The Thermal Shock Resistance and Mechanical Properties at Elevated Temperature of Transparent Ceramics

Abstract

In this work, the thermal shock resistance and mechanical properties at elevated temperature of transparent ceramics (spinel (MgAl₂O₄) and yttria (Y₂O₃)) were studied. The thermal shocks were done by fast inserting ceramic samples (disk shape) into a hot furnace (1000°C). Vickers indentations were made on the polished sample surfaces. Before and after shocks, the measurements of crack lengths were made and next a parameter R _m (an indicator of thermal stress resistance) was obtained. Hence the maximum thermal stresses was calculated using fracture toughness K _Ic . The measurements of bending strength σ _c and K _Ic as a function of temperature were carried out. Young’s modulus and Vickers hardness were measured at room temperature. For spinel, fracture toughness K _Ic reached the maximum value at room temperature and minimum at 800°C. Above this temperature, K _Ic increased up to 1400°C. Bending strength σ _c attained the minimum value at 800 and 1000°C. At room temperature and at 1200°C it has almost the same value. For yttria, K _Ic and σ _c are higher at temperature above 600°C than at room temperature and remains almost constant up to 1500°C. In order to explain these observations, some hypotheses were proposed.