The effect of alloy grain size on the transient oxidation behavior of an alumina-forming alloy

Abstract

In the early stages of alloy oxidation, diffusion of solute through the metal to the surface is important in determining the composition of the oxide scale that forms during the transient stage. Rapid solute diffusion to the interface will promote the formation of a protective scale, thereby suppressing the formation of base-metal oxide. The effect of alloy grain size on the formation of the transient oxide scale has been studied using a very fine grained NiCrAlY alloy produced by plasma spraying. The long-term oxidation behavior of this alloy was found to be independent of the grain size of the underlying alloy. However, the short-term, transient oxidation rate was found to decrease with decreasing alloy grain size. This is attributed to the rapid grain boundary transport of Al and Cr to the oxide/metal interface which promoted the formation of Cr2O3 and Al2O3.