Strengthening Mechanism in Alumina Matrix Nanocomposites
Seong-Min CHOI, Sawao HONDA, Tadahiro NISHIKAWA, Hideo AWAJI, Tohru SEKINO and Koichi NIIHARA
Abstract: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 1,300(1,573 K) in Ar gas atmosphere after sintering at 1,600(1,873 K) 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 862 Mpa for the 5 vol% SiC and 3.90 MpaEm1/2 for the 3 vol% 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. Key Words:Nanocomposites, Toughening mechanism, Strengthening mechanism, Frontal process zone