Three-Dimensional Quasi-Direct-Current Plasma Immersion Ion Implantation Into Biomedical Nickel–Titanium Shape Memory Alloy Rod

Near-equiatomic NiTi S-shape rods of 400 mm long, which are used for surgical correction of scoliosis, are treated by nitrogen plasma immersion ion implantation (PIII) to reduce leaching of harmful Ni ions into the human body. To accomplish this purpose, a TiN barrier is created by PIII on the S-shape bars using different experimental setups. Our results reveal that the special quasi-direct-current PIII process can improve the efficacy of the process. In this technique, the reliability is improved by using a grounded Al housing and stainless steel mesh surrounding the specimen. The color uniformity is improved, and the maximum applicable voltage can be increased with reduced arcing and minimal changes in the shape memory effects of the materials.