Microstructure And Properties Of Ni-based Self-lubrication Coatings By Laser Cladding/Friction Stir Processing Abstract

The preparation of KF-2-WC-CaF₂ Ni-based self-lubrication coatings were studies on the surface of 6061 aluminum alloy by laser cladding and laser cladding/friction stir processing?FSP?respectively.Optical microscope?OM?,scanning electron microscope?SEM?,energy dispersive spectrometer?EDS?and X-ray diffraction?XRD?were used to analyze the phase constituents and microstructure of the coatings,and the micro-hardness distribution and wear properties of the coatings were also analyzed.The optimized laser cladding parameters for Ni-based self-lubricating coating are laser power of 2500W,scanning speed of 600mm/min and spot diameter of 3mm.The surface of Ni-based self-lubricating coating is smooth.Smooth and good metallurgical bonding zone is formed between the coating and the substrate.There are a small number of pores in the KF-2 nickel base coating.With the increase of the mass percentage of WC,the number and diameter of pores of KF-2-WC Ni-based coatings increased.CaF₂ diminished the porosity of coatings,but did not remove them.The main phase constituents of the laser cladding Ni-based self-lubricating coating consist of?-Ni,?-Al,Al₃Ni,Al₃Ni₂,WC,W₂C and CaF₂.The microstructure of the coating is dendrite,cell crystal,columnar crystal and equiaxed crystal.With the increase of WC and CaF₂ particle content,WC spherical particles,W₂C plane crystals and reorganizations with WC core appear.The micro-hardness of KF-2 Ni-based coating is about 200HV_0.1.With the increase of WC,synergistic combination of dispersion density of WC spherical particles and irregular shape W₂C plane grain,the micro-hardness of the coating increased,but fluctuated,average 500HV_0.1,is 8 times of the substrate.The existence of CaF₂,the micro-hardness curve of coating decreased,but tended to be stable,and exerted the excellent abrasion resistance under the room temperature,friction coefficient is about 0.3.There are no pores and cracks in Ni-based self-lubricating coatings prepared by laser cladding and implantable FSP.After three times stir,uniform onion rings are distributed on the coating surface.The main phase constituents of the coating consist of?-Ni??-Al?Al₃Ni₂?Al Ni₃?WC?CaF₂.Density of microstructure distribution of shoulder deformation zone?SDZ?increased because of?connection and filling?structure under the stirring head shoulder"extrusion and wear"function.Implant particles of friction stir zone?FSZ?are broken and refined under the effect of the pin?extrusion and upward spiral transmission?function and?embedded?coating,and coating?coated?implant particles.There are multiple cell crystal growth phenomena in the thermo-mechanically affected zone?TMAZ?,and in the heat affected zone?HAZ?,the cell crystal boundary precipitated the?-Al flocculate tissue.The micro-hardness of laser cladding/friction stir processing Ni-based self-lubricating Coating Prepared is significantly higher than that of direct laser cladding.The micro-hardness of KF-2-WC-CaF₂ coating is about 600HV_0.1.Because the pin"squeeze+upward spiral conveyor"mechanical action makes the particles in the bottom of FSZ lower dispersed,and particle density decreased.With the increase of distance between coating and the stirring head,the mechanical effect gradually weakened,the micro-hardness curve and the friction coefficient showed a gradient feature along the thickness direction.However,the friction coefficient of the coating is lower than the direct laser cladding during the early period of wear test.