Study On Laser Cladding C_f-Ni/FeCoCrNiCu High Entropy Alloy Composite Coating

In the era of rapid development,the demand for train is increasing,the speed of train running is faster and faster,and the requirement of train brake disc is getting higher and higher.Laser cladding technology can not only improve the surface performance of brake discs,but also retain the original performance.It is one of the ideal methods for remanufacturing brake discs.In this paper,C_f-Ni and C_f-FeCoCrNiCu coating was coated on45#steel by laser.The study was mainly on carbon fiber surface modification,composite powder milling,laser power of composite coating was studied.Through the analysis of the microstructure of the composite coating,the hardness,friction coefficient,wear rate and carbon exploration fiber reinforcing mechanism of composite coating,the conclusions can be drawn as following:(1)During the purification process of carbon fiber,with the increase of purification time,the sizing agent and impurities on the surface of carbon fiber were gradually dissolved,and the ravine structure and functional group increased.When the purification time is 6h,the purification effect of carbon fiber is the best.The existence of ravine structure increases the bonding force between carbon fiber and nickel sphere.The increase of oxygen-containing functional groups improves the surface energy and the wettability of carbon fibers and therefore the carbon fibers distribute uniformly on the surface of nickel spheres.However,due to the existence of nickel layer on the surface of nickel coated carbon fiber,it has better dispersion in nickel powder,resulting in none agglomeration of nickel coated carbon fibers,and in the process of ball milling,nickel coated carbon fibers are evenly distributed in nickel powder.Compared with nickel coated carbon fiber reinforced nickel based composite coatings,the purified carbon fiber reinforced nickel based composite coating does not exist in the latter,and the microstructure is refined.Therefore,the nickel coated carbon fiber is more advantageous than the purified carbon fiber in laser cladding.(2)In the C_f-Ni composite coating,when the laser power is 1000W,the dilution rate and the powder utilization ratio of the composite coating are the best,and the average grain size of the composite coating is about 50?m.At this point,the nickel coated carbon fiber can effectively avoid carbon fiber damage.Under the influence of the Marangoni effect,carbon fiber flows in the molten pool.However,there are vacancies in the grain boundary,which leads to the existence of grain boundary in the grain boundary,which not only achieves grain refinement,but also makes the performance of the composite coating best.However,the hardness of C_f-Ni composite coating is relatively low(~181HV),which can not meet the requirements of high strength and high wear resistance of train brake discs.High entropy alloy has high strength and high thermal stability.It may be one of the ideal materials for train brake discs.(3)Instead of Ni base coating,the C_f-FeCoCrNi Cu high entropy alloy coating was prepared by laser.It was found that the grain size of the composite coating increased with the increase of laser power.When the laser power is 1000W,the dilution and powder utilization of the composite coating are the best,the size of the columnar crystal of the coating is about 8?m,and the size of the equiaxed crystal is about 5?m.It is known from EDS that carbon fibers exist in the grain boundary.This is because the Marangoni effect making the surface material from the centre to the edge of the pool,and the pool of materials and low flow to the surface.The movement of carbon fibers is mainly dependent on the convective effect.There are defects such as dislocations and vacancies on the grain boundary,and carbon fibers are trend to exist in these defects.However,carbon fiber and Cu do not dissolve,so that there is no segregation of Cu.The enthalpy of carbon fiber and Cr is small.Both of them give priority to the formation of chromium carbide and distribute along the grain boundary.The addition of carbon fiber does not change the phase of the coating,and the coating is still FCC phase,and with the increase of laser power,the peak of the FCC phase shifts to the right.Meanwhile,when the laser power is 1000W,the performance of the composite coating is the best,with the hardness of 271HV,the friction coefficient of 0.546 and the wear pit area of 0.00367mm~2.