Study On Tribological Properties Of Surface Texture And Coating Modified Stainless Steel Surface

Friction and wear is one of the common failure modes of metal materials.Wear not only causes resource and energy waste,but also brings security risks,environmental pollution and other problems.Based on these,it is of great significance to study the tribological behaviors of metal materials for developing national economy and environmental protection.In this paper,the grooved textures with different parameters were processed on 304 stainless steel(304SS)surface by laser surface texture(LST)machining technology.The friction and wear behaviors the textured samples were investigated under dry and oil-lubricated conditions.In addition,the comprehensive modification consisiting of PTFE coating and surface texture was employed to improve the tribological behaviors of the 304 SS substrate.By conducting experimental research,characterization and simulation,the following conclusions could be drawn.(1)The textured groove samples with varying widths and distances were prepared and their tribological properties were investigated by reciprocating wear tester under dry condition.It was found that the friction coefficient of the textured samples increased slightly as compared to the untextured surface under the high load of 20.0 N.As the applied load was 5.0 N,the friction coefficient of the textured samples was reduced by 10 % ～ 15 % compared to the untextured sample.The textured groove samples presented superior wear resistance.The groove sample with a width of 100 μm and a spacing of 100 μm had the lowest wear rate,which was reduced by 56 % when compared to the untextured one.By analyzing the morphology of the wear tracks,it could be inferred that the grooves could act as the “outlet” of the wear debris.The “outlet” reduced the accumulation of the wear debris and improved the wear resistance.(2)The textured samples with different groove depths were prepared and their tribological behaviors were studied by reciprocating wear tester under PAO6 lubricated condition.The results showed that the groove depth significantly affect the tribological properties of the textured samples.The sample with groove depth of 10 μm exhibited the minimum friction coefficient about 0.10,which is reduced by 60 % compared to the untextured surface.The samples with groove depth of 20 ～ 30 μm presented the friction coefficient of 0.30 ～ 0.40 at the initial stage.As the groove depth reduced to 10 ～ 15 μm due to the rubbing action,their friction coefficients were changed to be around 0.1.By CFD simulation analysis,it was found that the wedge effect of lubricating oil would generate lift force during the sliding process.The shallow groove provided larger lift force feedback.However,deeper grooves would result in the backflow phenomenon during the sliding process.The backflow weakened the wedge effect and led to the reduction of the lift force,corrponding to the increase of the friction coefficient.(3)PTFE coatings were prepared on the groove textured surface and the untextured surface on stainless steel substrate by spin-coating method,and the tribo-tests were carried out under different loads.It was found that the groove texture greatly improved the load-carrying capacity and anti-wear life of the PTFE coating.Then untextured surface worn out after sliding for 0.5 h,as the load was increased over 5 N.As expected,the PTFE coating on the texture surface could maintain very low and stable friction coefficient and didn’t fail for a long time rubbing,even though the applied load was increased more than 50 N.(4)The mGO/PTFE composite coatings were prepared on the groove textures by simple spin-coating method.Effect of the loading of mGO on the tribological properties of the mGO/PTFE composite coating on textured surface was evaluated.To improve the dispersion level of GO in PTFE,silane coupling agent A151 was employed to modify GO for preparing the modified GO(mGO).Reciprocating tribo-tests showed that modified mGO/PTFE coating exhibited good tribological properties.Compared with the pure PTFE coating,the friction coefficient of the composite coating with 1.0 wt% mGO was reduced by nearly 40 % at a load of 1 N and by 25 % at a load of 10 N.It was also found that mGO significantly improved the structural integrity and wear resistance of the composite coating.