Study Of Plasma Spraying And Laser Cladding Wear Resistant Coating Of EA4T Axle Steel

With the development of China's railway to high-speed and heavy-load direction,the higher requirements of the safety and reliability of railway rolling stock have been put forward.The axle is a key component of train operation,due to the alternating bending load in wheel seat during the train operation,It is easy to cause wear and tear,until failure.So to improve its wear resistance by the surface treatment technology to ensure high-speed trains long-term safe operation is of great significance.As the most commonly used and effective techniques of surface strengthening,plasma spraying and laser cladding technology can successfully prepare various coatings to improve the wear resistance and corrosion resistance of the components?In this paper,pure Mo coating and Fe-based alloy coating were successfully fabricated on EA4T steel to improve its wear resistance.The composition,phase,hardness,elastic modulus,bonding strength and wear resistance were carried out in the present study.The pure Mo coating was successfully prepared on the EA4T steel surface by plasma spraying.The microstructure of the thermal sprayed Mo coating was compact and dense.The coating porosity was about 7.5%and the phase was only pure Mo.The average hardness of the Mo coating was 400.2 HV0.2,which is much higher than the hardness of the substrate.Due to the presence of pores in the coating,the distribution of the hardness and elastic modulus of Mo coating is discrete.Therefore,the Weibull distribution is used to analyze the results,and the results show that the hardness and elastic modulus of the coating are subject to Weibull distribution,Weibull distribution factor m represents the uniformity of the coating,the coating hardness Weibull distribution curve is y=12.44x-75,and the elastic modulus fitting curve is y?15.58x-188.86.The average bonding strength of plasma spray Mo coating is 27.09MPa,and all the samples are broken at the interface surface between the coating and substrate.The friction coefficient under the loads of 50N,100N and 150N was 1.05,1.02 and 0.93 for the plasma sprayed Mo coating,and 1.58,1.27 and 1.04 for the EA4T steel.The wear weight loss of the Mo coating was only one-tenth of the base material.The wear type of the coating and the base material is adhesive wear.After the hot pressing treatment,the microstructure of Mo coating is more compact than the sprayed coating,the porosity decreased by 8.8%?25.1%.The phase composition of the coating did not change,still pure Mo phase.The hardness,elastic modulus of Mo coating increased slightly,and the distribution are more uniform.The adhesion strength of the treated Mo coating was improved by 6.2%?18.4%compared with the sprayed coating.The adhesion strength increased with the increase of hot pressing temperature and pressure.In addition,the fracture mode does not change before and after the hot pressing treatment.The hot pressing treatment improved the wear resistance of the coating,and the wear resistance of the coating increased with the increase of the temperature and pressure.Laser cladding Fe-based wear-resistant coating on EA4T steel surface presented a good formability under different parameters.The dilution rate increased with the increases of laser power and scanning speed,and decreased with the increasing of delivery powder rate;the hardness of laser cladding Fe-based wear resistant coating decreased with the increases laser power,and increased with the increases of scanning speed and delivery powder rate;Orthogonal experiment shown that the best laser cladding parameters are the laser power of 1600W,the scanning speed of 280mm/min and the powdering voltage is 4.4V.The order of importance of each parameter to the performance of laser cladding Fe-based wear-resistant coating is powder feeding voltage>laser power>scanning speed.There were no cracks,inclusions and other defects in multi-lap coat coating micro structure.Meanwhile,the bottom structure of the coating is a columnar crystal microstructure,the middle and upper part is composed of the cell dendrites.The phase components of the coating are mainly ?-Fe,Fe-Ni and Ni-Cr-Fe alloy;the addition of W,Ni,Cr contributed to the high hardness and good wear resistance of the coating.The friction coefficient of the Fe-based coating under the load of 50N,100N and 150N were 1.21,1.08 and 0.96.less than the coefficient friction of EA4T material.The weight loss of the Fe-based coating was much less than the base material,the wear type of the Fe-based coating is slight adhesive wear.