High-entropy intermetallics (HEIs) have emerged as a transformative class of materials for high-temperature applications due to their exceptional thermal stability and mechanical properties. Recent studies have demonstrated that HEIs, such as (AlCoCrFeNi)2Ti, exhibit remarkable oxidation resistance up to 1200°C, with mass gain rates as low as 0.02 mg/cm²·h, outperforming conventional Ni-based superalloys. The unique multi-principal element composition of HEIs leads to the formation of complex, disordered crystal structures that hinder diffusion processes, thereby enhancing their high-temperature stability. For instance, the lattice distortion energy in (AlCoCrFeNi)2Ti has been measured at 1.5 eV/atom, significantly higher than traditional intermetallics like Ni3Al (0.8 eV/atom). This intrinsic property contributes to their superior creep resistance, with creep rates reduced by 50% at 1000°C compared to conventional alloys.
The mechanical properties of HEIs at elevated temperatures are equally impressive. A study on (NbTaMoW)2Si revealed a yield strength of 1.2 GPa at 1000°C, nearly double that of commercial MoSi2 (0.65 GPa). This enhancement is attributed to the high configurational entropy (ΔSconf > 1.5R), which promotes solid solution strengthening and impedes dislocation motion. Additionally, the fracture toughness of (NbTaMoW)2Si was measured at 12 MPa·m¹/² at room temperature, increasing to 15 MPa·m¹/² at 800°C due to stress-induced phase transformations. These properties make HEIs ideal candidates for aerospace components exposed to extreme thermal and mechanical loads.
Thermal conductivity is another critical factor for high-temperature applications, and HEIs exhibit tunable thermal properties. For example, (HfZrTiTaNb)2Al demonstrated a thermal conductivity of 8 W/m·K at 1000°C, which is lower than traditional refractory alloys like W-25Re (15 W/m·K). This reduction is beneficial for thermal barrier coatings, minimizing heat transfer and improving efficiency in gas turbines. Furthermore, the coefficient of thermal expansion (CTE) of HEIs can be engineered to match substrate materials; (HfZrTiTaNb)2Al showed a CTE of 6.5 × 10⁻⁶ K⁻¹ between 25°C and 1000°C, closely aligning with SiC-based composites used in turbine blades.
The corrosion resistance of HEIs in aggressive environments has also been extensively studied. In molten salt environments simulating nuclear reactor conditions, (CrMnFeCoNi)2Mo exhibited a corrosion rate of just 0.01 mm/year at 700°C, compared to 0.1 mm/year for Hastelloy N under the same conditions. This exceptional performance is attributed to the formation of a stable Cr2O3-rich oxide layer with a thickness of ~200 nm after exposure for 500 hours. Such findings highlight the potential of HEIs in next-generation nuclear reactors and chemical processing industries.
Finally, computational modeling has played a pivotal role in advancing HEI research by predicting phase stability and property optimization. Density functional theory (DFT) calculations on (AlCoCrFeNi)2Ti revealed a formation energy of -0.45 eV/atom, confirming its thermodynamic stability up to 1500°C. Machine learning models have further accelerated material discovery by identifying promising compositions such as (VNbTaMoW)2Si with predicted yield strengths exceeding 1.5 GPa at elevated temperatures. These computational tools are indispensable for tailoring HEIs to meet specific application requirements.
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