Electrical & Computer Engineering, Department of
First Advisor
Craig A. Zuhlke
Date of this Version
8-2022
Document Type
Article
Abstract
Femtosecond laser surface processing (FLSP) is applied to a range of materials in this thesis. The materials studied were a carbon fiber reinforced polymer (CFRP), a thermosetting polymer, silicon nitride (Si3N4), and ceramic alumina. The CFRP is a composite material consisting of a thermosetting polymer and carbon fibers. The CFRP are referred to as a composite and the thermosetting polymer is referred to as a resin in this thesis. Alumina can exist in many different forms. The alumina used is 0.5 mm thick nonporous alumina sheets purchased from McMaster-Carr, and will be referred to as alumina in this thesis. While applying FLSP to the composite, the surface layer of resin was ablated away, and the carbon fibers were functionalized with laser induced periodic surface structures (LIPSS). The LIPSS formed over a range of fluence and pulse counts, from a fluence of 1 J/cm2 and a pulse count of 380 to a fluence of 4.5 J/cm2 and a pulse count of 3,800. Additionally, at a fluence of 0.14 J/cm2 and a pulse count of 3,800, selforganized mound-like microstructures formed. It appeared that these microstructures were created on the resin portion of the composite material, so additional studies were performed on resin material that did not contain the carbon fibers. While processing the resin, high aspect ratio pyramid-like micro- and nano-scale surface features formed at a fluence of 0.15 J/cm2 and a pulse count of 18,500. Preferential ablation was identified as the growth mechanism for these high aspect ratio pyramids, which is the same primary formation mechanism for FLSP pyramids on metals. On Si3N4, two different types of pyramid microstructures were created that were overlayed with nano-scale surface features. Larger pyramids with average heights of 1,250 μm were created at a fluence of 1.3 J/cm2 and a pulse count of 73,900. Smaller pyramid microstructures with average heights around 200 μm were created at a fluence of 0.85 J/cm2 and a pulse count of 50,200. Both of the pyramid microstructures on Si3N4 resulted superhydrophilic surfaces with a water contact angle of 0º. On ceramic alumina, low aspect ratio pyramids formed at a fluence of 1.1 J/cm2 and a pulse count of 13,000. The FLSP pyramids resulted in a superhydrophilic surface with a water contact angle of 0º and increased the hemispherical emissivity from 0.664 for unprocessed alumina to 0.861 for the FLSP-processed alumina.
Comments
A Thesis Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment Requirements For the Degree of Master of Science, Major: Electrical Engineering, Under the Supervision of Professor Craig A. Zuhlke. Lincoln, NE: August 2022
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