By introducing ZrO2（4Y）powder into the thermit

Al

2

O

3

/YSZ composite ceramic plates were prepared through combustion synthesis under high gravity

and microstructure and mechanical properties of the composite ceramics were investigated.The eutectic in-situ composite ceramics consist of the Al

2

O

3

matrix colonies in which t-ZrO2 submicron fibers are embedded

surrounded by the boundary region with t-ZrO2 and Al

2

O

3

irregular particles

and the hypoeutectic ceramics are composed of Al

2

O

3

grain surrounded by ZrO2 bands due to the divorced eutectic growth while the hypereutectic ceramics are mainly made up of fine isolated t-ZrO2 spherical grains.Vickers hardness of the eutectic composite ceramics were reached up to the maximum value of 16.7GPa due to high residual stress in the colony matrix and fine boundary regions of eutectic colony

while fracture toughness can reach up to 14.6 MPa·m1/2 in the hypereutectic composite ceramics due to toughening mechanism involving stress induced t-ZrO2 transformation toughening and transformation induced by micro-crack toughening.