Effect of laser remelting on the microstructures and properties of NiCoCrAlY-based coatings prepared by high-speed air fuel supersonic flame (HVAF)

Abstract

In order to improve the oxidation resistance of the coating, laser remelting technology was used to remelt the HVAF multi-component modified coating. The influence of laser remelting technology on the phase state, microstructure characteristics, and isothermal oxidation behavior of coatings was studied. The experimental results indicate that a coating with complete morphology and no defects was obtained on the surface. There is a significant amount of metallurgical bonding and partial mechanical interlocking between the remelted layer and the substrate. The remelted layer is mainly composed of β-NiAl phase, accompanied by a small amount of γ′ phase and oxide phase. The microhardness test results show that the average hardness of the remelted layer is 1.1–1.42 times that of the prepared coating, and the bonding strength has increased by 23 %. After 100 h of high-temperature oxidation, the oxidation rate of the 4N3T4H remelted layer is the lowest, at 1.5 × 10⁻¹⁵ cm²/s, which is one order of magnitude lower than that of the as-sprayed coating. This is because after laser remelting, the remelted layer has the inherent hysteresis diffusion effect of HEA, which can improve the high-temperature oxidation resistance of the remelted layer and basically eliminate many pores and cracks contained in the HVAF coating. The coating density is significantly increased, which is conducive to hindering the diffusion of oxygen. Meanwhile, the oxide of HVAF coating mainly accumulates at pores and cracks, and there is no or late formation of uniform and dense oxide film on the surface. The surface of the remelted coating after oxidation forms a relatively uniform and dense oxide film, providing more effective protection for the substrate.