Room-temperature creep and stress relaxation in commercial purity titanium-Influence of the oxygen and hydrogen contents on incubation phenomena and aging-induced rejuvenation of the creep potential

Creep and stress relaxation tests were run at room-temperature along the rolling and transverse directions in three batches of titanium with different solute oxygen and hydrogen contents. Oxygen-induced dynamic strain aging was shown to hinder creep at low stress level and solute hydrogen to enhance it and to promote a dramatic aging-induced rejuvenation of the creep potential. Primary creep could be described by a single power law equation in which both the anisotropy and the influence of the oxygen content were taken into account. Secondary creep rates varied exponentially with the applied stress, in the same way along rolling and transverse directions, but with a stress dependency which increased with the oxygen content. Creep of commercial purity titanium was controlled mainly by screw dislocations with a 〈1-210〉 Burgers vector gliding on prismatic and pyramidal planes, while for a Ti batch with a lower oxygen content and larger grain size, mechanical twinning also contributed to the creep strain. 33-40% of the flow stress was relaxed within 20. h, according to logarithmic kinetics, which did not depend on the loading direction or oxygen content.