Load partitioning and evidence of deformation twinning in dual-phase fine-grained Zr–2.5%Nb alloy

In situ neutron diffraction loading experiments were carried out on a cold-rolled dual-phase (α-phase, ∼10% β-phase) Zr–2.5%Nb alloy at room temperature. The specimens were cut at different angles from the rolling direction (RD) towards the transverse direction (TD), thus the loading axis changes gradually from the rolling to transverse direction. Due to the strong texture of the studied alloy, and unidirectional nature of deformation twinning, the changing loading direction with respect to initial texture has a significant impact on the collaborative slip-twinning deformation mode in the hexagonal close-packed (hcp) α-phase. The present neutron diffraction results provide direct evidence of {1−1.2}〈1−1.−1〉 “tensile” twins in the α-phase of dual-phase Zr–2.5%Nb alloy at room temperature. Additionally, TEM analysis was employed to confirm the presence of “tensile” twins, and determine if other type of twins were present. It is further clear from the neutron diffraction results that applied load is gradually transferred from the plastically softer α-phase to the plastically harder β-phase which acts as a reinforcing phase having a yield strength in the range 750–900 MPa depending on the loading direction.