Date of Award

Summer 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Abdelmageed Elmustafa

Committee Director

Helmut Baumgart

Committee Member

Miltos Kotinis

Committee Member

Xiaoyu Zhang

Abstract

Accelerator beam exit windows are designed to withstand intense radiation and mechanical stress while preserving beam transmission and structural integrity. This dissertation explores the structural and mechanical responses of pure metals and high-entropy alloys (HEAs), in both bulk and thin-film forms, under high-dose electron beam (e-beam) irradiation to identify optimal materials for next-generation accelerator exit windows. Monte Carlo simulations using FLUKA, conducted at Jefferson Lab, revealed that amongst Ni, Ti, Cr, and V, Ni exhibits the highest power dissipation, while Ti depicts the lowest power dissipation, with Cr and V demonstrating intermediate characteristics. Bulk polycrystalline (PC) and single-crystalline (SC) samples of Ni, Cr, V, and Ti were irradiated with 10 MeV electrons at a dose of ~66 kGy. Post-irradiation analysis revealed increased hardness in PC Ni due to significant grain refinement, while PC Ti softened due to grain elongation, twinning, and twin boundary formation. The contribution of twinning and twin boundaries to the overall stresses was negligible. In contrast, SC Ti demonstrated increased hardness, likely due to the formation of additional slip planes.

To identify alternatives to conventional metals, bulk πΆπ‘Ÿ33𝑀𝑛33𝑉33 and πΆπ‘Ÿ31𝑀𝑛31𝑇𝑖7𝑉31 HEAs were evaluated for high-power beam applications. Thermodynamic modeling and XRD confirmed solid-solution phases with BCC structures, and nanoindentation revealed hardness values 5–6 times higher than those of single metals, with favorable e-beam power dissipation characteristics. Irradiated bulk CrMnTiV samples exhibited organized deformation features consistent with twinning and twin boundaries, attributed to Ti’s HCP crystal structure.

Thin films of Ni, Cr, V, Ti, CrMnV, and CrMnTiV were deposited on silicon and metallic substrates using magnetron sputtering to further optimize performance. These films demonstrated significantly enhanced hardness compared to their bulk counterparts, e.g., Cr films were 3-4 times harder than bulk Cr, while Ti and V films were twice as hard as their bulk forms, regardless of the substrate type. HEA thin films outperformed their corresponding single-metal films and depicted minimal degradation post-irradiation. CrMnTiV thin films exhibited excellent uniformity, substrate compatibility, and mechanical performance.

Overall, this work highlights the superior mechanical performance, radiation resistance, and structural stability of HEA thin films, especially CrMnTiV, positioning them as strong candidates for high-power e-beam accelerator exit windows. This methodology provides a valuable framework for designing and optimizing free-standing HEA foils for advanced accelerator technologies.

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DOI

10.25777/0jnw-8r91

ISBN

9798293844432

ORCID

0000-0001-7056-2680

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Available for download on Friday, September 18, 2026

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