Twin and habit plane microstructures due to the tetragonal to monoclinic transformation of zirconia

We first construct Bain strains for the tetragonal to monoclinic (t --> m) transformation of zirconia (ZrO2), and then examine the resulting twin and habit plane microstructures. The (t --> m) transformation in zirconia occurs via two paths; transformation along path I has two Bain strains that involve shearing of a rectangular face of the tetragonal unit cell, and shearing of the square base corresponds to path II. The monoclinic variants resulting from each of the three Bain strains can form 12 twins, and four of the twins corresponding to path II are neither of type I nor of type II. Habit planes do nor exist for the transformation along path I, whereas transformation along path II has: (+/-0.8139 +/-0.3898, -0.4309)(t), (+/-0.6489, +/-0.6271, -0.4309)(t), (+/-0.7804, -0.4530, -0.4309)(t). We predict the exact twin planes observed by Bailey [(1964) Phase transformation at high temperatures in hafnia and zirconia. Proc. Roy. Soc. 279A, 395-412], Bansal and Heuer [(1972) On a martensitic phase transformation in Zirconia ZrO2-I. Metallographic evidence. Acta Metall. 20, 1281-1289] and Buljan el al. [(1976) Optical and X-ray single crystal studies of the monoclinic <----> tetragonal transition in ZrO2. J. Am. Ceram. Soc. 59, 351-354]; additional twins and habit planes that we predict have not yet been observed. (C) 1997 Elsevier Science Ltd.