Preparation And Study On Tribological Properties Of Polyamideimide/Molybdenum Disulfide-based Composite Coating

Advanced technologies,such as miniaturization,direct injection and turbocharging,improve the engine performance significantly although the operating environment is deteriorated obviously.The high-speed reciprocating motion of pistons in the cylinder for a long time must cause serious damage to pistons.For this,this paper describes a method to reduce their surface friction factor and the wear between skirt and cylinder,and thereby prolong the service life of engine by covering lubricant coating on piston skit according to the determined fit clearance between the piston skirt and the skirt/cylinder.This paper describes the environment-friendly self-lubricating composite coating by adopting the scraped and staged heating and curing technology with water-based polyamideimide(WPAI)as binder and with molybdenum disulfide(MoS₂),carbon fiber(CF)and graphene oxide(GO)modified carbon fiber(CF-GO)as solid fillers.The coating performance test is carried out to determine the optimal mixing ratio in the preparation of high-performance composite coating,including study on its friction mechanism.First,the impact of the change in the contents of solid filler MoS₂ on the performance of MoS₂/WPAI composite coating is explored.And the results show that the lubrication effect is enhanced while the bonding effect of WPAI is deteriorated sharply with the increased MoS₂contents(10%,15%and 20%).According to the overall coating performance including roughness,hardness,adhesion and tribological properties,the MoS₂/WPAI composite coating features the optimum performance in case of the solid filler MoS₂contents of 15%.Its tribological properties are significantly improved due to the shear slip between MoS₂ layers to form a lubricating film on the wear trace surface of the coating,while the wear resistance of the coating is the average due to the poor bridging effect of the material itself,its softer material and cracks on the lubricating film under the action of contact stress.Secondly,the impact of the change in CF contents in fillers on the performance of CF/MoS₂/WPAI composite coating is explored.In order to obtain a good bonding effect of WPAI,the total mass fraction of solid fillers in the coating material is 15%.The results show that adding solid fillers CF and MoS₂ does not change the thermal degradation behavior of WPAI resin,but can rise its thermal decomposition temperature.As the CF contents in filler increases(0%,15%,20%and 25%),the roughness and hardness of the coating will increase,and the adhesion and tribological properties increase and then decrease.The composite coating has the optimum performance in case that the ratio between MoS₂and CF is 80%:20%.When CF is introduced in the coating,the hardness is increased and the wear resistance enhanced.CF and MoS₂ will generate a synergistic effect in the friction and wear process,further improving the tribological properties of the coating.Thanks to the excellent bridging properties of CF,there are no obvious cracks on the surface of the lubricating film,but some CF peeling pits may be found.Then,CF-GO multi-scale reinforcement is prepared by grafting GO onto the CF surface through the amidation reaction with silane as a coupling agent.The results show that GO is tightly adsorbed on the CF surface via chemical bonds,the CF-GO surface is rough,and the thermal stability is GO<CF-GO<CF.The thermal stability of the CF surface grafted with GO is reduced.Finally,the impact of CF-GO on the coating performance is explored by applying CF-GO in the composite coating with the filler ratio of MoS₂:CF-GO=80%:20%and comparing with performance in case of MoS₂:CF=80%:20%.The results show that the thermal stability of CF-GO/MoS₂/WPAI composite coating is lower than that of CF/MoS₂/WPAI composite coating,while same as the thermal stability test results of CF-GO and CF.Compared with CF/MoS₂/WPAI composite coating,CF-GO/MoS₂/WPAI features the reduced roughness and improved hardness,adhesion and tribological properties.As the interface between CF and WPI is poorly bonded,resin matrix is easily pulled out of the wear surface of CF under the action of contact stress,causing damage to the integrity of the lubricating film.But the interface between CF-GO and WPAI is tightly bonded,so resin matrix is not easily pulled out under the action of contact stress,and GO can be used to fill resin gap,so,the overall quality of the lubricating film is better.Further studies on the tribological behavior of the CF-GO/MoS₂/WPAI composite coating under different loads and sliding frequencies show that the friction factor of the coating is decreased and the wear rate increased with the load increased(10N,15N and 20N)at a sliding frequency 1 Hz;under a load of 10N,the change in the friction factor of the coating is small,the fluctuation of the friction factor curve increases and the wear rate is increased with the sliding frequency increased(1Hz,2Hz,and 3Hz).