Oxidation, hot corrosion, and interdiffusion behavior of NiAlTa coating by electro-spark deposition

A novel NiAlTa blade tip protective coating is designed and its oxidation, hot corrosion, and interdiffusion with DD5 single-crystal superalloys are investigated. NiAlTa coatings exhibit low oxidation rates. The dragging effect of Ta on Al hinders the external diffusion of Al. Ta that accumulates at the Al2O3 grain boundaries reduces the internal diffusion of O by combining or reacting with it. NaCl aggravates the hot corrosion through self ustaining cycles of chlorination/oxidation. b-NiAl phase fails first as a diffusion channel for the corrosive medium. Significant element interdiffusion occurs. An interdiffusion zone and a secondary reaction zone are formed. Interdiffusion changes the percentage of elements, causing a phase transition of the coating. The volume change caused by the phase transition induces bulging and cracking of the oxide film. Furthermore, the oxidation, hot corrosion, and interdiffusion mechanisms are discussed.