2003 Volume 52 Issue 11 Pages 1374-1378
In a previous report, we proposed strengthening and toughening mechanisms in nanocomposites based on thermally induced residual stresses around nano-particles within matrix grains. These residual stresses generate dislocations at elevated temperatures and the dislocations release tensile residual stresses along grain boundaries in the matrix. Conversely, the dislocations in alumina are immovable at room temperature, act as nano-crack nuclei when a main crack tip approaches and expand the size of the frontal process zone. In this paper, alumina matrix/silicon carbide dispersed nanocomposites were fabricated to clarify the strengthening mechanism in nanocomposites by means of hot-press processing. To compare the effects of the annealing process on the mechanical properties of sintered specimens, heat treatment was carried out at 1300°C (1573K) in Ar gas atmosphere after sintering at 1600°C (1873K) for 1h. Bulk densities of the specimens were more than 98% of relative density, but some specimens had relative densities lower than 95%. The mean values of fracture strength and fracture toughness were 862MPa for the 5vol% SiC and 3.90MPa·m1/2 for the 3vol%SiC, respectively. Even though the fracture strength of the nanocomposites was 2 to 3 times higher than that of the monolithic alumina, the fracture toughness was almost same as the monolithic alumina.
