Wear and corrosion properties of in-situ grown zirconium nitride layers for implant applications

Abstract

Zirconium (Zr) and its alloys are considered as promising materials for implant applications due to their excellent biocompatibility. However, the poor tribological properties of Zr are limiting its widespread applications. Therefore, in this investigation thermal nitriding of laser processed Zr was carried out with an aim to improve its wear and corrosion properties for potential wear resistant implant applications. The influences of nitriding temperature and time on the nitride layer thickness, phase constituents, wear and corrosion properties of nitrided Zr layer were studied. The Zr samples were nitrided at 600°C and 800°C for 2 and 6h in flowing nitrogen. The results demonstrated that the nitriding temperature had relatively stronger influence on the nitride layer thickness, wettability, hardness and wear resistance than nitriding time. In general, the nitride layers found to contain ZrN and ZrO2 as major phases and Zr2N and Zr7O8N4 as minor phases. The nitride layer thickness increased from 5±0.7μm to 26±5μm with increase in the nitriding temperature and time. Nitriding also enhanced the wettability and passivity of Zr. The samples nitrided at 600°C for 2h resulted in noblest Ecorr of −130mV vs SCE with Icorr of 0.001μA/cm2 in Hank's balanced salt solution. Lowest in vitro wear rate of 4.4×10−7mm3/N·m was recorded, against Al2O3,when the samples were nitrided at 800°C for 6h, which is 93% lower than that of pure Zr. These results demonstrate that thermal nitriding of Zr can be used to increase the corrosion and wear resistance of Zr in physiological environment.