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 degrees, 1200 degrees and 1350 degrees 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. (C) 1999 Elsevier Science B.V. All rights reserved.