Hall—Petch relation in two-Phase TiAl alloys

The Hall—Petch relation in lamellar—gamma duplex structures of TiAl alloys has been evaluated using Fan and Miodownikʹs model, by assuming that the friction stress varies linearly with the lamellar volume fraction. The results reasonably predict the strength of lamellar—gamma duplex structures at various grain sizes and volume fractions. The individual contributions from three constituting boundaries, lamellar—lamellar (α-α), gamma—gamma (γ-γ), and lamellar—gamma (α-γ) boundaries to the overall strengthening have been calculated as a function of α volume fraction: the α-γ phase boundaries are not effective obstacles to dislocation motion. The α-α grain boundaries are rather the strongest obstacles to dislocation motion.