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

9622497弗雷泽这是一项对一些内在和外在因素的作用的研究，包括化学和微观结构效应，对钛铝化物系统中的变形机制起作用。本研究的目的有四个：(1)确定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。用四圈X射线衍射法在已知组成的标准样品上测定了德拜-沃勒因子的精确值。在此基础上，推导了TiAl的低阶结构因子，并由此估算了成键电荷密度的各向异性。然后评估了由此产生的电荷密度对变形机制的可能影响。(2)确定了替代和间隙溶质添加对位错迁移率的影响。在这里，我们对TiAl的单相样品进行了实验，以加深对TiAl中氧杂质和位错之间的相互作用的理解。(3)评价了TiAl基合金中Ti3Al对变形行为和断裂微观机制的影响。研究了Ti3Al在层状、等轴和双相组织中的变形行为，重点研究了Ti3Al的滑移传输和TiAl与Ti3Al界面的应变积累。(4)与镍基高温合金类似，研究了通过溶质添加来控制TiAl基系界面性质的能力。这项研究考察了钛铝化物合金的变形机制，由于缺乏对与其力学行为相关的许多重要因素的了解，其实际应用受到限制。这一努力也为高温中间化合物的科学基础做出了贡献。***

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. ***