Development and Application of a New Model for High Temperature Creep Based on the Jogged-Screw Model

该项目旨在开发一种新的结构金属和合金高温变形行为的模型，该模型基于使用透射电子显微镜的直接显微组织证据。工作的重点是钛合金在交通、电力和能源等领域的应用，目前还没有足够的模型来描述这些材料的位错蠕变。传统形式的螺杆模型严重高估了观测到的蠕变速率。在缺乏对这一关键变形模式的基本了解的情况下，预测蠕变响应，并为未来的应用开发改进的合金和微观组织，仍然是一个昂贵且耗时的经验过程。这项研究的主要目的是结合最新的微观结构观察，对螺杆位错上的弯曲的性质和特征进行观察，以便提出一种基于物理的蠕变预测描述。这是通过蠕变测试和详细的位错特征的电子显微镜分析相结合的实验工作来实现的；通过将该模型的应用扩展到Ti2Al和Ti6Al的单相单晶；最后通过将这些模型应用于更广泛的材料，包括体心立方固溶体、钻石-立方体和锌-混合结构。该模型提供了原子水平过程和宏观性质之间的联系，是建立位错蠕变多尺度处理的天然平台。%这项研究对高温蠕变的基本机制有了新的理解，并在几个重要的材料系统中具有重要意义，在这些系统中，高温性能的基础知识对目前和未来的应用至关重要。*

This project is aimed at the development of a new model for high temperature deformation behavior of structural metals and alloys based on direct microstructural evidence using transmission electron microscopy. The emphasis of the work is on Ti alloys that find application in many technologies including transportation, power and energy, etc. Currently there is no adequate model for the dislocation creep of these materials. The jogged-screw model in its conventional form severely over-predicts the observed creep rates. In the absence of such a fundamental understanding of this critical deformation mode, prediction of creep response, and developing improved alloys and microstructures for future applications, will remain a costly and time-consuming empirical process. The main goals of this study are to incorporate the recent microstructural observations on the nature and character of jogs on screw dislocations so that a predictive, physically based description of creep can be put forth. These are accomplished by combined experimental work on creep testing and detailed electron microscopy analyses of dislocation characteristics; by extending the application of the model to single-phase single crystals of Ti2AI and Ti6AI; and finally by applying these models to a wider range of materials including BCC solid solutions, diamond-cubic and zinc-blend structures. The model provides a link between atomic-level processes and macroscopic properties, and is a natural platform from which to build multi-scale treatments of dislocation creep. %%%This research develops new understanding of the ftmdainental mechanisms involved with high temperature creep and has significance in several important materials systems where a fundamental knowledge of high temperature performance is crucial for present and future applications.***