抄録
Structural ceramic composites can be divided into three categories: microcomposites, nanocomposites and nanocomposites combined with microcomposites. In the microcomposites, the second-phase micrometer-size dispersions such as particulates, plateletes, whiskers and fibres are dispersed at the grain boundaries of the matrix, while in the nanocomposites the second-phase nanometer-size dispersions such as particulates and whisker are incorporated within the matrix grains. The main advantage of the microcomposites is to improve the fracture toughness (and then fracture strength). On the other hand, the nanocomposites such as Al2O3/SiC, Al2O3/Si3N4, MgO/SiC and Si3N4/SiC, in which the second phase particulate dispersions are dispersed within Al2O3, MgO and Si3N4 matrix grains, were recently developed in our laboratory. In these nanocomposites, the fracture toughness and strength were approximately 2-4 times improved by dispersing the nano-size second phase particles into the matrix grains. The remarked improvement of hardness and strength were also observed even at high temperatures. In this paper, the toughening and strengthening mechanisms of various nanocomposites will be reviewed briefly, and the possibility of the nanocomposites combined with microcomposites for developing the strong and tough ceramics even at high temperatures will be also discussed.
