Phase evolution of MgAlON in the pressureless presintering and its influence on the fabrication of transparent ceramics

Abstract While phase transformations had been reported during the preparation of (Mg)AlON transparent ceramics, their impact on sintering remained insufficiently understood. In this study, Mg 0.27 Al 2.58 O 3.73 N 0.27 green bodies were sintered under tailored thermal schedules designed to induce varying degrees of transient α‐Al 2 O 3 precipitation. Phase analysis revealed α‐Al 2 O 3 formation within 1250–1600°C, reaching a maximum of 7.83 wt% at 1500°C after 2 h of soaking, followed by redissolution at 1650°C. Microstructural characterization and phase analysis confirmed that the crystallization and subsequent dissolution of α‐Al 2 O 3 followed a time–temperature‐dependent nucleation‐growth model. Dilatometry results indicated that the effect of transient α‐Al 2 O 3 vanished once the relative density exceeded 61.5% (continuous heating) or 65.9% (2 h soaking at 1500°C) before final stage of sintering. The pore size decreased from 210 to 187 nm during α‐Al 2 O 3 precipitation and returned to 208 nm after redissolution. Despite the intentionally varied degrees of precipitation introduced by different sintering schedules, the final ceramics exhibited convergent microstructures and comparable in‐line transmittance (∼65%), highlighting the minimal influence of transient decomposition on the ultimate transparency.