Pressureless sintering of Al2O3 containing up to 20 vol% zirconium diboride (ZrB2)

The production of particle composites by pressureless sintering provides a cost-effective alternative to production variants such as hot-pressing. However, minimal quantities of additives are sufficient to impede the densification of oxidic matrix components. The sintering behaviour of alumina powder is studied as a function of the volume fraction of ZrB2 (up to 20 vol%). A distinction can be made between two sintering ranges according to temperature: at T less than or equal to 1700 C a solid-state process applies. This process is decisively influenced by the B2O3 contained in the raw material ZrB2. The validity of the Lange model, which describes the influence of increasing volumes of inclusions on the densification behaviour of a crystalline matrix phase, is confirmed in this temperature range. At T greater than 1700 C, an aluminium borate melt occurs, accelerating the sintering process substantially. As a result, the composites quickly attain matrix densities greater than 95% of theoretical. At higher firing temperatures the ZrB2 particles coalesce, resulting in the formation of an electrically conductive penetration structure at a content level of 20 vol%. 13 refs.