Sintering and Contact Damage of Spinel/Mica Composites Prepared from Alumina, Magnesia and Mica-Composition Glass Powder Mixtures

Conventional alumina and magnesia powders were mixed with a mica-composition glass powder, compacted, and fired. A dense spinel/mica composite was obtained at a low temperature of 1200°C for the specimen of 20% mica-composition glass addition. The sintering was promoted by not only the dissolution of fluorine ion but also the formed liquid phase. The liquid phase allowed the volume expansion caused by the reaction between the alumina and the magnesia to be effective for ensication, like a closer packing of particles. Furthermore, the liquid phase caused particle rearrangement and dissolution-precipitation. Numerous flakelike mica crystals of several micrometers separated out in the interparticle regions of the spinel. Both brittle and quasi-plastic damage modes were competitive on the surface and in the subsurface of the specimen. The bending strength was slightly decreased by Hertzian indentation. The fracture site in the post-indented specimen was a cornlike crack. However, the quasi-plasticity prevented catastrophic failure from the cor-nlike crack. These results indicate that the composite had flaw tolerance.