Implications of Transformation Plasticity in ZrO 2 ‐Containing Ceramics: II, Elastic‐Plastic Indentation

Indentation hardness of partially stabilized zirconia was found to be 8.2 times the uniaxial compressive yield stress. This ratio is anomalously high for ceramic materials and is attributed to pressure hardening in transformation plasticity. An analytic solution of elastic‐plastic indentation using the spherical‐hole model is given, based on a pressure‐sensitive idealized yield criterion. The theory correctly predicts a higher hardness and a larger plastic zone, both in quantitative agreement with the experimental observations in Mg‐PSZ. Data analysis further reveals a large disparity of yield stress and hardness values among cubic, tetragonal, and monoclinic zirconias, resulting from their different phase transformation and twinning capabilities. The broader implications of pressure sensitivity in elastic‐plastic Indentation are rationalized.