Ultra fine MgO powders with or without a small amount of SiC whisker were capsulated in a metallic mold with dimensions of O.D. 22φ-I.D. 10φ×30lmm. The mold was preheated at a temperature of 900°-1600°C for 8-10 minutes, and was press-forged in few seconds under an uniaxial compressive load. The deformation ratio of the mold was about 30% of the original height, and the maximum pressure was about 5000kgf/cm2.
The polycrystalline MgO without SiC whisker prepared by the hot-forge processing at 1300°C was composed of submicron grains, and its Vickers hardness was almost the same as that of the theoretically dense polycrystalline MgO prepared by hot-pressing.
The hardness of the MgO-SiC whisker composite ceramics prepared by this processing, on the otherhand, decreased with increasing whisker content, and the whiskers in the composites were preferentially orientated perpendicular to the press-forging axis. The fracture toughness of the MgO-SiC whisker composite ceramics was about 1.5 times as large as that of the polycrystal without SiC whisker.