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

在高应变率下，金属和合金表现出通过形成绝热剪切带而变形的趋势。当塑性变形所耗散的热量不能足够快地耗散时，发生局部软化，并且随后的变形在非常薄的材料区域中进行。这种（准）绝热剪切带的形成一方面受（热）机械载荷的影响;另一方面，材料特性（机械、物理、微观结构）影响剪切带。一个尚未完全理解的关键影响因素是材料的初始微观结构状态：它决定了初始力学行为和在随后的剪切带过程中可能发挥作用的不同微观结构变形机制。一个系统的微观结构变形机制和剪切带与不同的微观结构特征的相互作用的分析是需要一个更基本的，微观力学和微观结构的剪切带的理解。本文提出的研究项目将技术相关的钛合金Ti-10 V-2Fe-3Al视为模型系统，其中定义明确的热处理可用于创建显着不同的初始微观结构，然后允许单独研究（准绝热）剪切带在不同应变速率下的形成。特别关注剪切带的微观结构表征;它们的形态;局部微观结构特征;宏观和局部力学行为;不同施加应力状态的影响。此外，该项目旨在开发一个经验模型，可以预测剪切带形态（传统的块状带与显微结构特征分裂的多个细带）。该项目的目标是有助于更详细地了解微观结构参数之间的关系，（热）-机械边界条件，力学行为和由此产生的剪切带形态。

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.