Experimental and Theoretical Study of Ductility in Lamellar Titanium Aluminum

本研究是一个实验与理论相结合的项目，主要研究铝化钛（TiAl）的塑性变形机理。实验部分作为理论部分的输入，反之亦然。本研究的目的是充分表征和确定钛基合金的复合孪晶单晶和层状多晶的变形模式，以显示变形是如何跨越各种类型的边界（包括域和晶界）传递的，并确定位错和孪晶的来源。采用的实验技术是对单晶和多晶进行力学测试，然后使用光学、原子力和透射电子显微镜对变形模式进行表征。理论程序涉及位错核心结构，界面反应和孪生过程的原子模型，使用各种原子间电位。要使用的势是嵌入原子和/或Finnis-Sinclair型，以及基于量子力学的键序势。开发用于这种非立方结构的新的原子间电位将是该计划的重要组成部分，同时也将开发用于确定变形模式的新实验技术。这项研究的结果有望在理解如何以及在什么情况下，低对称性材料可以增韧方面有很大的用处。此外，它还可以显示出可以用来使金属间化合物增韧的技术。＊＊＊

9626344 Vitek This study is a combined, experimental and theoretical project on mechanisms of plastic deformation in titanium aluminide, TiAl. The experimental portion is used as input for the theoretical portion and vice versa. The objectives of the study are to fully characterize and identify the deformation modes in polysynthetically twinned single crystals and in lamellar polycrystals of TiAl-based alloys, to show how deformation is transmitted across the various types of boundaries (including domain and grain boundaries), and to determine the sources of the dislocations and twins. The experimental techniques to be employed are mechanical tests on single crystals and polycrystals, followed by characterization of the deformation modes using optical, atomic force, and transmission electron microscopy. The theoretical program involves atomistic modeling of dislocation core structures, interfacial reactions, and twinning processes, using a variety of interatomic potentials. The potentials to be used are the embedded atom and/or Finnis-Sinclair type, as well as quantum mechanically- based bond order potentials. The development of new interatomic potentials for use in this non-cubic structure will be an important part of the program, as will the development of new experimental techniques for the determination of deformation modes. %%% The results of the study are expected to be of great utility in understanding how, and under what circumstances, low symmetry materials can be toughened. Furthermore, it could show what techniques might be used to toughen intermetallic compounds. ***