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% WS 2 coating and double-layer NiCrBSi-30 wt% WS 2 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% WS 2 coating compared to NiCrBSi-30 wt% WS 2 coating. The NiCrBSi-30 wt% WS 2 coating consists of γ-(Ni,Fe) solid solution, (Fe,Ni) 9 S 8 , Cr 7 S 8 and M 7 C 3 phases. The metal sulfide layer consists of γ-(Ni, Fe) solid solutions, Fe 3 S 4 , Cr x S y and M 7 C 3 phases. The double-layer NiCrBSi-30 wt% WS 2 coating is 4 mm thicker than the NiCrBSi-30 wt% WS 2 coating. The average microhardness values of NiCrBSi coating, NiCrBSi-WS 2 coating and double-layer NiCrBSi-WS 2 coating are 412.6 ± 15.2HV 0.3 , 383.9 ± 14.5HV 0.3 , and 368.6 ± 13.3HV 0.3 , respectively. The average coefficient of friction of the double-layer NiCrBSi-30 wt% WS 2 coating is 0.29, which is 37 % and 14.7 % lower than that of the NiCrBSi coating (0.46) and the NiCrBSi-30 wt% WS 2 coating (0.34), respectively. The wear rate of the double-layer NiCrBSi-30 wt% WS 2 coating is 1.51 × 10−5 mm3/(N·m), which is 47.6 % and 34.9 % lower than that of NiCrBSi coating (2.88 × 10−5 mm3/(N·m)) and NiCrBSi-30 wt% WS 2 coating (2.32 × 10−5 mm3/(N·m)), respectively. Therefore, double-layer NiCrBSi-30 wt% WS 2 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% WS 2 coating, which explains its lowest coefficient of friction and wear rate. • A metal sulfide layer was formed on top of double-layer NiCrBSi-30 wt.% WS 2 coating. • Formation mechanism and tribological behavior of metal sulfide layer were studied. • A more continuous lubricating film is formed on the metal sulfide layer, resulting in the lowest coefficient of friction(0.29) and wear rate(1.51×10-5 mm3/(N·m)). [ABSTRACT FROM AUTHOR]