Study On Composition And Microstructure And Wear Resistance Of Copper-based Friction Material

Copper-based powder metallurgy friction materials are made of copper matrix,reinforcement components,lubrication components and friction components,manufactured by powder metallurgy process.Because of the sample manufacturing process,at the same time,both having excellent thermal conductivity,high temperature resistance of metal and wear resistance of ceramic,leading to the copper-based powder metallurgy friction materials have become the main research direction in the field of braking friction materials.However,at present,there is still a certain gap between domestic copper-based powder metallurgy braking friction materials and abroad on usability.Therefore,in order to explore the differences of compositions,microstructures and properties between existing domestic copper-based powder metallurgy braking friction materials and abroad,this paper is focused on the comparative analyses of compositions,microstructures,micro-hardness and wear resistance under different applied loads and sliding speeds of two kinds of copper-based powder metallurgy braking friction pads produced abroad,and a domestic copper-based powder metallurgy braking friction pad.Synthesizing respective characteristics and advantages,the composition optimization design and materials preparation were carried out,meanwhile,the high temperature wear resistance performances were analyzed.The results are as follows:（1）The main components of three kinds of domestic and external copper-based friction pads are all matrix of copper-tin alloy,iron,graphite and ceramic（ZrSiO₄）,but there are significant differences in content.The foreign copper-based friction pad 2 and domestic copper-based friction pad are mainly composed of copper matrix,while,the content of copper matrix in foreign copper-based friction pad 1 is the least,iron,graphite and ceramic are the most.The porosity and micro-hardness of copper matrix of foreign copper-based friction pad 2 are the highest,followed by foreign copper-based friction pad 1,the microstructure of domestic copper-based friction pad is compact relatively,but the micro-hardness of copper matrix is the lowest.The applied loads range from 20⁸0 N,at medium and high load of 40⁸0 N,foreign copper-based friction pad 1 is more suitable.The sliding speeds range from 30²10 mm/min,domestic copper-based friction pad is more suitable for high sliding speed of210 mm/min.（2）Optimized composition system of copper-based friction material is 67%copper matrix,13%iron,3%zinc,5%graphite and 12%ceramic phase.Copper-based friction materials were prepared by powder metallurgy route,sintering process specification is:820℃sintering,20 MPa sintering pressure,holding time1 h.The porosity of sintering samples is low,and the wear resistance is better under different applied loads.The wear resistance of sintering copper-based friction materials with different copper-tin ratio were analyzed,and it is found that the wear resistance performances under different applied loads is better when Sn/（Cu+Sn）is 9%.（3）At the test condition of 25℃,250℃,350℃and 450℃,friction and wear test were carried out on homemade copper-based friction materials,and compared with foreign copper-based friction pad 1.The results show that the surfaces color of samples deepened gradually with the increasing of experimental temperature,and the oxidation products changed.At high temperature,the main oxidation product of copper matrix is Cu₂O rather than CuO.The oxidation products of metallic iron change with temperature,and the iron oxidation products of different samples are different at the same temperature,generally,they all change from Fe₂O₃ to Fe₃O₄.In the range of250⁴50℃,the high temperature oxidation resistance of composition optimization of copper-based friction material sample is better.The optical microstructures and three-dimensional morphologies of worn surfaces at high temperature were analyzed.It is found that the main wear mechanisms of homemade copper-based friction material sample are abrasive wear and oxidation wear,the adhesive wear is lighter than foreign sample 1.Meanwhile,the wear rates are lower relatively of homemade sintering copper-based friction materials samples,showing excellent high temperature wear resistance performances.