Properties of zirconia-ceria-hafnia alloys

Tetragonal zirconia alloys containing up to 18 mol% ceria and 30 mol% hafnia were prepared by several wet-chemical techniques, sintered to high density, and their microstructural and mechanical properties studied. Toughening in such alloys depends on the retention of the metastable tetragonal phase and the stress required for its transformation to the monoclinic phase. The degree of metastability of the tetragonal phase in these ternary zirconia alloys was a function of the relative amounts of ceria and hafnia present. Such alloying, along with control of grain size, provides an ability to modify the fracture toughness and the temperature range over which the toughness is optimized