High-entropy metallic glasses for structural applications

High-entropy metallic glasses (HEMGs) have emerged as a revolutionary class of materials, combining the disordered atomic structure of metallic glasses with the compositional complexity of high-entropy alloys. Recent studies have demonstrated that HEMGs exhibit exceptional mechanical properties, such as ultrahigh strength exceeding 3 GPa and fracture toughness surpassing 100 MPa·m^1/2, making them ideal for structural applications in aerospace and automotive industries. For instance, a ZrTiHfCuNiBe HEMG system achieved a compressive strength of 3.2 GPa and an elastic strain limit of 2.5%, outperforming conventional metallic glasses by 20-30%. These properties are attributed to the unique atomic-scale heterogeneity and suppressed shear band formation, as revealed by advanced synchrotron X-ray diffraction and molecular dynamics simulations.

The thermal stability of HEMGs is another critical aspect, with glass transition temperatures (Tg) ranging from 600 K to 900 K, significantly higher than traditional metallic glasses. A recent study on a FeCoNiCrPd HEMG reported a Tg of 850 K and a crystallization temperature (Tx) of 950 K, with a supercooled liquid region (ΔT = Tx - Tg) of 100 K, enabling precise thermoplastic forming. This thermal stability is crucial for applications in high-temperature environments, such as turbine blades and nuclear reactors. Furthermore, the activation energy for crystallization was found to be 450 kJ/mol, indicating enhanced resistance to devitrification compared to conventional systems.

Corrosion resistance is a standout feature of HEMGs, with some compositions exhibiting passivation currents as low as 10^-7 A/cm^2 in aggressive environments like 3.5% NaCl solution. For example, a AlCrFeCoNi HEMG demonstrated a corrosion rate of 0.001 mm/year in seawater, outperforming stainless steel by two orders of magnitude. This exceptional performance is attributed to the formation of dense, self-healing oxide layers enriched with Cr and Al, as confirmed by X-ray photoelectron spectroscopy (XPS). Such properties make HEMGs promising candidates for marine engineering and biomedical implants.

The fabrication scalability of HEMGs has been significantly improved through advanced techniques like additive manufacturing (AM). Recent work on laser powder bed fusion (LPBF) produced defect-free HEMG components with relative densities exceeding 99.5% and hardness values up to HV0.1 = 650. AM-enabled compositional gradients have also been explored, yielding tailored mechanical properties across the same component—e.g., hardness variations from HV0.1 = 500 to HV0.1 = 700 within a single part—opening new avenues for multifunctional structural designs.

Finally, the economic viability of HEMGs is being addressed through the development of low-cost compositions using abundant elements like Fe and Al. A FeAlNiCrMo HEMG achieved comparable mechanical properties (strength = 2.8 GPa, hardness = HV0.1 = 600) at a material cost reduction of 40% compared to rare-earth-based systems. Life cycle assessments suggest that adopting such compositions could reduce the carbon footprint by up to 30%, aligning with global sustainability goals.

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