Elucidating the Mechanisms of Irradiation Induced Softening in Nanocrystalline BCC Metals

非技术描述：高应力和辐照的耦合极端需要新的材料设计方法，通过精确控制材料结构来提高强度和辐射容忍度。在过去的二十年里，人们一直在追求含有大量内部界面的纳米晶金属，以解决传统工程合金的性能限制。这些独特的材料在机械性能（如强度和耐磨性）方面表现出显著的改善，但在某些辐照条件下，会产生内部缺陷，降低这些性能，并限制其在极端环境应用中的技术效用。利用集成的计算和实验框架，本研究将建立对这种性能退化机制的基本理解，特别是表征纳米晶金属在辐照下产生软化和硬化的复杂缺陷网络。技术上，辐照对纳米晶金属机械性能影响的新见解将促进极端环境下材料设计的创新，推动下一代核技术成为安全、可持续的能源，同时大大减少对环境的影响。将研究活动整合到教育计划中，将促进未被充分代表的学生对材料科学的参与，并通过在石溪大学建立新的材料科学与工程专业，为工程专业提供丰富的课程。技术描述：本研究将阐明含氦辐照缺陷的纳米晶体心立方（BCC）金属从软化到硬化转变的机制。指导假设是，聚集在晶界的纳米级氦缺陷作为应力集中，降低了晶界介导的位错成核的能垒，这反过来表现为一种软化效应，最终与经典的辐照硬化相竞争。研究团队将原子模拟、原位力学测试实验和纳米压痕相结合，探索氦辐照缺陷对纳米晶BCC金属钨和铁的基本变形过程的影响。通过考虑变形行为中晶内缺陷环损伤与晶界缺陷的耦合，探讨了在粗晶多晶金属中发现的经典辐照硬化与在纳米晶材料中普遍存在的软化之间的竞争。这些机制在力学响应中的表现将被量化，并用于在变形机制与辐照缺陷集体相互作用的基础上建立机制-性能图。从这项研究中，研究小组将对辐射效应及其对纳米晶体BCC金属机械性能的影响有一个新的认识。对耦合缺陷状态导致的竞争机制的基本理解将促进对抗辐照损伤引起的机械性能退化的新创新，从而通过协同设计合金化方法为界面工程提供机会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: Coupled extremes of high stresses and irradiation necessitate new materials design methodologies for enhancing strength and radiation tolerance through precise control over material structure. Over the past two decades, nanocrystalline metals that contain a large fraction of internal interfaces have been pursued to address the performance limitations of traditional engineering alloys. These unique materials exhibit significant improvements in mechanical properties such as strength and wear resistance, but under certain irradiation conditions, develop internal defects that degrade these properties and limit their technological utility for extreme environment applications. Using an integrated computational and experimental framework, this research will build a fundamental understanding of the mechanisms responsible for such property degradations, specifically characterizing the intricate defect networks that produce softening and hardening in nanocrystalline metals under irradiation. Technologically, new insights into the impact of irradiation on the mechanical performance of nanocrystalline metals will foster innovations in materials design for extreme environments to advance next-generation nuclear technologies as safe, sustainable energy sources with drastically reduced environmental impacts. The integration of research activities into educational initiatives will advance the engagement of underrepresented students in materials science and provide curriculum enrichment for engineering majors through the establishment of a new materials science and engineering major at Stony Brook University. TECHNICAL DESCRIPTION: This research will elucidate the mechanisms responsible for the transition from softening to hardening in nanocrystalline body centered cubic (BCC) metals containing helium irradiation defects. The guiding hypothesis is nanoscale helium defects aggregated in grain boundaries act as stress concentrations that reduce the energetic barrier for grain boundary mediated dislocation nucleation, which in turn manifests as a softening effect that ultimately competes with classical irradiation hardening. The research team will combine atomistic simulations with in situ mechanical testing experiments and nanoindentation to explore the influence of helium irradiation defects on the fundamental deformation processes in the nanocrystalline BCC metals tungsten and iron. The competition between classical irradiation hardening found in coarse-grained polycrystalline metals and softening prevalent in nanocrystalline materials will also be explored by considering the coupling of intragranular defect loop damage with grain boundary defects in the deformation behavior. The manifestation of these mechanisms in the mechanical response will be quantified and used to build mechanism-property maps on the basis of collective interactions of deformation mechanisms with irradiation defects. From this research, the team will gain a new understanding of radiation effects and their implications for the mechanical performance of nanocrystalline BCC metals. A fundamental understanding of competing mechanisms due to coupled defect states will foster new innovations for combating mechanical property degradation from irradiation damage, thereby providing opportunities for interface engineering through synergistic alloying-by-design methodologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.