HYDROGEN INFLUENCE ON PLASTIC-DEFORMATION MECHANISM OF BETA-TITANIUM ALLOYS OF TI-NB SYSTEM

The influence of hydrogen on the mechanism of cold plastic deformation at room temperature of beta-Ti-Nb alloys with Nb content from 20 to 5 0 wt% is studied. It is shown that hydrogen increases the mechanical s tability of the beta-phase and hinders shape changes which occur due t o a martensitic transformation or twinning. Hydrogen influences strong ly the slip mechanism in the beta-plane. The dislocation unpinning und er hydrogen atmosphere during deformation causes the formation of 'upp er' and 'lower' yield points. That causes the formation of a higher yi eld point during compression of the samples and leads to a strong loca tion of deformation during tension tests. In general, hydrogen assists in lowering the deformation energy, and increases the ductility and m echanical instability of beta-titanium alloys containing from 20 to 40 % Nb.