Electronic Theses and Dissertations (Masters)

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Browsing Electronic Theses and Dissertations (Masters) by Faculty "Faculty of Commerce, Law and Management"

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    Characterisation and surface finish evaluation of Direct Energy Deposited AlCoCrCuFeNi High Entropy Alloys
    (University of the Witwatersrand, Johannesburg, 2024-01) Modikwe, Thembisile Patience; Mathe-Maleboho, Ntombi; Maledi, Nthabiseng
    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.