Graduate Thesis Or Dissertation
 

Additive Manufacturing of FeCrCoCuNi High Entropy Alloy via Laser Powder Bed Fusion and Nickel Aluminum Bronze via Laser Directed Energy Deposition

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7p88cq497

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  • High Entropy Alloys (HEA) exhibit unusual properties and are gaining interest as new materials for challenging applications in the aerospace, hypersonic and medical fields. The application of HEAs have been limited by the development of powder production at scale. A recently developed process of plasma spheroidization by 6K, inc. has the potential to produce HEAs at commercial scale. An exemplary HEA powder with chemical composition of 25Fe-18Ni-18Cr-17Co-16Cu (wt%) was produced via mechanical alloying followed by plasma spheroidization. This study characterizes the HEA powder and optimizes laser scanning strategy for the laser powder bed fusion process. Laser powers of 110-200 W and scanning speeds of 200-1000 mm/s were varied in nitrogen atmosphere to determine maximum density. A relative density of 99.8% was achieved with a laser power of 200 W and scan speed of 600 mm/s. Scanning electron microscopy of the as printed condition revealed refined sub-micron cellular substructures. Energy dispersive X-ray spectroscopy revealed a single ferritic phase of the as printed sample. A heat-treatment of 1050 C for 2 hours followed by furnace cooling promoted the formation of stable chromium and molybdenum rich precipitates. Heat-treatment relieved the residual stress and recovered 0.79% elongation at the cost of significant reductions in strength. The as printed condition exhibited superior tensile strength 753 MPa, yield strength 421 MPa, and microhardness 304 Hv when compared to the heat-treated condition (UTS=653MPa, YS=353MPa, Hv=242). A similar parameter selection process was completed for nickel aluminum bronze (NAB) fabricated via wire-fed laser directed energy deposition (LDED). Laser powers (600-1200 W) and print head traverse speeds (300-1200 mm/min) were used to fabricate characterization cubes for density and microstructure evaluation. The microstructure of the as printed NAB consisted of ⍺-phase containing κ phase and martensitic β phase. An annealing heat treatment of 675ºC for 6 hours followed by furnace cooling was conducted. The as printed condition demonstrated superior tensile strength 757 MPa, yield strength 410 MPa, and microhardness 218 Hv in comparison to the heat-treated condition (UTS=714 MPa, YS=372 MPa, Hv=204).
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  • Pending Publication
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  • 2022-08-22 to 2023-09-22

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