Micro-Abrasive Wear Testing of Surface Engineered Surgical Grade CoCrMo Alloy for Biotribological Applications

Wear of metal-on-metal hip joints is a concern due to the toxicity and biological reaction of wear debris. Retrieved CoCrMo hip implants have shown that abrasive wear is the predominant failure mechanism in such joints. There have been some efforts to improve the wear resistance of joint implants through the application of hard biocompatible ceramic coatings. However, the adhesion of the coatings has been a concern. The aim of the present work was to study the wear resistance of surface engineered CoCrMo alloy intended for biotribological applications by means of an abrasive wear test, based on the ball-crater technique. Different surface conditions were obtained on surgical grade wrought CoCrMo alloy: plasma nitrided, physical vapor deposition (PVD) coated (monolayer CrN and multilayer (TiN/CrN) x 3) and modified using duplex surface engineering technology (a combination of the two previous approaches: plasma nitriding followed by plasma assisted PVD). The engineered surfaces were characterized by scanning electron microscopy, nanoindentation and, atomic force microscopy (AFM). Scratch test was used to determine the influence of the duplex technology on the adhesion of the coatings to substrate. The wear resistance of the different surface conditions was determined using a slurry abrasive micro-abrasion testing device. It was found that the duplex engineering technology enables a significant rise in the resistance of surfaces against concentrated loading modes, improving the adhesion of the coatings to the substrate; however, it has no significant influence improving the wear resistance of the samples during the abrasive wear tests.