MICROWAVE AND CONVENTIONAL SINTERING OF RAPIDLY SOLIDIFIED AL2O3-ZRO2 POWDERS

The Al2O3-ZrO2 eutectic composition was rapidly solidified, forming amorphous and crystalline structures. The as-quenched material was crushed and pressed into pellets which were sintered conventionally or with microwaves. Conventional and microwave sintering at temperatures up to 1600-degrees-C resulted in a microstructure where 100-200 nm ZrO2 grains were present intergranularly in the alpha-Al2O3 grains. Larger ZrO2 grains (approximately 1 mum) were found intergranularly. The as-quenched lamellar structure spheroidized during sintering at high temperatures. Boron contamination of the powders resulted in more homogeneous and dense as-fired samples but promoted the ZrO2 tetragonal-to-monoclinic transformation, which was attributed to increased grain boundary diffusivity. Conventional sintering at low temperatures resulted in the formation of ''rods'' of an Al2O3-rich phase which grew from a low-melting B2O3-rich liquid.