Experimental Investigation On Laser Remelting Of Remanufacturing FeNiCrAl Coating

The remanufacturing compound technology of high velocity arc spraying and laser remelting is a new kind of materials processing and surface modification technology.Using the composite process of remanufacturing has important significance to repair worn-out parts with large area.In this paper,FeNiCrAl coating is prepared,which contains Fe,Ni,Cr,Al,B,Si and other elements,adopting high velocity arc spraying technology,and then laser remelting treatment is proceeded on spraying coating.Respectively by single track and multi track laser remelting experiment,the best process parameters of single track laser remelting is obtained.The microhardness,microstructure,phase composition,sliding wear resistance and corrosion resistance of coatings before and after remelting are researched and analyzed.Remelting processing is conducted on spraying coating with laser remelting process technology.The experiment of two factors with three levels is designed selecting laser power,scanning speed as influencing factors and using microhardness,alloy zone height and poriness as evaluation indexes.By range analysis,the single track optimum process parameters of laser remelting is obtained.Using the single track optimum process parameters of laser remelting,multi track overlapping remelting experiment research is conducted.Through the comparative analysis of microstructure and microhardness of remelting coating under different overlapping step distance,the best overlapping step distance is obtained.The microstructure and phase composition of coating are researched and analyzed before and after remelting.Laser remelting process eliminates the original layered stack structure.The recrystallization of micorstructure happens,and becomes uniform dense,further more poriness is decreased significantly.The bonding way of coating and substrate shifts from mechanical bonding to metallurgical bonding.Along the bottom-up thickness direction of remelting coating,the microstructure of remelting coating is dendrites which are from coarse to fine columnar and has the trend of becoming dense.The top microstructure is the densest.The mass transfer and convection mechanism of molten inside makes the mutual diffusion of elements between the remelting coating and substrate,which verifys the metallurgical bonding between remelting coating and substrate.The phase composition of spraying coating and remelting coating is comparatively analyzed.The phase composition that makes microhardness of remelting coating increase is identified.By sliding friction and wear experiment,the wear resistance of substrate,spraying coating and remelting coating is tested and analyzed,and the friction and wear properties of substrate and coatings under different load are analyzed.The experiment results show that the wear form of substrate surface is adhesion and fatigue wear,the wear surface emerges sheet structure with cracks;the wear surface of spraying coating emerges peeling pit characteristic;the wear form of remelting coating surface is plough cutting wear,and the wear surface emerges furrow shaped features.The wear resistance performance of substrate is poorer.After laser remelting of spraying coating,the solid solution and hard phase remelting coating produced play an important role in improving wear resistance of the coating.By electrochemical corrosion experiment and Tafel polarization curve fitting,the comparative analysis of self-corrosion potential and self-corrosion current density of remelting and spraying coating is conducted.Thus it is concluded that corrosion resistance is significantly improved after laser remelting of spraying coating.By the analysis of electrochemical impedance spectroscopy,it is verified that corrosion resistance performance of remelting coating is obviously higher than spraying coating.