Effect of Y2O3 addition on the densification, microstructure and mechanical properties of MgAl2O4CaAl4O7CaAl12O19 composites

With the aim to obtain dense composites containing spinel (MgAl2O4) and calcium hexaluminate (CaAl12O19), the effect of Y2O3 addition on the sintering, microstructure and mechanical properties of MgAl2O4CaAl4O7CaAl12O19 composite was investigated by solid state reaction sintering at 1500-1600 °C. The results showed that the Y2O3 addition had significant effects on the densification and microstructure at sintering temperature of 1600 °C. For the composites with addition of 2 and 3 wt% Y2O3, the aspect ratios of CA6 grains were dramatically decreased. This change of the CA6 grain morphology indirectly promoted the development of the MA and CA2 grains. Accordingly, highly uniform and dense microstructures were formed, with the apparent porosity decreased from 18.3% to 4.8% and 4.2%, respectively. Significant improvements in the mechanical properties were also achieved for the Y2O3 added composites after heating at this temperature. The optimum flexural strength was obtained by adding 2 wt% Y2O3, achieving an increase from 186 to 292 MPa, while the optimum fracture toughness was obtained by adding 3 wt% Y2O3, with the value increased from 2.3 to 3.7 MPa m1/2.