Application of Precipitate Free Zone Growth Kinetics to the beta-Phase Depletion Behavior in a CoNiCrAlY Coating Alloy: An Analytical Approach

摘要

This paper concerns the beta-phase depletion kinetics of a thermally sprayed free-standing CoNiCrAlY (Co-31.7 pct Ni-20.8 pct Cr-8.1 pct Al-0.5 pct Y, all in wt pct) coating alloy. An analytical beta-phase depletion model based on the precipitate free zone growth kinetics was developed to calculate the beta-phase depletion kinetics during isothermal oxidation. This approach, which accounts for the molar volume of the alloy, the interfacial energy of the gamma/beta interface, and the Al concentration at gamma/gamma + beta boundary, requires the Al concentrations in the beta-phase depletion zone as the input rather than the oxidation kinetics at the oxide/coating interface. The calculated beta-phase depletion zones derived from the current model were compared with experimental results. It is shown that the calculated beta-phase depletion zones using the current model are in reasonable agreement with those obtained experimentally. The constant compositional terms used in the model are likely to cause the discrepancies between the model predictions and experimental results. This analytical approach, which shows a reasonable correlation with experimental results, demonstrates a good reliability in the fast evaluation on lifetime prediction of MCrAlY coatings. (C) The Minerals, Metals & Materials Society and ASM International 2018