| With the continuous development of modern machinery manufacturing industry,especially precision equipment,the requirement of wear resistance and noise reduction service performance of parts is getting higher and higher.Crankshaft(QT500-7 material)is an important transmission part of compressor.It forms friction pair with connecting rod,which converts the rotational motion of motor into linear motion of piston and provides compressive force.It is of great economic value and social significance to improve the wear resistance of the contact interface between crankshaft and crank friction pair,prolong service life,increase compression ratio and reduce working noise for the production of high-end compressors.Copper and copper/graphite coatings have been widely used in precision friction pairs with anti-wear and self-lubrication due to their excellent self-lubrication properties.In this paper,copper,copper/graphene composite modified coatings were prepared by in-situ synthesis,and the wear resistance/friction reduction properties were investigated.In this paper,nano-CuO layer was pre-coated on the surface of the workpiece during gas nitriding surface modification treatment,and nano-copper was obtained by in-situ reduction of hydrogen decomposed in the furnace.The surface nitriding treatment of the matrix was realized by active nitrogen decomposed in ammonia,thus nano-copper/microalloyed composite surface modification layer was obtained.The copper-graphene composite surface modification layer was prepared by introducing graphene into the copper layer,optimizing the coating method of nano-CuO slurry and adjusting the process parameters of gas nitriding.The microstructures of the samples were analyzed by OM and FESEM,the composition and phase analysis of the infiltrated layer were carried out by EPMA and X-ray diffractometer,and the hardness distribution of the modified layer and the bonding strength of the composite layer were tested by microhardness tester,friction tester and scratch test,and the mechanical properties were evaluated.Further small batch processing of crankshaft products of QT500-7 was carried out.The effects of nitriding temperature,time,microstructure and phase on lubrication and friction reduction mechanism were systematically studied through crankshaft bench life testing machine,which provided theoretical basis and technical support for accurate size control and friction reduction and self-lubrication of crankshaft.The results show that:(1)The nano-copper oxide particles with a diameter of 18.7 nm were pre-coated on the surface of the samples by hand.The thickness of the nano-copper layer prepared on the surface of nodular cast iron under gas nitriding at 530℃ for 3 h was 5μm,the bonding force was between 40 and 50N,and the surface microhardness was 650 HV0.05.(2)The crankshaft bench test results show that the wear mechanism is mainly abrasive wear and adhesion wear.The porous nano-copper layer can store debris and transfer copper layer on the surface of the grinding couple crank to reduce friction.(3)Graphene was introduced into nano-copper.The mass ratio of nano-CuO to graphene was 50:1.Copper/graphene composite modified layer was obtained.The thickness of the modified layer was 1-2 μm,and the binding force was 60-70 N greater than that of single nano-copper layer.The reason was that the addition of graphite increased the bonding between copper layers.(4)The bonding force of nano-copper layer on 42CrMo surface is much greater than that of nodular cast iron.The bonding force between copper layer and compound layer is reduced to a certain extent due to the existence of carbon pits on the surface of nodular cast iron.The preparation method of surface nano-copper is suitable for wear-resistant and self-lubricating modification of other materials,and has a good industrial application prospect. |
PDF Full Text Request