Stress-induced martensitic transformation and ferroelastic deformation adjacent microhardness indents in tetragonal zirconia single crystals

The stress-induced tetragonal to monoclinic (t --> m) martensitic transformation, stress-induced ferroelastic domain switching, and dislocation slip were induced by Vickers microindentation at elevated temperatures in polydomain single crystals of 3 mol%-Y2O3-stabilized tetragonal ZrO2 single crystals (3Y-TZS). Chemical etching revealed traces along (310)(t) directions adjacent to indentations, and Raman spectroscopy and TEM have shown that these traces are caused by products of the martensitic transformation, i.e. the monoclinic product phase forms primarily as thin, long plates with a habit plane approximately on ((3) over bar 01)(m). This habit plane and the associated shear strain arising from the transformation, visible in TEM micrographs at the intersection of crystallographically equivalent martensite plates, were successfully predicted using the observed lattice correspondence and the phenomenological invariant plane strain theory of martensitic transformations. The extent of the martensitic transformation increased with increasing temperature from room temperature up to 300 degrees C, but then decreased at higher temperatures. Ferroelastic deformation of tetragonal ZrO2 has been observed at all temperatures up to 1000 degrees C. At the highest temperature, only ferroelastic domain switching and dislocation slip occurred during indentation-induced deformation. (C) 1998 Acta Metallurgica Inc.