Research Microstructure And Properties Of Mo₂C/Co-based Alloy Composite Coating On Stainless Steel By Laser Cladding

Aimed at stainless steel surface modification, Mo2C/Co-based compo-site coating were fabricated on409L stainless steel by laser cladding with10kw CO2laser. The processing parameters and proportion of alloy powder were optimezed, the coating were obtained with an excellent formability and performance. The composite coating was investigated by optical micro-scopy (OM), scanning electron microscop (SEM) and attachment (EDS), X-ray diffraction (XRD). Utilize micro-hardness tester, wear and tear test machine and electrochemistry corrode system to analyze microhardn-ess,hard-wearing and corrosion-resistant performance.The optimal processing parameters of laser cladding were as follows: laser output power P=3.2～3.8kw, laser scanning speed V=8mm/s, and beam diameter D=5mm. The coating without pores and crscks were obtained, and excellent metallurgiccal to matrix, which was composed of heat affected zone, fusion area and clad layer. With the distance incressed to fusion area, the microstructure began to more and more small and present transition characteristion of plane crystal�'columna�'crystal�'dendrite. Besides, the content of Mo2C had significant effect on the microstructure of Mo2C/Co-based composite alloy powder. When the content of Mo2C was less than or equal to40%, the microstructure were consisted of dendrite (γ-Co) and eutectic ((Mo,Cr)23C6、(Mo,Cr)7C3and Mo2C) and when greater than or equal to60%, the cladding layer was mainly mechanism of fusion and to separate out about Mo2CThe laser cladding compound layer of Mo2C/Co-based performance analysis indicate detailed to not firm to dissolve strengthen,second phase strengthen and grain refinement, the microhardness, wearability and corrosion-resistant performance had improved. Microhardness (1212～1371HV0.2) of laser cladding were raised by541～603%than substrate (195HV0.2) under the best craft parameters. In friction and wear experiment, the wear mechanism of coating was mainly abrasive wear, and friction coeffi-cient, wear rate had decreased with different extent,which attributed to hard phase effectively burthened load to restrain plastic deformation. The abras-ion resistance had improved. In the electrochemical corrosion, the anodic polarization curves existed active region, activate-passivate region and passivated region in lmol/L H2SO4electrochemical corrosion.The409L stainless steel had repeatedly activate-passivate transformation, which result in high corrosion tendency. The logip was adopted as evaluation parameters of corrosion resistance. The result of corrosion resistance were as follows:20%wt (Mo2C)>40%wt (Mo2C)>0%wt (Mo2C)>60%wt (Mo2C)>409L stainless steel. In order to research the pitting resistance performance, it utilized circle anode polarization curve in3.5wt%NaCl solution. The value of Eb about Mo2C/Co-based composite coating were higher than substrate. When the cotent of Mo2C was20percentage, the pitting resistance performance of coating improved and the value of (Eb-Ep) and relative Enveloping Area was minimum.