TRANSFORMATION TEXTURES IN ZIRCONIA

The large shear component of the tetragonal-to-monoclinic transformation in zirconia causes a stress-induced preferred orientation of the tetragonal and monoclinic variants. The resultant texture, which is dependent on the loading condition, has been analyzed in terms of stress assistance to transformation and experimentally verified in simple tension and compression. Such a preferred orientation is a clear indication of the shear contribution to transformation plasticity and to fracture. Other implications of this analysis are also explored. For example, while the monoclinic texture is obviously most relevant to generating strains and plastic work, it is the tetragonal texture which might be advantageously tailored to enhance transformability and toughness. Transformation texture causes the ratio of {111} monoclinic and tetragonal X-ray peaks in tensile fracture to be higher than the actual ratio of monoclinic-to-tetragonal phase fractions, making it generally unsuitable for estimating phase fraction in stress-induced transformation.