Study Of The Metal-Ceramics Gradient Coating Melted By Plasma Arc

In this paper,plasma cladding process was used to prepare the Ni60B+TiC composite coating pre-coating on mild steel substrates(Q235). The microstructure and composition of the coating were investigated by optical microscopy,scanning electron microscopy,x-Ray diffraction.TEM and electron probe. The coating near the base had a typical flat epitaxial growth morphology;and near the top had relatively regular dentritic morphology. The growth of grains was effected by crystallographic aeolotropy.The different composition increased or decreased generally,but was disturbed from microscopic view from the interface of coating/substrate to the surface of the coating.The white-bright band occurred between the coating and the substrate,which proved metallographic bond .It could be found by statistic analysis that the Vickers microhardness near the base was less than that of the middle and the top,which was related with the TiC content. TiC added in the coating increased the Vickers microhardness significantly.On the ground of the theories of heat transference and heat stress,residual heat stress equations were decuced according to the plasma cladded coating.And specific calculations were done with physical property factors.In the end ,analogy calculations were also finished by FEA.The results were compared with measured stress and analyzed.Influencing factors were discussed in detail.and improved methods were presented.