The Effects of Chemistry and Microstructure on Deformation Mechanisms in Titanium-Aluminides

这是一项关于一些内在和外在因素的作用的研究，包括化学和微观结构的影响，在钛铝基体系中运作的变形机制。本研究的目的有四个方面：(1)确定铝化钛（TiAl）中键合电荷密度的各向异性，并评估其对变形过程的影响。用四圆x射线衍射法测定了已知成分的标准样品的德拜-沃勒因子的准确值。随后，推导出TiAl的低阶结构因子，并以此评价了键合电荷密度的各向异性。然后评估由此产生的电荷密度对变形机制的可能影响。(2)确定了取代溶质和间隙溶质添加对位错迁移率的影响。本文在TiAl的单相样品上进行了实验，以了解TiAl中氧杂质与位错之间的相互作用。(3)评价了Ti3Al对tial基体系变形行为和断裂微观机制的影响。通过透射电镜（TEM）研究了Ti3Al在片层、等轴和双相微观结构中的变形行为，特别强调了通过Ti3Al的滑移传递，以及TiAl和Ti3Al界面处的应变积累。(4)研究了以类似于镍基高温合金的方式，通过添加溶质来设计TiAl基系统界面性能的能力。该研究考察了钛铝合金的变形机制，由于缺乏对与其力学行为相关的一些重要因素的理解，其实际应用受到限制。这一努力也为高温金属化合物的研究奠定了科学基础。＊＊＊

9622497 Fraser This is a study of the role of a number of intrinsic and extrinsic factors, including chemical and microstructural effects, on the deformation mechanisms operative in titanium aluminide-based systems. The objectives of this research are fourfold: (1) one aim is to determine the anisotropy of the bonding charge densities in titanium aluminide (TiAl) and assess its influence on deformation processes. Accurate values of the Debye-Waller factors are determined on standard samples of known compositions using four-circle x- ray diffraction. Subsequently, low-order structure factors for TiAl are deduced from which the anisotropy of bonding charge densities are assessed. The possible influence of the resulting charge densities on deformation mechanisms are then assessed. (2) the effects of both substitutional and interstitial solute additions on dislocation mobilities are determined. Here, experiments are performed on single phase samples of TiAl to develop an understanding of the interaction between oxygen impurities and dislocations in TiAl. (3) an assessment of the role of Ti3Al on the deformation behavior and micro-mechanisms of fracture in TiAl-based systems is made. The deformation behavior of Ti3Al in lamellar, equiaxed and duplex versions of the microstructures is determined by post-mortem transmission electron microscopy (TEM) studies, with particular emphasis being placed on slip transmission through Ti3Al, and the accumulation of strain at interfaces between TiAl and Ti3Al. (4) the ability to engineer interface properties in TiAl- based systems by solute addition, in an analogous manner to that in Ni-base superalloys, is investigated. %%% The research examines deformation mechanisms in titanium aluminide alloys, whose practical applications are limited by a lack of understanding of a number of important factors related to their mechanical behavior. The effort also contributes to the scientific base for elevated temperature interme tallic compounds. ***