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Event Scheduled for Aug 28, 2018


Event: MSE PhD Dissertation Proposal - Gyuho Song

Location: IMS-101C

Time: 10:45 am

Details of Event:
PhD Dissertation Proposal

Presenter: Gyuho Song
Major Advisor: Dr. Seok-Woo Lee
Associate Advisors: Dr. Avinash M. Dongare, Dr. Bryan D. Huey, Dr. Pu-Xian Gao and Dr. Barrett O. Wells

Date: Tuesday, August 28th, 2018
Time: 10:45 AM
Place: IMS 101 C

Title: In-situ Investigation on Mechanical Behavior of Superelastic Intermetallic Compound CaKFe4As4 at the Micrometer Scale

Superelasticity and superconductivity are exhibited in the novel intermetallic compound CaKFe4As4, one of the modified ThCr2Si2-type intermetallic compounds, through a reversible phase transformation between the tetragonal and the half-collapsed tetragonal phases. Our preliminary study shows that uni-axial compression of CaKFe4As4 single crystal along c-axis exhibits a high strength of ~5.1 GPa as well as excellent recoverable strain of ~17%. Note that this uni-axial reversible deformation mechanism is inherently distinct from the conventional shear mechanism, martensite-austenite phase transformation of shape memory intermetallic compounds. This giant elastic limit exceeds that of most of known shape memory materials (ceramics, alloys, single crystalline or polycrystalline), even the current state-of-the-art shape memory material (a single crystal shape memory ceramic exhibits a maximum strain of about 7% and a maximum stress around 2.5 GPa at room temperature). Density Functional Theory simulation revealed that this superelasticity results from the formation of As-As bond, collapse of magnetic moment and significant local compliance. Note that superelasticity and its related deformation-induced phase transformation behaviors are often influenced by temperature and loading condition. Therefore, the objective of this study is to understand how temperature and loading condition influence superelasticity in terms of a phase transformation mechanism in the intermetallic compound CaKFe4As4.

To begin with, solution growth methods are used to produce a single crystal specimen. In-situ micropillar compression is carried to characterize mechanical properties. Furthermore, the temperature control capability will be developed to investigate a cryogenic mechanical behavior at the micrometer scale. Note that this large elastic strain could make strain engineering possible, leading to the development of mechanically switchable functional materials, for instance, superconductivity-switching devices and shape memory devices that work even under uni-axial loading, which is considerably desirable for device applications. ThCr2Si2 structure is considered to be the most populous of all crystal structure type. Thus, our observation can be extended to search for a huge group of super-elastic and strain engineerable functional materials.

Target Audience: Not Available

Sponsored By: Materials Science and Engineering Program

Pamphlet/Flyer: No Pamphlet/Flyer Available

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