纯锆晶界强化的取向依赖性机制研究

Orientation-Dependent Mechanism of Grain Boundary Strengthening in Pure Zirconium

摘要:

Hall-Petch斜率k表示晶界强化的程度，本研究报道了纯锆的k值具有强烈的取向依赖性，即纯锆板材沿RD拉伸的k值（84 MPa·μm^1/2）远低于TD拉伸的k值（220 MPa·μm^1/2），其中RD和TD分别为板材的轧制方向和横向。结合实验与粘塑性自洽模型，分析了纯锆板材的变形机制，板材晶粒尺寸随退火温度的升高而增大，且织构类型不发生变化。不同加载方向的变形机制不同，即沿RD拉伸时以柱面滑移为主导，沿TD拉伸时柱面滑移和基面滑移共同协调变形，并且沿TD拉伸激活了｛｝孪晶。基于相邻晶粒的激活应力差σ_d和几何协调因子m'，揭示了纯锆板材k值的取向依赖性机制。结果表明，沿RD拉伸的相邻晶粒的几何协调因子m'（0.67）与沿TD拉伸的相邻晶粒的几何协调因子（0.71）相近，而沿TD拉伸的相邻晶粒的激活应力差σ_d（103.72 MPa）远高于沿RD拉伸的相邻晶粒的激活应力差（32.17 MPa），导致沿TD拉伸比沿RD拉伸具有更高的k值。

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.