Insights into intragranular precipitation and strengthening effect in Al2O3/SmAlO3 ceramic with eutectic composition

This work concerns the microstructure-mechanical properties relationship in Al2O3/SmAlO3 composites prepared by hot pressing at temperatures from 1450 degrees C to 1650 degrees C. Dense samples have been prepared using coprecipitated trigonal alpha-Al2O3 and orthorhombic SmAlO3 at the pseudo-binary eutectic composition. The overall microstructure coarsens with increasing processing temperature, but the nanoscale precipitates within alpha-Al2O3 and SmAlO3 grains contribute to coherency strains and distortions in Al2O3/SmAlO3 prepared at 1650 degrees C. The intragranular SmAlO3 precipitates in Al2O3 grains exhibit semi-coherent interface and an orientation relationship of the intragranular phase SmAlO3 and alumina matrix close to two different zone axes, namely [2 (3) over bar1](SmalO3) and [(4) over bar 401](Al2O3). Consequently, significant strengthening effect is found from the measured hardness values on the sample sintered at 1650 degrees C. The measured flexural strength and single edged notched beam fracture toughness of the Al2O3/SmAlO3 ceramic are comparable to traditional secondary phases reinforced alumina composites. The sample sintered at 1500 degrees C exhibits a flexural strength of 558 MPa and a fracture toughness of 5.59 MPa.m(1/2).