Doctoral Dissertations

Abstract

"Multi-principal element (MPE) alloys, unlike traditional alloys, consist of five or more principal elements with near equi-atomic compositions creating a large new compositional space for exploring new alloy possibilities. However, designing MPE alloys with the desired phases, microstructures and properties is challenging task, and there is a demand for basic research for a better understanding of structure-processing-property relations in these alloys.

In this Ph.D. research, different computational models and experiments were integrated to study phase formations, and mechanical properties of different MPE alloys. Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations were used to determine crystal structures, phase stability, and plastic deformation mechanisms. A modified thermodynamic approach was developed to calculate the phase diagrams of MPE alloys, and the accuracy of this approach was tested against commercial software. Experimental casting and characterization, and literature data were used to validate modeling predictions.

The phase diagram calculations of AlFeCoNiCu HEA showed coexistence of two phases at room temperature and stabilization of one phase above 1070 K at the equiatomic composition. The characterization experiments confirmed the crystal structures and composition of phases. To investigate the plastic deformation mechanisms and ductilities of CoCrFeNi-based HEAs, unstable and intrinsic stacking fault and unstable twinning energies were determined by DFT calculations. Finally, the effects of interstitial carbon on the phase formations in AlxFeCoCrNiCu HEAs were investigated, showing formation of different possible carbides and inter-granular graphite"--Abstract, page iv.

Advisor(s)

Asle Zaeem, Mohsen

Committee Member(s)

Newkirk, Joseph William
Smith, Jeffrey D.
Zhou, Caizhi
Medvedeva, Julia E.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Sponsor(s)

University of Missouri Research Board
Extreme Science and Engineering Discovery Environment

Comments

The authors would like to acknowledge the funding support provided by the University of Missouri Research Board. The authors are grateful for the computer time allocation provided by the Extreme Science and Engineering Discovery Environment (XSEDE), award number TG-DMR140008.

Publisher

Missouri University of Science and Technology

Publication Date

Fall 2017

Journal article titles appearing in thesis/dissertation

  • Investigating phase formations in cast AlFeCoNiCu high entropy alloys by combination of computational modeling and experiments
  • Generalized stacking fault energies, ductilities and twinnabilities of CoCrFeNi-based face-centered cubic high entropy alloys
  • Current capabilities in thermodynamic calculations of phase diagrams of high entropy alloys
  • Investigation of interstitial carbon impact in microstructures of AlxCoCrFeNiCu (x=0.3, 1.5, 2.8) high entropy alloys
  • Effect of alloying elements on unstable and intrinsic stacking fault energies and phase transformations of Fe-Mn-Si-Al-C high strength steel

Pagination

xi, 121 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2017 Mohsen Beyramali Kivy, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 11492

Electronic OCLC #

1104294651

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