α锆中螺形位错与空位盘的相互作用模拟
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摘要
金属锆及其合金是一种重要的核工业材料,由于其较小的中子吸收截面,常被用于制作燃料包壳管。因此,这种材料在辐射条件下的稳定性对核反应堆的正常安全运转起到至关重要的作用,研究锆在辐射作用下金属内部缺陷的产生与变化方式具有重要意义。近来随着材料科学与计算机技术的发展,分子设计和分子模拟技术得到了迅速发展,其应用前景广泛,己受到很多研究者特别是材料研究者的重视。基于位错和缺陷簇理论的计算机模拟缺陷间的相互影响是当今较流行的材料研究课题。
     本文使用了修正共轭梯度法和修正格林方程自由边界条件研究α-锆中双层盘状空位簇的临界坍塌压应变与空位盘尺寸和螺形位错之间的关系。模拟过程中通过改变空位盘半径大小,改变引入的螺形位错与空位盘心间的距离,得出不同情况下的临界坍塌压应变值,并对坍塌的原子晶体结构进行分析。计算结果显示:空位盘尺寸越大,所需的临界坍塌压应变越大。螺形位错的存在会显著减小临界坍塌压应变值,使得空位盘更易坍塌,这种影响在小尺寸空位盘中表现更明显。坍塌结构中出现了正弗兰克不全位错环和负弗兰克全位错环,但没有出现堆垛层错。螺形位错致使中间层位错环发生伯氏矢量为[0001]的错位,形成不闭合的位错环,而且这种错位会随空位盘尺寸增大而在外层原子结构中表现出来。
     空位盘的坍塌对金属的宏观塑性变形具有深远影响,因此金属的机械性能在很大程度上取决于这种微观结构的改变,本实验对锆金属的工作寿命和机械性能变化预估有重要参考作用。
Zirconium is an important nuclear industry material used as fuel cladding tube due to its low thermal neutron capture cross section. Hence the stability of this material under irradiation condition is crucial to the safety of nuclear reactors. It is of great significance to study the mode of generation and evolution defects. Molecular design and simulation is developing quickly with the development of material science and computer technology which has bright future for application. Many researchers, especially working in material science, have been paying great attention to this technique. Computer simulation of defects cluster and dislocation interaction is a popular subject based on defect theories.
     In this thesis, a compressive strain is applied to a double-layer vacancy cluster platelet which lies in (0001) plane ofα-zirconium. The critical collapse compressive strain under the influence of platelet size and screw dislocation are obtained by using a combination of modified conjugate gradient method and modified Green’s function flexible boundary condition. In this simulation, the radius of platelets and the distance between the screw dislocation and the platelet are changed to get corresponding critical collapse strains. Besides, the collapse atomic-level configurations are analyzed. The results indicate: critical collapse strain becomes larger as the vacancy cluster platelet size increases when screw dislocation is absent. However, it decreases obviously when the screw dislocation is introduced in the simulation box. The influence of the screw dislocation on small vacancy cluster platelets is stronger than on the big ones, which causes the collapse of small vacancy platelet more easily. There are two kinds of dislocation loops including positive Frank partial dislocation loop and negative Frank partial dislocation loop in collapsing atomic-level configuration but no stacking fault loops. A relative slip in middle layers with displacement of Burgers vector [0001] emerges under the impact of the screw dislocation. This kind of slip also appears in outer layers when platelet size is large and leads to dislocation loops unclosed.
     The macroscopic plastic deformation due to microscopic configuration evolution plays an important role on mechanical properties of metals. Therefore, our study can help us predict the serve life and the changes of mechanical properties of zirconium.
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