Effect of sulphur on the strengthening of a Zr–Nb alloy

The effect of sulphur on the strengthening and the thermally activated deformation of cold-worked Zr–1 Nb alloy was investigated. In the present study, the sulphur strengthening was observed even at room temperature unlike the previous study of Ferrer et al. The flow stress increased by 65 MPa at room temperature with the addition of sulphur as little as 20 ppm. With further increase of sulphur content up to 300 ppm, negligible change of the flow stress was observed. The additive strengthening behavior in which the entire stress–strain curve shift upward by the friction stress due to the addition of sulphur was observed in the Zr–Nb alloy of the present study. The activation volume decreased slightly (from 110b3 to 80b3) with the addition of 300 ppm sulphur at room temperature. The rate-controlling mechanism of the deformation can best be explained by the dislocation interaction mechanism in which the segregation of alloying elements such as oxygen and sulphur atoms affects the activation length of dislocations.