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

La2O3 and Nb2O5 doped Al2O3 ceramics [5Nb(2)O(5)/xLa(2)O(3)-(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 5Nb(2)O(5)/xLa(2)O(3)-(95-x)Al2O3 composite ceramics were investigated. The results show that all investigated specimens consisted of alpha-Al2O3, LaNbO4 and LaAl11O18. The sintering temperature of La2O3/Nb2O5 doped Al2O3 ceramic was at least 150 degrees C lower than that of Al2O3 ceramic. The specimens sintered at 1500 degrees 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 5Nb(2)O(5)/xLa(2)O(3)-(95-x)Al2O3 composite ceramics was above 70% higher than that of Al2O3 ceramic. 5Nb(2)O(5)/7.5La(2)O(3)-82.5Al(2)O(3) composite ceramic presented excellent mechanical properties: HV = 12.6 GPa, K-IC = 6.3 MPa center dot m(1/2) (1500 degrees C). (C) 2014 The Ceramic Society of Japan. All rights reserved.