Effects of Micro and Nano Surface Roughness onCavitation Damage of Metallic Surfaces

by

Juan Carlos Gonzalez-Parra

Doctor of Philosophy, Graduate Program in Mechanical EngineeringUniversity of California, Riverside, September 2022 Dr. Guillermo Aguilar and Dr. Natanael Cuando-Espitia, Co-Chairpersons

Surface parameters modification via laser irradiation has been a technique used to process materials since de discovery of the laser itself. One of these techniques is nano texturization of a surface by the means of focusing laser irradiation onto it and creating Laser-Induced Periodic Surface Structures (LIPSS). Despite the fact LIPSS have been around since the early dates of laser processing, their physical mechanism is still discussed. These LIPSS’ formation theories have been proposed since the 1980s with the Surface Plasmon Polariton model and Sipe’s theory, and, more recently, the Sipe-Drude model. In recent years, the research has been shifting to their applications. On this work, we suggest a modification of the surface via laser processing for reducing cavitation erosion damage. This proposal is divided in 2 main sections. First, a surface was nanotextured by scribing LIPSS on it. As it is described in the following sections, this processing avoids remnant microbubbles generated after the collapse of a cavitation bubble to attach to the surface, impeding those microbubbles to be activated near the surface and act as a nucleation point when another cavitation bubble is formed. Secondly, by adding a microstructure, a hierarchical structure was generated. This hierarchical structure allowed not only minimizing attached remnant microbubbles, but also the modification of the cavitation bubble’s rebound dynamics. By exclusively generating LIPSS on the surface of the material, we achieved a reduction of erosion by a factor of 3 when compared to an untreated surface. On the other hand, by evaluating it on a hierarchical structure we obtained an improvement of up to a factor of 22. This demonstrates the feasibility of using laser processing of materials as an easy, unexpensive and scalable approach of reducing cavitation erosion.