Structure and wear properties of NiTi modified by nitrogen plasma immersion ion implantation

NiTi shape memory alloy samples were plasma-implanted with nitrogen at voltages ranging from −10 to −40 kV. X-ray photoelectron spectroscopy results disclose the formation of gradient TiN layers which thicknesses and elemental in-depth distributions depend on the applied voltages. The effects of the implantation voltages on the wear characteristics were investigated by pin-on-disk tests. In the initial period of our friction test, the implanted samples exhibit low friction coefficients compared to the untreated sample. The wear resistance of the plasma-implanted NiTi samples increases with implantation voltages and decreases with the applied loads. Our results reveal that the wear mechanism of the implanted samples is adhesive-dominant under low applied loads but becomes abrasive-dominant at high applied loads.