Improvements of tribological properties of CrNiMo and CrCoMo alloys by nitrogen plasma immersion ion implantation

Alloys made of CrCoMo and CrNiMo are commonly used materials with UHMWPE (Ultra High Molecular Weight Polyethylene) as joint couple components in the orthopedic prosthesis. We have applied the plasma immersion ion implantation (PIII) to the samples made of these alloys to enhance their tribological properties and hence to make it possible to extend considerably their lifetime as joint components when implanted in humans. As a result, we obtained CrCoMo surface with 70% improvement in hardness and 10% in modulus of elasticity and CrNiMo surface with 250% improvement in hardness and practically no change in modulus. Peak nitrogen concentrations as high as 40% and 30% were achieved by nitrogen PIII for CrCoMo and CrNiMo, respectively. Formation of γN phases in CrNiMo sample was clearly seen by XRD.