Comparative Study on the Friction Property of Bearing Steel Modified Bygraphite/MoS2 Composite Coating and Manganese Phosphate Coating

Surface modification is an important method to improve the contact fatigue life of transmission parts. The preparation of high performance coating with good tribological properties on the gears and bearings has become the research trends. This paper presents graphite/MoS2 composite spray and manganese phosphate conversion coating prepared on the AISI52100 steel surface and investigates their anti-fatigue mechanism. The tribological properties of the modified layers were studied using a SRV-IV multifunctional friction and wear tester. The microstructure and interfacial components of the coating and wear surfaces were analyzed by SEM and EDS, respectively. The surface morphology and phase composition of the coating were evaluated through laser 3D microscopy and XRD analyses, respectively. Both modified layers showed good anti-friction and anti-wear properties. The friction coefficients of the surfaces modified by manganese phosphate coating and graphite/MoS2 decreased by 7 % and 14 %, respectively, and the corresponding extreme pressure properties increased by 11 % and 55 %, respectively. But the mechanism of anti-fatigue wear and the corresponding interfacial phenomena of the surface modification of the graphite/MoS2 composite spraying layer is different from those of manganese phosphate coating. The hard-ceramic particles with graphite and MoS2 are sprayed on the substrate to obtain the surface hardening layer, resulting in higher wear resistance. The graphite and MoS2 modified layer can greatly reduce the friction coefficient and improve the lubrication performance on the surface. Manganese phosphate coating serves as a chemical soft coating and is filled with rough corrugated caused by surface processing, which induces an ideal meshing surface after initial friction phase. The obtained hole-shaped structure and "infiltration" role contribute to the storage of lubricants and thus improves the lubrication performance.