CAREER: Towards a Fundamental Understanding of Interface Strain-Driven Pseudomorphic Phase Transformation in Multilayered Nanocomposites

在适当的条件下，一种材料在另一种材料上的沉积可以呈现出衬底的结构，而不是通常的过度生长材料的结构。这种异常晶体结构中的过度生长称为假晶相。当沉积为多层膜时，每个膜包含数千种过度生长-衬底组合，可以在环境温度和压力下合成很大比例的膜体积以包含假晶相；以前只有通过极端压力或温度才能实现这种相变。从结构和功能的角度来看，这些假晶相都具有很高的吸引力，并且在压力、温度和应变速率的极端情况下表现出很高的稳定性。该学院早期职业发展(CALEAR)奖支持探索薄膜合成技术进步的研究，以便从根本上了解多层建筑中的假象相变和由此产生的假象相的性质。该项目将允许学生与国家和国际实验室合作，例如在EMPA(瑞士联邦材料科学和技术实验室)进行为期一学期的国际实习，以便在实验室内发展新的科学和基础设施，并提高机构研究能力。该项目有三个主要目标：i)确定诱导相变所需的伪晶相和相邻衬底的最大和最小层厚度，ii)在纳米层合成过程中利用合金化元素和成分分级来最大化伪晶相的层厚度，以及iii)基本了解通过界面应变工程转变的合金伪晶相的变形特性。系统地研究了多层纳米晶系，即(1)立方到类立方转变(Cu在Ni上，面心立方fcc到fcc，Ni在Cu上，fcc到面心四方fct)，(2)六方到立方(Mg On Nb)和Zr在Nb上。选择的顺序取决于假象相变的日益复杂的程度，它们在合成/沉积中的难度以及它们潜在的技术应用。该项目将利用一个集成的原子层和物理气相沉积平台，允许在原子尺度上精确地定制纳米层状物的微结构。与工业合作伙伴的合作将促进这项研究的知识转移到工业应用。该项目是在工程局土木、机械和制造业创新(CMMI)部门的先进制造(AM)计划和数学和物理科学局(DMS)材料研究(DMR)部门的金属和金属纳米结构(MMN)计划的支持下实现的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Under the right conditions, deposits of one material on another can take on the structure of the substrate rather than the usual structure of the overgrowth material. Such overgrowths in the abnormal crystal structure are termed pseudomorphic phases. When deposited as a multilayer, where each film contains thousands of overgrowth-substrate combinations, a large proportion of the film volume can be synthesized to contain the pseudomorphic phase at ambient temperatures and pressures; previously such phase transformations were accessible only via extreme pressures or temperatures. These pseudomorphic phases can be highly attractive from both structural and functional viewpoints, and show high stability under extremes of pressure, temperature and strain rate. This Faculty Early Career Development (CAREER) award supports research to explore advancements to the thin film synthesis technique in order to obtain a fundamental understanding of the pseudomorphic phase transformation and the resultant properties of the pseudomorphic phases in a multilayered architecture. This project will allow students to collaborate with both national and international laboratories, such as semester-long international internships, at EMPA, the Swiss Federal Laboratories for Materials Science and Technology, in order to develop new science and infrastructure within the laboratories and increase the institutional research capacities. This project has three main objectives: i) To identify the largest and smallest layer thicknesses for the pseudomorphic phase and the adjoining substrate, respectively, required to induce the phase transformation, ii) To maximize the layer thickness of the pseudomorphic phases by use of alloying elements and compositional grading during the nanolaminate synthesis, and iii) To gain a fundamental understanding of the deformation properties of the alloyed pseudomorphic phases that are transformed by interface strain engineering. Multiple nanolaminate systems will be studied systematically, namely (1) cubic to cubic-like transformations (Cu on Ni, face centered cubic fcc to fcc, and Ni on Cu, fcc to face centered tetragonal fct), (2) hexagonal to cubic (Mg on Nb) and Zr on Nb, in that order. The order of selection is dictated by both the increasing degrees of complexity of the pseudomorphic phase transformation, their difficulties in the synthesis/deposition, and their potential technological applications. This project will utilize an integrated atomic layer and physical vapor deposition platform that allows the microstructure of nanolaminates to be precisely tailored at the atomic scale. Collaborations with industrial partners will promote knowledge transfer of this research to industrial applications.This project is made possible with the support of the Advanced Manufacturing (AM) program in the Division of Civil, Mechanical and Manufacturing Innovation (CMMI) of the Directorate for Engineering, and the Metals and Metallic Nanostructure (MMN) program in the Division of Materials Research (DMR) of the Directorate for Mathematical and Physical Sciences (DMS).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.