Microstructure And Mechanical Properties Of Laser Fabricated Self-Lubricating Composite Coatings On 304 Stainless Steel

304 stainless steel is widely used in mechanical manufacture and petrochemical industries due to its good heat resistance,corrosion resistance and mechanical properties.However,304 stainless steel has low microhardness and poor wear properties,which restrict its applications as important tribological moving components.Basically,wear occurs on the surface of materials and components,fabricating high-temperature self-lubricating anti-wear composite coatings using laser surface alloying technology is one of the most economic and efficient ways to solve the problem.This paper was combined with the Natural Science Foundation of China(U1737112)and Natural Science Foundation of Hunan Province(2018JJ2677).Self-lubricating anti-wear composite coatings were prepared on 304 stainless steel by laser in-situ synthesizing with preplaced Ni-WS2-TiC powders.Friction and wear properties of composite coatings and 304 stainless steel substrate were tested by HT-1000 high temperature tribometer and MT-500 surface profilometer at 20,300,600 and 800?,respectively.The phase compositions,microhardness,microstructure and worn surface topographies of composite coatings were analyzed by X-ray Diffractometer(XRD),microhardness tester,scanning electron microscope(SEM)and energy spectrum analyzer(EDS),and the microstructure evolvement and wear mechanisms were discussed in the paper.Results indicated that under the laser power 1.8 kW,laser dimension 3×4 mm2 and scanning speed 4 mm/s,the coating has a good metallurgical bond with 304 stainless steel substrate without macroscopical cracks.The coating consists of Cr0.19Fe0.7Ni0.11 solid solution,Cr7C3/Fe2C reinforced phases and Ti2SC/CrS/WS2 lubricating phases.The microstructure on the upper of the coating is uniform and compact,yet the middle and bottom parts are dispersed.The average microhardness of coating is 302.0 HV0.5 and about 1.17 times than that of the 304 stainless steel substrate.Owing to the synergistic lubricating function of oxides(Fe2O,Cr2O3,TiO2,Cr2TiO5 and NiCr2O4)and lubricating phases(Ti2SC,CrS and WS2),the friction coefficient of coating is significantly reduced compared to the 304 stainless steel substrate at 300 and 600?,and the friction coefficient was 0.303 and 0.351 at 300 and 600?.From 20? to 800?,the wear rates of coating were lower than that of the 304 stainless steel substrate due to the combined effects of Ti2SC/Cr7C3/Fe2C reinforced phases,and the coating possesses the lowest wear rate(9.70×10-5 mm3/Nm)at 600?.The coating exhibits good high-temperature anti-wear and friction reduction properties at 600?,and the main wear mechanisms are oxidation wear and abrasive wear.