Characteristics of a layered and graded alumina/calcium-hexaluminate composite

A novel route to simple processing of a layered and graded material (LGM) based on alumina/calcium-hexaluminate (CA 6) is described. The processing involves partial infiltration of a porous alumina preform with hydrolysed calcium acetate to yield a homogeneous layer of alumina and a heterogeneous graded layer of CA 6/alumina. Analysis by X-ray diffraction (XRD) has revealed the existence of concentration gradients, the CA 6 content decreasing with increasing sample depth. In-situ high temperature neutron diffraction (HTND) shows that the formation temperatures of CA, CA 2, and CA 6 are respectively 1000°, 1200° and 1350°C. The presence of CA 6 appears to hinder the shrinkage and thus densification during sintering, as well as causing a reduction of hardness and flexural modulus. Scanning electron microscopy (SEM) has revealed the presence of plate-like morphology of CA 6 grains and the graded microstructure within the LGM.