Influences Of Laser Remelting Paths On Microstructure And Tribological Property Of Fe-based Ni/WC Spraying Coatings

Laser remelting uses a high-energy laser beam to scan the alloy pre-coating layer to rapidly melt the alloys of different compositions and properties,so that the entire pre-coating layer and part of the matrix body are melted,thereby forming a metallurgical bond on the surface of the substrate but having completely different surface modification layers.In this paper,the surface of the substrate is strengthened by flame spraying and laser remelting composite process,which can enhance the bonding strength,wear resistance,corrosion resistance and impact resistance of the coating-substrate.Fe-based Ni/WC cermet coatings were prepared on the surface of 45 steel substrate by flame spraying method.Laser remelting treatment was applied with four different laser scanning trajectories,such as dot,rectangle,parallel and circular.SEM,EDS and XRD were carried out to study micro-structure,micro-tissue components,phase structure and residual stress respectively.The normal temperature dry wear test was conducted by MMG-10 friction wear test machine.The effect of the different laser re-melting trajectory on the micro-structure defects and the tribological properties of the coating were discussed.The main research results include the following:?1?The formation and development can be effectively restrained of pores and cracks under the circular remelting trajectory,the micro-structure of the remelted layer was fine equiaxed crystal,and no preferred orientation or fragile interface existed in the coatings.Besides,the strengthening mechanism of the coating after laser remelting changed from the original deformation strengthening to second phase strengthening,fine grain strengthening and solid solution strengthening.The W₂C and other hard phases distributed in the re-melted coatings and played a role of dispersion strengthening.?2?The laser remelting trajectory had great influence on the improvement of the tribological properties of the remelted layer.The wear loss of circular remelting trajectory was30.2%of that under spot remelting trajectory.And the wear resistance life of circular remelting trajectory was 3.3 times of that under spot remelting trajectory.The improvement of wear resistance of point remelting track is the worst.Cr-alloy compounds could improve the plasticity and alleviate the external force,which could suppress crack source formation and subsequent crack development.The hard phase in the remelted layer acts as a"skeleton"in friction and wear,and is embedded in the metal having plastic deformation in the remelted layer to form a strong bonding mechanism.?3?The micro-hardness of the four scanning tracks of dot,rectangle,parallel and circular are 1706,1811,1956 and 2065HV_0.2,respectively,and the surface residual stresses are-261Mpa,-249Mpa,-217Mpa and-213Mpa,respectively.The particles of??Fe,Ni?,M₂₃C₆ and WC,W₂C and other ceramic particles distributes among the remelting layer,which play the role of dispersion and solid solution strengthening and improve the hardness of the remelting layer.The higher hardness and lower friction coefficient,were found in the remelting coatings under circular and parallel remelting trajectories than that under other two remelting trajectories.which meant these two trajectories were the ideal remelting coating track.