INDENTATION SIZE EFFECT AND 3D DISLOCATION STRUCTURE EVOLUTION IN (001) ORIENTED SrTiO_3: HR-EBSD AND ETCH-PIT ANALYSIS

摘要

Most crystalline materials exhibit an indentation size effect (ISE), i.e., an intrinsic increase in hardness with decreasing penetration depth. During indentation testing, the material underneath the indenter is heavily deformed, introducing strain gradients in the materials, causing high local dislocation densities. In the present work, the three-dimensional (3D) dislocation structure evolution and ISE in (001) oriented Strontium Titanate (STO) have been studied by direct observation of dislocations using chemical etching and high-resolution electron backscattered diffraction (HR-EBSD) analysis. The sequential polishing, etching and imaging technique was used to reveal the 3D dislocation etch-pit structure at various sub-surface depths using confocal laser and scanning electron microscopy (Fig. 1). The 3D dislocation etch-pit analysis of spherical indentations confirm that, at the early stage of plastic deformation, the dislocation pile-ups were aligned in <100> directions, lying on {110}_(45) planes, inclined at 45° to the (001) surface. At higher mean contact pressure and larger indentation depth, however, dislocation pile-ups along <110> directions appeared, lying on {110}_(90) planes, perpendicular to the (001) surface. These observations were qualitatively confirmed by corresponding direct Molecular Dynamics Simulations.