Microstructure evolution and properties of NiCrBSi thick coating remelted by gas tungsten arc

The self-fluxing NiCrBSi coating with 800 μm thickness was prepared on the surface of AISI 1045 steel substrate by plasma spraying. Subsequently, the coating was remelted by gas tungsten arc (GTA) process. The microstructure and phase composition of the NiCrBSi thick coating before and after remelting were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometer (XRD). The elastic modulus, fracture toughness, hardness and wear resistance of the two coatings were also tested. The results indicate that micro-defects such as many inclusions, voids, unmelted particles, microcracks and lamellar structure in the as-sprayed coating were almost completely eliminated by GTA remelting. The main phases in the as-sprayed coating are γ-Ni, Cr7C3 and Cr2B. While, the remelted coating is mainly composed of fine dendrite γ-Ni and thin interdendritic lamellar eutectic Cr23C6 and CrB. Moreover, there are some submicron particles Ni3B in the grain interior of γ-Ni, and a large number of nanocrystallines CrB and Fe3C in the grain boundary of γ-Ni. The elastic modulus and hardness of the remelted coating is 84.4% and 34.5% respectively higher than that of as-sprayed coating, and the fracture toughness of the remelted coating is 19.5 times as that of the as-sprayed coating. While, the wear mass loss of the remelted coating is only 36.2% of the as-sprayed coating. The main wear mechanism of as-sprayed coating is lamellar cracking, and the main wear mechanism of the remelted coating is micro-abrasive wear. Therefore, a Ni-based thick coating with good properties can be obtained by plasma spraying and remelting technique.