Orientation-Dependent Mechanism of Grain Boundary Strengthening in Pure Zirconium

Abstract:

The Hall-Petch slope k represents the magnitude of grain boundary strengthening. A strong orientation dependence of the k value of pure zirconium (Zr) is revealed in this research. Namely, k value of the pure zirconium plate along the RD-tension (84 MPa·μm^1/2) is much lower than that along the TD-tension (220 MPa·μm^1/2), where RD and TD are the rolling direction and transverse direction of the plate, respectively. By combining experiments with the visco-plastic self-consistent model, the deformation mechanisms of pure zirconium plate were analyzed. The grain size of the plates are increased with the increase in annealing temperature, and the texture type do not change. Different deformation mechanisms are activated along different loading directions: prismatic slip dominates during RD-tension, whereas prismatic and basal slips collaborate to deform during TD-tension, while the {} twinning is also activated along TD. The orientation-dependent mechanism of the k value in pure zirconium was revealed based on the activation stress difference σ_d and the geometric coordination factor m' between neighbouring grains. The results indicate that the geometric coordination factor m' between neighbouring grains under RD-tension (0.67) is similar to that under TD-tension (0.71), while the activation stress difference σ_d under TD-tension (103.72 MPa) is significantly higher than that under RD-tension (32.17 MPa), resulting in a higher k value under TD-tension compared to RD-tension.