| High-speed railway brake disc is an important factor to ensure the safe operation of high-speed railway.During the operation of high-speed railway,the main failure modes of brake disc are wear and thermal fatigue.Therefore,in order to improve the hardness and wear resistance of brake disc,increase its effective life and reduce costs,laser cladding technology is used to coat or repair the surface of brake disc.In this experiment,Ni60A alloy powder was cladded on 20CrNiMo steel by single factor experiment.In order to find out the optimum process for multi-channel cladding,the effects of different laser processing parameters on the macro-morphology,micro-structure and hardness of the cladding layer were investigated.The corrosion resistance and wear resistance of the cladding coating and the uncoated matrix were analyzed and compared.The results show that there are more cracks when the laser power is small in single cladding.With the increase of laser power,the melting width,melting height,melting depth,contact angle and dilution rate of the coating increase correspondingly;with the increase of scanning speed,the melting width,melting depth and melting height decrease,dilution rate increases,contact angle increases first and then decreases;with the increase of powder feeding speed,the probability of crack occurrence increases.Additionally,the melting width,melting height and contact angle of the coating increase,and the melting depth and dilution rate decrease.Laser processing parameters have an important impact on the microstructure and hardness of the coating.With the increase of laser power,the plane crystal width at the interface increases,the secondary dendrite spacing increases,the microstructure in the coating gradually becomes coarse from fine,and the microhardness of the coating decreases.With the increase of scanning speed,the plane crystal width increases,the secondary dendrite spacing increases first and then decreases,and the coating microstructure becomes thicker and the microhardness decreases.With the increase of powder feeding speed,the plane crystal width at the interface decreases,and the secondary dendrite spacing also increases first and then decreases,the coating microstructure becomes smaller and the microhardness increases.It is concluded that the optimum technological parameters are laser power of 2 kW,scanning speed of 350 mm/min and powder feeding rate of2 r/min.Under this parameter,the coating mainly consists of?-Ni,?-?Ni,Fe?based solid solution,and some phases such as M23C6,Ni-Cr-Fe,Ni3B,FeNi3,NiC,FeNi,etc.The dilution ratio of the coating interface to the top of the coating becomes smaller and smaller.The electrochemical test and wear performance test were carried out after multi-pass lapping under the optimum process parameters.The self-corrosion potential of the cladding coating is-0.808 V,the self-corrosion current density is 4.608×10-6 A·cm2,the self-corrosion potential of the uncoated matrix is-0.974 V,and the self-corrosion current density is 9.183×10-5A·cm2.It can be seen that the corrosion resistance of the cladding coating is obviously better than that of the uncoated matrix.At room temperature,the wear loss of uncoated matrix is larger,and the wear resistance of cladding coating is more than ten times of that of matrix.The main wear mechanism of uncoated matrix is adhesive wear,and the main wear mechanism of cladding coating is abrasive wear.At high temperature,the wear weight loss of uncoated matrix and cladding coating decreases,and the friction coefficient decreases accordingly.In general,the wear resistance of the cladding coating is much higher than that of the uncoated matrix. |
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