Improvement of wear resistance for carburised steel by Ti depositing and plasma nitriding

In order to improve the wear resistance of carburised M50NiL steel, the surface layer was deposited with Ti coating by magnetron sputtering and then plasma nitrided for 2 h with hollow cathode equipment. The influence of nitriding temperature (750, 800 and 850°C) on microstructure and mechanical properties of the coating were investigated. Results show that the coating of specimen 750 containing Ti-based-nitrides possesses higher nanohardness (13.769 ± 0.738 GPa) than the carburised layer (7.695 ± 0.338 GPa) and the load bearing capacity reaches 18 N due to the supporting carburised layer. The friction coefficient and wear rate of the specimen 750 decrease 23.1 and 72.2%, respectively, compared with the carburised specimen. The hardness and wear performance of the specimen 800 and 850 were underestimated by traditional test criterion because a loose and porous a′ _C(N) layer was formed on the surface due to sputtering effect of steel hollow cathode.