Alloying behaviour 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 aluminium diffused from their bearing alloys, Ni₂AlTi or NiAl, and were incorporated into the lattice of yttria—partially stabilized zirconia (Y-PSZ) when the cermet was sintered at temperatures in the range 1400–1600°C. The specimens sintered with Ni₂AlTi 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. NiAl₂O₄ spinel containing stacking faults was formed at the expense of both Ni₂AlTi and NiAl, which also dissolved a small amount of zirconium and yttrium. In specimens sintered in the liquid phase with the addition of Ni₂AlTi, a metastable phase of orthorhombic symmetry derived from the spinel structure and a precipitate-free zone formed by ZrO₂ grain-boundary migration, were identified at the grain boundary between the spinel and the zirconia.