Study On Tribological Properties Of The Composite Coating Of The Engine Valve Mechanism

The research background is based on the valve-train engine, and it discussed around the worn phenomenon of cam tappet. Firstly, the reasons of the friction was discussed. Secondly, the movement and stress of the friction pair is analyzed. Thirdly, preparation of coating method is proposed to improve the wear resistance. Lastly, friction and wear test was been made, the wear mechanism was been studied, and the optimal composition was been determined.3D model was built, dynamic simulation and the motion analysis was completed. Simulation proved that the cam follower motion is smooth, and it does not have the phenomenon of "beat", which is affecting normal work. In the biggest stress position, stress was calculated and contact stress was compared with the material allowable stress. Due to the maximum contact stress of the position was greater than the allowable stress of material, accelerate wear phenomenon was appearing. The method of coatings was applied for surface treatment, Ni base coating and AlCr FeNi high entropy alloys coating were chose, and the theoretical calculation and finite element simulation of coatings were completed. Result shows that the maximum contact force on the position of the maximum contact stress on coating is less than the material allowable stress, thus the method of coating is feasible.AlCrFeNi high entropy alloy coating powder was fabricated in the method of mechanical ball milling. Microscopic characterization and phase structure of the high entropy alloys powder was studied. Result shows that powder has the solid solution with simple structure of BBC. The method of hot-pressing sintering was used to fabricate coating, and the micro-morphology of the coating was observed by SEM, and the formation mechanism of the coating was discussed. Results show that the microstructure of the coating is compact, and the ingredients is even. Coating bonding strength complies with the design standards, and the hardness is greatly increased by the coating.The Ni base coating powder was prepared, and it concludes Ni60, Ni60+15WC(wolfram carbide) and Ni60+35WC three composition coating powders. Hot-pressing sintering process was adopted to the coating preparation. Microstructure of the coating, and the bonding strength, surface hardness and other performance test were analyzed. Result proved that the Ni base coating which prepared by hot-pressing sintering has excellent performance, and the coating hardness is increased by WC. The coating bond strength declined, and all coatings comply with the design standards.Friction and wear test was designed. Test parameters was determined, the wear tests of substrate and coating were completed, abrasion resistance was calculated by the method of "weightless". The friction coefficient of comparative was analyzed. The microscopic characterization of the wear morphology was observed, the mechanism of friction and wear was researched, and the optimal coating was determined. Test results show that abrasion resistance of each components coating have great increased, in which the Ni60+15WC coating is the most outstanding in tribological performance.