Measurement of the effective activation volume in 45XD titanium aluminides by repeated transient tests

The mechanical behavior of Ti–45Al–2Mn–2Nb (at.%) containing 0.8 vol.% TiB2 was studied from room temperature up to 1090 K. The alloy shows a slight anomalous increase of flow stress with temperature around 700 K, which is rarely encountered in two-phase γ/α2 TiAl. The technique of repeated stress relaxations allows the determination of the apparent and effective activation volumes along the stress–strain curve up to 900 K. The activation volume shows two important features: (i) large variations with strain at room temperature and (ii) a sharp increase with temperature in the stress anomaly domain, indicating the existence of two different dislocation mechanisms operating, respectively, below and above the flow stress anomaly.