Influence of dislocation density on the pop-in behavior and indentation size effect in CaF2 single crystals: Experiments and molecular dynamics simulations

• Published in: Acta materialia Vol. 59; no. 11; pp. 4264 - 4273
• Main Authors: LODES, M. A, HARTMAIER, A, GÖKEN, M, DURST, K
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 01.06.2011
• Subjects: Applied sciences; Calcium fluoride; Dislocation density; Dislocations; Exact sciences and technology; Indentation; Metals. Metallurgy; Molecular dynamics; Plastic zones; Simulation; Single crystals; Dislocation density; Atomic force microscopy; Simulation; Size effect; Nanoindentation; Molecular dynamics; Indentation; Single crystal; Dislocation; Calcium fluoride; Dislocations
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2011.03.050

In this work, the indentation size effect and pop-in behavior are studied for indentations in undeformed and locally pre-deformed CaF2 single crystals, using both nanoindentation experiments and molecular dynamics simulations. To study the influence of dislocation density on the indentation behavior, small-scale indentations are carried out inside the plastic zone of larger indentations. This experiment is mimicked in the simulations by indenting a small sphere into the center of the residual impression of a larger sphere. The undeformed material shows the well-known pop-in behavior followed by the indentation size effect. Pre-deforming the material leads to a reduction in the indentation size effect both for experiments and simulations, which is in accordance with the Nix-Gao theory. Furthermore, the pop-in load is reduced in the experiments, whereas a smooth transition from elastic to plastic deformation is found in the simulations. There, plasticity is initiated by the movement of pre-existing dislocation loops in the vicinity of the plastic zone. The simulations thus give a detailed insight into the deformation mechanism during indentation and highlight the importance of the dislocation microstructure for the indentation size effect and dislocation nucleation.