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We report the development of intergranular and interphase constraints in textured Zircaloy-2, Zr-2.5Nb, and Excel alloy during room temperature tension and compression loading in two or three directions relative to the parent texture. Neutron diffraction was used to track the lattice strain development in the ?-phase (all alloys) and ?-phase (Zr-2.5Nb and Excel) in three principal directions relative to the parent texture. Zircaloy-2 at room temperature is essentially single phase hcp ?Zr. The active deformation mechanisms appear to be, in order of increasing critical resolved shear stress, prism (a) slip, basal (a) slip, tensile twinning and pyramidal (c+a) slip. No compressive twinning was observed. Combined with intergranular constraints due to prior thermal treatment, these mechanisms result in substantial asymmetry in the yield stress and lattice strain development (compression versus tension). In Zr-2.5 Nb and Excel, the ?-phase appears to deform by the same slip mechanisms as Zircaloy-2, and similar assymmetry of the yield stress and lattice strain development is observed. However, the existence of tensile twinning is not clearly evidenced. The ?-phase also deforms by slip, but the critical resolved shear stress is much higher than that for the slip mechanisms in the ?-phase, leading to the development of very large interphase constraints in the plastic deformation regime. This is attributed to a combination of solution strengthening of the ?-phase (by Nb and, in Excel, Mo) and by grain size.
While residual stress can be a problem in many industries and lead to early failure of component, it can also be introduced deliberately to improve lifetimes. Knowledge of the residual stress state in a component can be critical for quality control of surface engineering processes or vital to performing an accurate assessment of component life unde
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Zircaloy-2 and its sister alloy, Zircaloy-4, have extensive applications in the nuclear industry as core components in heavy water reactors and fuel cladding in both heavy and light water reactors. Intergranular stresses and texture can greatly affect the mechanical performance of these components. A complete understanding of the development of intergranular constraints and texture in Zircaloy-2 will allow an improved understanding of the plastic deformation of zirconium alloys, and the prediction of in-reactor deformation of tubes made by different manufacturing routes. Neutron diffraction was used to track the development of lattice strain and peak intensity in three dimensions for various crystallographic planes in samples cut from a rolled Zircaloy-2 slab. The samples were subject to room temperature compression or tension in-situ in the neutron spectrometer in each of the three principal directions of the slab. Textures in the deformed samples were measured using neutron diffraction. Strong evidence was found for tensile twinning in tensile tests in the plate normal direction and compression tests in the transverse and rolling directions. The lattice strain development inside the newly formed twins was recorded for the first time in a Zr alloy. An elasto-plastic self-consistent model and a visco-plastic self-consistent model were used to interpret the lattice strain and texture data, respectively. Various slip and twinning modes were considered in both models. Prism a slip, basal a slip, pyramidal c+a slip and tensile twinning were concluded to be indispensable, while pyramidal a slip was unnecessary in the modeling. The critical resolved shear stresses and hardening parameters were obtained by simultaneously achieving a 'best-fit' with the complete experimental data set. The effects of anisotropic latent hardening due to dislocation interactions were found to be critical, and the inclusion of Lankford coefficients as modeling constraints was necessary. This research provided a comprehensive experimental data set obtained by neutron diffraction, forming a sound basis to investigate active plastic deformation mechanisms and to rigorously test plasticity models and twinning models. The research also made a substantial improvement in understanding the plastic deformation of Zircaloy-2 through polycrystalline modeling by introducing extensive data sets to constrain the modeling parameters.
The proceedings of the Ninth International Symposium on [title], held in Kobe, Japan, November 1990, address current trends in the development, performance, and fabrication of zirconium alloys for nuclear power reactors. the bulk of the most recent work on zirconium alloy behavior has concerned corr