Short-term oxidation behavior of powder metallurgy Al0.8Co0.5Cr1.5CuFeNi HEA in high-temperature solid and semi-solid intervals

Abstract

In this work, possible short-term thermal exposure oxidation in hot processing including semi-solid processing is focused. We aim to investigate the short-term oxidation behavior of a novel powder metallurgy Al0.8Co0.5Cr1.5CuFeNi high entropy alloy (HEA) in high-temperature solid (1000–1100 °C) and semi-solid (1125–1225 °C) intervals. From 1000 to 1225 °C, mass gain increases from 0.31 to 0.45 mg cm–2 after 60 min oxidation, presenting superior oxidation resistance in the semi-solid state compared with other semi-solid alloys. Equiaxed α-Al2O3 grains are the predominant component of oxide scales and no obvious internal oxidation layer occurs in both solid and semi-solid intervals. Al2O3 scale growth is predominantly determined by outward Al3+ diffusion. For solid oxidation, different scale formation kinetics occur on various phases and the BCC(B2) phase has faster scale formation kinetics. This is attributed to outward Al3+ diffusion rate differences in various component systems. During semi-solid oxidation, the increased degree of chaos and number of vacancies in the liquid phase provide a diffusion channel, leading to rapid Al2O3 formation. Oxidation resistance in the semi-solid state is attributed to dense Al2O3 scales formed through selective oxidation of Al.