SUBJECT: M.S. Thesis Presentation
BY: Omar Elsayed
TIME: Monday, July 20, 2020, 3:00 p.m.
PLACE:, Online
TITLE: The Effect of Pure and Compound Laser Incidence Angles on Bead Geometry, Microstructure and Texture in Direct Energy Deposition Processes
COMMITTEE: Dr. Christopher Saldana, Co-Chair (ME)
Dr. Thomas Kurfess, Co-Chair (ME)
Dr. Katherine Fu (ME)


The purpose of this study is to examine the effect of varying laser incidence angles on textural, microstructural and geometric characteristics of DED-processed materials, provide a more comprehensive outlook on participating laser-matter interaction phenomena and ultimately devise strategies to ameliorate print performance. In this study, single-layer, single-/multi-track specimens were processed to examine the effect of non-orthogonal angular configurations on bead morphology, microstructure, phase composition and textural representation of DED-processed materials. Laser power measurements were also conducted to understand the effect(s) of laser spot size changes and laser attenuation on the effective power reaching the substrate surface. It has been observed that bead morphology experienced a normal curve behavior with increasing lead angles, while it experienced a decrease with decreasing lean angles. The orthogonal setting exhibited the most promising bead morphology values. An asymmetry in the distribution of the bead morphology plots indicates that there is preferential bias in utilizing a certain angular configuration over another in terms of potential incorporation of non-orthogonal deposition operations in industrial applications. No significant differences in phase composition, texture and microstructure were observed with processed samples of various angular configurations as well as raw, unprocessed powders, indicating that a potential route for enhanced process robustness is achievable without significantly affecting bulk material properties. In unfocused beams, laser incidence angles have little effect on the extent of laser power loss due to both laser spot size variations as well as powder cloud laser attenuation, indicating that more involved studies are required.