Transparent Sintered Corundum with High Hardness and Strength

Commercial corundum powder and a liquid‐shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4–0.6 μm at relative densities of >99.9%. High macrohardness (HV10 = 20–21 GPa) and four‐point bending strength (600–700 MPa; 750–900 MPa in three‐point bending) are associated with a real in‐line transmission of 55%–65% through polished plates. The submicrometer microstructure and the optical properties can be retained for use at >1100°C using dopants that shift the sintering temperature to high values without additional grain growth.