High-performance structural materials are critical to the development of transportation, energy, and aerospace. In recent years, newly developed high-entropy alloys with a single-phase solid-solution structure have attracted wide attention from researchers due to their excellent properties. However, this new material also has inevitable shortcomings, such as brittleness at ambient temperature and thermodynamic instability at high temperature. Efforts have been made to introduce a small number of intermetallic compounds into single-phase solid-solution high-entropy alloys as a secondary phase to their enhance properties. Various studies have suggested that the performance of high-entropy alloys can be improved by introducing more intermetallic compounds. At that point, researchers designed an intermetallic compound-strengthened high-entropy alloy, which introduced a massive intermetallic compound as a coherent strengthening phase to further strengthen the matrix of the high-entropy alloy. Inspired from this, Fantao obtained a new alloy—high-entropy intermetallics—by introducing different alloying elements to multi-principalize the material in a previous study. This new alloy treats the intermetallic compound as the main phase and has advantages of both structural and functional materials. It is expected to become a new generation of high-performance amphibious high-entropy materials across the field of structure and function. In this review, we first demonstrate the inevitability of intermetallic compounds in high-entropy alloys and explain the importance of intermetallic compounds in improving the properties of high-entropy alloys. Secondly, we introduce two new high-entropy alloys mainly from the aspects of composition design, structure, underlying mechanism, and performance. Lastly, the high-entropy materials containing intermetallic compound phases are summarized, which lays a theoretical foundation for the development of new advanced materials.

In this study, a C/TiC nanocomposite coating has been prepared by magnetron sputtering technology and vacuum heat treatment technology on a titanium surface, which is used for bipolar plates (BPs) in a proton exchange membrane fuel cell (PEMFC). This prepared C/TiC nanocomposite coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, electrochemical testing and interfacial contact resistance (ICR). The results show that a C/TiC nanocomposite coating consists of a single C surface layer (~28.88 nm) and TiC interface layer (~19.5 nm). In addition, compared with commercially pure titanium substrate (i_corr = 345.10 μA cm⁻²), the corrosion resistance of a C/TiC nanocomposite coating (i_corr = 0.74 μA cm⁻²) was greatly improved in 0.5 M H₂SO₄ + 5 ppm HF solution at 80 °C. The corrosion current density (i_corr) decreased 3 orders of magnitude in a simulated cathodic environment. Moreover, the interfacial contact resistance of a C/TiC nanocomposite coating is 2.34 mΩ cm² under 1.4 MPa compaction force, which is much lower than that of raw CP Ti (38.66 mΩ cm²).

A β-solidifying Ti–43Al–2Cr–2Mn–0.2Y alloy was directionally solidified by the optical floating zone melting method. The microstructure is mainly characterized by γ/α₂ lamellae with specific orientations, which exhibits straight boundaries. The β phase is randomly distributed in the lamellar microstructure, indicating that the β phase cannot be directionally solidified. The directional solidification of γ/α₂ lamellae was not affected by the precipitation of the β phase. Hot compression tests show that the deformation behavior of the β-containing lamellar microstructure also exhibits the anisotropic characteristic. The deformation resistance of the lamellae is lowest when the loading axis is aligned 45° to the lamellar interface. Microstructural observation shows that the decomposition of the lamellar microstructure tends to begin around the β phase, which benefits from the promotion of a soft β phase in the deformation. Moreover, the deformation mechanism of the lamellar microstructure was also studied. The bulging of the γ phase boundaries, the decomposition of α₂ lamellae and the disappearance of γ/γ interfaces were considered as the main coarsening mechanisms of the lamellar microstructure.

Transition metal based high entropy alloys (HEAs) are often used in electrocatalytic (water electrolysis) applications due to the synergistic effect operating among its constituent elements and unpaired electrons in d orbitals of the concerned metal. In this study, a low cost NiMnFeCu high entropy alloy was successfully synthesised using the combined techniques of mechanical milling (MA) and vacuum sintering. X-ray diffraction was used to analyse the phase composition, optical microscopy, and scanning electron microscopy were used to characterise the fabricated material’s microstructure and chemical homogeneity, thermal, and mechanical properties were tested using the differential scanning calorimetry method and a universal testing machine, respectively. Electrochemical workstation was used to carry out preliminary electrochemical studies such as linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry. The results showed that the as- sintered NiMnFeCu HEA possessed a single- phase FCC structure. The HEA NiMnFeCu sintered at 1050 °C (S4) and 1000 °C (S2) with a holding time of 2 h showed a yield strength of 516.3 MPa and 389.8 MPa, respectively, and the micro-hardness values were measured to be 233.45 ± 9 HV and 198.7 ± 8 HV, respectively. Preliminary electrochemical studies proved that the alloy sintered at 1000 °C (S2) with a holding time of 2 h exhibited excellent electrocatalytic properties with a measured overpotential of 322 mV at 10 mA cm⁻² at 100 cycles of CV and good stability for 10 h when compared to state-of-the-art electrocatalytic materials ${\mathrm{IrO}}_2$ and Ru${\mathrm{O}}_2$. This suggested that the HEA NiMnFeCu fabricated under the condition S2 could potentially be used for industrial-scale water electrolysis as it possesses permissible mechanical and good electrochemical properties.