Sid Pathak: Materials for tunable strength and toughness


Mechanistic-Design of Multilayered Nanocomposites: Hierarchical Metal-MAX Materials for Tunable Strength and Toughness


Sid Pathak


Chemical and Materials Engineering


I plan to integrate education and research to provide a multitude of enrichment opportunities for the undergraduate students to gain exposure to advanced research in the areas of experimental materials science and mechanics. Students participating in this project will be trained in research methods structural and chemical analysis (X Ray Diffraction, Scanning Electron Microscopy, and Transmission Electron Microscopy), synthesis, and nano-mechanical testing. Select students will also have the opportunity to present their work at international conferences, as well as publishing their work in peer-reviewed journals, depending on the quality of work performed.

I have mentored multiple undergraduates at UNR, both from programs such as the McNair Scholars Program, underrepresented students (3 female and one Hispanic), as well as regular undergraduates. Undergraduate students in my lab have gone on to receive a number of fellowships and scholarships, including the 2018-19 Nevada NASA Space Grant Consortium Undergraduate scholarship, 2018 TMS Structural Materials Division (SMD) Undergraduate Scholarship, 2017 Nevada Undergraduate Research Award and the Nevada National Science Foundation's Experimental Program to Stimulate Competitive Research (NSF EPSCoR) 2016 Academic Year Undergraduate Research Opportunity Program (UROP) fellowship.

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Project Overview

Multilayered materials have come into greater focus due to their promising mechanical, chemical and functional properties, making them practically useful in a wide range of temperatures, mechanical loadings, and environmental conditions. One primary scientific interest stems from improvements in mechanical properties such as strength, ductility, and toughness that motivate continuous research and exploration in this field. While the vast majority of efforts primarily focus only on engineering the macroscale structure for improvement through trial-and-error, an emerging trend in the materials community lies at engineering the nanoscale mechanisms that ultimately govern the material properties. By understanding the role of the fundamental deformation or strain accommodation mechanisms, predictable alterations to the material layers are possible, which in turn can lead to physics-based tunability of the material properties. Such an approach is even more warranted, and attainable, when the layer thicknesses approach the nanoscale. The objective of the proposed research program is 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. We will accomplish this objective through an integrated computational and experimental research partnership. The proposed nanocomposite is composed of alternating metallic and MAX phase layers with a lamellar thickness reduced to the nanoscale. Unlike other multilayered systems that have been pursued in the past, the proposed metal-MAX nanocomposites detailed here are composed of a unique hierarchical laminate topology - as interfaces between the layers are in direct competition with the internal interfaces within the MAX layers.

In this work we aim to leverage the recently demonstrated operative deformation mechanism within the MAX phase layers- termed ripplocation - which is active at or near room temperatures and exhibits unprecedented strain reversibility and strain energy accommodation potential. Currently there is no literature on the tunability of MAX phases by controlling the activation barrier of ripplocation nucleation. We propose to tune the strength and ductility of the metal-MAX multilayer by confining the MAX phase to suppress its propensity for ripplocation nucleation, thus enabling cooperation/competition of both dislocations and ripplocations during deformation. The objectives of this combined modeling and experimental research are to: a) design and synthesize multi-layered nanocomposites composed of alternating metallic and MAX phase layers with a lamellar thickness reduced to the nanoscale, b) establish a fundamental understanding of the hierarchical interface driven microstructure and microstructure-property relationships, and c) formulate and validate atomistic models that outline the premise for controlling the activation of specific deformation mode(s) through hierarchical design of metal-MAX nanolaminates, thus tuning their mechanical properties to achieve improved strength and toughness.