Study On Antifriction And Wear Resistance Of Bearing Steel Modified By Coating-Texture Composite

After quenching and low-temperature tempering,GCr15 bearing steel has high hardness,homogeneous microstructure,good abrasion resistance and high contact fatigue performance,so it was widely used in the manufacture of bearing balls,rollers,mould and other mechanical parts,that require high abrasion resistance,high elastic limit and high fatigue strength.In mechanical field,frictional and wear would reduce the stability and reliability of mechanical system and it was also an important cause of energy waste and loss.Therefore,improving the anti-friction and wear resistance of GCr15 bearing steel surface through surface treatment was of great significance to improve the service life of mechanical systems.The combination of surface texturing technology and surface coating technology provided a new idea for improving the friction and wear performance of the GCr15 bearing steel surface.This paper uses the Babbitt coating to construct a coating-texture composite surface on the GCr15 bearing steel surface,that not only improved the machining quality of laser surface texturing but utilizes the gaps of the Babbitt coating as a secondary texture for the benefit of storing oil and abrasive particles,thereby improve surface tribological properties.A 2D simulation model of micro-dimples textured lubrication area was created.The influence of cross-sectional shape,depth-diameter ratio of micro-dimples texture,and relative motion velocity on hydrodynamic effect was analyzed.The optimal micro-dimples texture with best lubrication performance was obtained,providing a theoretical basis for designing and machining of micro-dimple texture.The simulation results show that the existence of microdimple texture can generate hydrodynamic effect and increase load-bearing capacity of oil film.When the micro-dimple texture cross-sectional shape was triangular and the depth-diameter ratio was 0.3,the micro-dimple texture had the best load-bearing capacity of oil film,and the fluid dynamic pressure generated by the micro-dimple texture was positively correlated with the fluid velocity.A thin Babbitt coating was arc-sprayed on GCr15 bearing steel substrate surface.Picosecond fiber laser was used to process micro-dimple texture on the surface of the coated specimens under the Babbitt coating mask.The influence of laser processing parameters on the micro-dimple texture morphology was explored by changing the processing power and scanning times.Finally,the micro-dimple texture with a cross-sectional shape of approximately triangular and a depth-width ratio of 0.3 was machined by power of 6.92 W and 10 scanning times.Compared with processing directly on GCr15 bearing steel substrate(CA=71°),the coatedtexture composite surface has higher hydrophobicity(CA=127.49°),which was more conducive to forming a stable dynamic pressure lubricating oil film.The laser surface texturing also improved the hardness of the Babbitt coating,thereby enhancing its load-carrying capacity.In addition,the Babbitt coating improved the laser ablation efficiency.Under the same power,the depth of the micro-dimple texture processed by laser under the coating mask was better than that directly ablated on the GCr15 bearing steel substrate.Friction and wear tests were performed on processed specimens to analyze the variation of friction coefficient and wear morphology.Investigating the friction and wear properties of specimens with different treatment states(untreated surface,only machined coating surface,only textured surface,and coated-textured composite treated surface)under different working conditions with oil lubrication.The results showed that,under oil lubrication conditions,a 15%area density exhibited the best wear resistance performance.Increasing the axial load would increase the wear rate of the workpiece.The surface with a coating-texture composite treatment exhibited the lowest wear rate and more stable friction coefficient due to its good ability to store oil and abrasive debris,that reduced the contact fatigue wear and abrasive wear mechanisms.Although simulation results showed a positive correlation between speed and hydrodynamic pressure,in actual working conditions,with the increasing of speed,the lubricating oil would centrifuge off the contact surface of the friction pair.The oil storage capacity of the GCr15 bearing steel surface with only texture processing decreased with the increasing of speed,leading to rapid degradation of the friction coefficient under high-speed conditions of 0.8 m/s.However,the surface with a coating-textured composite treatment had better oil storage performance due to the secondary texture on the surface of the Babbitt coating,and the main micro-dimples texture produced by laser surface texturing,which facilitated the formation of a stable oil film.