Influence of granule characteristics on fabrication of translucent alumina ceramics with high strength and reliability

Abstract

Translucent alumina ceramics with high strength and reliability were fabricated through dry pressing of industry-grade granules and subsequent vacuum-sintering prior to hot isostatic pressing (HIP). The raw materials consisted of two types of granules, containing acrylic binder with and without 500ppm MgO. The internal structures of samples in each manufacturing step were evaluated by the liquid immersion method using an optical microscope. Large defects and their transitions were observed in the samples after each processing step. The fabricated ceramics had high relative density (<99.6%) and very fine microstructures with grain sizes smaller than 1μm. In the granule system with the binder non-uniformly distributed, interstices in the granules were observed in the powder compacts and samples after vacuum sintering. Alumina ceramics derived from the granule system with uniformly distributed binder and MgO additive exhibited high translucency with 50% in-line transmittance and strength greater than 700 MPa. This result suggests that characteristics of the granules considerably affect not only the packing structures in powder compacts but also the microstructure and properties of the sintered ceramics.