Laser Surface Modification Of Copper-based Powder Metallurgy Friction Materials

Now heavy-load wet copper-based powder metallurgy (Cu-PM) friction material produced in china has some defects, for instance, lower friction coefficient, heavier wear, lower allowable heat-load value and so on. Thus, it can not meet the challengc of the new heavy-load transmission device. To solve the above problems, this paper presents a plan that laser surface modifying to the Cu-PM friction materials using the unique advantages of laser surface modification technology, which also is the innovation.In this paper, the investigating object is a heavy-load copper powder metallurgy friction plate produced in China now. and surfacc treated by Broad-bcam lascr. On the basis of the numerical analysis of temperature field and the basic technical study, the microstructure, hardness, density and the friction and wear characteristics of thc copper-based powder metallurgy friction material treated by laser surface transformation were systematically studied by means of SEM. TEM. EDS. XRD. microhardness tester, Brinell hardness tester as well as friction and wear tester. In the end, the performance contrast tests have bcen done between the laser-treated and untreated copper-based powder metallurgy friction plate using the wet clutch dynamic performance tester.Using the nonlinear transient heat conduction differential equations, the mathematical model of the laser surface heat treatment of copper-based powder metallurgy friction material has been established. And on the basis of heat physical processes analysis, the vertical section temperature distribution maps and surfacc tcmpcraturc distribution routes have been obtained, using the ANSYS heat simulation.The test results show that after the laser surface modification under the lascr power is 1.3k W and the scanning speed is 150ram/rain, the lattice parameters of Cu enlarge by 0.54%0, theα-Cu aggrcgatc occurs edge dissolvcd and the large aggrcgatcs ofα-Cu dismember to small mass, in theα-Cu aggregate nanocrystais is generated. And under thc abovc conditions, thc dcnsity of friction material incrcascs by 6%. the hardness increases by 12.7%, the wear resistant performance increases by 45%. the friction coefficient enlarge by 1%。The wet clutch dynamic performance tests show that after laser surface modification treatment, compared with original untrcatcd state, the static friction coefficient of copper-based powder metallurgy friction plates increased from 0.136 to 0.146. increased by 7.4%, the sliding friction cocfficient incrcascd from 0.065 to 0.071, incrcased by 9.2%. and the friction coeMcient is stable and less changes with speed. At the same time, the wear extcnt decrcases from 0.009mm down to 0.006mm, decreased by 33%, wear rate decreases from 6.49×10^-15m³/J to 3.27×10^-15m³/J. decreased by 49.6%. the wear rcsistancc improvcs obviously. And the allowable heat-load valuc increases from 3.33 to 4.67, increased by 40%. and the heat resistance has been markedly improved.In this paper, the changes above have bccn systematic analysis from microscopic and macroscopic view angles. Including theα-Cu aggregate edge dissolved mechanism. nanocrystals generated mechanism, sintcring densification kinetics mcchanism and friction wear of PM mechanism. The changes of microstructure is due to the composition complexity of PM and the heating and cooling rapidity of laser modification, and the changes of microstructure influence the changes of macroscopic performance.