علی شانقی

Plasma immersion ion implantation is one of the common methods to enhance the corrosion resistance, mechanical properties, and biological characteristics of NiTi alloys. Herein, the nano-mechanical behavior and distribution of compressive and tensile stress of NiTi alloy samples modified by carbon plasma immersion ion implantation (C-PIII) are analyzed by atomic force microscopy (AFM), nano-indentation test, and finite element method (FEM) simulation. C-PIII produces a modified layer with a thickness of 48 nm. The average surface roughness decreases from 34.023 to 25.180 nm and the hardness and Young’s modulus increase to 80.7 and 21.8%, respectively, after C-PIII. FEM simulation reveals that elastic and plastic deformation similar to that observed experimentally arises from the increase in strength and changes in the surface phases stemming from C-PIII. The larger Young’s modulus and hardness of the C-PIII sample reduces the penetration depth and plastic strain during nano-indentation resulting in a decrease of the compressive residual stress by 46% from –0.619 to –0.313 GPa at the tip of the indenter. Our results show that the durability and service lifetime of NiTi alloys can be improved by C-PIII thus boding well for biomedical applications in harsh environments such as blood vessel stents and bone joints.