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A Chemical/Powder Metallurgical Route to Fine-Grained Refractory Alloys
thesisposted on 09.08.2021, 13:43 by Sona N AvetianSona N Avetian
Ni-based superalloys remain state-of-the-art materials for use in the high-temperature, corrosive environments experienced by turbine blades in gas turbine engines used for propulsion and energy generation. Increasing the operating temperatures of turbine engines can yield increased engine efficiencies. However, appreciably higher operational temperatures can exceed the capabilities of Ni-based superalloys. Consequently, interest exists to develop high-melting refractory complex concentrated alloys (RCCAs) with the potential to surpass the hightemperature property limitations of Ni-based alloys. RCCAs are multi-principal element alloys, often comprising 5 or more elements in equal or near equal amounts. Conventional solidificationbased processing methods (e.g., arc melting) of RCCAs tend to yield coarse-grained samples with a large degree of microsegregation, often requiring long subsequent homogenization annealing times. Additionally, the large differences in melting temperatures of component elements can further complicate solidification-based fabrication of RCCAs.
Herein, the feasibility of a new chemical synthesis, powder metallurgy route for generating fine-grained, homogenous RCCAs is demonstrated. This is achieved by first employing the Pechini method, which is a well-developed process for generating fine-grained, oxide powder mixtures. The fine oxide powder mixture is then reduced at a low temperature (600°C-770 ºC) to yield fine-grained metal alloy powder. Hot pressing of the metallic powder is then used to achieve dense, fine-grained metallic alloys. While this process is demonstrated for generating fine-grained, high-melting MoW and MoWCr alloys, this method can be readily extended to generate other finegrained RCCA compositions, including those unachievable by solidification-based processing methods.