Disruption of Plastic Flow in Metals by Adsorbed Organic Monolayers

非技术摘要该项目将支持研究，从而获得结构金属的新知识，从而提高其耐用性、加工和再利用。通过这样做，它将推进极其重要的材料和制造工艺的科学基础，并为能源系统、地面交通和航空航天等不同行业领域提供技术优势。该项目将探索最近发现的与金属有关的现象——即使在其表面应用纳米级有机薄膜，也会导致其断裂和塑性流动行为发生巨大变化。它将研究薄膜对金属表面特性（例如表面和界面能、表面应力、强度）产生的变化。基于对特性及其与薄膜属性（例如化学、链长、吸附）的关系的研究，它将确定控制流动和断裂现象的因素。该方法将结合先进的实验技术，例如高速成像和图像分析以及纳米级计量学，以及有机分子结构和金属表面属性之间相互作用的原子建模。这些发现将影响材料加工、环境辅助开裂和磨损等多种领域，在这些领域，机械载荷和化学的协同效应往往发挥着关键作用。通过定制有机膜化学来控制机械化学现象将能够增强金属的材料去除（例如切割、粉碎）和表面变形（例如摩擦搅拌处理）过程。该研究整合了材料工程、表面科学和计量学等多个学科。多学科方法还将通过国家聋人技术学院的暑期学生的参与，有助于扩大代表性不足的少数群体对研究的参与，促进多学科科学合作，并对工程教育产生积极影响。技术摘要拟议的研究将通过对最近发现的机械化学效应（吸附的有机单分子层破坏塑性流动和表面脆化）的基础研究，增进我们对金属表面塑性化学效应的理解。 通过将表面分子探针（自组装单分子层（SAM））和高分辨率原位变形分析与单分子层属性和材料行为的原子和连续模型相结合，该研究将解决关于该效应的两个密切相关的假设：1）吸附的单分子层足以破坏表面塑性流动并诱导局部延性到脆性的转变； 2）单层-金属界面的能量学（表面应力与界面能）控制表面流动和流动-断裂转变。假设探索以四个目标为指导：1）利用分子自组装（SAM）将各种单分子层锚定到金属表面上，并表征它们的属性。表面的主要热力学参数，即表面/界面能和表面应力，将通过分子化学和链长而变化； 2) 在高表面积与体积比的样品的受控机械载荷（例如简单剪切、单轴拉伸）下，分析有或没有有机薄膜的金属的塑性变形响应以及相关的流动动力学； 3）开发一个模型来解释吸附单分子层引起的机械化学效应——从纳米级表面特性的变化到塑性流动的介观尺度转变； 4) 整合实验和建模，了解吸附膜如何影响金属的表面塑性，以及哪些单层属性控制机械化学效应。该研究将专门针对商业纯铝和铁进行，选择它们是因为它们在结构和变形响应、实验适用性和技术兴趣方面的多样性。这些发现对于材料加工、环境辅助开裂和磨损等多种领域都具有价值，其中机械载荷和化学的协同效应往往发挥着关键作用。教育和推广活动涉及本科生创建结构金属和加工的塑性流动/断裂现象的视频库；在研究生学习中适度关注创业精神；国家聋人技术学院暑期学生的参与。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 SUMMARYThis project will support research leading to new knowledge for structural metals that will improve their durability, processing and re-use. By doing so, it will advance the science base of critically important materials and manufacturing processes, and provide technological benefits for industry sectors as diverse as energy systems, ground transportation and aerospace. The project will explore a recently uncovered phenomenon pertaining to metals - a large change in their fracture and plastic flow behavior arising from application of even nanoscale organic films onto their surface. It will study the changes produced in surface properties of the metals (e.g., surface and interface energy, surface stress, strength) by the films. Based on this study of the properties, and their relation to film attributes, e.g., chemistry, chain length, adsorption, it will identify the factors that control the flow and fracture phenomenon. The approach will combine advanced experimental techniques such as high-speed imaging and image analysis and nanoscale metrology, with atomistic modeling of interactions between organic molecule structure and metal surface attributes. The findings will impinge upon areas as diverse as materials processing, environmentally-assisted cracking and wear – areas, where synergistic effects of mechanical loading and chemistry often play a key role. Controllability of the mechanochemical phenomenon by tailoring of the organic film chemistry will enable enhancements in material removal (e.g., cutting, comminution) and surface deformation (e.g., friction-stir processing) processes for metals. The research integrates several disciplines including materials engineering, surface science and metrology. The multi-disciplinary approach will also contribute to broadening the participation of underrepresented minorities in research via involvement of summer students from the National Technical Institute for the Deaf, foster multi-disciplinary scientific collaborations, and positively impact engineering education. TECHNICAL SUMMARYThe proposed research will advance our understanding of chemical effects in surface plasticity for metals through a fundamental study of a recently uncovered mechanochemical effect - disruption of plastic flow and surface embrittlement by adsorbed organic monolayers. By integrating a surface molecular probe (Self-Assembled Monolayers (SAMs)) and high-resolution in situ deformation analysis, with atomistic and continuum modeling of monolayer attributes and materials behavior, the research will address two closely-related hypotheses on the effect: 1) an adsorbed monolayer is sufficient to disrupt surface plastic flow and induce a local ductile-to-brittle transition; and 2) energetics of the monolayer-metal interface (surface stress vs. interface energy) controls the surface flow and the flow-fracture transition. The hypotheses exploration is guided by four objectives: 1) Utilize molecular self-assembly (SAMs) to anchor various monolayers onto metal surfaces, and characterize their attributes. The principal thermodynamic parameters of the surface, namely surface/interface energy and surface stress, will be varied via molecule chemistry and chain length; 2) Analyze the plastic-deformation response of the metal and associated flow dynamics, with and without the organic films, under controlled mechanical loading (e.g., simple shear, uniaxial tension) of specimens with high surface area-to-volume; 3) Develop a model for explaining the mechanochemical effect due to adsorbed monolayers – from changes in nanoscale surface properties to mesoscale transitions in plastic flow; and 4) Integrate the experiments and modeling to understand how adsorbed films influence surface plasticity in metals, and what monolayer attributes control the mechanochemical effect. The study will be conducted specifically with commercially pure aluminum and iron, selected for their diversity in structure and deformation response, experimental suitability and technological interest. The findings will be of value for areas as diverse as materials processing, environmentally-assisted cracking and wear, wherein synergistic effects of mechanical loading and chemistry often play a key role. The education and outreach activities involves undergraduate students in creating a video gallery of plastic flow/fracture phenomena for structural metals and processing; a modest focus on entrepreneurship in graduate study; and involvement of summer students from the National Technical Institute for the Deaf.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.