Characterization and modeling of the interplay between grain boundaries and heterogeneous plasticity in titanium

晶界强化效应是现代结构材料发展的关键组成部分之一。过去十年来，超细晶材料、晶界工程和纳米晶材料的重大研究成果就说明了这一点。然而，晶界效应的确切性质还没有被理解到允许理论指导优化微观结构和加速合金发展的水平。我们建议结合、改进和应用最近发展的方法来研究和量化晶界的微观力学行为。我们将使用最近开发的一种评估压痕形貌的技术来实现这一点，以产生对单晶体塑性各向异性的详细了解。该方法的一个突出优势是它在生成高质量数据方面的效率，而以前只能通过仔细的单晶和双晶实验才能产生高质量的数据，这两种实验都涉及大量的实验工作。通过应用这种压痕方法，结合最新的表征和模拟方法，我们将首次对钛多晶中晶界和异质塑性之间的相互作用有一个良好的理解。我们的研究计划的目标是：(1)在大颗粒a-钛的内部进行压痕，以有效地收集单晶数据，并广泛地表征产生的压痕周围的塑性缺陷场。通过与压痕模型的关联，我们将得到单晶钛各向异性塑性的精确本构描述。(2)将这种方法推广到接近晶界的压痕，即准双晶变形。(3)将测得的晶界压痕特性与用单晶压痕标定的本构模型预测的模拟压痕äS进行了比较。这将使我们对不同类型的晶界如何调节局部变形模式有一个定性的理解。(4)基于这种定性的理解，我们将把晶界透过率公式应用到我们的非局域晶体塑性公式中，该公式充分考虑了描述边界和界面两侧变形系统之间的三维关系的结晶学和几何参数的所有相关影响。(5)利用收集到的压痕特征对该晶界感知本构模型进行了验证。(6)一旦建立了本构模型，将使用先前从大量样品中变形的多晶微结构贴片收集的高分辨率实验数据进一步验证本构模型。广泛影响：很难想到材料加工的一个方面比能够可靠地预测非均匀变形更影响社会，这是在能够以物理为基础的置信度预测性能或可靠性之前所必需的。这将通过密歇根州立大学(MSU)和德国杜塞尔多夫的Max-Planck-Institut für Eisenforschung(MPIE)的联合研究项目来实现，该项目提供了相互有用的技能，当整合到国际合作研究计划中时，这些技能可以达到上述目标。这项工作将由三名博士生在密歇根州立大学的比勒和克里普教授的指导下进行，一名博士后和一名博士后由MPIE的克劳迪奥·赞巴迪博士和菲利普·艾森洛尔博士指导。两个实验室之间将进行广泛的交流，以便将实验和分析方法结合起来，以实现这些目标。

The strengthening effect of grain boundaries is one of the key components in the development of modern structural materials. This is illustratcd by the intcrisificd research efforts 011 ultra fine grained materials, grain boundary engineering, and nanocrystalline materials over the last decade. The precise nature of the often beneficial effects of grain boundaries, however, have not been understood to a level which would allow for theory guided optimization of microstructures and accelerated alloy development.We propose to combine, improve, and apply recently developed approaches to investigate and quantify the micromechanical behavior of grain boundaries. We will achieve this using a recently developed technique that evaluates indentation topographies to generate a detailed understanding of plastic anisotropy of single crystals. A prominent advantage of the method is its efficiency in generating high quality data that previously could only be generated by careful single and bi-crystal experimentation, which both involve significantly higher amounts of experimental effort. By applying this indentation approach, combined with state of the art characterization and Simulation methods, we will develop a sound understanding of the interplay between grain boundaries and heterogeneous plasticity in titanium polycrystals for the first time.The goals of our research program are: (1) Carry out indentation within the interiors of large grains of a-titanium to effectively collect single crystal data coupled with extensive characterization of the resulting plastic defect fields surrounding the indents. By correlating with models of the indentation, we will arrive at a precise constitutive description of the anisotropic plasticity of single-crystalline titanium. (2) Extend this methodology to indentations close to grain-boundaries, i.e. quasi bi-crystal deformation. (3) Compare the measured characteristics of indentations at grain boundaries to simulated indentations äs predicted by the constitutive model calibrated using the single crystal indentations. This will lead us to qualitative understanding on how different types of grain boundaries modulate the local deformation patterns. (4) Based on this qualitative understanding we will implement a grain boundary transmissivity formulation into our non-local crystal plasticity formulation that fully accounts for all relevant influences from the crystallographic and geometric parameters that describe the boundary and the 3-dimensional relations between deformation Systems on both sides of the interface. (5) This grain boundary aware constitutive model will be validated against the collected indent characteristics. (6) Once the constitutive model has been developed, it will be further validated using data from previously collected high resolution experimental data from a polycrystalline microstructural patch deformed in a bulk specimen.Broad Impact: It is difficult to think of an aspect of material processing that affects society more than being able to reliably predict heterogeneous deformation, which is required before prediction of performance or reliability can be made with physically based confidence. This will be accomplished in a joint research project involving Michigan State University (MSU) and Max-Planck-Institut für Eisenforschung (MPIE) in Düsseldorf, Germany, where mutually useful skills are present which can reach the above goals when integrated into an international cooperative research program. The work will be carried out by 3 Ph.D. students under the guidance of Profs Bieler and Crimp at MSU, and a post-doc and one Ph.D. Student guided by Claudio Zambaldi, Dr. Philip Eisenlohr at MPIE. Extensive exchanges between the two laboratories will occur in order to integrate experimental and analytical methods to reach these goals.