Performance Characteristics of Hot-dip and Plasma Spray Aluminide Coated Nickel-Based Superalloy 718 under Cyclic Oxidation in Water Vapour

Abstract

Aluminium coating due to its ability to form stable alumina oxide scale are commonly used to protect materials such as inconel 718 superalloys at high operational temperatures. Relevant properties of the oxide scale formed; growth rate and coating adherence is not only determined by the composition of the coating material used but is also influenced by the coating manufacturing process and the test condition. In the present work, effect of water vapour and thermocycling commonly prevailing on the morphology and composition of the alumina scales formed during high temperature oxidation was studied using hot-dip and plasma spray aluminium coatings. The coatings highly improved oxidation resistance of the alloy substrate with hot dip coating showing the lowest mass change compared to plasma spray. The results also show that the hot-dip coating has an inherently different morphology and growth rate compared to those formed on the plasma spray coating. High rate of oxidation, spallation and large voids with little protective alumina oxide layer were observed in moist condition test especially in plasma spray coatings.