Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States.
Department of Mechanical Engineering, Clemson University, Clemson, South Carolina 29634, United States.
ACS Appl Mater Interfaces. 2023 Feb 15;15(6):8709-8722. doi: 10.1021/acsami.2c20795. Epub 2023 Jan 31.
We report a systematic computational analysis of the mechanical behavior of plasma-facing component (PFC) tungsten focusing on the impact of void and helium (He) bubble defects on the mechanical response beyond the elastic regime. Specifically, we explore the effects of porosity and He atomic fraction on the mechanical properties and structural response of PFC tungsten, at varying temperature and bubble size. We find that the Young modulus of defective tungsten undergoes substantial softening that follows an exponential scaling relation as a function of matrix porosity and He atomic content. Beyond the elastic regime, our high strain rate simulations reveal that the presence of nanoscale spherical defects (empty voids and He bubbles) reduces the yield strength of tungsten in a monotonically decreasing fashion, obeying an exponential scaling relation as a function of tungsten matrix porosity and He concentration. Our detailed analysis of the structural response of PFC tungsten near the yield point reveals that yielding is initiated by emission of dislocation loops from bubble/matrix interfaces, mainly /⟨111⟩ shear loops, followed by gliding and growth of these loops and reactions to form ⟨100⟩ dislocations. Furthermore, dislocation gliding on the ⟨111⟩{211} twin systems nucleates /⟨111⟩ twin regions in the tungsten matrix. These dynamical processes reduce the stress in the matrix substantially. Subsequent dislocation interactions and depletion of the twin phases via nucleation and propagation of detwinning partials lead the tungsten matrix to a next deformation stage characterized by stress increase during applied straining. Our structural analysis reveals that the depletion of twin boundaries (areal defects) is strongly impacted by the density of He bubbles at higher porosities. After the initial stress relief upon yielding, increase in the dislocation density in conjunction with decrease in the areal defect density facilitates the initiation of dislocation-driven deformation mechanisms in the PFC crystal.
我们报告了对面向等离子体部件（PFC）钨的力学行为的系统计算分析，重点研究了空洞和氦（He）气泡缺陷对超出弹性范围的力学响应的影响。具体来说，我们探讨了孔隙率和 He 原子分数对 PFC 钨的力学性能和结构响应的影响，考察了不同温度和气泡尺寸下的情况。我们发现，有缺陷的钨的杨氏模量会发生显著软化，这种软化遵循与基体孔隙率和 He 原子含量呈指数关系的规律。在超出弹性范围后，我们的高应变速率模拟显示，纳米级球形缺陷（空空洞和 He 气泡）的存在以单调递减的方式降低了钨的屈服强度，这种降低与钨基体孔隙率和 He 浓度呈指数关系。我们对接近屈服点的 PFC 钨的结构响应进行了详细分析，结果表明，空洞/基体界面上的位错环发射是屈服的起始机制，主要是 /⟨111⟩剪切位错环，随后这些位错环会滑移和生长，并发生反应形成 ⟨100⟩位错。此外，在 ⟨111⟩{211}孪晶系上的位错滑移会在钨基体中形成 ⟨111⟩孪晶区。这些动力学过程会大大降低基体中的应力。随后的位错相互作用以及孪晶相的耗尽，通过脱孪晶部分的形核和扩展来实现，会使钨基体进入下一个变形阶段，表现为在施加应变时应力增加。我们的结构分析表明，在较高孔隙率下，He 气泡的密度强烈影响孪晶边界（面缺陷）的耗尽。在屈服后的初始应力释放之后，位错密度的增加以及面缺陷密度的降低会促进 PFC 晶体中位错驱动变形机制的启动。
