Preparation and high-temperature oxidation behaviors of MgAl2O4-MgAlON composites by in-situ nitriding

Abstract

In this study, MgAl2O4-MgAlON composites with Al, α-Al2O3, MgO and MgAl2O4 raw materials were fabricated through in-situ nitriding and reaction sintering, with a tunable MgAlON composition from 10 wt% to 25 wt%. Subsequently, the sintered samples were calcined at 1500 ℃ for 3 h in an oxidation atmosphere. The densification, mechanical properties, phase assemblage, microstructures, and oxidation behaviors of MgAl2O4-MgAlON composites were investigated. Results reveal that the MgAlON grains were well-crystallized and exhibited a spinel structure in sintered body. The mechanical properties were markedly improved with the increase of MgAlON mass fraction and reached the maximum at 25 wt%. After oxidation, the densification and mechanical properties have both declined, despite the composites were oxidized to a core-shell structure. Additionally, the weight gain rate and linear expansion rate of oxidized samples simultaneously exhibited a gradual rise with the increase in MgAlON contents. More specifically, the MgAlON grains were transformed into many submicron MgAl2O4 and α-Al2O3 grains with particle sizes< 1 µm after oxidation, while the oxidation reaction was carried out along the particle gaps created by MgAlON grains oxidized from surface to interior. Our findings provide some scientific guidance for enhancing the oxidation resistance and application potentials of MgAlON composites in high-temperature.