Basic microstructures in nanocomposites are classified into three types:

Intra-type, inter-type, andnano/nano-type.

With respect to mechanical properties such as strength and fracture toughness, the most important structure is an intra-type nanostructure where dispersed particles are embedded within the matrix grains, .The highest strength or fracture toughness is mostly achieved when only a few percent of the second-phase particles are dispersed in alumina.According to observations regarding alumina/ silicon carbide system by transmission electron microscopy (TEM), silicon carbide nano-size particles are dispersed homogeneously both inside the alumina grains and on the grain boundaries. Moreover, there are advantages such as that ceramics with a low percent of second-phase particles have better sinter ability, while less dispersed particles have a higher possibility of existing in matrix grains.

The characteristics of nanocomposites observed by many researchers are summarized as follows;

(A) Drastic change of fracture mode from intergranular fracture of monolithic alumina to transgranular fracture of nanocomposites.
(B) Moderate to significant improvement in strength.
(C) Moderate improvement of fracture toughness.
(D)Improvement of several mechanical properties.