The hardening of beta -titanium due to the presence of hydrogen in solid so
lution was investigated. The steady-state flow of a series of beta -Ti-H al
loys containing up to 31at.% of dissolved hydrogen was analysed using the t
heory of thermally activated glide. This approach permitted the stress and
temperature dependences of the strain rate to be separated into that part r
elating to the preexponential Factor and that to the Gibbs free energy. At
a given flow stress, the pre-exponential factor decreased and the Gibbs fre
e energy increased when the hydrogen concentration was increased owing to t
he strengthening effect of hydrogen on the elastic moduli. It is concluded
that the steady-state flow of beta -Ti-H alloys is controlled by a single t
hermally activated mechanism and that the observed hydrogen-induced hardeni
ng is largely caused by the stiffening effect of hydrogen on the shear modu
lus.