Study On Laser Cladding Of CNTs/SIC/Ni Based Composite Coating Based On Mechanical Alloying

The brake material of high-speed train is facing severe challenges,such as instantaneous high temperature,heavy load and high speed.The existing iron based materials can not meet the requirements of modern transportation tools.Surface engineering technology is expected to solve this problem.Mechanical alloying mixed composite powder was used in this test,CNTs/SiC/Ni based composite coatings were prepared by laser cladding.The effects of the mechanical alloying process parameters on the dispersion and protection of carbon nanotube in composite powder were studied.The composition ratio of nickel base superalloy was optimized by orthogonal experiment.The effect of laser process parameters on the microstructure and properties of the composite coating are both explored.The main results are drawn as following:?1?The CNTs/SiC/Ni based composite powder is evenly dispersed by mechanical alloying.The carbon nanotubes are mainly embedded in the softening layer on the surface of nickel spheres,and formed a dense protective film with the powder,which ensures the integrity of carbon nanotubes in the composite coating.?2?With the amount of 1.6g Al,0.4g Co,18.5g Cr,0.6g Ti,4g Mo,the hardness of composite coating is the highest and the amount of wear is the lowest,so it is the best of the powder proportion.With the increaseing of cooling rate,the precipitation of Laves phase decreases greatly,the Mo elements are mainly concentrated in the Laves phase,while Ti and Al elements are the main components of precipitation strengthening phase.?3?The CNTs/SiC/Ni based superalloy composite coating materials with no pores and excellent properties were prepared by laser cladding.When the laser power is 900W and scanning speed is 360mm/min,the microstructure of CNTs/SiC/Ni-based composite coating forms equiaxed crystal,dendritic crystal,cell crystal and planar crystal structure from top to bottom,with the minimum wear loss of 0.0019g and the highest hardness of 400HV_0.2.The hardness is 2 times higher than the substrate,while the wear loss is only half of that of the substrate.The single-track multilayer hardness changes with a gradient,the maximum hardness of about 650HV_0.2,3.2 times higher than the substrate.?4?Carbon nanotubes are insoluble in austenite.They disperse mainly in the composite coating in the way of dispersion strengthening.The strength and toughness of coatings are enhanced.The tendency of porosity and microcrack in composite coating were reduced.?5?By introducing?as the ratio of the friction coefficient to the wear volume,the numerical relationship between the friction coefficient and the wear volume is numerically expressed.With the increase of?value,the wear resistance of the material becomes better.