With the rapid development of aerospace, automotive turbine, armor protection, mechanical metallurgy, nuclear industry, and cutting tools, the industry has a great demand for materials that can work stably in extreme special environments. When traditional materials cannot meet the production and lifestyle needs of human beings, high-performance materials emerge as required by the times. High-entropy ceramics have gained significant attention as an ultra-high performance material since their introduction. The concept of high-entropy ceramics is derived from high-entropy alloys. High-entropy ceramics are single-phase solid solutions formed by the random distribution of four or more cations at the same site, including high-entropy oxides, borides, carbides, nitrides, and silicide ceramics. High entropy (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)B₂ (HEB) ceramics are expected to be widely used in aerospace, automotive turbines, and armor protection due to their high melting point, high hardness, adjustable properties, high temperature stability, and good oxidation resistance. In order to obtain HEB ceramics with high densification, excellent mechanical properties, and tribological properties, the preparation of high-quality HEB powders is very important.

At present, research on the influence of preparation process conditions on HEB powder is still insufficient, and the tribological properties of HEB ceramics are also less studied. Therefore, HEB powders were prepared using the boron/carbon thermal reduction method. The effects of different heating methods (spark plasma sintering furnace and vacuum furnace), reaction temperature (1 400~1 800 °C), B₄C excess (mass fraction of 0~30%), and C addition (mass fraction of 5%) on the phase composition and microstructure of HEB powders were investigated. The influence mechanism was explored, and high-quality HEB powders were finally prepared. The phase composition, microstructure, mechanical properties, and tribological properties of sintered HEB ceramics were compared. The results of the study were as follows: the effects of different reaction temperatures (1 400~1 700°C) and B₄C excess (0%~20%) on the preparation of HEB powder were studied by spark plasma sintering (SPS). The results showed that with the increase of reaction temperature and B₄C excess, HEB powder gradually solidifies. When the reaction temperature was 1 700°C, the holding time was 10 min, and the B₄C excess was 15%, the single-phase HEB powder could be prepared, but the oxygen content was high, which was 1.603%. After sintering, the open porosity was the highest, which was 1.22%, the hardness was higher, which was 20.01±1.36 GPa, and the fracture toughness was the highest, which was 3.70±0.46 MPa·m^1/2. At 1 000° C, the friction coefficient was 0.255±0.010, and the wear rate was (2.612±0.523) × 10⁻⁵ mm³/(N·m).

The effects of different B₄C excess (0~30%) on the preparation of HEB powder were studied using a vacuum furnace. The results showed that HEB powder gradually dissolved with an increase in reaction temperature. When the reaction temperature was 1 700 °C, the holding time was 1 h, and the B₄C excess was 30%, there was some undissolved phenomenon in the HEB powder, and the oxygen content was high at 2.010%. After sintering, the open porosity was 0.18%, the hardness was 19.50±1.16 GPa, and the fracture toughness was 3.41±0.45 MPa·m^1/2. The lowest friction coefficient was 0.188±0.047 at 1 000 °C, and the highest wear rate was (3.023±0.467) × 10⁻⁵ mm³/(N·m).

The effects of different reaction temperatures (1 600~1 800° mmmmmC) on the preparation of HEB powder were studied by adding 5% C in a vacuum furnace. The results showed that HEB powder gradually dissolved with the increase of reaction temperature. When the reaction temperature was 1 700 °C, the holding time was 1 h, the B₄C excess was 20%, and 5% C was added, a single-phase HEB powder could be obtained, and the oxygen content was low, only 0.614%. After sintering, the open porosity was the lowest at 0.12%, the hardness was the highest at 25.30±1.25 GPa, and the fracture toughness was higher at 3.47±0.32 MPa·m^1/2, but the second phase B₄C appeared. At 1 000 °C, the friction coefficient was the highest at 0.281±0.037, and the wear rate was the lowest at (1.875±0.610) × 10⁻⁵ mm³/(N·m).

The addition of C could significantly reduce the Gibbs free energy (ΔG) of the reaction, lower the reaction temperature, enhance the reaction yield and facilitate the boron/carbon thermal reduction reaction. The higher the density of HEB ceramics, the superior their mechanical properties. The high temperature tribological properties of HEB ceramics were characterized by the synergistic lubrication mechanism of B₂O₃ and metal oxides. The wear mechanism of the three HEB ceramics involved a combination of abrasive wear and oxidation wear.