Effects of pulsing frequency on shape recovery and investigation of nickel out-diffusion after mechanical bending of nitrogen plasma implanted NiTi shape memory alloys

Nickel–titanium shape memory alloy bars were treated by nitrogen plasma immersion ion implantation at 50 and 100 Hz to investigate the effects of pulsing frequencies on the shape recovery ability. The shape recovery of the treated and untreated control samples was assessed using bending tests. It was found that the 50 Hz sample retained the same shape recovery ability similar to the untreated control sample but the 100 Hz sample could not return to the original shape. Immersion tests in simulated body fluids on the bent-and-recovered bars show that the amount of Ni leached from the treated NiTi bars was 18.2% of that of the untreated control samples. The results show that the nitrogen plasma treatment is effective in impeding the out-diffusion of nickel even after extensive shape deformation.