Inhibited Surface Diffusion in Nanoporous Refractory Multi-Princiapal Element Alloy Thin Films Prepared by vacuum Thermal Deallying

(Das Gupta, T.; Balk, T.J. Inhibited Surface Diffusion in Nanoporous Multi-Principal Element Alloy Thin Films Prepared by Vacuum Thermal Dealloying. Metals 2024, 14, 289. https://doi.org/10.3390/met14030289)

Nanoporous structures with 3D interconnected networks are traditionally made by dealloying a binary precursor. Certain approaches for fabricating these materials have been applied to refractory multi-principal element alloys (RMPEAs), which can be suitable candidates for high-temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated from magnesium-based thin films (VMoNbTaMg) that had been prepared by magnetron sputtering. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pressure element, is a novel technique for synthesizing nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was created by the sublimation of the highest vapor pressure element (Mg). X-ray photoelectron spectroscopy depth profiling indicated significantly less ligament oxidation during VTD as compared to traditional dealloying methods. Furthermore, np-RMPEAs exhibited outstanding stability against coarsening, retaining smaller ligaments (~25 nm) at elevated temperature (700 °C) for a prolonged period (48 h).

The top left image shows thin films made by magnetron sputtering and annealing of thin films in high vacuum. Bottom Left: Nanoporous RMPEA cross section image by FIB ion milling. RIght: Plane view of Nanoporous RMPEA.

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COMBINATORIAL THIN FILM SCREENING OF NON-EQUIATOMIC MPEA SYSTEM FOR IMPROVED PHASE STABILITY, CORROSION RESISTANCE AND STRENGTH

Multi-principal element alloys (MPEAs) have attracted increasing interest due to their ability to exhibit a unique combination of mechanical and chemical properties arising from high configurational entropy. While early studies primarily focused on equiatomic compositions, growing evidence suggests that non-equiatomic MPEAs can deliver superior performance. Using a combinatorial thin-film approach for rapid and efficient compositional screening, this work identifies a single-phase non-equiatomic MnFeCoNiCu alloy with enhanced hardness, tensile strength, and corrosion resistance compared to the equiatomic composition. Systematic characterization using X-ray diffraction, nanoindentation, and corrosion testing enabled rapid evaluation across a wide compositional space. The optimized non-equiatomic composition retained a single-phase face-centered cubic structure at elevated temperatures while exhibiting improved properties. These performance enhancements were further confirmed through bulk alloy fabrication and testing, demonstrating that the improved mechanical and corrosion behavior observed in thin films is preserved at the bulk scale.

The top left image shows EDM cut micro samples, Bottom Left: Ingot fabricated by arc melting, Right: full project experiment flowchart

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HOT DEFORMATION BEHAVIOR of MULTI-PRINCIPAL ELEMENT ALLOY

The hot deformation behavior of the non-equiatomic MPEA was studied using high-temperature compression tests across a range of temperatures and strain rates. A constitutive model was developed to describe the alloy’s flow stress as a function of temperature and strain rate. Processing maps identified stable deformation windows with high power dissipation efficiency and regions prone to microstructural instability. Two optimal processing regimes were established, providing practical guidance for thermomechanical processing of MnFeCoNiCu alloys.

The top left image shows vacuum arc melter and tube furnace,, Bottom Left: arc-melted ingots and EDM cut cylindrical compression test samples. Right: Gleeble thermomechanical simulator for high temperature compression testing

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