Tribological and corrosion testing of surface engineered surgical grade CoCrMo alloy

One of the main causes of hip prostheses failure is the premature wear of its components. Wear of metal-on-metal joints is a concern due to the toxicity and biological reaction of wear debris and metallic corrosion. The main aim of the present study was to investigate the tribological and corrosion behavior of surface engineering CoCrMo alloy. Different surface conditions were obtained on surgical grade wrought CoCrMo alloy: plasma nitrided (520 °C by 7 h at gas mixture of 10% N2 + 90% H2), PVD coated (monolayer CrN and multilayer (TiN/CrN) × 3) and modified using duplex surface engineering technology (a combination of the two previous approaches: plasma nitriding followed by plasma assisted PVD). Surfaces were characterized using scanning electron microscopy, nanoindentation, AFM and scratch test. The tribological response of the different surface conditions was studied by means of a ball-on-disc testing machine. Potentiodynamic polarization measurements were done to determine the corrosion rate. Ringerʹs solution was used as lubricant and electrolyte during the tribological and electrochemical tests, respectively. It was found that the duplex engineering technology enables a significant rise in the resistance of surfaces against concentrated loading modes (evaluated by scratch method); however it has no significant influence in the tribological performance of the samples during wear tests. PVD multilayer (TiN/CrN) × 3 coatings showed the higher wear and corrosion resistance whereas CoCrMo nitrided sample showed the lowest.