Graduate Studies, UNL

 

Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–

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First Advisor

Yongfeng Lu

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Bai Cui, Eva Schubert, Yanan Wang

Department

Electrical Engineering

Date of this Version

4-27-2026

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy

Major: Electrical Engineering

Under the supervision of Professor Yongfeng Lu

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Qiuchi Zhu. Used by permission

Abstract

This dissertation comprises three parts addressing laser microprocessing of metallic and composite materials through nanosecond pulsed laser surface melting, laser shock peening, and femtosecond laser machining. The first part discusses nanosecond pulsed laser surface melting for corrosion mitigation in stainless steel. Commercial 304 stainless steel (SS) was first used to establish a processing window for stable shallow remelting and rapid resolidification. The approach was then extended to 304L/308L SS welded joints relevant to nuclear dry storage canisters. The results show that nanosecond laser surface melting refines the near-surface microstructures in the heat-affected zone and improved pitting corrosion resistance. Electrochemical and surface analyses further indicated enhanced passive-film stability after laser treatment.

The second part focuses on laser shock peening in two material systems: sensor-fused metallic components with embedded optical fibers and aluminum/carbon fiber (Al/CF) composites. In the fiber-sensor-embedded metallic system, laser shock peening produced compressive strain transfer and improved resistance to thermally induced slippage at elevated temperatures. In Al/CF composites, the treatment increased hardness and generated a subsurface plastic deformation zone, with microstructural evidence of deformation-related structural evolution. These results show that laser shock peening can effectively modify mechanical response through shock-induced plastic deformation without relying on surface melting as the primary mechanism.

The third part explores femtosecond laser machining for millimeter-scale precision structuring. A two-step machining strategy was developed to improve edge quality, reduce sidewall taper, and achieve better dimensional control in deep machining. The results demonstrate that millimeter-scale holes and related geometries with sharp edges and high-quality sidewalls could be fabricated when angle-of-incidence control and process-compensation strategies were properly designed.

Collectively, these three parts demonstrate the versatility of laser microprocessing in addressing distinct engineering objectives in metallic and composite materials. Each part is evaluated based on the material response, process design, and performance requirements relevant to the application, providing insight into nanosecond-pulsed laser surface melting for corrosion mitigation, laser shock peening for inducing compressive residual stress, enhancing surface hardness, and improving interfacial stability, and femtosecond laser machining for precision structuring.

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