The bending strength of bulk polycrystalline alumina from room temperature to melting point

The knowledge of the fracture strength of solids from room temperature to melting point is not only important for practical application but also useful for the understanding of the failure mechanisms of materials at elevated temperatures. In the present work, an apparatus for high-temperature mechanical testing has been developed and described in detail. The loaddisplacement curves of the bulk polycrystalline alumina from room temperature to melting point are measured on a three-point bending configuration. The bending strength is calculated from the updated formula of material mechanics which includes the temperature-dependent thermal expansions of the fixture and specimen. The brittle-ductile transition temperature of polycrystalline alumina is identified and is ~1500°C. The strength-temperature curves below and above brittle-ductile transition temperature are convex and concave, respectively. Strength is sensitive to defects at lower temperatures. Not only the values also the temperature dependence of the strength are affected by impurity and microflaws significantly. This is different from Young's modulus whose temperature dependence is insensitive to microstructure of materials.