Date of Award

12-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Peter K. Liaw

Committee Members

Carl D. Lundin, Carl J. McHargue, Hairong Qi

Abstract

The objective of the present study is to provide a fundamental understanding of fatigue, fracture, and environmentally-assisted behavior of high-entropy alloys (HEAs). The work involves fatigue, fracture, and environmentally-assisted behavior of a new kind of advanced engineering materials, called HEAs. Three tasks are studied: (1) microstructures and fracture mechanisms of HEAs, (2) fatigue failure and life prediction of HEAs, and (3) corrosion and environmentallyassisted behavior of HEAs.

In the first task, microstructural stability and fracture mechanism of the AlCoCrFeNi alloy are studied and compared with thermodynamic calculations. In the second task, high-cycle fatiguefailure mechanisms of the cold-rolled Al0.5CoCrCuFeNi alloy are explored, and the experimental results are used to develop lifetime-prediction capabilities and safety models for future applications. In the third task, a single-phase Al0.3CoCrFeNi alloy is computational-alloyeddesigned and developed, and electrochemical-polarization and fatigue-environmentally-assisted behavior are investigated.

Intellectual merit

The current study of fatigue fracture on HEAs advances the fundamental understanding of the mechanisms of the fatigue fracture and environmentally-assisted behavior of HEAs, which is a very new area. The experimental approaches provide the critical information for the mechanistic study of the heat-treatment effects, such as hot isostatic pressing (HIP), annealing, cold rolling, and forging, on microstructures and mechanical properties of HEA systems. This research program have a transformative impact on the research, development, and applications of HEAs. The goal is accomplished by utilizing the strength at The University of Tennessee (UT)’s mechanical behavior and failure analysis of advanced structural alloys, and materials processing. UT is well equipped with the synthesis equipment, mechanical-testing instruments, and microstructuralcharacterization tools. The synergetic efforts facilitate the effectiveness and success of the proposal research.

Broader impacts

The current research on fatigue-fracture and environmentally-assisted behavior of HEAs enriches the research and teaching efforts on advanced materials at UT. The presentations at professional conferences and the publications in academic journals achieve the wide national and international impact. The efforts not only increase the public awareness on the fatigue-fracture and environmentally-assisted behavior of HEAs and their scientific importance, but also stimulate the interests of the student in pursuing the science, engineering, and technology fields of study.

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