Effects of Nitrogen Ion Implantation on Microhardness and Surface Roughness of Ti-6al-4v Eli Medical Alloy

Abstract

Total Knee Replacement has been under development for over 50 years. Its primary objectives are for normal articulation of a diseased joint, to relieve pain and restore function. Over the years three main surgical types of alloys have been used: 316L stainless steel, titanium and cobalt-chrome based alloys. Titanium, despite its superior biocompatibility, closest to bone’s Young’s modulus and lack of nickel in its composition, has poor resistance to wear. This major disadvantage of titanium alloys is the reason for which their use in load bearing prostheses is limited. Various methods of surface modifications have been investigated in order to improve wear performance by improving mechanical and tribological properties of medical grade titanium alloys. In this work, the effect of nitrogen ion implantation on micro- and nano-hardness and surface roughness of medical grade titanium alloy (Ti6Al4V ELI) has been investigated, and compared to those of unimplanted Ti6Al4V ELI, cast and wrought CoCrMo alloys. Due to the formation of a smooth and hard nitride layer on the surface of the ion implanted Ti6Al4V ELI alloy significant improvement in micro- and nano-hardness was achieved. This hardened layer is thought to improve the wear resistance of Ti-based alloys and hence can maximise their use for more demanding prosthetic applications.