Electrochemical Behaviour of PACVD TiN-Coated CoCrMo Medical Alloy

Abstract

CoCrMo alloys have been used in hip replacements for many years, and their properties can be enhanced with hard coatings. The TiN layer can be deposited on a CoCrMo alloy to its improve corrosion properties, such as reduction of the release of potentially harmful metal ions from CoCrMo-based surgical implants. In this work, a medical grade CoCrMo alloy was coated with TiN by means of plasma-assisted chemical deposition from the vapor phase (PACVD) technique at 500 °C for 4.5 h. The TiN/substrate interface and thickness of the TiN layer were analysed by scanning electron microscopy (SEM). Corrosion parameters Ecor, Rp, and Icor were determined via direct current (DC) and alternating current (AC) electrochemical techniques. The SEM analysis showed a highly dense and quite uniform TiN layer, with a thickness of 2 µm. The results obtained by the DC electrochemical methods show better corrosion stability of the TiN/CoCrMo samples in comparison with CoCrMo in 0.9% NaCl at (25 ± 1) °C and (36 ± 1) °C. The electrochemical impedance spectroscopy (EIS) results show that there are nuclei on the TiN coating which reduce the corrosion stability.

Keywords

• cobalt-chromium alloy
• TiN
• PACVD
• electrochemical testing
• scanning electron microscopy