Recent advancements in TiZrHfNbTa high-entropy ceramics (HECs) have demonstrated their exceptional mechanical properties, with a hardness of 18.5 GPa and fracture toughness of 6.2 MPa·m^1/2, surpassing traditional ceramics like Al2O3 and SiC. These properties are attributed to the unique multi-principal element composition, which induces severe lattice distortion and enhances solid solution strengthening. The entropy-stabilized structure also provides superior thermal stability, with a melting point exceeding 3000°C, making them ideal for extreme environments such as aerospace and nuclear applications.
The electronic structure of TiZrHfNbTa HECs has been investigated using density functional theory (DFT), revealing a complex interplay of d-band hybridization that enhances their catalytic performance. Experimental results show a hydrogen evolution reaction (HER) overpotential of 45 mV at 10 mA/cm^2, comparable to Pt-based catalysts. This is due to the optimized adsorption/desorption kinetics of hydrogen on the multi-element surface, which reduces activation energy barriers. Such findings position these ceramics as promising candidates for sustainable energy technologies.
Thermal conductivity studies of TiZrHfNbTa HECs have uncovered ultralow values of 1.2 W/m·K at room temperature, driven by phonon scattering from atomic mass and size fluctuations. This property is critical for thermal barrier coatings (TBCs) in gas turbines, where reducing heat transfer can improve efficiency by up to 15%. Additionally, their coefficient of thermal expansion (CTE) of 8.7 × 10^-6 K^-1 closely matches that of superalloys, minimizing interfacial stresses and enhancing durability under thermal cycling.
The corrosion resistance of TiZrHfNbTa HECs in aggressive environments has been quantified through electrochemical impedance spectroscopy (EIS), showing a corrosion rate of 0.002 mm/year in molten salt at 800°C. This outperforms conventional Ni-based alloys by two orders of magnitude, making them viable for next-generation concentrated solar power (CSP) systems. The formation of a stable oxide layer rich in ZrO2 and Ta2O5 further enhances their passivation behavior, ensuring long-term operational integrity.
Additive manufacturing (AM) techniques have been successfully applied to fabricate TiZrHfNbTa HECs with complex geometries, achieving a relative density of 99.3% and tensile strength of 1.2 GPa. Laser powder bed fusion (LPBF) parameters were optimized to minimize defects and control grain size to ~5 µm, enhancing mechanical performance. This breakthrough opens new avenues for custom-designed components in industries requiring high strength-to-weight ratios and intricate designs.
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