Tribological behavior and mechanisms of graphite/CaF2/TiC/Ni-base alloy composite coatings
(College of Field Engineering, PLA University of Science and Technology, Nanjing 210007, China)
Abstract: In order to reduce the friction coefficients and improve the wear resistance of mechanical parts, which work in the severe friction and wear conditions at heavy loads, the graphite/CaF2/TiC/Ni-base alloy composite coatings were prepared by plasma spray and their tribological behavior and mechanisms were investigated. The results show that the friction coefficients of the composite coatings are in the range of 0.22-0.288, which are reduced by 25.9% to 53% compared with those of the pure Ni-base alloy coatings, and the wear rates of the former are 18.6%-70.1% less than those of the latter. When wear against GCr15 steel balls, a transferred layer mainly composed of ferric oxides, graphite and CaF2 may gradually develop on the worn surface of the composite coatings, which made the friction and wear between GCr15 steel ball and the composite coatings change into that between the former and the transferred layer. So the friction coefficients and the wear rates of the composite coatings are greatly reduced because of the solid lubrication effect of the transferred layer. The main wear mechanism of the composite coatings is delamination of the transferred layer in friction process.
Key words: plasma spray; composite coatings; Ni-base alloy; graphite; TiC; CaF2; tribology