Advanced materials: development of high-entropy alloys via additive manufacturing

Date

2024-8

Author

Altınok, Sertaç

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Technological advancements necessitate the development of robust, lightweight, and sustainable materials, particularly in aerospace, where efficiency and material availability are crucial, including extraterrestrial environments such as Mars. High-entropy alloys (HEAs) emerged as a promising option, offering the potential for superior properties using readily available elements. However, traditional alloy production methods face challenges like element segregation and coarse microstructures, limiting HEAs' capabilities. Additive manufacturing offers a solution by enabling incremental processing to refine properties and create complex, lightweight structures through in-situ alloying and site-specific properties optimization. This research delves into the development of single-phase and dual-phase HEAs using L-PBF and DED processes. It starts with generating a database with five and six principal components through thermodynamic models and the selected compositions are validated via arc and induction melting processes. The study then focuses on the CoFeNiCuMn composition as a model base alloy, produced via gas atomization and refined into four grades for thorough characterization to assess their compatibility with L-PBF and DED methods. A three-stage high-throughput L-PBF experimental optimization process utilizing 15-45 μm particles significantly enhances the CoFeNiCuMn alloy’s characteristics, achieving a 99.94% relative density and a grain size of 1.6 μm within a uniform FCC structure. The addition of Cr, modeled via the CALPHAD approach, facilitates phase transformation studies under different cooling conditions. In-situ Cr alloying in DED with 44-106 μm powders leads to a compositionally graded material enabling the identification of a specific composition with notably high properties, where the hardness peaks at 2.5 times its original value due to the nanoprecipitation of a Cu-based FCC phase within a Cr-based BCC matrix. Alloying with Ga, using predictive modeling, resulting in functionally graded material with dual-phase HEA compositions, showcasing the potential for customizing site-specific properties through composition adjustment. This generated material exhibited transformations between multi-principal FCC and BCC phases, demonstrating adaptability to specific conditions. The findings underscore the rapid development and customization potential of HEAs via a streamlined three-stage L-PBF route and compositional grading in DED. This research highlights AM's crucial role in bypassing traditional material constraints and facilitating high-throughput development of advanced HEAs with tailored properties for applications.

Subject Keywords

high-entropy alloys, additive manufacturing, functional-graded materials, powder metallurgy, advanced characterization

URI

https://hdl.handle.net/11511/111025

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Graduate School of Natural and Applied Sciences, Thesis