Y. Mishin

Diffusion in the Ti-Al system

Many properties of industrial Ti–Al alloys, such as high-temperature stability of the lamellar structure and creep resistance, are determined by diffusion rates in the phases and along the interfaces. The knowledge of diffusion characteristics and fundamental understanding of diffusion mechanisms are of great importance to the research and design of industrial Ti–Al alloys. This paper gives an overview of recent progress in experimental and theoretical studies of diffusion behavior in the phases of the Ti–Al system. The experimental methods used in modern diffusion measurements are briefly described, and recent experimental results for Ti and Al diffusion in α-Ti(Al), β-Ti(Al), and intermetallic phases α2-Ti3Al and γ-TiAl, are summarized. The results for interdiffusion and impurity diffusion in these phases are also discussed in detail. The second part of the paper provides an overview of current understanding of point defects and diffusion mechanisms in Ti3Al and TiAl. A statistical model of point-defect disorder in ordered compounds is presented and applied to Ti3Al and TiAl using input data generated with embedded-atom potentials. Possible atomic mechanisms of diffusion in these compounds are analyzed in detail, and methods of diffusion calculations under different mechanisms are reviewed. The relative importance of different mechanisms in Ti3Al and TiAl is evaluated by comparing their estimated activation energies. Prospective topics of further experimental and theoretical research in this area are outlined.

Interatomic potentials for atomistic simulations of the Ti-Al system

Semiempirical interatomic potentials have been developed for Al,

An embedded-atom potential for the Cu–Ag system

\ensuremath{\alpha}\ensuremath{-}\mathrm{Ti},

Grain boundary diffusion : recent progress and future research

and

Development of an interatomic potential for the Ni-Al system

\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}

Duality of dislocation content of grain boundaries

within the embedded atom method (EAM) formalism by fitting to a large database of experimental as well as ab initio data. The ab initio calculations were performed by the linearized augmented plane wave (LAPW) method within the density functional theory to obtain the equations of state for a number of crystal structures of the Ti-Al system. Some of the calculated LAPW energies were used for fitting the potentials while others for examining their quality. The potentials correctly predict the equilibrium crystal structures of the phases and accurately reproduce their basic lattice properties. The potentials are applied to calculate the energies of point defects, surfaces, and planar faults in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al system, the proposed potentials provide a reasonable description of the lattice thermal expansion, demonstrating their usefulness for molecular-dynamics and Monte Carlo simulations at high temperatures. The energy along the tetragonal deformation path (Bain transformation) in

Structural phase transformations in metallic grain boundaries

\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}

Effect of Interface Phase Transformations on Diffusion and Segregation in High-Angle Grain Boundaries

calculated with the EAM potential is in fairly good agreement with LAPW calculations. Equilibrium point defect concentrations in

Atomistic simulation of point defects and diffusion in B2 NiAl: Part I. Point defect energetics

\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}

Atomic Mechanisms of Grain Boundary Motion

are studied using the EAM potential. It is found that antisite defects strongly dominate over vacancies at all compositions around stoichiometry, indicating that