Infiltration and physical characteristics of functionally graded alumina/calcium-hexaluminate composites

A novel route to simple processing of functionally graded materials (FGMs) based on alumina/calcium-hexaluminate (CA6), and the associated infiltration and physical characteristics are 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 CA6/alumina. Two contrasting heat-treatment schedules, namely pre-sintered annealing and post-sintered annealing, were used to investigate their influence on the resultant phase compositions and physical properties. Analysis by X-ray diffraction has revealed the existence of concentration gradients, the CA6 content decreasing with increasing sample depth. The presence of CA6 appears to hinder the shrinkage and thus densification during sintering, as well as hindering grain growth of alumina matrix. Scanning electron microscopy has revealed the presence of plate-like morphology of CA6 grains and the graded microstructure within the FGM.