High-Gravity Assisting Combustion Synthesis to Prepare High-Strength Al2O3/ZrO2 (Y2O3) Eutectics

By adding ZrO₂ and Y₂O₃ powder blend into the thermit, large bulk Al₂O₃/ZrO₂ (Y₂O₃) eutectics were prepared by combustion synthesis under high gravity, and the influences of high gravity on microstructures, crystal growth and properties of the materials were also discussed. The XRD patterns showed that the introduction of high gravity field did not change phase constitution of the ceramics, and the ceramic matrix was mainly composed of α-Al₂O₃, t-ZrO₂ and m-ZrO₂. SEM images and EDS analyses showed that with increasing high gravity level, the morphologies of the ceramic microstructures transformed from the cellular eutectics to the rod-shaped colonies, and volume fraction and aspect ratio of the rod-shaped colonies increased while the rod-shaped colonies were refined; as the high-gravity field was larger than 200g, the microstructures of composite ceramics developed as the randomly-orientated rod-shaped colonies with a symmetrical triangular dispersion of tetragonal ZrO₂ fibers of 300nm in the average diameter. Relative density, hardness, flexural strength and fracture toughness simultaneously reached the highest values of 98.6%, 18.6GPa, 1248MPa and 15.6MPa·m^1/2 as the maximum high-gravity level of 250g was achieved. The increases of relative density and hardness of the ceramics with the high-gravity level are attributed to the acceleration of gas-escape from ceramic melts and the elimination of shrinkage cavity in the ceramics. The increase in fracture toughness results from the enhancement of the coupled toughening mechanisms while the increase in flexural strength comes from the refinement of the microstructures, the decrease of critical defect size and the achievement of high fracture toughness.