In situ indentation in a high-resolution transmission electron microscope (HRTEM) is used to observe and quantify dislocation dynamics in crystalline solids. Two examples will be highlighted. First, migration of incoherent twin boundaries that leads to detwinning, and a dislocation multiplication mechanism in nanotwinned Cu. Second, dislocation nucleation and glide in single crystalline TiN thin films. The structural images acquired under load are used to measure lattice strains and the corresponding local stresses are inferred from first-principles computed non-linear elastic stress-strain response. This experimental approach is shown to estimate local resolved shear stresses corresponding to partial or full dislocation nucleation and motion of full dislocations in high strength materials, and validate the first-principles calculated Peierls stresses. The insights from in situ TEM measurements are used to interpret unusual nano-mechanical response of nanoscale materials.
Seminars are open to alumni, friends of the Department, and the general public.