Collaborative Research: Nanoscale Structural and Compositional Instability-Driven Ductility in Refractory High-Entropy Alloys

非技术总结工程术语中，材料通过拉伸而不断裂的能力被称为“延展性”。这项合作研究计划正在发展一个原子的理解如何耐火高熵合金之间的关系，使他们的延展性反应。这些合金含有几乎等量的多种元素，具有高强度和高熔点，是高温应用的理想选择。然而，这些合金的主要缺点是它们在室温下的低延展性。本研究项目旨在解决这一问题，试图提高这些合金的韧性强度与孪生诱导塑性和过渡诱导塑性。这些方法可能导致晶格的变化，称为扭曲。为了尽快在原子水平上检测这些晶格畸变，正在开发一种基于数据挖掘的透射电子显微镜方法。这项研究是由一个互补的努力，使新材料，机械测试这些材料，并表征其结构的帮助。 结果有助于设计新的耐火合金，数据挖掘显微镜技术也可以应用于其他材料，因此预计对其他合金研究产生广泛影响。 该项目还与跨多个层面的外联工作相结合，旨在为合金设计和表征领域的可持续，适应性强和具有全球竞争力的科学，技术和工程劳动力做出贡献。该研究计划还旨在提高公众对材料，数据科学和相关技术的认识，同时丰富对科学和工程感兴趣的代表性不足的群体。技术总结这个合作项目探讨了第IV族元素（Ti，Zr和Hf）的合金相稳定性及其相关的孪生诱导塑性和过渡诱导塑性效应。具体来说，研究的重点是相变的前体，在无序的多主成分合金的结构诱导的局部晶格畸变和化学短程有序的形式。这项研究的动机是高熵合金概念设计新合金的承诺和缺乏了解的化学复杂性对相稳定性和物理性能的影响。本研究以难熔高熵合金的延展性为模型，探讨体心立方动态不稳定性，以及化学无序与晶格畸变对相稳定性的影响。该项目还在进一步发展基于倒谱的电子纳米衍射图中电子漫散射分析。在选定的合金晶格畸变和短程有序的相关性正在协助努力合成和表征的多主元素耐火合金的集合。具体来说，这项研究是回答以下问题：如何才能确定当地的化学秩序及其对动态不稳定性的影响？在扭曲的晶格中，相变是如何表现的？上述两种效应对应力诱发马氏体相变和形变孪晶有何影响？该项目还支持为STEM领域具有全球竞争力的劳动力做出贡献的目标，同时也丰富了将参与此类劳动力的代表性不足的群体。该奖项反映了NSF的法定使命，并通过使用基金会的智力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 SUMMARYThe engineering term for a material’s ability to be stretched by pulling, without breaking, is known as “ductility”. This collaborative research program is developing an atomistic understanding of the relationship between how refractory high-entropy alloys are made and their ductility response. These alloys, which have near equal amounts of multiple elements can have both high strength and high melting points and are ideal for elevated-temperature applications. A main drawback of these alloys however, is their low ductility at room temperature. This research project addresses this issue by seeking to increase the ductile strength of these alloys with twinning-induced plasticity and transition-induced plasticity. These approaches can result in changes to the crystal lattice known as distortions. To detect these lattice distortions as soon as possible and at the level of atoms, a data mining-based transmission electron microscopy approach is being developed. The study is assisted by a complimentary effort to make new materials, mechanically test these materials, and characterize their structure. Results are assisting in the design of new refractory alloys and the data mining microscopy technique can be applied to other materials as well, therefore a broad impact on other alloy research is expected. This project also integrates with an outreach effort across multiple levels tasked with contributing to a sustainable, adaptable, and globally competitive science, technology, and engineering workforce in the areas of alloy design and characterization. This research program is also seeking to increase public awareness of materials, data science, and related technologies, while simultaneously enriching the pool of underrepresented groups interested in science and engineering. TECHNICAL SUMMARYThis collaborative project explores the phase stability of group IV elements (Ti, Zr, and Hf) containing alloys and their related twinning-induced plasticity and transition-induced plasticity effects. Specifically, the research focuses on the precursors of phase transformation, in the form of structure-induced local lattice distortions and chemical short-range ordering in disordered multi-principal component alloys. The study is motivated by the promise of the high-entropy alloy concept for designing new alloys and the lack of understanding concerning the effects of chemical complexity on phase stability and physical properties. This research uses ductility in refractory high-entropy alloys as a model problem for the studies of body-centered-cubic (bcc) dynamic instability, and the effects of chemical disorder and lattice distortions on phase stability. This project is also further developing the cepstrum-based analysis of electron-diffuse scattering in electron nano-diffraction patterns. Correlation with lattice distortions and short-range ordering in selected alloys is being assisted by efforts to synthesize and characterize a collection of multi-principal element refractory alloys. Specifically, this study is answering the following questions: How can one determine local chemical ordering and its impact on dynamic instability? How do phase transformations manifest in a distorted lattice? How do the above two effects influence stress-induced martensitic transformation and deformation twinning? This project also supports the goal of contributing to a globally competitive workforce in STEM while also enriching the pool of underrepresented groups who will be participants in such a workforce.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.