Precipitation hardening characterization and stress prediction model in electrically-assisted Ti₂AlNb uniaxial tension

In this study, we reported the ultrafast precipitations of O phase in Ti2AlNb alloy caused by pulse current in the range of 450degree celsius-750 degree celsius, which results in an abnormal increase of strength with increasing temperature in electrically-assisted uniaxial tension. The morphology of precipitate phase is controlled by the increase in thermal and non-thermal free energy with increasing pulse current. The elongated needle-like O phase, caused by high temperature, would reduce flow stress, whereas nano-sized alpha(2) precipitates, formed at specific pulse current density and temperature, could enhance the strength of Ti2AlNb. To describe the stress changes caused by precipitation hardening effect, S-curve has been introduced. The modified Z-A model reduces parameter amount but keeps accuracy. This model efficiently predicts the stress change caused by pulse currents, which combines with the linear model of pure electroplasticity and S-curve. Furthermore, the specific impacts of temperature, effective pulse current density and strain on the stress reduction are decoupled.