Diffusion in the Ti-Al system

Many properties of industrial Ti-Al alloys, such as high-temperature stabil ity of the lamellar structure and creep resistance, are determined by diffu sion rates in the phases and along the interfaces. The knowledge of diffusi on characteristics and fundamental understanding of diffusion mechanisms ar e of great importance to the research and design of industrial Ti-Al alloys . This paper gives an overview of recent progress in experimental and theor etical studies of diffusion behavior in the phases of the Ti-Al system. The experimental methods used in modern diffusion measurements are briefly des cribed, and recent experimental results for Ti and Al diffusion in alpha-Ti (AI), beta-Ti(AI), and intermetallic phases alpha(2)-Ti3Al and gamma-TiAl, are summarized. The results for interdiffusion and impurity diffusion in th ese phases are also discussed in detail. The second part of the paper provi des an overview of current understanding of point defects and diffusion mec hanisms in Ti3Al and TiAl. A statistical model of point-defect disorder in ordered compounds is presented and applied to Ti3Al and TiAl using input da ta generated with embedded-atom potentials. Possible atomic mechanisms of d iffusion in these compounds are analyzed in detail, and methods of diffusio n calculations under different mechanisms are reviewed. The relative import ance of different mechanisms in Ti3Al and TiAl is evaluated by comparing th eir estimated activation energies. Prospective topics of further experiment al and theoretical research in this area are outlined. (C) 2000 Acta Metall urgica Inc. Published by Elsevier Science Lin. All rights reserved.