Advisor(s)
Yogesh Vohra
Committee Member(s)
Kannatassen Appavoo
Nenad Velisavljevic
Shane Catledge
Wen Chen
School
College of Arts and Sciences
Document Type
Dissertation
Department (new version)
Physics
Date of Award
9-11-2025
Abstract
The overall goal of this research is to understand the mechanism of phase transformations in far-from-equilibrium micro/nano-structures produced by additive manufacturing of compositionally complex alloys. The eutectic high entropy alloys based on nickel were selected for this study because of their high tensile strength as well as high ductility. This study examines the high-pressure behavior and phase transformations of laser powder-bed fusion manufactured eutectic high-entropy alloys, specifically AlCoCrFeNi2.1 and Al18Co20Cr10Fe10Ni40W2. Both alloys exhibit a nano-lamellar structure composed of body-centered cubic and face-centered cubic phases. The BCC to FCC phase transformation under high pressures was observed below 21 Giga-Pascals (GPa) in both alloys and the FCC phase was observed to be stable up to a pressure of 300 GPa. The high-pressure high-temperature studies revealed melting of AlCoCrFeNi2.1 and Al18Co20Cr10Fe10Ni40W2 near 1700K under high pressure up to 6.2 GPa. Our high-resolution transmission electron microscopy studies on samples recovered after pressure cycling revealed the diffusion-less nature of BCC to FCC phase transformation and preservation of nano-lamellar morphology after the phase change. High pressure studies on suction-cast AlCoCrFeNi2.1 show a lower transition pressure of 3 GPa as compared to 21 GPa for additively manufactured alloy. Molecular dynamics studies show that a lower transition pressure is related to the presence of the ordered B2 phase in the suction cast alloy. Laser heating studies at 40 GPa on AlCoCrFeNi2.1 show the presence of a BCC phase at temperatures of 2100 C before melting. The occurrence of BCC phase at high pressures and high temperatures is also supported by laser shock compression experiments on AlCoCrFeNi2.1. The fundamental understanding of phase behavior and nano-lamellar morphology will lead to design of novel additively manufactured alloys for applications in high-pressure high-temperature extreme environments.
ProQuest ID
Recommended Citation
Pope, Andrew Dobbs, "High Pressure And High Temperature Exploration Of Phase Transformations In Eutectic High Entropy Alloys" (2025). All ETDs from UAB. 7437.
https://digitalcommons.library.uab.edu/etd-collection/7437
