Infiltration-processed, functionally graded aluminium titanate/zirconia–alumina compositePart I Microstructural characterization and physical properties

A novel route for processing aluminium titanate (AT)/(alumina–zirconia (AZ)) with graded microstructure and properties is described. This process offers a simple means of tailoring the composition and microstructure of ceramic materials. The processing involves infiltrating porous AZ preforms with a solution of TiCl4, followed by sintering at 1550°C for 3 h. The resultant material has a homogeneous core encased with a graded and heterogeneous layer of AT/AZ. Analyses by X-ray diffraction and energy-dispersive spectrometry have revealed the existence of concentration gradients, the AT content decreasing with increasing sample depth. The presence of both AT and zirconia inhibits the growth of alumina grains through a pinning mechanism. The existence of microcracking in AT and zirconia grains has been revealed by scanning electron microscopy. The graded material displays gradual changes in thermal expansion values due to the presence of AT which gradually reduces in amount from the surface to the core. The inclusion of zirconia has a favourable effect on the thermal stability of AT against phase decomposition. © 1998 Kluwer Academic Publishers