Deformation of high β-phase fraction Zr–Nb alloys at room temperature

A series of in situ compression tests has been carried out at room temperature for three dual-phase Zr–Nb alloys with different Nb contents. Changes in the Nb content change the relative fraction of β-phase present in the alloy. The evolution of interphase and intergranular strain was monitored during deformation by neutron diffraction. Surprisingly the strength difference between the three alloys is caused principally by changes in the α-phase strength rather than being due to changes in the β-phase volume fraction; the yield strength of the Nb-rich β-phase is ∼400 MPa and is almost unchanged in the three alloys. The strength of the α-phase significantly changed between alloys due to the combined effects of increasing oxygen content and decreasing grain size. The change in strengthening mechanisms in the α-phase is crystallographically anisotropic, e.g. more change was observed for prismatic slip than for pyramidal slip. As a result, the mechanical anisotropy of the α-phase decreases with increasing strength. Depending on the β/α strength ratio, the β-phase can be either weaker or stronger than the average material strength. A soft β-phase helps to produce compressive residual stresses in the α-phase, while a strong β-phase produces tensile residual stresses in α-phase. A combined finite-element method and elastoplastic self-consistent multiscale model is used to interpret the experimental results. Despite the inability to capture the rapid stress relaxation observed, the combined method is shown to be effective in interpreting the deformation behavior of these dual-phase Zr–Nb alloys. The results are relevant to the study of other two-phase alloys, particularly titanium-based alloys.