Thermally activated flow of beta titanium and titanium-hydrogen alloys

Compression tests were carried out on titanium and on a series of titanium-hydrogen alloys containing up to 31 atomic percent of dissolved hydrogen. The tests were performed within the beta phase field at strain rates of 10(-3) to 1 s(-1). The measured flow stresses increased appreciably with hydrogen addition. Steady stale flow was observed and analyzed within the framework of dislocation glide controlled by linear elastic obstacles. The stress and temperature dependencies of the strain rate were separated in this way into those of the pre-exponential factor and the Gibbs free energy. The free energy of activation increases and the pre-exponential decreases when the hydrogen concentration is increased, mostly through the stiffening effect of hydrogen on the shear modulus. It is concluded that the steady-state flow of beta Ti - H alloys is controlled by a single thermally activated mechanism and that the hydrogen-induced hardening observed is caused by the stiffening effect of hydrogen on the elastic moduli.