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

纳米复合材料是一类复合材料，其中基础或组成材料的尺寸在纳米长度尺度上-一纳米是十亿分之一米。它们可以提供超出目前研究和使用的前所未有的特性。该奖学金提案的目标是通过选择性激活纳米级的变形机制来增强金属-陶瓷纳米复合材料中多层设计的优势，该纳米复合材料被假设为具有可调的强度和韧性。金属-陶瓷多层纳米复合材料由交替的金属和MAX相层组成，其层状厚度减小到纳米级。由于整个薄膜具有理想的高度取向结构，每个薄膜都包含数千个“相似层”和高密度的界面。MAX相是由层状三元碳化物或氮化物材料组成的陶瓷材料家族，并且它们代表了一类新的层状固体，其中Mn+1Xn层与纯A族元素层交错。这些金属-MAX多层纳米复合物薄膜在整个膜中显示出均匀的界面间距（间隔约2至100 nm）和均匀的界面平面和晶体学。MAX相在多个技术领域中具有应用，包括高温结构应用、保护涂层、传感器、用于微机电系统的可调阻尼膜等，沿着在核用途的包层材料中的潜在应用。具有强而韧性的金属-MAX复合材料的能力，具有改善的机械性能，以满足这些应用的需求，将提供可观的技术和经济效益。这项研究是主要研究者（PI）和桑迪亚国家实验室综合纳米技术中心（CINT-SNL）之间计划的综合合作，该中心将支持博士后研究人员，并在全国首屈一指的国家实验室CINT-SNL实现扩展的合作访问和基础设施开发机会。PI大学材料系的顶级高级设计项目的本科教育将特别受益于这种合作，因为他们有来自国家实验室和大学的导师（以及可能访问CINT-SNL）。该奖学金项目的目标是利用对与多层纳米复合材料纳米级层次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。与过去追求的其他各种多层系统不同，这里研究的金属-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，以驱动可调的宏观机械行为。在PI的实验合成和新型纳米机械测试能力的指导下，CINT-SNL的计算建模将补充实验部分，以研究基本机制（例如，位错和波纹）内的金属MAX分级结构。该奖学金项目的成果将包括metal-MAX分级结构、其基本变形机制和由此产生的机械性能（即强度和韧性）之间的相关性的发展。该奖项反映了NSF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.