbon ion implantation

Annealed NiTi thin films (~51.2~at.%Ni) were implanted with carbon and nitrogen ions with 80~keV energy and 3~10¹⁷ cm^-2 ion dose. X-ray photoelectron spectroscopy confirmed the existence of implanted ions in the surface structure of the films. Atomic force microscopy showed an increase of roughness and decrease of grain size after ion implantation. Grazing incidence X-ray diffraction showed the formation of new phases in the films such as TiN, Ti₂N, TiC and different kinds of oxides. Nanoindentation and nanoscratching tests revealed the improvement of wear behaviour of NiTi thin films after ion implantation via increasing nanohardness (3.1-6.2 and 7.3-GPa after carbon and nitrogen ion implantation, respectively) and decreasing of scratch coefficient (0.22-0.18 and 0.17 after carbon and nitrogen ion implantation) and wear depth.