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 α₂phase can cause stress concentration at the grain boundaries before plastic deformation occurs. Fracturing occurs at the strips of α₂phase when micro-deformation occurs, so that the accumulated stresses are rapidly released.