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MM: Fachverband Metall- und Materialphysik
MM 64: Mechanical Properties: Plasticity, fracture, fatigue, wear - II
MM 64.2: Vortrag
Donnerstag, 19. März 2020, 17:45–18:00, IFW B
Atomistic and continuum simulation of brittle and ductile crack in titanium aluminide single and bi-crystals — •Anupam Neogi, Alexander Hartmaier, and Rebecca Janisch — ICAMS, Ruhr-Universität Bochum, Germany
Ti-Al alloys are well known for their excellent mechanical properties. However, they often exhibit low-ductility, which leads to in-service brittle failure. The fracture behavior of metallic materials is primarily governed by the competition between emission of dislocations and Griffith cleavage at the crack tip. In two-phase Ti-Al however, this simple picture is questionable. Here the anisotropy of the major phases, γ-TiAl and α2-Ti3Al, with a limited number of slip systems, leads to complex crack propagation mechanisms.
We investigate crack propagation under mode I loading in single-crystal γ and α2 Ti-Al, as well as at γ/γ interfaces, using anisotropic linear elastic fracture mechanics (LEFM) and atomistic simulations. The latter show a significant directional dependence of crack tip behavior. For instance, a (111)-crack in γ-TiAl propagates by Griffith cleavage along [211], but by dislocation emission along [112]. Basal cracks in α2-Ti3Al are generally assumed to propagate in a brittle manner, but we observe nucleation of dislocations if the crack propagates along [1010]. The complexity increases in the vicinity of γ/γ interfaces, in which the mechanism depends on the orientation of the crack plane with respect to the interface. Nevertheless, it is the remarkable conclusion of this study that the predictions of LEFM agree well - qualitatively and quantitatively - with atomistic simulations.