In-situ synthesis and wear mechanism of Ni- based self-lubricating composite coating with a dense continuous metal sulfide layer prepared by laser cladding

The friction and wear of bearing cages, sealing rings and other transmission components working in harsh environments such as high vacuum and heavy load directly affect the operational stability and safety reliability of the equipment. Therefore, it is vitally important to improve the tribological properties of machine components. In this paper, NiCrBSi alloy coating, NiCrBSi-30 wt% WS2 coating and double-layer NiCrBSi-30 wt% WS2 coating were prepared on 38CrMoAl steel by laser cladding. The results show that a metal sulfide layer is formed on the double-layer NiCrBSi-30 wt% WS2 coating compared to NiCrBSi-30 wt% WS2 coating. The NiCrBSi-30 wt% WS2 coating consists of gamma-(Ni,Fe) solid solution, (Fe,Ni)9S8, Cr7S8 and M7C3 phases. The metal sulfide layer consists of gamma-(Ni, Fe) solid solutions, Fe3S4, CrxSy and M7C3 phases. The double-layer NiCrBSi-30 wt% WS2 coating is 4 mm thicker than the NiCrBSi-30 wt% WS2 coating. The average microhardness values of NiCrBSi coating, NiCrBSiWS2 coating and double-layer NiCrBSi-WS2 coating are 412.6 +/- 15.2HV0.3, 383.9 +/- 14.5HV0.3, and 368.6 +/- 13.3HV0.3, respectively. The average coefficient of friction of the double-layer NiCrBSi-30 wt% WS2 coating is 0.29, which is 37 % and 14.7 % lower than that of the NiCrBSi coating (0.46) and the NiCrBSi-30 wt% WS2 coating (0.34), respectively. The wear rate of the double-layer NiCrBSi-30 wt% WS2 coating is 1.51 x 10-5 mm3/ (N & sdot;m), which is 47.6 % and 34.9 % lower than that of NiCrBSi coating (2.88 x 10-5 mm3/(N & sdot;m)) and NiCrBSi-30 wt% WS2 coating (2.32 x 10-5 mm3/(N & sdot;m)), respectively. Therefore, double-layer NiCrBSi-30 wt% WS2 coating has the best wear resistance and friction reduction performance at room temperature. A more continuous lubricating film was formed on the surface of the double-layer NiCrBSi-30 wt% WS2 coating, which explains its lowest coefficient of friction and wear rate.