Study On Performance And Defects Improvement Of Laser Cladding Ni-based WC Coating By Vacuum Environment And Matrix Preheating

Laser cladding is an emerging surface modification technology,which can prepare a cladding layer with low dilution rate,good combination,high hardness and high wear resistance on the surface of the substrate.However,laser cladding has high input energy and short action time,and the pores and crack defects often exist in the prepared coating,which restricts the development and application of laser cladding technology.Therefore,it is very meaningful to study how to solve the porosity and crack defects in the laser cladding layer.In this paper,the optimal layer cladding was prepared under the preheating of the substrate and the vacuum environment by controlling the process parameters of the experiment by using the Rofin FL020 fiber laser through a test method.The improvement of substrate preheating and vacuum environment to improve the porosity and crack defects in laser cladding Ni-based WC coating was studied.The microstructure of the cladding layer and the distribution of each element in the longitudinal direction of the cladding layer were observed using SEM and EDS;The phase composition of the cladding layer was tested using XRD;The hardness,friction coefficient and abrasion resistance of the cladding layer were tested using a micro hardness tester and a multifunctional friction and wear tester.The test results show that the substrate preheating can effectively improve the crack defects in the coating.When the preheating temperature reaches 200 ?,the macro-cracks on the coating surface disappear,and the number of microcracks in the coating is also significantly reduced,but there are still obvious pore defects in the coating;the hard phase aggregation phenomenon inside the coating disappears,and the coating structure is more uniform;however,as the preheating temperature increases,the coating dilution rate increases,the dendrite structure in the coating becomes larger,and the improvement of the overall performance of the coating is not obvious.The vacuum environment can effectively reduce the porosity defects in the coating,but there are some obvious macroscopic cracks on the coating surface;the coating structure is uniform and compact,and the microstructure is fine cell crystal,columnar crystal and dendrites;the comprehensive performance of the coating is improved.significantlyThe results of the microstructure and performance test of the cladding layer show that when the vacuum environment is combined with the preheating of the substrate,the performance of the cladding layer is the best when the substrate is preheated at 200 ° C in a vacuum environment.There is no macro-crack on the surface of the coating,the micro-cracks inside the coating are obviously reduced,there is no obvious pore defects,and the microstructure of the coating is uniform and dense.The hardness of the coating can reach 724 HV,which is about 3 times of the hardness of the substrate,and the wear amount is 2.05×10-3mm3,the wear resistance is improved by about 58.6%.The observation of the wear scar morphology of the coating by SEM shows that the wear form of the coating prepared by preheating the substrate at 200°C in a vacuum environment is mainly abrasive wear.