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 degrees C for 15 h in a gas mixture of 98 vol.-% H-2 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 carburised 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 degrees 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 degrees 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.