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In this paper, the processes of grain refinement and phase transformations in the Ti-15Mo b-alloy during high-pressure torsion (HPT) at room temperature are investigated. The non-monotonic character of the variation of the v-phase volume fraction has been demonstrated for an increasing number of turns; in particular, the HPT processing of 1 turn leads to the precipitation of 10% v-phase from the b-matrix, but at 10 turns of HPT a reverse phase transformation is observed. It is shown that nanostructure formation with a minimum content of the v-phase allows for achievement of significant strengthening in the alloy while preserving a relatively low elastic modulus.

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The main aim of this study is to analyze the effect of the severe plastic deformation (SPD) on the mechanical properties and defect structure of metastable beta Ti alloys. Experiments were performed on two different β-Ti alloys: Ti-15Mo and Ti-6.8Mo-4.5Fe-1.5Al which were subjected to severe plastic deformation (SPD) by high pressure torsion (HPT). The increase of hardness with increasing equivalent strain was determined by microhardness mapping. Dislocation density was studied by advanced techniques of positron annihilation spectroscopy (PAS). Microhardness and dislocation density increases with increasing equivalent strain inserted by severe plastic deformation.