Effect of TiC content on microstructure,hardness and corrosion resistance of TiC/Ni composite coatings
In order to improve the service life of low-cost 45 steel parts in harsh environments,TiC/Ni cladding coatings with different TiC contents were prepared on its surface by laser cladding technology.Microstructure,hardness and corrosion resistance of the coatings were analyzed using X-ray diffractometer,optical microscope,scanning electron microscopy,microhardness tester and electrochemical workstation.The results show that the dendrites in the Ni35 cladding coating are γ-Ni solid solutions rich in Fe and Ni,and the intergranular is eutectic structures composed of γ-Ni solid solutions and M23C6 and Cr2B rich in B and C.The Ni35 cladding coating is composed of planar crystals,cellular crystals,columnar crystals,columnar dendrites,equiaxed crystals and fine equiaxed crystals from the bottom to the upper layer,and Cr element in the dendrites is enriched as the distance from the bottom of the cladding coating increases.The bottom layer of the cladding coatings with 10％ and 20％ TiC added consists of coarse columnar crystals and dendritic crystals,while the middle and upper layers are equiaxed crystals,and the TiC is distributed between the dendrites in block and quadrilateral shapes.The cladding coating with 30％ TiC added includes block shaped,rod-like,granular,fishbone-like and petallike TiC,and the dendrites are fine equiaxed crystals.The hardness of the cladding coatings with different TiC contents shows a phenomenon of high hardness in the bottom and upper layers,and low hardness in the middle layer.The average hardness of the cladding coating containing 10％TiC is the lowest,while the average hardness of the cladding coating containing 30％TiC is the highest.The Ni35 cladding coating without TiC addition has the lowest corrosion current density,the best passivation film stability,and the best corrosion resistance.After adding TiC,the corrosion resistance of the cladding coatings decreases,but as the TiC content increases,the corrosion resistance of the cladding coatings gradually increases.
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