By introducing ZrO2 （4Y） powder into the thermit

the large-scale plates of novel Al2O3/ZrO2 （4Y） composite ceramics with different component and microstructure were prepared through combustion synthesis under high gravity

and the correlations of component

microstructures and mechanical properties of composite ceramics were investigated. XRD

SEM and EDS showed that Al2O3/33%ZrO2 （4Y） were composed of random-orientated rod-shaped colonies consisting of a triangular dispersion of orderly t-ZrO2 submicron fibers

surrounded by inter-colony regions consisting of nano-micronmeter spherically-shaped t-ZrO2 grains; meanwhile

Al2O3/40%ZrO2 （4Y） were comprised of micron-meter spherically-shaped t-ZrO2 grains

surround by irregularly-shaped α-Al2O3 grains and a few colonies. Compared to the international directionally-solidified Al2O3/ZrO2 （Y2O3）

the increase in hardness and flexural strength of Al2O3/33%ZrO2 （4Y） in the experiment was due to high densification

small-size defect and high fracture toughness induced by compressive residual stress toughening and transformation toughening mechanisms; meanwhile

in despite of the moderate decrease in hardness

flexural strength and fracture toughness of Al2O3/40%ZrO2 （4Y） were increased by 19.0% and 311.1%

respectively

and the reinforcing of the materials was considered to be a result of small-size defect in micron-meter spherically-shaped t-ZrO2 grain matrix and high fracture toughness induced by stress-induced t-ZrO2 transformation toughening and transformation-induced micro-crack toughening mechanisms.