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

摘要

The mechanical behavior of Ti-45Al-2Mn-2Nb (at.%) containing 0.8 vol.% TiB_2 was studied from room temperature up to 1090K. The alloy shows a slight anomalous increase of flow stress with temperature around 700 K, which is rarely encountered in two-phase γ/α_2 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.