In this study, the effect of sulphur on the deformation behavior of cold rolled and annealed Zr-1.5Nb, Zr-1.5Nb-S alloys were studied. The beneficial effect of sulphur on the strengthening was observed both in the cold rolled and annealed Zr-1.5Nb-S alloys. The loss of ductility was intensified with the addition of sulphur in the annealed Zr-1.5Nb-S alloys in the region of dynamic strain aging, implying the interdependent effect of oxygen and sulphur. The activation volumes, V, for the cold rolled alloys are not much different from those of annealed alloys. The activation volume, V, decreased slightly with the increase of the sulphur content at room temperature and 300 °C. Insensitivity of the activation volume to the dislocation density and the decrease of the activation volume with the addition of sulfur support the suggestion linking the activation volume with the activated bulge of dislocations limited by segregation of oxygen and sulphur atoms. The higher flow stress increase with the addition of sulfur in Zr-1.5Nb alloy of the present study with the higher oxygen content (～1600 ppm) is compatible with the suggestion of the interdependent strengthening effect of sulfur and oxygen.
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