The influence of pre-strain on the flow strength and microstructural evolution of polycrystalline γ-TiAl

Abstract

Specimens of single-phase polycrystalline γ-Ti₄₇Al₅₁Mn₂ have been tested in compression at 300 and 550°C. Monotonic and Cottrell-Stokes temperature change experiments have been conducted, and the deformation microstructure associated with these tests has been characterized by transmission electron microscopy. The transient experiments indicate that the flow stress is reversible both when the temperature is dropped from 550 to 300°C, and when it jumps from 300 to 550°C. Deformation at the lower temperature has been associated with superdislocation motion and the formation of faulted dipoles, while ordinary dislocation motion dominates at the higher temperature. Dislocation motion and strain hardening in this alloy have both been characterized as fully reversible processes that are unaffected by prior deformation history. Implications for modelling the yield strength anomaly in this alloy are discussed.