ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 46 iTSSe TSS iTSSe TSS Fig. 4 — Formation of grains and grain boundaries, and thereafter, large-scale, commercial grade components. This dispersion is similar to the strengthening of stainless steel via nanoparticle oxide dispersion. Now, as the RHEA lattices grow, they form grains that grow in different directions, until being bounded at the grain boundaries, as noted in Fig. 4. Depending on the additive manufacturing process (such as thermal spray coating process) and its process and post-process para- meters, grains can be on the order of microns; certainly, annealing can increase grain size and ductility, although typically at the expense of material strength. However, the dispersion of nanoparticles within the RHEA will also increase its strength. CONCLUSION Though relatively new, RHEAs and single refractory- element thin and thick coatings already show remarkable properties for stainless steel, Inconel, and Haynes substrates, as well as electronic components, as shown in Fig. 5. The upper portion of the figure shows an uncoated 4-in. diffuser on the left-hand side, while the right-hand side shows the coated diffuser. Hence, RHEA coatings can now be consistently applied to complex geometries, as noted in Fig. 5, as well as components ranging from microns to large scales in the 2 to 3 m range. For example, the bottom portion of Fig. 5 depicts thin film chemical vapor deposited RHEA for quantum computer hardware and high-power density components. The RHEA powder can also be synthesized into solid test samples, such as billets for computer numerical control, or near-net shape commercial components[14]. ~iTSSe Acknowledgment The authors would like to thank the DoE (DE-SC0023591) for funding the project and Mr. Chirag Raval of Hannecard Roller Coatings Inc. for his assistance with cold spray work. For more information: Satish Dixit, director of engineering and R&D, Plasma Technology Inc., 1754 Crenshaw Blvd., Torrance, CA 90501, 310.320.3373. s.dixit @ptise.com, www.ptise.com. References 1. O.N. Senkov, et al., Refractory High-Entropy Alloys, Intermetallics, 18, p 1758-1765, 2010, doi.org/10.1016/j. intermet.2010.05.014. 2. D.B. Miracle and O.N. Senkov, A Critical Review of High-entropy Alloys and Related Concepts, Acta Mater., 122, 2017. 3. E.P. George, D. Raabe, and R.O. Ritchie, High-Entropy Alloys, Nature Reviews Materials, 4, p 515-534, 2019. 4. A. Meghwal, et al., Thermal Spray High-Entropy Alloy Coatings: A Review, J. Therm. Spray Technol., 29, p 857-893, 2020, doi.org/10.1007/s11666-020-01047-0. 5. ORNL, Oak Ridge National Laboratory, Fluoride- Salt-Cooled High-Temperature Reactors, January 30, 2018, https://www.ornl.gov/content/fluoride-salt-cooled-high- temperature-reactors. 6. B. Gorr, et al., Current Status of Research on the Oxidation Behavior of Refractory High Entropy Alloys, Adv. Eng. Mater., 23, 2021, doi.org/10.1002/adem.202001047. 7. X.B. Feng, et al., Size Effects on the Mechanical Properties of Nanocrystalline NbMoTaW Refractory High Entropy Alloy Thin Films, Int. J. Plast., 95, p 264-277, 2017, doi.org/10.1016/j.ijplas.2017.04.013. Fig. 5 — RHEA thick and thin coatings. FEATURE 12
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