Pressureless reaction sintering and hot isostatic pressing of transparent MgAlON ceramic with high strength

Abstract

A fine-grained (~ 10 µm) MgAlON ceramic combining the advantage of high strength and high transparency was reported by pressureless reaction sintering and hot isostatic pressing (HIP) at relative lower processing temperature (~ 150–200 °C lower than reported previously) for the first time. It was sintered from MgO, AlN and Al2O3 mixed powders at 1650 °C for 15 h, followed by HIP at 1670 °C for 5 h under 180 MPa Ar. Sintering and densification were carefully investigated by the microstructure and phase evolution at 1600–1800 °C. It turned out that, the densification was mainly attributed to the solute drag effect of residual Al2O3 before full solid-solution at 1650 °C, thus resulting in limited grain growth. The in line transmittance and flexural strength reached 86.1% (3.7 µm), 386 ± 5 MPa (> 40% higher than previous results), respectively. The origin of the high strength was the combination of Hall-Petch effect (finer grains) and twin lamella strengthening mechanism. The MgAlON transparent ceramic exhibited the prospect of high-performance infra red (IR) dome to rival AlON and sapphire.