Study On Friction And Wear Properties Of 24CrNiMo Powder Laser Cladding Layer On High Speed Train Brake Disc

The material of high-speed train brake discs requires excellent mechanical properties,low wear rate,and high and stable friction coefficient.Using laser cladding technology to prepare a laser cladding layer on the surface of cast steel brake discs can strengthen the surface of the brake discs and improve their wear resistance.The powder composition and heat treatment process both affect the performance of the 24CrNiMo laser cladding layer.Therefore,this study uses a combination of pin disk experiments and scaled inertia experiments to explore the effect of powder composition on the friction and wear performance of the laser cladding layer.After determining the optimal powder composition according to relevant standards,the optimized powder composition is used to prepare the laser cladding layer and undergo heat treatment,Explored the effect of heat treatment on the friction and wear properties of the optimized powder laser cladding layer,and conduct tensile performance testing on the laser cladding layer after heat treatment.Firstly,different mass fractions of TiC,WC,and Cu powders were added to the24CrNiMo powder to prepare a laser cladding layer and conduct microstructure analysis and performance testing.The results show that the grain morphology in the laser cladding layer is mainly composed of dendrites and equiaxed grains;As the mass fraction of TiC increases,the microstructure of the laser cladding layer gradually refines.The addition of TiC has a fine-grain strengthening effect on the laser cladding layer,increasing microhardness.As the mass fraction of WC increases,the grain arrangement becomes more and more regular.The fishbone-like structure generated in the laser cladding layer is W₂C and intermetallic compounds,which have a solid solution-strengthening effect on the laser cladding layer.However,excessive WC addition reduces the quality of the laser cladding layer,and the microhardness first increases and then decreases.With the increase of Cu mass fraction,the dendrite structure is elongated,the Cu-Ni solid-solution phase and Cu phase in the structure increase,and the microhardness presents a downward trend.Secondly,pin disk experiments were conducted on laser cladding layers with different powder components,and the optimal content of each component was selected for scaled inertial friction and wear experiments.The results show that as the TiC mass fraction increases,the wear amount of the laser cladding layer first decreases and then increases,and the worn form is abrasive wear;The overall friction coefficient of the pin disk experiment shows a downward trend;The laser cladding layer with a TiC content of 15 wt.%had friction coefficients of 0.17,0.19,0.23,and 0.22 in various stages of the scaled inertia experiment,and a wear amount of 0.92 g.When the addition amount of WC is less than 25 wt.%,the wear amount and friction coefficient of the laser cladding layer decrease with the increase of the additional amount,and the worn form is abrasive wear;When the addition amount is 25 wt.%,the wear amount increases and the worn surface undergoes fracture.The wear forms are adhesive wear and fatigue wear,and the friction coefficient also increases;The laser cladding layer with a WC content of 20 wt.%has friction coefficients of 0.15,0.15,0.21,0.20,and a wear amount of 0.80 g in various stages of the scaled inertia experiment.As the mass fraction of the Cu element increases,the wear amount of the laser cladding layer gradually increases,and the wear form changes from abrasive wear to adhesive wear;The friction coefficient of the pin disk experiment gradually increases;The laser cladding layer with a Cu content of 6 wt.%had friction coefficients of 0.29,0.30,0.38,and 0.36 at various stages in the scaled inertial experiment,and the wear amount was 1.6 g.Among the three powder components,the friction coefficient of the laser cladding law yer prepared by adding 6 wt.%Cu powder is closest to the relevant technical standards where the friction coefficient is between 0.3 and 0.5 when braking at different speeds.Finally,the laser cladding layer with a Cu content of 6 wt.%was subjected to a heat treatment of 860℃quenching for 0.5 hours+400℃,550℃,and 650℃tempering for 1 hour,and friction,wear,and tensile properties was tested.The results show that the grain size of the laser cladding layer increases with the increase of tempering temperature,and the grain boundaries gradually disappear;When the tempering temperature is 400℃,the microstructure is tempered troostite,and at 550℃and 650℃,it is tempered sorbate;The microhardness during tempering at 400℃,550℃,and 650℃is 340,318,and 280 HV_0.5,respectively;The wear amount increases with the increase of tempering temperature,and the main form of wear is adhesive wear;The friction coefficient of the pin disk experiment gradually increases.After 860℃quenching and 550℃tempering heat treatment,the friction coefficients of the Cu laser cladding layer in each stage of the shrinkage inertia experiment are 0.31,0.33,0.42,0.40,and the wear amount is 1.9 g,which is lower than the wear amount of the cast brake disc matrix.The tensile strength is 1060 MPa,and the elongation is 9.4%,meeting the technical standards.The research results indicate that TiC and WC can effectively improve the wear resistance of laser cladding layers,but will reduce the friction coefficient;The addition of Cu will increase the friction coefficient of the laser cladding layer.The laser cladding layer with the addition of 6 wt.%Cu can be quenched at 860℃and tempered at 550℃for heat treatment,ensuring the laser cladding layer’s mechanical properties and wear resistance while obtaining a friction coefficient that meets relevant technical requirements.This provides technical support for strengthening the surface of the brake disc using laser cladding technology.