ALLOYING BEHAVIOR OF NI2ALTI AND NIAL IN YTTRIA PARTIALLY STABILIZED ZIRCONIA

The X-ray lattice parameter and energy-dispersive X-ray (EDX) analysis indicated that titanium, nickel and a small amount of aluminum diffused from their bearing alloys, Ni//2AlTi or NiAl, and were incorporated into the lattice of yttria-partially stabilized zironia (Y-PSZ) when the cermet was sintered at temperatures in the range 1400-1600 degree C. The specimens sintered with Ni//2AlTi rather than with NiAl as the additive had a higher growth rate of zirconia, more contraction of the cubic (c-) zirconia lattice and a larger lattice misfit between c- and tetragonal (t-) zirconia. NiAl//2O//4 spinel containing stacking faults was formed at the expense of both Ni//2AlTi and NiAl, which also dissolved a small amount of zirconium and yttrium. In specimens sintered in the liquid phase with the addition of Ni//2AlTi, a metastable phase of orthorhombic symmetry derived from the spinel structure and a precipitate-free zone formed by ZrO//2 grain-boundary migration, were identified at the grain boundary beween the spinel and the zirconia.