RII Track-4: Mechanistic Design of Hierarchical Metal-MAX Multilayered Nanocomposites

纳米复合材料是一类复合材料，其基本材料或组成材料的尺寸在纳米尺度上，一纳米是一米的十亿分之一。它们可以提供前所未有的性能，超越目前研究和使用的性能。该研究计划的目标是通过在纳米尺度上选择性激活变形机制，增强金属-陶瓷纳米复合材料多层设计的优势，该复合材料被假设为具有可调节的强度和韧性。金属-陶瓷多层纳米复合材料由交替的金属相层和MAX相层组成，层板厚度减小到纳米级。由于理想的、高度定向的结构在薄膜上普遍存在，每个薄膜都包含数千个“相似层”和高密度的界面。MAX相是一类由层状三元碳化物或氮化物材料组成的陶瓷材料，它们代表了一类新型的层状固体，其中Mn+1Xn层与纯a族元素层相互交织。这些金属- max多层纳米复合薄膜具有均匀的界面间距（~2 ~ 100 nm）和均匀的界面平面和晶体结构。MAX相在多个技术领域都有应用，包括高温结构应用、保护涂层、传感器、微机电系统的可调阻尼膜等，以及在核包层材料中的潜在应用。能够拥有坚固而延展性的金属- max复合材料，并改善机械性能，以满足此类应用的要求，将提供可观的技术和经济效益。这项研究是首席研究员（PI）和桑迪亚国家实验室（CINT-SNL）集成纳米技术中心之间的综合合作计划，该中心将支持博士后研究人员，并在CINT-SNL的国家主要国家实验室进行扩展的合作访问和基础设施开发机会。PI所在大学材料系高级设计项目的本科教育将特别受益于此次合作，因为该合作将拥有来自国家实验室和大学的导师（以及可能访问的CINT-SNL）。该奖学金项目的目标是利用对多层纳米复合材料中与纳米级结构直接相关的变形机制的激活和限制的基本理解，以潜在地实现可调的强度和韧性。与过去所追求的其他各种多层体系不同，本文研究的金属-MAX纳米复合材料由独特的分层拓扑结构组成，因为层之间的界面与MAX层内的内部界面直接竞争，从而驱动可调的宏观力学行为。在实验合成和新颖的PI纳米力学测试能力的指导下，CINT-SNL的计算建模将补充实验组件，以研究金属- max分层结构中的基本机制（例如位错和波纹）。该奖学金项目的成果将包括开发金属- max分层结构，其基本变形机制和由此产生的机械性能（即强度和韧性）之间的相关性。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。

Nanocomposites are a class of composite materials where the size of the base or constituent materials are on the nanometer length scale - one nanometer being one-billionth of a meter. They can offer unprecedented properties beyond those currently studied and used. The goal of this fellowship proposal is to augment the advantages of a multilayered design in a metal-ceramic nanocomposite that is hypothesized to exhibit tunable strength and toughness, by the selective activation of deformation mechanisms at the nanoscale. The metal-ceramic multilayered nanocomposite is composed of alternating metallic and MAX phase layers with a lamellar thickness reduced to the nanoscale. Because of the ideal, highly oriented structure that prevails across the film, each film contains thousands of "like layers", and a high density of interfaces. MAX phases are a family of ceramic materials consisting of laminated ternary carbide or nitride materials, and they represent a novel class of layered solids, where Mn+1Xn layers are interleaved with pure A-group element layers. These metal-MAX multilayered nanocomposite thin films show uniform interface spacing (~2 to 100’s of nm apart) and uniform interface plane and crystallography throughout the film. MAX phases have applications in multiple technological fields, including high temperature structural applications, protective coatings, sensors, tunable damping films for microelectromechanical systems, etc., along with potential applications in cladding materials for nuclear use. The ability to have a strong yet ductile metal-MAX composite with improved mechanical behavior to satisfy the demands of such applications will provide considerable technological and economic benefits. This research is an integrated collaboration planned between the principal investigator (PI) and the Center for Integrated Nanotechnologies, Sandia National Laboratories (CINT-SNL), which will support a postdoctoral researcher, and enable extended collaborative visits and infrastructure development opportunities at the nation’s premier national laboratory at CINT-SNL. Undergraduate education in the capstone senior design projects in the Materials department at the PI’s university will particularly benefit from this collaboration by having mentors (and possible visitations to CINT-SNL) from both national laboratory and university. The objectives of this fellowship project are to leverage a fundamental understanding of the activation and confinement of deformation mechanisms directly linked to the hierarchical structure at the nanoscale in multilayered nanocomposite materials, to potentially enable tunable strength and toughness. Unlike other various multilayered systems that have been pursued in the past, the metal-MAX nanocomposites studied here are composed of a unique hierarchical topology - as interfaces between the layers are in direct competition with the internal interfaces within the MAX layers to drive the tunable macroscopic mechanical behavior. Guided by experimental synthesis and novel nanomechanical testing capabilities of the PI, computational modeling at CINT-SNL will complement the experimental component to study the fundamental mechanisms (e.g., dislocations and ripplocations) within the metal-MAX hierarchical structure. Outcomes from the fellowship project will include the development of correlations between the metal-MAX hierarchical structure, its fundamental deformation mechanisms and the resulting mechanical properties, namely strength and toughness.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.