Effects of elemental Nb addition on the microstructures and mechanical properties of Ti/Al2O3 composites by pressureless sintering

Nb and Nb2O5 were used, respectively, as sintering additives for pressureless sintering of Ti/Al2O3 composites, and the effect of elemental Nb on the microstructures and mechanical properties of the composites were investigated. The X-ray diffraction results indicated that the addition of both Nb and Nb2O5 resulted in the solution of Nb in Ti. Compared to metal Nb, the addition of Nb2O5 made the composites easier to sinter, and the density of the Ti/Al2O3 composite rose with increases in the Nb2O5 addition. When metal Nb was added, the changes in flexural strength and micro-hardness were basically consistent with the variations in density. The strength of the Ti/Al2O3 composites was found to increase at first and then to decrease, however when Nb2O5 was added. The phase formation and strengthening mechanisms are illustrated. The best performance occurred when 5 vol.% Nb2O5 was added, with a relative density, micro-hardness and flexural strength of 89.3%, 5.6 GPa and 115.78 MPa, respectively. (C) 2019 The Ceramic Society of Japan. All rights reserved.