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X‐ray diffraction data are presented in support of the existence of ferroelasticity in tetragonal zirconia. Reorientation of ferroelastic domains by externally applied stress is proposed as a toughening mechanism. Toughening by this mechanism can occur in addition to transformation toughening and also explains high toughness of some zirconias which exhibit no transformation to the monoclinic form. Zirconia ceramics toughened by the ferroelastic mechanism have the potential to retain high toughness at elevated temperature unlike transformation toughening.
Virkar et al. (1986) studied this question.