The high-temperature steam oxidation behaviour of nickel-based coatings based on multiphase carbide evolution

The in situ synthesis of multiphase carbide synergistically reinforced Ni-based composite coatings was achieved via laser cladding. Its microstructure, properties, and high-temperature steam oxidation behavior were investigated, with emphasis on the effects of the reinforcing phase ratio and environmental temperature. The results revealed that with the reinforcing phase ratio increases, the coating microstructure transitioned from columnar grains, equiaxed grains, and partial cellular to a disordered structure. The white granule structure tended towards a uniform blocky distribution, and the dispersed leaf structure evolved into a denser reticular structure. Furthermore, the increased content of carbides induced the coating’s nano-hardness to elastic modulus ratio (H/E), enhancing resistance to plastic deformation, which originated from the interaction between multiphase carbides (e.g., TiC and (Ti,W)C) and dislocations. In the high-temperature steam oxidation experiments, the oxide films on coatings with 5%–20% reinforcement phase were primarily composed of Cr 2 O 3 . The scale thickness exhibited negligible fluctuations, with no observable spallation or cracking. However, the oxide scale structures exhibited distinct temperature-dependent evolution: at lower temperatures (1000–1100 °C), it primarily comprised Cr 2 O 3 and Ni-based oxides, with parabolic oxidation kinetics demonstrating optimal oxidation resistance. At 1200 °C, it developed a stratified structure: Ni-rich oxide particles dominated the outer layer, whereas Cr-rich oxides prevailed in the inner layer, forming alternating strata. The formation of WO 3 , NiCr 2 O 4 spinels, and Cr volatilization induced scale cracking and spallation, severely compromising its stability and oxidation resistance.