Degree
Doctor of Philosophy (PhD)
Department
Engineering Science
Document Type
Dissertation
Abstract
This thesis presents the microstructural evolution and mechanical performance of Additive Friction Stir Deposition (AFSD) components made from four hard metal systems: Aluminum alloy 6061 (Al6061), AISI 1018 carbon steel (CS1018), Inconel 625 (IN625), and HY80 high-strength steel.
Chapter 1 introduces AFSD as a solid-state additive manufacturing approach and emphasizes the need to understand process–microstructure–property correlations for hard and high-strength alloys that are difficult to produce using fusion-based methods.
Chapter 2 compares spindle speed on Al6061 components made by AFSD on warmed substrates. Microhardness and electrical conductivity experiments show that lower spindle speeds produce deposits with higher hardness and precipitate retention. Preheating the substrate to 300 °C reduces property gradients during deposition.
Chapter 3 studies the microstructure and mechanical properties of AFSD-produced CS1018 low-carbon steel after two post-processing heat treatments at 210 and 518 °C. The processed material has a ferrite–pearlite microstructure and lower hardness and tensile strength than the raw material, but it has increased ductility. EBSD and XRD investigations characterize grain structure and phase history, but fractographic analyses show that annealing preserves microstructural integrity without adding flaws.
In Chapter 4, the AFSD method is used to treat IN625 nickel-based superalloy and compare its microstructure and mechanical properties to the as-received material. Dynamic recrystallization during deposition refined grain, increasing hardness by 41% and final tensile strength. The absence of harmful secondary phases is confirmed by XRD. Tensile tests show virtually isotropic behavior across build directions, whereas fractography shows fully ductile fracture behavior under all conditions.
Chapter 5 presents the AFSD method for producing HY80 high-strength steel and two heat treatment methods: conventional furnace heating and superheating. The results show that superheating reduces inter-layer mechanical brittleness caused by imbalanced residual stresses. A more homogenous strengthening mechanism and better inter-layer bonding improve tensile strength and ductility.
Date
4-17-2026
Recommended Citation
Emanet, Selami, "Additive Friction Stir Deposition (AFSD) of Hard Metals: Microstructural Evolution and Mechanical Performance of Al6061, CS1018, IN625, and HY80 Alloys" (2026). LSU Doctoral Dissertations. 7079.
https://repository.lsu.edu/gradschool_dissertations/7079
Committee Chair
Shengmin Guo
LSU Acknowledgement
1
LSU Accessibility Acknowledgment
1
Included in
Engineering Science and Materials Commons, Materials Science and Engineering Commons, Mechanical Engineering Commons