Indentation Mechanics of Monocrystalline Substrates

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0084948PeraltaInstrumented sharp indentation provides valuable information on the mechanical properties of materials and is the test of choice when small volumes are involved. This is usually the case in single crystal studies, since they are often produced in small quantities and can be too delicate for conventional testing. Single crystal behavior is intrinsically anisotropic and so is the response of textured polycrystals and thin films, which are also often characterized using indentation. However, most of the models used to analyze hardness are isotropic and, therefore, cannot capture all the aspects of the anisotropic behavior of monocrystalline and/or strongly textured materials. Furthermore, models to account for crystallographic slip around indents on monocrystals do not seem to be available. It is then necessary to perform experimental and theoretical work to relate load-penetration data, slip and hardening behavior around indents on single crystals to their mechanical properties.A dual experimental/theoretical approach can be used to understand the effect of anisotropy on the indentation mechanics of materials. Monocrystals will be grown from selected materials and instrumented indentation tests performed on high symmetry planes. Profilometry, atomic force microscopy and reference grids will be used to determine surface displacements. The slip behavior around indents will be characterized using slip trace analysis and transmission electron microscopy. Meanwhile, small-scale yielding models for sharp indenters will be developed for anisotropic elasticity as well as models to account for plasticity due to crystallographic slip. These models will be used to obtain load-penetration curves and the evolution of the contact area between the sample and the indenter. Finally, correlations between the experimental data and basic material properties in single crystals, such as the elastic moduli and critical resolved shear stresses, will be established through the models. This project will also actively involve undergraduate and graduate students in experimental and theoretical research. ***