The Study On The Microstructure And Properties Of Vacuum Fusion Sintering Nickle-base-Cermet Composite Coating With Rare Earth Joined

The Ni-base —WC with rare earth composite coating was obtained by the technique of vacuum fusion sintering on the 45 steel. By virtue of SEM, X-ray diffraction and EDX, the microstucture and phase-structure of coating were investigated. This paper slao stuies the active mechanism of WC and rare earth elements on microstructure, chemical component and properties of vacuum fusion sintering coating in the way of examining and evaluating in hardness, wear resistance, corrosion resistance and oxidation resistance of coating. The results show that with the addition of WC and rare earth elements (Ce+La), the microstrcture, distribution of chemical elements and properties of vacuum fusion sintering Ni-base —WC coating change remarkably. Such kind of change can be described as the followings. Firstly the microstruture of coating is composed of Ni-base solid solution and a lot of needle phase, massive phase and WC phase in the solid solution. The microstructure of coating will change with the content of WC. Secondly the metallurgical bonding between the matrix and coating has been realized. Thirdly the composite coating adding rare earth elements make needle microstruture reduced or vanished, microstruture changes smaller and uniformity, and precipitate new phase, such as NiB. Fourthly rare earth elements change the distribution of Ni, Cr and W among the coating and make the content of Ni, Cr and W in Ni-base solid solution and some harden-phases changes. Fifthly 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. Sixthly 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 side 0.6mm or 0.8mm to interface. Seventhly the wear resistance, corrosion resistance and oxidation resistance of coating are enhanced. The corrosion resistance of coating is better in NaCl and NaOH solution, the same of corrosion rate in HC1 and H₂SO₄ solusion and the worst in HNO3 solution. Lastly in contrst with different addition content of WC, its influence is very complex and it has the best addition content.