Ceramic composition

Novel transformation toughened ceramic compositions comprising finely divided Zr02-Hf02 solid solution particles dispersed in a Al203-Cr203 (alumina) or 3Al203.2Si02-3Cr203.2Si02 (mullite) solid solution matrix phase. It is found that increased hardness and modulus associated with higher relative Cr203 content (e.g. 20 mole % ) in the matrix phase and increased fracture toughness associated with higher relative Hf02 content ( e.g. 10 to 20 mole % ) in the disperse phase represent viable and improved ceramic compositions. Such transformation toughened ceramic compositions are considered useful in superhot light diesel engine applications, high temperature gas turbines and ultrahigh temperature ceramic heat exchangers.