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

A novel route to simple processing of a layered and graded material (LGM) b ased on alumina/calcium-hexaluminate (CA(6)) is described. The processing i nvolves partial infiltration of a porous alumina preform with hydrolysed ca lcium acetate to yield a homogeneous layer of alumina and a heterogeneous g raded layer of CA(6)/alumina. Analysis by X-ray diffraction (XRD) has revea led 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 re spectively 1000 degrees, 1200 degrees and 1350 degrees C. The presence of C A(6) appears to hinder the shrinkage and thus densification during sinterin g, as well as causing a reduction of hardness and flexural modulus. Scannin g electron microscopy (SEM) has revealed the presence of plate-like morphol ogy of CA(6) grains and the graded microstructure within the LGM. (C) 1999 Elsevier Science B.V. All rights reserved.