Reduced tribocorrosion of CoCr alloys in simulated body fluid after nitrogen insertion

Tribological studies in air and simulated body fluid (SBF) after surface modification by nitrogen plasma immersion ion implantation of medical CoCr alloys were compared. The PIII treatment temperatures were varied between 390 and 570 °C. Subsequent wear measurements in air exhibit reduced wear rates for the PIII treated specimens. In SBF, a minimum wear rate was observed for a process temperature near 400 °C. For higher PIII temperatures, fretting corrosion leads to an elevated cobalt ion release. Apparently a weakened chemical bonding of cobalt as well as chromium immobilization caused by the nitrogen insertion and a subsequent reduction of passivating oxide layer causes the selective high Co ion release for samples with high process temperatures. A compromise for the PIII treatment temperature must be found as the minimum particle release rate does not correspond to the minimum Co ion release rate.