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

A fine-grained (similar to 10 mu m) 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 (similar to 150-200 degrees C lower than reported previously) for the first time. It was sintered from MgO, AlN and Al2O3 mixed powders at 1650 degrees C for 15 h, followed by HIP at 1670 degrees C for 5 h under 180 MPa Ar. Sintering and densification were carefully investigated by the microstructure and phase evolution at 1600-1800 degrees C. It turned out that, the densification was mainly attributed to the solute drag effect of residual Al2O3 before full solid solution at 1650 degrees C, thus resulting in limited grain growth. The in line transmittance and flexural strength reached 86.1% (3.7 mu m), 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.