Corrosion and corrosion wear behaviour of plasma carburised stellite 21 Co-Cr alloy

Low temperature plasma surface alloying with carbon (i.e. plasma carburising) of Stellite 21 Co- Cr alloy was conducted at temperatures from 400 to 500°C for 15 h in a gas mixture of 98 vol.-%H₂ and 2 vol.-%CH₄. The surface treated layers were characterised by XRD, SEM and microhardness tests. The corrosion and corrosive wear behaviour of the plasma carburized Stellite 21 Co-Cr alloy were studied respectively using electrochemical tests and well designed reciprocating wear tests in 3.5% NaCl solution. The results show that low temperature ((≤460°C) plasma carburising can improve the corrosion resistance of Stellite 21 alloy; the corrosive wear resistance of Stellite 21 can be enhanced by up to three times; and the best corrosive wear resistance is achieved at the highest treating temperature (500°C). The detailed studies on the wear tracks indicate that the corrosive wear process was dependent on the individual wear and corrosion, as well as the synergetic effect.