DMSE Doctoral Thesis Defense - Jackie Cho

Monday, August 30, 2021 at 3:30pm to 4:30pm

Virtual Event

DMSE Doctoral Thesis Defense

Design of Superelastic Secondary Phase Toughened Alloys

Jackie Cho

Monday, August 30, 2021

3:30 – 4:30pm ET

Contact for Zoom link.

As the global demand for metals increases, the resulting production is creating a growing strain on the environment. One strategy to combat this sustainability challenge is to increase material lifetime through alloy design for improving damage-resistance. This thesis explores an alloy design strategy that benefits from transformation toughening without retention of the transformation product. This can be achieved by designing a multi-phase alloy with a superelastic secondary phase in a stable ductile matrix phase. In particular, nano- and micro-scale precipitates, lamellar structures, and bulk matrix morphologies of TiNi are investigated in combination with stable (V,Nb)-Ti matrix phases. These structures allow the study of phase stability as a function of morphology, size, and composition. The phase stability of each form of the superelastic phase is not only investigated in isolation, but also in its role in the various phase mixtures within the alloy. The effects of the complex microstructure on the phase stability as well as the effects of the transformation on the deformation micro-mechanics of the microstructure have been probed through a variety of in-situ micro-mechanical tests, including in-situ SEM tensile experiments combined with μ-DIC, in-situ synchrotron tensile experiments, in-situ TEM micro-pillar compression tests, and in-situ SEM crack propagation experiments. These results provide a statistical view of the importance of the properties of the incorporated phases on phase stability, co-deformation, and ultimately crack propagation behavior.

Thesis Supervisor
C. Cem Tasan
, Thomas B. King Associate Professor, Materials Science and Engineering, Massachusetts Institute of Technology

Thesis Committee
Ju Li, Battelle Energy Alliance Professor, Nuclear Science and Engineering, Materials Science and Engineering, Massachusetts Institute of Technology

Krystyn Van Vliet, Michael (1949) and Sonja Koerner Professor, Materials Science and Engineering, Massachusetts Institute of Technology

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