Elaboration and mechanical characterization of multi-phase alumina-based ultra-fine composites

Al₂O₃-10 vol.% YAG and Al₂O₃-10 vol.% ZrO₂ bi-phase composites as well as Al₂O₃-5 vol.% YAG-5 vol.% ZrO₂ tri-phase composite were developed by controlled surface modification of an alumina powder with inorganic precursors of the second phases. Green bodies were produced by dry pressing and slip casting and then sintered at 1500 °C. In particular, slip casting led to fully dense, defect-free, and highly homogenous samples, made of a fine dispersion of the second phases into the micronic alumina matrix, as observed by SEM. The mechanical characterization proved the predominant role of the final density on the Vickers hardness, while the elastic modulus was affected by the volume fraction of the constituent phases, in fairly good agreement with the rule of mixture prediction. The fracture toughness values of the bi- and tri-phase materials were similar, and their crack paths revealed the importance of the thermal residual stresses at the matrix-reinforcement interfaces, promoting inter-granular propagations.