Effect of multi-phase microstructures on rate-dependent shear band formation in the meta-stable beta-titanium alloy Ti-10V-2Fe-3Al

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At elevated stain rates, metals and alloys exhibit a tendency to deform by the formation of adiabatic shear bands. When the heat dissipated by plastic deformation cannot be dissipated quickly enough, local softening occurs, and subsequent deformation proceeds in an exceedingly thin material region. The formation of such (quasi-)adiabatic shear bands is on the one hand affected by the (thermo-)mechanical loading; on the other hand, the material properties (mechanical, physical, microstructural) influence shear banding. A key influence factor that is not yet fully understood is the initial microstructural state of the material: it determines both the initial mechanical behavior and the different microstructural deformation mechanisms that can come into play during subsequent shear banding. A systematic analysis of microstructural deformation mechanisms and of the interaction of shear bands with different microstructural features is needed for a more fundamental, micromechanical and microstructural understanding of shear banding. The research project proposed here considers the technologically relevant titanium alloy Ti-10V-2Fe-3Al as a model system where well-defined heat treatments can be used to create significantly different initial microstructures, which then allows to individually study (quasi-adiabatic) shear band formation at different strain rates. Special focus is placed on microstructural characterization of the shear bands; their morphologies; local microstructural features; the macroscopic as well as local mechanical behavior; the effect of different applied stress states. Moreover, the project aims at the development of an empirical model that allows to predict shear band morphology (conventional massive band vs. multiple fine bands split by microstructural features). The goal of this project is to contribute to a more detailed understanding of the relation between microstructural parameters, (thermo)-mechanical boundary conditions, mechanical behavior and the resulting shear band morphologies.