Modikwe, Thembisile Patience2024-07-082024-07-082024-01Modikwe, Thembisile Patience. (2024). Characterisation and surface finish evaluation of Direct Energy Deposited AlCoCrCuFeNi High Entropy Alloys. [Master's dissertation, University of the Witwatersrand, Johannesburg]. WIReDSpace. https://hdl.handle.net/10539/38881https://hdl.handle.net/10539/38881A dissertation submitted to the school of Chemical and Metallurgical Engineering, Faculty of Engineering and Built Environment, University of the Witwatersrand, Johannesburg. In fulfilment of the requirements for the degree of Master of Science in Engineering in 2024.This study focused on the use of direct energy deposited (DED) techniques for the fabrication of AlCrCoCuFeNi high entropy alloy (HEAs) samples. HEAs have become a ground-breaking research field that provides solutions to complex problems in the aerospace industry. The industry requires improvement in the application of structural materials that are well-functioning at a low cost for example turbine blades. The fabrication of HEAs via DED commonly produces poor surface finish Ra in the range of 5 μm - 20 μm due to the layer-by-layer deposition method, as a result, it fails the industrial application requirements where the usual range of roughness tolerance required in the industry ranges from Ra is 0.8 μm < Ra < 1.6 μm thus, the need to deploy post-processing methods. This study focused on electropolishing (EP) and centrifugal barrel finishing (CBF) of AlCrCoCuFeNi-HEA samples. The polishing was performed using 80% methanol and 20% per-chloric acid solution used as the electrolyte. The samples were polished for 30 and 60 seconds in a Struers LectroPol-5 electrolytic polishing and etching device. The surface removal at 1200W for 30 sec on sample a was 50.29%, 58.65% for sample b, and 75.48% for sample c. The surface removal at 1400W for 60 sec on sample d is 63.25%, 45% for e, and 49.19% for f. The samples were polished for 7 and 14 hours in a CB320-CBF. During the period of 14 hours, a surface removal where the proportion of material removed for sample a was 55.37%, sample b was 43.13%, and sample c was 32.2% at a laser power of 1200W. After 7 hours of polishing, sample d achieved a surface removal of 86.02%, sample e achieved a surface removal of 43.18%, and sample f achieved a surface removal of 90% at a power of 1400W. Oxidation tests were conducted in static air at 1000˚C for 200h. The presence of FCC, BCC, and Fe2O3 oxide scales resulted in a noticeable increase in mass, with Fe2O3 scales being the most prevalent.en©2024 University of the Witwatersrand, JohannesburgAdditive ManufacturingHigh Entropy AlloyElectropolishingCentrifugal Barrel FinishingHigh-temperature OxidationSurface RoughnessDirect Energy DepositionUCTDSDG-7: Affordable and clean energyDissertationUniversity of the Witwatersrand, Johannesburg