The Study On The Thermal Properties And Corrosion Resistance Of Vacuum Sintering Ni-based Cermet Composite Coating With Rare Earth Joined

Vacuum fusion sinter technique was used to form Ni-based cermet composite coatings with rare eatth joined on 45 steel substrate. The microstrucure, morpholo- gy and micro-hardness was observed and analyzed by scanning electron microscopy (SEM),optical microscope, X-ray diffractemeter and microhardness instrument. The thermal properties and corrosion resistance were especially investigated. The coati- ng is composed of Ni-based solidlution and dispersion hard phase such as carbides and borides. The elements of both the coating and the substrate diffuse to each oth- er.The excellent metallurgy bonding was formed between the coating and the subsr- ate.At high tempretute, WC transformation occurs. The dominant characteristics are that it transforms into lots of needle phase and particle phase.on the verge of hard phase.The uniformity of the microstructure can be improved by adding arth element LaLa, and the fusion between coating and substrate is formed easily ,which incress their bonding. The rare earth elements also hinder the diffusion of Fe atom from matrix to coating and hold back the dilution of Fe, ensuring the chemical composition of the coating. Meanwhile the composite coating adding rare earth element La makes needle phases reduced or vanished, microstructure changes to be smaller and uniform, and precipitate new phase. The hardness of coating surface and the micro-hardness of Ni-base solid solution and some phases have been largely increased.The micro-hardness of transition area between the matrix and coating changes more mildly and the peak value of hardness appears in the coating from 0.2mm to 0.4mm beyond interface. The corrosion resistance of coating is better in NaCl and NaOH solution but bad in acid. Influence of WC on corrosion resistance is very complex and need to be analyzed according to definite corrosion solution.