Microstructure and mechanical properties of hot pressed Al₂O₃-ZrO₂ ceramics prepared from ultrafine powders

The microstructure and mechanical properties of hot pressed Al₂O₃-ZrO₂ ceramics prepared from ultrafine powders were studied by means of hardness and fracture toughness tests, X-ray diffraction, scanning and transmission electron microscopy, and electron probe microanalysis. Experimental results show that Al₂O₃-ZrO₂ceramics combine the high modulus of Al₂O₃and phase transformation toughening of ZrO₂ and give good mechanical properties. The fracture toughness of the samples increases monotonically with increasing ZrO₂content. When the content ofZrO₂is low, the ZrO₂particles are surrounded by Al20Jgrains and the matrix is thus strengthened, but when the content of ZrO₂ is high, the microcracks resulting from the tetragonalmonoclinic phase transformation decrease the strength of the material. The relative density of the samples also increases with increasing ZrO₂content, which is beneficial to both strength and toughness. Banded abnormal growth of the Al₂O₃grains parallel to the hot pressing plane wasfound in the samples. This phenomenon is considered to be a result of the priority of Al₂O₃ grain growth and aggregation of ZrO₂ along the pressing direction in the later stages of hot pressing.