Observation of yielding and strain hardening in a titanium alloy having high oxygen content

Plastic deformation behavior and its relation to tensile properties were investigated in an attractive β-type titanium alloy (Ti–29Nb–13Ta–4.6Zr) with the oxygen content of 0.1–0.7 mass% subjected to hot rolling and solution treatment after hot rolling. Hereafter, Ti–29Nb–13Ta–4.6Zr is abbreviated to TNTZ. With the increase of oxygen content, the tensile strength and 0.2% proof stress of all the samples increase, however, their elongation indicates special change, which is contradictory to that reported conventionally. The elongation firstly decreases and then increases with the increase in the oxygen content. Therefore, TNTZ with high strength and high ductility due to the addition of high oxygen content (0.7 mass%) is obtained. Remarkable yielding phenomenon and strain hardening are observed in TNTZ, which can be explained by the interaction between oxygen atoms and a lot of screw and edge dislocations leading to the easy activation of the multiple slip systems. The deformation behavior changes with the addition of oxygen in TNTZ. The plastic deformation mode changes from the deformation-induced martensite transformation to slip mechanism. It is realized that there is a specific compositional area of oxygen in which the TNTZ exhibits strain hardening and high strength, and appropriate Youngʹs modulus value.