Enhancing resistance against water vapor in columnar crystal Ni coating through double glow plasma surface alloying technique

Abstract

Water vapor from hydrogen engines could corrode superalloys. We deposited Ni coatings by using the Double Glow Plasma Surface Alloying technique and studied corrosion resistance in the atmosphere, water vapor, and water vapor containing 30 % CO2, respectively. In the Ar+ bombardment process, dislocations and twins are formed on the substrate, leading to an acceleration of diffusion behavior. The γ-Al2O3, dispersed along the grain boundaries, restricts the migration of grain boundaries which results in grain boundaries strengthening. Columnar crystal boundaries facilitate corrosion between the interdiffusion zone (IDZ) and the external environment. In atmospheric conditions, Cr generates thermally grown oxide (TGO) at a considerable distance from the IDZ. The dissociation of O2– from water vapor is insufficient to establish a consistent TGO layer. Furthermore, the elevated solubility of CO2 in water vapor hastens the corrosion process within the IDZ, indicating the desirability of avoiding its use as a cooling gas whenever feasible.