Mechanical and Thermal Properties of Pressureless-Sintered MgO-Mg₄Ta₂O₉ Composites

Abstract

MgO-based composites containing 10 to 30vol% Mg₄Ta₂O₉ were fabricated by pressureless sintering of MgO and Ta₂O₅ powders at 1400° to 1600°C. Mechanical properties and the thermal expansion coefficient of the composites were studied. Under all sintering conditions, Ta₂O₅ reacted with MgO completely to form Mg₄Ta₂O₉ and dense (>95% of theoretical density) composites were obtained. Dispersion of Mg₄Ta₂O₉ particles inhibited the grain growth of MgO and improved mechanical properties. The maximun bending strength and fracture toughness of composites were 260MPa and 3.2MPa⋅m^1/2, respectively, in contrast with 150MPa and 1.6MPa⋅m^1/2 for a MgO monolith. The composites may be toughened by the crack deflection due to Mg₄Ta₂O₉ particles. The thermal expansion coefficient of the composites decreased slightly with increasing Mg₄Ta₂O₉ content and was 12.9×10^-6°C^-1 for the composite with 30vol% Mg₄Ta₂O₉.