Microstructure and interface characteristics of NiCrBSi thick coating remelted by TIG process

A NiCrBSi coating of 800 μm thick is prepared on AISI 1045 steel via plasma spraying, subsequently, the coating is remelted by tungsten inert gas arc (TIG) process. The microstructure and interface characteristics of remelted coating were intensively studied. The results show that, upon remelting, the microstructure of the thick coating comprises planar crystal and dendritic crystal. And the main phases in the as-sprayed coating are changed from γ-Ni, Cr7C3 and Cr2B to γ-(Ni,Fe), (Fe,Cr)23C6, CrB, Ni3B and Fe3C. The combining state between the coating and the substrate is changed from mechanical bonding to metallurgical bonding. A ″bright area" was formed between the remelted coating and substrate. The diffusion mechanism of Fe, Ni and Cr atoms at the interface is vacancy diffusion, and that of C and B atoms is interstitial diffusion. In addition, the differences of elastic modulus and hardness between the both sides of the interface of the coating is greatly reduced by remelting, which is beneficial to improve the bonding strength of the interface. Therefore, TIG remelting treatment is a feasible method to improve the microstructure and the interfacial characteristics of the thick as-sprayed coating.