Study Of Microstructure And Corrosion Resistance Of Remelting And Restoring Plasma-sprayed Ni Coated WC Coatings

Plasma spraying is one of the most commonly used thermal spray techniques for ceramic coatings on metal surface. It has the advantages of quick deposition velocity and high production efficiency. However, some defects, such as porosity, micro cracks, lamellar structure were existed in plasma sprayed coating unavoidably. The bonding state between the coating and substrate is a kind of mechanical combination. Laser remelting was applied to reduce these problems, by which excellent properties of ceramic coatings could be obtained.In this paper, Ni coated WC ceramic coating on 45^# steel surface was obtained by plasma spraying. The laser remelting and vacuum restoring technologies were employed to eliminate the defects of plasma sprayed coating.Microstructure and phase composition of the coatings were studied by means of X-ray Diffusion (XRD), Optical Microscopy (OM), Scan Electron Microscope (SEM) and Energy Disperse Spectroscopy (EDS). The corrosion resistance of the three different coatings was tested by salt fog test and electrochemical experiment. The conclusions were stated as below:Firstly, the result showed that the plasma sprayed coating had a lot of defects. The microstructure of the coating could not be improved by vacuum restoring significantly, while laser remelting could eliminate the lamellar structural properties of plasma sprayed coating and reform a continuous and compact coating.Secondly, the phases constitution was detected by XRD. W₂C phase was not found among of the three coatings. Compared with the plasma-sprayed coating, the phases of the laser remelting and vacuum restoring coatings were changed. But the purpose of the WC restoring in vacuum restoring was not achieved.Thirdly, the effects of the laser remelting parameters on the plasma-sprayed coatings were studied. Adjusting the laser remelting parameters could reduce the defects of plasma-sprayed coating.The corrosion resistance of the three different coatings was checked by salt fog test and electrochemical test. The results showed that the corrosion resistance of laserremelting coating had been greatly improved than those of plasma-sprayed and vacuum restored coatings. The reason might be that the compact coating was obtained by laser remelting. It could prevent the electrolyte to penetrate into the inner part of coating.