Effect of microstructure on the fracture behavior of micro–nano ZTA composite

The microstructural effect on the crack propagation was investigated using two kinds of micro–nano ZTA composites made of micro-Al2O3 and nano-ZrO2 particles. The results indicated that with low ZrO2 content (10 vol.%) in the composite the presence of both large ZrO2 particles located along Al2O3 grain boundary and very fine ZrO2 particles embedded inside of Al2O3 grains was responsible for the appearance of transgranular fracture. Consequently, the composite showed a typical R-curve of rising up more quickly and better toughness than the composite with high ZrO2 content (20 vol.%). The crack propagation inside of Al2O3 grains, depending on the nature of residual stress produced due to the thermal mismatch of Al2O3 and ZrO2 as well as the phase transformation of ZrO2 from tetragonal to monoclinic, was found to be in the way of either bypassing or splitting ZrO2 particles.