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

Iowa State University, Ames IA

Investigators

Abstract

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.