Evidence for basal ⟨a⟩-slip in Zircaloy-2 at room temperature from polycrystalline modeling

Polycrystalline modeling has been used to interpret the evolution of lattice strain and texture in zirconium based alloys. Challenges in matching model and experimental results have mainly arisen from an insufficient knowledge of intrinsic deformation mechanisms (slip and twinning). Specifically, there is little concrete evidence that basal < a >-slip occurs during room-temperature deformation or whether pyramidal < a >-slip is an alternate mechanism. Also, the critical resolved shear stresses (CRSSs) for slip and twinning systems relevant to polycrystals are not well established. We have developed an understanding of the contribution of basal < a >-slip to deformation by applying an elasto-plastic self-consistent model to an extensive experimental database, obtained by neutron diffraction measurements on textured Zircaloy-2. By considering a variety of slip system combinations, the roles of each slip system in lattice strain development were investigated. Parameters for the model were obtained by best fitting to a large experimental database, including both macroscopic data (flow curves and Lankford coefficients) and microscopic internal strain data. Based on optimized agreement between model and experimental data we conclude that there is evidence that basal slip does occur, while the effects which might be attributed to pyramidal < a >-slip can be represented by the influence of other combinations of slip systems. We propose reasonable ranges of initial CRSSs for each slip system, which should benefit the modeling of similar materials (e.g. Zircaloy-4). (C) 2007 Elsevier B.V. All rights reserved.