Study On The Brake Disc Composite Coating Of CNTs/SiC/Ni60A Superalloy By Laser Claddingi

Vehicles for high-speed and heavy load have become inevitable trend of modern traffic tools while the traditional iron brake disc cannot meet the instantaneous high temperature performance of the modern conveyances brake disc, which seriously hindered the development of conveyances tools.The laser cladding composite coating of CNTs/SiC /Ni60 A superalloy used in brake disc in this paper is much important. And the effects of ceramic-metal ingredient and laser processing parameters on microstructure, interface dilution,tribology properties and microhardness were investigated systemly. The following conclusions are obtained:(1) Due to the poor wettability of CNTs, a electroless nickel plating process was used to modify the surface of CNTs. The results show that many functional groups such as carboxyl(-COOH) and hydroxy(-OH) were obtained on the surface of CNTs after mixed acid purification, which improves the dispersion of CNTs in the electroless plating liquid. When the stabilizer NH4 Cl was 35g/L, with the increase of solution temperature, the content of Ni increases and then decreases. When the temperature was 85°C, the coating of Ni was optimum and the mass fraction of Ni was 69.05%. The layer from Ni-P into Ni3 P after heat treatment can make the layer more smooth and dense.(2) With the increase of SiC content, the microstructure of SiC/Ni60 A upper coating is refined obviously, the wear resistance,friction coeffient and microhardness have peak value.When the SiC mass fraction is 20%, the wear resistance of the cladding coating is the best one,which is only 1/36.3 that of the matrix; the minimum friction coefficent is 0.464, the friction process is most stable,the mighest microhardness is 1039HV0.2,which is 3.5 times that of the substrate.(3) With the increase of laser power, the scanning speed, the amount of feed powder and the overlapping rate, the composite coating have peak value. When the laser power is1800 W, the scanning speed is 180mm/min, the feed powder is 30g/min and the overlapping rate is 40%, the composite coating is fine, the content of cracks and holes is low and microstructure is fine. the highest microhardness and good wear resistance of coating is obtained and the worn mechanism of composite coating is adhesive worn and grain worn.(4) when the mass fraction of CNTs is 3%, the CNTs/SiC /Ni60 A alloy composite coating surface is smooth and the composite coating has a homogenous fine grain, the best wear performance is achieved. But when the mass fraction of CNTs is excess 3%, the CNTs will be reunited and the performance of composite coating will decline.