Oxidation of nickel-based single-crystal superalloys for industrial gas turbine applications

The oxidation resistance of three prototype single-crystal nickel-based superalloys for industrial (electricity generating) gas turbine applications is studied All contain greater quantities of Cr than in most existing single-crystal superalloys, two are alloyed with Si All alloys are found to be marginal Al2O3-formers, with the performance being better at 1000 degrees C rather than 900 degrees C, and when Si is added Microstructural analysis indicates that the ability to form an Al2O3 layer is better in the interdendritic regions, the dendrite regions are prone to internal oxidation In all cases, an outer scale of Cr2O3 is formed which is in contact with either Ta2O5 (at 1000 degrees C) or NiTa2O6 (at 900 degrees C) To explain the results, the factors known to influence the rate of Al2O3 scale formation are considered A model is developed to predict whether any given alloy composition will form a continuous Al2O3 scale This is used to rationalize the dependence of Al2O3 scale formation on alloy composition in these systems It is useful for the purposes of alloy design (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserved