Indentation Mechanics of Monocrystalline Substrates

Peralta仪表式尖锐压痕提供了有关材料机械性能的有价值的信息，是涉及小体积时的首选测试。在单晶研究中通常是这种情况，因为它们通常是小批量生产的，对于常规测试来说可能太微妙了。单晶的行为本质上是各向异性的，织构多晶和薄膜的响应也是如此，它们也经常使用压痕来表征。然而，大多数用于分析硬度的模型是各向同性的，因此不能反映单晶和/或强织构材料的各向异性行为的所有方面。此外，解释单晶上压痕周围晶体滑移的模型似乎还不存在。因此，有必要进行实验和理论工作，将载荷穿透数据、压痕周围的滑移和硬化行为与单晶的力学性能联系起来。可以使用双重的实验/理论方法来理解各向异性对材料压痕力学的影响。单晶将从选定的材料和在高对称性平面上进行的仪器化压痕测试中生长出来。将使用轮廓术、原子力显微镜和参考网格来确定表面位移。压痕周围的滑移行为将用滑移轨迹分析和透射电子显微镜来表征。同时，将开发用于各向异性弹性的小尺度尖头屈服模型以及考虑晶体滑移引起的塑性的模型。这些模型将被用来获得载荷-穿透曲线和样品与压头之间接触面积的演变。最后，通过这些模型将建立单晶材料的基本性质与实验数据之间的关系，如弹性模数和临界可分解剪应力。该项目还将积极吸收本科生和研究生参与实验和理论研究。***

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. ***