Investigation of CVD Processes to Perform Dense α-Alumina Coating on Superalloys

Abstract

Coated nickel-based superalloys are widely used as superior material systems in gas turbines, where the overlay coatings help withstand hot corrosion and serve as bond coats for the thermal barrier layer, However, interdiffusion may limit the coatings' lifetime, a potential remedy being a diffusion barrier layer. In this context, the chemical vapor deposition (CVD) process was investigated to deposit α-Al2O3 on superalloy substrates. Deposited films using an AlCl3/CO 2/H2 gas mixture at low and atmospheric pressure were characterized. Difficulties including whisker growth at low pressure and the growth of noncompact large crystals at atmospheric pressure are discussed jointly with strategies for suppressing them. In addition, the potential of alternative precursors to produce α-Al2O3 films was investigated using aluminum tri-isopropoxide in an adequate reactor geometry. © 2004 The Electrochemical Society. All rights reserved.