Abstract
EnThe oxidation behavior of nanograined and coarse-grained alloys may differ significantly. This empirical observation has been justified on the basis of accelerated grain boundary diffusion. However, thermal destabilization of nanograined microstructures studied in model sputter deposited NiCrAl alloys progresses concurrently with the onset of oxidation. This phenomenon makes it challenging to pinpoint the specific contribution of the original grain boundary network. In this study, dilute additions of Y are used to delay the onset of microstructural evolution at elevated temperatures through nanocluster formation and grain boundary pinning. The enhanced microstructural stability resulted in measurably different oxide morphologies during the transient stages of oxidation and slower oxidation rates overall. This coupling between the earliest stages of oxidation and microstructural evolution are directly manipulated to study fundamental oxidation processes in sputtered NiCrAl. Insights gained from this study may ultimately be used to develop novel strategies for improved oxidation resistance in structural alloys.
Highlights
The role of the columnar, nanograined microstructure is found to be crucial to the rapid diffusion of desirable oxygen-active species like aluminum and chromium
Limiting the oxygen partial pressure during oxidation provided an alternate route to promote the oxidation of aluminum and chromium
In addition to a desirable oxide chemistry, the oxide morphology and adherence improved by limiting the oxygen partial pressure
Summary
The process and underlying mechanisms of high temperature oxidation have been studied extensively across a wide range of alloy systems.[10,11,12,13] The longterm oxidation resistance, regardless of the alloy, is typically dictated by the chemistry, microstructure, and quality (i.e., density, continuity, adherence, and mechanical robustness) of the oxide All of these factors impact the rate of transport of oxidizing species or metal cations across the oxide and the rate of oxide growth.[14] Alumina and chromia have been widely targeted as protective oxides because they serve as effective diffusion barriers between the alloy and its environment.[15,16].
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