Influence of microstructure on the oxidation behaviour of the Ni-based single crystal superalloy AM1 between 850 and 1050 °C in air.

The influence of the as-cast and fully heat-treated microstructures on the isothermal behaviour of the Ni-based single crystal superalloy AM1 was investigated at 850-1050 °C. It appears that the kinetics transition regime is a function of time, temperature and also of bulk microstructure. The various characterisation techniques allowed elucidating that the growth of a continuous inner layer of α-Al 2 O 3 governs the oxidation mechanisms, irrespective of the microstructure. Such layer is favoured for high oxidation temperatures, long exposure times and high γ' precipitate surface fraction. However, the chemical segregation of the as-cast state is responsible for the growth of inhomogeneous oxide layers. • Differences in oxidation unveiled for as-cast and FHT AM1 Ni-based superalloy. • Oxidation mechanism governed by internal Al 2 O 3 scale on the γ/γ' structure of AM1. • Transition regime linked to the allotropic transformation of Al 2 O 3 and of Cr. • None of the AM1 microstructure develops Al 2 O 3 at low temperatures and short times. • Chemical segregation in as-cast AM1 is responsible for the uneven growth of oxides. [ABSTRACT FROM AUTHOR]