Experimentally investigation of the high temperature oxidation mechanism for Ni-Al-Pt alloy supported by CALPHAD calculations

Abstract

Abstract High temperature oxidation experiments combined with CALPHAD (CALculation of PHAse Diagram) thermodynamics calculations have been performed in Ni-20Al-5Pt (in at.%) alloy at 1100°C, to attain a more detailed fundamental understanding of the high temperature oxidation behavior of Ni-Al-Pt alloy. And the influences of alloy composition on the formation, growth and spallation behavior of TGO scales formed during isothermal tests at 1100°C have also been discussed. It is indicated that the whole oxidation process developed in stages, Al2O3 formed firstly at the bottom, NiO overgrow and undercut the Al2O3. The formation of NiO results in nickel depletion and aluminum enrichment, as soon as the Al content reaches the critical value, θ-Al2O3 transfers into α-Al2O3 with compacted structure, the outward diffusion of Al dominates, inward diffusion of O secondarily. The α-Al2O3 would establish itself as a complete layer to shut down further Ni outward diffusion. When Al is not enough, Al2O3 will react with NiO to form NiAl2O4. The subsequent oxidation process may also result in nickel enrichment at the oxide scale/alloy interface. It is demonstrated that the vacancies coalesce into small voids due to unequal diffusion of Al towards the Al2O3 scale and backward diffusion of Ni in the opposite direction, leading to extensive scale spallation. While Pt has the active effect to contribute thinner oxide scale that is more resistant to spallation.