Mechanical properties of La₂O₃ and Nb₂O₅ doped Al₂O₃ ceramics prepared by microwave sintering

Abstract

La₂O₃ and Nb₂O₅ doped Al₂O₃ ceramics [5Nb₂O₅/xLa₂O₃–(95–x)Al₂O₃, x = 2.5–15.0, volume percent] were prepared by microwave sintering processes. The effects of La₂O₃ content and sintering temperature on densification, phase composition, microstructure and mechanical properties of 5Nb₂O₅/xLa₂O₃–(95–x)Al₂O₃ composite ceramics were investigated. The results show that all investigated specimens consisted of α-Al₂O₃, LaNbO₄ and LaAl₁₁O₁₈. The sintering temperature of La₂O₃/Nb₂O₅ doped Al₂O₃ ceramic was at least 150°C lower than that of Al₂O₃ ceramic. The specimens sintered at 1500°C exhibited relative density higher than 92.0%, revealing good sinterability. During the sintering period, LaNbO₄ and plate-like LaAl₁₁O₁₈ were formed in-situ. The fracture toughness of 5Nb₂O₅/xLa₂O₃–(95–x)Al₂O₃ composite ceramics was above 70% higher than that of Al₂O₃ ceramic. 5Nb₂O₅/7.5La₂O₃–82.5Al₂O₃ composite ceramic presented excellent mechanical properties: HV = 12.6 GPa, K_IC = 6.3 MPa·m^1/2 (1500°C).