Effect of β-Phase on Deformation and Stress Partitioning in Zr-2.5Nb Pressure Tubes

Zr-2.5Nb alloy is widely used in nuclear pressure tubes due to its favorable mechanical properties. The alloy consists of α-zirconium with hexagonal close-packed (HCP) crystals and a minor β-zirconium phase with body-centered cubic (BCC) crystals, mainly located between the α-grains. This study investigates the effect of β-phase grains on deformation behavior and stress partitioning in Zr-2.5Nb using crystal plasticity finite element (CPFE) modeling. The higher yield stress of β-phase grains compared to α-phase grains significantly influences stress redistribution under high plastic deformation. Two cases were analyzed: a material with random texture and a material with a preferred grain orientation (textured). The textured material exhibited anisotropic mechanical behavior, leading to greater variations in stress compared to the random texture. As plastic strain increases, the β-phase grains experience higher stresses than the surrounding α-grains. The study also examines residual stresses after unloading, showing that as macrostrain increases, the variation in residual stresses approaches that seen in the loaded state. Additionally, for a given macrostrain, hydrostatic stresses are higher in textured materials compared to randomly oriented ones when loaded along the direction of maximum material strength. These findings not only offer insights into the stress and deformation behavior of Zr-2.5Nb but also have important implications for hydrogen embrittlement, as hydrogen distribution is closely linked to the state of stress. Understanding these relationships is essential for improving the mechanical reliability and safety of nuclear pressure tube applications.