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物可以呈现基底的结构，而不是过度生长材料的通常结构。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，其中每个膜包含数千个过度生长-衬底组合，大部分膜体积可以在环境温度和压力下合成为包含假晶相;以前这种相变只能通过极端压力或温度来实现。这些假晶相从结构和功能的角度来看都是非常有吸引力的，并且在极端的压力、温度和应变速率下显示出高稳定性。该学院早期职业发展（CAREER）奖支持研究探索薄膜合成技术的进步，以获得对假晶相变和多层结构中假晶相的所得性质的基本了解。该项目将允许学生与国家和国际实验室合作，例如在EMPA（瑞士联邦材料科学与技术实验室）进行为期一学期的国际实习，以便在实验室内开发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）为了分别确定诱导相变所需的假晶相和邻接基底的最大和最小层厚度，ii）为了在纳米层压合成期间通过使用合金元素和组成分级来最大化假晶相的层厚度，以及iii）获得对通过界面应变工程转化的合金化假晶相的变形性质的基本理解。将系统地研究多个纳米层压系统，即（1）立方到类立方转变（Ni上的Cu，面心立方fcc到fcc，以及Cu上的Ni，fcc到面心四方fct），（2）六方到立方（Mg）Nb上）和Nb上的Zr，按此顺序。选择的顺序取决于赝晶相变的复杂程度的增加，它们在合成/沉积中的困难，以及它们潜在的技术应用。该项目将利用集成的原子层和物理气相沉积平台，使纳米层压材料的微观结构能够在原子尺度上精确定制。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中。该项目是在工程局土木，机械和制造创新（CMMI）部门的先进制造（AM）计划的支持下实现的，以及数学和物理科学理事会（DMS）材料研究部（DMR）的金属和金属纳米结构（MMN）计划该奖项反映了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。

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.