The Changes of Surface Texture Parameters of the Duplex Systems: Nitrided Layer – Coating at CoCrMo Alloy

Abstract

CoCrMo alloys have been used for biomedical implants for a number of years. One of the important parameters which influences durability of the coating and thus whole implant are parameters of surface texture, namely Ra and Rt, which are determined by standards ISO 7206-2:2011 and ISO 7207-2:2011. Three duplex surface systems were applied to improve mechanical properties. The combination of plasma nitriding and subsequent deposited thin films of the nACo3®, DLC and ZrN were used as a duplex treatment. Plasma nitriding was implemented under these conditions: duration time 10 hours, the ratio of gases H2:N2=3:1, process temperature 450 °C, 500 °C and 550 °C. The surface texture parameters were measured on the polished surface of the CoCrMo alloy at first, then on the polished surface after plasma nitridation process and finally on the polished surface of deposited coating. It has been demonstrated that deposition of the selected coatings on the nitride surface influences the surface texture parameters Ra and Rt.