A study of the sharp yield point of a Ti-22Al-25Nb alloy

Ti-22Al-25Nb alloy containing 0.2 wt. % hydrogen exhibits a sharp yield point on the stress-strain curve when it is tested above 960 °C. The main reason for this phenomenon can be attributed to the unidirectional crystal orientation and low level of lattice distortion above 960 °C, so that the dislocations tend to move in parallel directions with greater mobility and the stress can be rapidly released. Furthermore, strips of brittle α2 phase can cause stress concentration at the grain boundaries before plastic deformation occurs. Fracturing occurs at the strips of α2 phase when micro-deformation occurs, so that the accumulated stresses are rapidly released.