Plastic deformation and allotropic phase transformations in zirconia ceramics during high-pressure torsion

Severe plastic deformation using high-pressure torsion (HPT) is successfully applied at room temperature to partially stabilized ZrO2. X-ray diffraction and Raman spectroscopy analyses reveal that appreciable strain is introduced in the sample and a phase transformation with a coherent interface occurs from the metastable tetragonal phase to the monoclinic phase during HPT. The fraction of the stress-induced monoclinic phase increases with straining, reaches a saturation level. Transmission electron microscopy shows that nanograins of high dislocation density but with no twins are formed during HPT.