EFFECT OF MICROSTRUCTURAL SCALE ON THERMAL-SHOCK RESISTANCE OF ALUMINUM-REINFORCED ALUMINA

Thermal shock data are presented for two types of Al/Al2O3 composites (35 vol% Al) with different microstructural scale and compared to a monolithic alumina. The fine-scale Al/Al2O3 material exhibits high room-temperature strength (765 MPa) and a gradual decrease in retained strength with increasing quenching temperature difference, DELTAT, and improved thermal shock resistance-as compared to monolithic alumina-even at DELTAT = 600-degrees-C. The coarse-scale Al/Al2O3 composite shows high long-crack fracture toughness (10.5 MPa.m1/2) and almost no strength degradation up to DELTAT = 500-degrees-C. A qualitative picture for the effect of microstructural scale on thermal shock resistance emerges by employing a simple fracture mechanics description contrasting the crack driving force for transient stress fields with R-curve behavior.