Effect of Initial Microstructure on High Temperature Oxidation of MAR‐M247 Nickel‐Based Superalloy: Experiment and Modelling

Abstract

The influence of initial microstructure on the high‐temperature oxidation behaviour of MAR‐M247 nickel‐based superalloy was investigated experimentally and supported by CALPHAD modelling. Fine‐grained, coarse‐grained, and columnar microstructures were produced by casting and oxidised in air at 900°C for 1–500 h. Oxide evolution was characterised by SEM/EDS and X‐ray diffraction, while Thermo‐Calc was used to predict equilibrium oxide stability. All microstructures exhibited the same overall oxidation sequence, with initial NiO and Cr 2 O 3 formation followed by development of an Al 2 O 3 ‐rich external scale and a chromium‐enriched subsurface region. Thus, the initial microstructure did not alter the fundamental oxidation mechanism but significantly affected oxidation kinetics and scale morphology. The higher grain‐boundary density of the fine‐grained microstructure promoted elemental transport and oxide nucleation, enabling earlier development of a more uniform protective scale. After 500 h, the oxide scale was thinnest for the fine‐grained material (1.56 μm), compared with 1.67 μm for the columnar and 2.24 μm for the coarse‐grained material.