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

本项目旨在基于透射电子显微镜的直接显微结构证据，开发一种新的结构金属和合金高温变形行为模型。工作的重点是钛合金在许多技术中的应用，包括交通、电力和能源等。目前还没有合适的模型来描述这些材料的位错蠕变。常规形式的缓动螺杆模型严重高估了所观察到的蠕变速率。在缺乏对这种关键变形模式的基本理解的情况下，预测蠕变响应，并为未来的应用开发改进的合金和微观结构，将仍然是一个昂贵且耗时的经验过程。本研究的主要目的是结合最近关于螺旋位错的性质和特征的微观结构观察，以便提出一种预测的、基于物理的蠕变描述。这是通过结合蠕变试验和详细的电子显微镜分析来完成的；将该模型扩展到Ti2AI和Ti6AI单相单晶；最后，通过将这些模型应用于更广泛的材料，包括BCC固溶体，钻石立方和锌共混结构。该模型提供了原子水平过程与宏观性质之间的联系，是构建位错蠕变多尺度处理的天然平台。这项研究对涉及高温蠕变的基本机制有了新的认识，在一些重要的材料系统中，高温性能的基本知识对现在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.***