发表机构
École Polytechnique Fédérale de Lausanne (EPFL); Laboratory of materials design and simulation (MADES), Institute of Materials, École Polytechnique Fédérale de Lausanne (EPFL); National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne (EPFL); EMPA - Swiss Federal Laboratories for Materials Science and Technology; Laboratory for Multiscale Modeling in Mechanics (LAMMM), Institute of Mechanical Engineering, École Polytechnique Fédérale de Lausanne (EPFL); School of Engineering, Brown University, Providence, RI 02906 USA（洛桑联邦理工学院; 洛桑联邦理工学院材料研究所材料设计与模拟实验室; 洛桑联邦理工学院新型材料计算设计与发现国家中心; 瑞士联邦材料科学与技术研究院; 洛桑联邦理工学院机械工程学院多尺度力学建模实验室; 布朗大学工程学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出原子尺度应力波动增强难熔BCC合金延展性的机制，建立局部延展性准则，并通过实验验证了HfMoNbTi合金的室温延展性，为设计延展性多组分合金提供定量基础。
AI 中文摘要
难熔体心立方（BCC）合金是极端温度下结构应用的有吸引力的候选材料，但将室温延展性与高温强度相结合仍然是未解决的挑战。晶体中的延展性要求位错在脆性解理之前从尖锐裂纹尖端发射，但将无序合金视为化学均匀的连续介质理论错误地预测了许多实验上具有延展性的合金的脆性。在这里，我们表明无序合金中的原子尺度应力波动在裂纹尖端产生额外的局部应力强度，使得位错环在解理阈值以下成核。考虑这些波动产生了一个局部延展性准则，根据该准则，传统断裂力学认为脆性的合金可以是本征延展的。使用机器学习原子间势的原子模拟和分析断裂力学模型正确预测了二元和三元Mo-Nb-Ti合金、4 K下的Nb-Ti合金以及几种商用BCC合金在室温下的成分驱动的脆性到延性转变。在此准则的指导下，我们预测、制备并测试了Hf$_{15}$Mo$_{15}$Nb$_{32}$Ti$_{38}$合金，确认了其室温延展性。这种波动驱动的机制为设计延展性多组分BCC合金提供了定量基础。
英文摘要
Refractory body-centered cubic (BCC) alloys are attractive candidates for structural applications at extreme temperatures, yet combining room-temperature ductility with high-temperature strength remains the unsolved challenge. Ductility in crystals requires that dislocations emit from a sharp crack tip before brittle cleavage, but continuum theories that treat disordered alloys as chemically homogeneous incorrectly predict brittleness for many experimentally ductile alloys. Here we show that atomic-scale stress fluctuations in disordered alloys create an additional local stress intensity at the crack tip, enabling dislocation loop nucleation below the cleavage threshold. Accounting for these fluctuations yields a local ductility criterion where alloys deemed brittle by conventional fracture mechanics can be intrinsically ductile. Atomistic simulations with machine-learned interatomic potentials and an analytic fracture mechanics model correctly predict composition-driven brittle-to-ductile transitions in binary and ternary Mo-Nb-Ti alloys, in Nb-Ti alloys at 4 K, and in several commercial BCC alloys at room temperature. Guided by this criterion, we predict, fabricate, and test the Hf$_{15}$Mo$_{15}$Nb$_{32}$Ti$_{38}$ alloy, confirming its room-temperature ductility. This fluctuation-driven mechanism provides a quantitative basis for designing ductile multicomponent BCC alloys.
