This paper describes molecular dynamics simulations of fracture along a grain boundary (GB) in nickel (Ni) decorated with helium (He)-filled bubbles. We find that the quantity governing embrittlement of the GB is its areal coverage by He bubbles. Indeed, there is a threshold coverage—approximately 18%, for the GB studied here—above which the GB undergoes brittle fracture. During brittle fracture, intergranular cracks advance by the growth and coalescence of He-filled cavities ahead of the crack front. This process is enabled by plastic deformation of inter-bubble ligaments. In models with lower He bubble coverage, dislocation activity initiates in the adjoining grains prior to cavity growth and coalescence, relaxing crack tip stresses and averting brittle crack propagation. We conclude that the ductile-to-brittle transition observed in this study is governed by a competition between dislocation emission ahead of the crack tip and localized deformation confined to the inter-cavity ligaments.

本文描述了用充有氦（He）的气泡装饰的镍（Ni）中沿晶界（GB）的断裂的分子动力学模拟。我们发现，控制GB脆化的量是He气泡的覆盖面积。实际上，存在一个阈值覆盖率（对于此处研究的GB而言约为18％），超过该阈值GB会发生脆性断裂。在脆性断裂过程中，由于He填充型腔在裂纹前沿之前的生长和聚结，导致晶间裂纹发展。气泡间韧带的塑性变形使该过程成为可能。在He气泡覆盖率较低的模型中，位错活动在腔体生长和聚结，松弛裂纹尖端应力并避免脆性裂纹扩展之前在相邻晶粒中开始。