Oxidation kinetics and mechanisms of growth of alumina scale on precipitation-hardened Pt–Al–Cr–Ru alloys

To understand the mechanisms of oxidation at different conditions, water-quenched and air-cooled Pt84:Al11:Cr3:Ru2 (at.%) samples were oxidised in air between 1150 and 1350 °C, for up to 100 h. Well-adhering and protective external α-Al2O3 scales, which are non-uniform in thickness, formed. Parabolic scaling kinetics were established, and Pt84:Al11:Cr3:Ru2 (at.%) exhibited slower scale growth rates and lower activation energies, compared to most other Pt-, Ni- and Fe-based superalloys. Mechanisms of α-Al2O3 growth were proposed to be mainly by inward diffusion of oxygen along the oxide grain boundaries, with some outward diffusion of aluminium ions along the short circuit paths, such as pores.

► We examine two alloys having similar compositions but quenched in different media.
► Oxidation at high temperatures results in formation of well-adhering α-Al2O3 scale.
► The growth kinetics obeyed the parabolic law, and the water-quenched samples show slower rate.
► Counter-current diffusion of ions within the scale and the substrate control the scale growth.