Microstructure and mechanical property of Ni-based thick coating remelted by gas tungsten arc

Abstract Herein a NiCrBSi coating with 800 μm thickness was fabricated via plasma spraying on AISI 1045 steel, whereupon gas tungsten arc welding (GTA) process was employed to remelt the coating. The microstructure and mechanical properties of the coating before and after remelting were investigated. The results indicate that microstructural inhomogeneity in the as-sprayed coating were almost completely eliminated by GTA remelting. The main phases in the as-sprayed coating are γ-Ni, Cr 7 C 3 and Cr 2 B. While, the remelted coating is mainly composed of fine dendrite γ-(Ni,Fe,Cr) and thin interdendritic lamellar eutectic (Fe,Cr) 23 C 6 . Moreover, there are some submicron particles Ni 3 B, CrB and Ni 3 Si in the grain interior of γ-(Ni,Fe,Cr), and a large number of nanocrystallines in the grain boundary of γ-(Ni,Fe,Cr). After remelting, a compact and complete solid solution γ-(Ni,Fe,Cr) is formed at the interface between the remelted coating and substrate, hence the interface is transformed from mechanical bonding to metallurgical bonding. In addition, remelting the coating was found to induce a 84.4% increase in the elastic modulus, a 18.5 times increase in the fracture toughness, and a 42.8% increase in the microhardness. Therefore, GTA remelting is found a feasible method to significantly improve the microstructure and mechanical properties of the coating.