Abstract:

Previously, the in-plane mechanical anisotropy of Zr hot-rolled plates is ascribed mainly to the different activities of the deformation modes activated when loading along different directions. In this work, a quantitative study on the deformation behavior of a pure Zr hot-rolled plate under tension along the rolling direction (RD) and transverse direction (TD) reveals that both the activities of deformation modes and the anisotropy of grain boundary strengthening account for a tensile yield strength anisotropy along the TD and RD. Crystal plasticity simulations using viso-plastic self-consistent model show that prismatic slip is the predominant deformation mode for tension along the RD (RD-tension), while prismatic slip and basal slip are co-dominant deformation modes under tension along the TD (TD-tension). A low fraction of $\left\{10\bar{1}2\right\}$ twinning is also activated under TD-tension, while hardly activated under RD-tension. The activation of basal slip with a much higher critical resolve shear stress under TD-tension contributes to a higher yield strength along the TD than along the RD. The grain boundary strengthening effect under tension along the TD and RD were compared by calculating the activation stress difference ($\Delta {\text{Stress}}$) and the geometric compatibility factor (${m}^{\prime}$) between neighboring grains. The results indicate a higher grain boundary strengthening for TD-tension than that for RD-tension, which will lead to a higher yield strength along the TD. That is, the anisotropy of grain boundary strengthening between TD-tension and RD-tension also plays an important role in the in-plane anisotropy along the RD and TD. Afterward, the reasons for why there is a grain-boundary-strengthening anisotropy along the TD and RD were discussed.

Key words: Zirconium, Strengthening, Grain boundary, Orientation