Effect of interstitial oxygen and iron on deformation of Zr-2.5Â wt% Nb

A series of in situ compression tests have been carried out at room temperature on three dual-phase Zr-2.5 wt% Nb alloys with different concentrations of the interstitial alloying elements oxygen and iron. Oxygen and iron are potent strengthening additives in two-phase alloys with a hexagonal-close packed α phase and body-centred cubic β phase, such as the Zr-Nb and Ti-V-Al systems. The evolution of interphase stress, along with the progression of twinning, were monitored during deformation by neutron diffraction. The twin volume fraction measured following deformation was not strongly dependent on ingot chemistry, contrary to previously reported results. Annealing in the α+β and the β region allowed for variation in the initial residual stress distribution and crystallographic texture, respectively, and the effect of these parameters on deformation mode selection was also investigated. Interstitial oxygen has a greater strengthening effect on prismatic 〈a〉 slip than on basal 〈a〉 slip at room temperature. High impurity contents were not observed to suppress {101¯2}〈101¯1〉 tensile twinning. Despite being an α-stabilizer, oxygen is observed to strengthen the β phase under suitable heat treatment conditions.