(Georgia Institute of Technology, 2023-04-25)
Johnson, Camilla E.
This thesis develops and implements high-throughput indentation protocols which require
small sample volumes to rapidly characterize the cyclic behaviors of metals through extraction of intrinsic material properties. First, novel spherical microindentation protocols are developed on wrought Ti-6Al-4V (Ti64) samples then extended to laser powder bed fusion processed Inconel 718 (IN718) samples. In these studies, repeatable load-displacement loops are successfully converted into hysteresis stress-strain loops. Hysteresis energy density plots allowed the indentation stress at which significant plastic deformation began to be pinpointed. Peak indentation stress and strain values are used to create cyclic stress-strain curves which showed great agreement to that from conventional uniaxial cyclic tests of material from the same sample blocks. The study on IN718 samples captured changes in the cyclic response as a function of post-processing heat treatments and anisotropy of the as-printed samples. Finally, cyclic spherical nanoindentation protocols are developed and demonstrated on titanium alloy Ti-6Al-2Sn-4Zr-2Mo (Ti6242) to evaluate the cyclic behavior as a function of grain orientation of the primary-alpha phase and morphology between the globular primary-alpha and dual-phase alpha -beta basketweave grains. Due to the small length scales of this study, unique features tied to dislocation motion were captured in the load-displacement and stress-strain loops as well as the final cyclic indentation stress-strain curves. Outcomes from this work contribute to material design rules and provide reliable mechanical data useful for refining crystal plasticity models. These case studies critically evaluate the effectiveness of the newly developed high-throughput cyclic response screening methods. It is seen that the protocols have a large applicability across multiple materials and length scales and contribute to expediting materials design, innovation, and characterization of advanced materials.