Wear of UHMWPE against nitrogen-ion-implanted and NbN-coated Co–Cr–Mo alloy formed by plasma immersion ion implantation and deposition for artificial joints

NbN thin film was deposited on the Co–Cr–Mo alloy by plasma immersion ion implantation and deposition (PIII&D) to reduce the volume wear rate of UHMWPE. In addition, nitrogen ions were implanted on the surface of the Co–Cr–Mo alloy prior to the NbN film deposition in order to increase the hardness of the substrate. XPS analysis revealed that nitrogen ions were implanted into the surface of the Co–Cr–Mo alloy, leading to the formation of CrN and Cr2N. The UHMWPE volume wear rate was measured using a pin-on-disk tribometer. The wear test result showed that the volume wear rate of UHMWPE against NbN-coated Co–Cr–Mo alloy declined by 20% as compared to that in the untreated Co–Cr–Mo alloy. In addition, the UHMWPE wear rate against the nitrogen-ion-implanted and NbN-coated Co–Cr–Mo alloy could be drastically reduced by up to 48%. It can be concluded that a combination of prior nitrogen ion implantation and NbN coating via PIII&D is a promising surface treatment tool for extending the lifetime of metal-on-polymer artificial joints.