Author: Lee, Seok-Woo

Seok-Woo and Zhongyuan attended the GRC Ceramics!

Zhongyuan participated in the GRC ceramics and gave a poster presentation!

Title of poster: Micromechanical characterization on amorphous carbon and its nonporous structure.

(Bryan, Karla, Seok-Woo, Zhongyuan, Luis): Prof. Bryan Huey’s group were there together!

Abstract:

Micro-mechanical characterization on amorphous carbon and its nanoporous structures

Zhongyuan Li1,*, Ayush Bhardwaj2, James Watkins2, Seok-Woo Lee1

  1. Department of Materials Science and Engineering & Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269-3136, United States
  2. Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA

Carbon materials, such as diamond, graphite, and their related structures, have been often classified as a ceramic due to their high melting point, high hardness, and high brittleness. Carbon materials has a strong potential as a structural material due to their strong ionic/covalent C-C bond, but the brittleness of most carbon materials have limited their structural applications. In this study, we have developed amorphous carbon and its nanoporous structures with 40, 50, and 60% of porosity by rapid thermal annealing of Brush block copolymer and have investigated their plasticity and fracture behaviors. To evaluate the mechanical response, we performed nanoindentation and in-situ compressive tests on a micropillar, which was fabricated by utilizing focused-ion-beam milling. Both fully dense and nanoporous structures exhibit a large compressive fracture strain up to ~40% with a high work hardening rate. This exceptional fracture strain could result from dynamic re-distribution of sp2 and sp3 bonds during plastic deformation. In addition, we found that compressive fracture strength is nearly independent of porosity unlike the indentation hardness that scales with the porosity. We think that the porosity-independent fracture strength could be related to the size-affected strength of nanoscale ligands. The size reduction of ligand at the nanoscale could enhance its fracture strength, leading to the negligible decrease in fracture strength of the entire nanoporous structure. Also, we found that all samples demonstrate the excellent modulus of resilience the orders of magnitude higher than most engineering materials due to their low Young’s modulus, implying that amorphous carbon materials have a strong capability to absorb and release the mechanical energy. However, the yield strength of our fully dense amorphous carbon (1.5 GPa) is much lower than that of amorphous carbon that includes tetra-type C-C bonds (20 GPa). Lack of the halo ring pattern in TEM diffraction pattern indicates that our amorphous carbon possesses the random atomic arrangement even for the nearest neighbor carbons. This fully liquid-like atomic arrangement does not seem to be desirable for the yield strength but to be greatly beneficial for the ductility. It would be necessary to control the degree of a short-range C-C ordering or the population of tetra-type C-C bond to enhance the yield strength without sacrificing the ductility through the optimization of synthesis conditions or the post thermal and mechanical treatments.

Kyle gave a poster presentation at CSAT 2022!

Kyle gave a poster presentation at CSAT 2022. Kyle’s poster discussed micro-mechanical characterization of Ta cold spray deposits. He used nanoindentation, spherical indentation, and microvillar compression to investigate the spatial variation of mechanical properties of Ta.

Title of poser: “Micromechanical Characterization of Cold Sprayed Tantalum Powders Using Nanoindentation and Ex-situ Microvillar Compression

 

Many Congratulations on Jessica’s graduation!

Many Congratulations on Jessica’s Graduation. Fifth PhD student from our group!

thesis title “Micromechanical characterization of nanocrystalline and medium-range ordered materials

We wish Jessica a great success at her new position (EATON)!

<Farewell Party for Jessica @ The Spot, Tolland, CT, May 6, 2022 >

<Graduation Ceremony @ Jorgenson Center for the Performing Arts, May 9, 2022>

 

Jessica passed her PhD defense! Many Congratulations!

Jessica passed her PhD defense! Many Congratulations!

She gave a presentation entitled “Grain size effect on the mechanical properties of Nanocrystalline magnesium aluminum spinel at the microscale“. She discussed how grain size affects hardness, fracture strength, and fracture toughness of Nanocrystalline MgAl2O4, which can be potentially used as a transparent armor. This work has been supported by US Naval Research Laboratory.

Lee’s group attended TMS 2022 at Anaheim, CA!

Lee’s group attended TMS 2022 at Anaheim, CA!

Three excellent oral presentations were given. Wonderful jobs!

  • Jessica Maita: “Micromechanical Behavior of Nanocrystalline Spinel and Its Core-Shell Structures” – Symposium: Mechanical Behavior at the Nanoscale VI, 02/28/2022.
  • Shuyang Xiao: “Effects of Temperature and Composition on the Superelasticity of SrNi2P2 Single Crystal” – Symposium: Mechanical Response of Materials Investigated Through Novel In-Situ Experiments and Modeling, 02/28/2022.
  • Zhongyuan Li: “Achieving the Near Theoretical Maximum Modulus of Resilience in Polymer Nanocomposites via Sequential Infiltration of Nanoscale Metal Oxides” – Symposium: Mechanical Response of Materials Investigated Through Novel In-Situ Experiments and Modeling,03/03/2022.

Zhongyuan gave an oral presentation at MRS Fall 2021!

Zhongyuan gave an oral presentation at MRS Fall 2021!

This presentation discusses the unique microstructures created by sequential infiltration of nanoscale oxide into SU-8 negative photoresist, which is used for MEMS structures. These Nanocomposites materials exhibit ultrahigh modulus of resilience (200 MJ/m^3), which is much higher than any other engineering materials. Their high modulus of resilience results from metal-like high strength but polymer-like low Young’s modulus. This unusual combination is potentially useful for developing a strong-but-flexible material that can be used for flexible display.