Grain growth inhibition in microwave sintered Al2O3 with two-step hybrid sintering

Abstract

In this study, a novel two-step hybrid sintering approach was employed using α-Al₂O₃ to address the primary limitation of microwave sintering, which is excessive grain growth occurring during the final stage of sintering. The first step involved microwave sintering of α-Al₂O₃, while the second step consisted of prolonged conventional sintering. To optimize this process, 3D modeling and simulation were conducted to identify the relative density at which the open porosity network in the sub-micron powder destabilized. It was identified that 90 % relative density was the critical point, beyond which closed porosity increased significantly. A holding time of 40 h at 1300 °C yielded a relative density of 98.6 % and an average grain size of 1.1 μm, approximately half the size of grains in microwave single-step sintered Al₂O₃ samples. This novel two-step hybrid sintering method demonstrates potential for effectively controlling grain size in Al₂O₃, both at laboratory and industrial scales.