Particulate Composites in the Al2O3-YAG System

摘要

Contrary to the composites in the Al2O3-ZrO2 system, materials with Al2O3 matrix and YAG (Y3Al5O_(12)) inclusions are much less recognized. YAG is one of the three compounds in the Y2O3-Al2O3 system of the highest alumina content. It is well known that YAG polycrystals belong to the materials of especially high creep resistance. Since coefficients of thermal expansion of YAG and alumina do not differ essentially from each other, the YAG inclusions in the alumina matrix seem to lead to a material of interesting mechanical properties. Only a few publications concern the preparation of such composites by powder sintering. In the present work Y2O3 was introduced to alumina by yttrium hydroxide precipitated within the alumina powder suspension. By low temperature calcinations a homogenous alumina/ yttria mixture was received. Yttria content corresponded to 20 vol.% YAG after the reaction. It was found that at 1500°C YAG and α-alu-mina were the only phases present in the system. The investigation of the resulting material microstructure revealed a uniform distribution of sub-micrometer YAG particles. Hardness of the material was similar to that of dense alumina and fracture toughness (K_(lc) = 6 MPa·m~(1/2)) was close to the observed in the case of the 3-YTZP material.