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

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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.***