Dynamic strain aging and serrated flow behaviour of Ta-2.5 W alloy

Abstract

The compression behaviour of the Ta-2.5 W alloy was investigated over the temperature range from room temperature to 450 °C at strain rates of 0.001 s⁻¹, 0.01 s⁻¹, 0.1 s⁻¹, 1 s⁻¹, 5 s⁻¹, and 10 s⁻¹. The test results are thoroughly analysed with particular attention to the typical features and mechanism of dynamic strain aging (DSA) and its effects on microstructure evolution. The stress-strain curves clearly exhibit the serrated flow behaviour, and a continuous variation in serration style from A to A + B or A + C_A with increasing deformation temperature occurred. The typical characteristics of serrated yielding, positive temperature sensitivity in flow stress, increased work hardening rate and negative strain rate sensitivity indicate the occurrence of DSA. With increasing accumulated strain, the negative strain rate sensitive region moves to high temperatures and contracts at low strain rates, whereas it expands at higher strain rates. The alloy exhibited both normal and inverse Portevin-Le Chatelier effects, which originate from the interaction between interstitial or substitutional solute atoms and moving dislocations, resulting in the appearance of planar slip, dislocation loops and dislocation walls. Higher strain rates and DSA inhibit dynamic recovery and result in higher dislocation densities and low angle grain boundary frequency.