Al_0.5CoCrFeNi high-entropy alloy (HEA) was prepared by spark plasma sintering (SPS) using Al_0.5CoCrFeNi gas atomized powder and was treated with different cooling rates (furnace cooling, air cooling, water quenching). The phase composition, microstructure, tensile properties, Vickers hardness, compactness, and fracture morphology of the alloy were systematically studied. The results show that the cooling rate can change the phase composition and phase shape of Al_0.5CoCrFeNi HEA from BCC + FCC phase to BCC + FCC + B2 phase, and the BCC phase coarsens. The ultimate tensile strength and yield strength of the heat-treated Al_0.5CoCrFeNi HEA decreased with increasing cooling rate, but elongation and Vickers hardness increased with increasing cooling rate. The ultimate tensile strength and yield strength of the furnace cooling (FC) samples reached the maximum value of 985.2 MPa and 524.1 MPa, respectively. The elongation and hardness of the water quenching (WQ) samples reached a maximum value of 43.1% and 547.3 HV, respectively, and the compactness of the alloy is higher than 98.8%. Therefore, the properties of Al0.5CoCrFeNi HEAs can be greatly improved by treatment with different cooling rates.

A series of five-element CoCrFeNi-Nbx (x = 0, 1, 3, 5, 7, and 9 wt%) high-entropy alloys were prepared using high-energy ball milling and discharge plasma sintering methods. Then, the effects of doping with Nb elements on the organization and properties of the CoCrFeNi HEAs were systematically investigated by tensile testing, hardness testing, and examining their micro-morphologies. The results show that with the addition of the Nb element, the lattice distortion of the alloy due to the large size of the Nb atoms causes the microstructure of CoCrFeNi HEAs to change from a single-phase FCC structure to a dual-phase structure of FCC and Laves. With the increase in the Nb content, the increase in the volume fraction of the hard and brittle Laves phase leads to the enhancement of the HEA’s tensile strength, yield strength, and hardness, and a decrease in plasticity. The Nb5 alloy showed the most excellent comprehensive performance, with a tensile strength, yield strength, and plasticity of 879.1 MPa, 491.8 MPa, and 39.8%, respectively, and all the properties were improved compared with those of the HEAs obtained by the arc melting method. The increase in the hardness of the HEAs was nearly proportional to the increase in the volume fraction of the Laves phase, which was the direct cause of the increase in the hardness of the HEA. Therefore, since the Laves phase is the direct cause of the increase in HEA hardness, the doping of CoCrFeNi HEAs with Nb can significantly improve the properties of HEAs.

High-entropy alloys (HEAs) of AlxCoCrFeNi (x = 0.2, 0.5, and 1) were created using the spark plasma sintering (SPS) method in conjunction with an aerosolized powder. Their microstructure and phase constituents were characterized by X-ray diffractometry, scanning electron microscopy, and projection electron microscopy. The tensile properties, hardness, compactness, and damping properties were also tested. The results showed that the crystal structure of AlxCoCrFeNi HEAs changed significantly with the Al content, from the original single face-centered cubic FCC phase (Al0.2CoCrFeNi) to an FCC + BCC + B2 structure (Al0.5CoCrFeNi), and then to FCC + BCC + B2 + Sigma (σ) phase structures (AlCoCrFeNi). Twin crystals with FCC structure were also observed in the TEM of AlCoCrFeNi. A chemical composition analysis showed that the crystal structure transformation was related to the segregation caused by the increase of Al element content. The hardness of the AlxCoCrFeNi HEAs increased with the Al content, and the hardness of AlCoCrFeNi reached the highest value of 585.4 HV. The tensile properties of the alloy showed a trend of increasing and then decreasing values with the increase in Al content. The yield strength, ultimate tensile strength, and elongation of the Al0.5CoCrFeNi alloy reached the highest values of 557.7 MPa, 954.4 MPa, and 32.2%, respectively. Moreover, the fracture mechanism of the Al0.2CoCrFeNi and Al0.5CoCrFeNi alloys was that of a typical ductile fracture, while for the AlCoCrFeNi alloy, it was that of a cleavage fracture. The compactness of the alloy increased with the Al content. The combination of the FCC + BCC + B2 phase resulted in the damping capacity of Al0.5CoCrFeNi alloy reaching 0.018 at the corresponding strain amplitude of 6 × 10⁻⁴.

This study focuses on the preparation of fine-grained WC/Co composite powder using rolling ball milling and spray drying techniques. The cemented carbide composition achieved through low-pressure sintering technology was WC-10Co-0.5${\mathrm{Cr}}_3{\mathrm{C}}_2$-1TaC-0.5Ru (wt.%). To study the effect of sintering temperature on the microstructure and mechanical properties of WC-10 wt.% cemented carbide, the microstructure and phase constituents of the material were analyzed using X-ray diffractometry and scanning electron microscopy. Additionally, the physical and mechanical properties of the material were examined. The results indicate that as the sintering temperature increased from 1390 °C to 1450 °C, the grain size of WC in the alloy increased, resulting in a slight decrease in hardness, an increase in fracture toughness, and the transverse fracture strength increasing first and then decreasing. The sintered hard alloy prepared at 1410 °C exhibited fewer pores and a uniform and fine grain size, reaching a density of 99.98%, a hardness of 91.8 HRA, a fracture strength of 3962 MPa, and a fracture toughness of 14.7 $\mathrm{MPa}\cdot {\mathrm{m}}^{1/2}$

A high-temperature water steam (H₂O(g)) between 300 °C and 1000 °C reacted with the Al surface in this study. The Al surface states were characterized and analyzed using XRD °C, XPS, and SEM after and before the reaction, and the effects and mechanism of H₂O(g) on the Al surface morphology and chemical composition were studied. The experiment showed that for an Al sheet reacting with H₂O(g), its oxide layer morphology changed from nano-needle to flaky and granular oxides gradually with the rise of temperature, and finally the Al surface became porous as a whole. Its oxide crystals were amorphous and were determined to be aluminum oxide (Al₂O₃) using XPS. The needle-like oxide in the Al sheet surface tended to grow toward the surface, and no obviously inward oxidizing corrosion layer occurred in the aluminum substrate; the oxide layer between the oxide and Al sheet substrate was compact, and could effectively prevent the infiltration and corrosion of water molecules.

Gel precursors were formed by reacting bismuth nitrate pentahydrate, acetic acid, sodium metavanadate, and NaOH. pH was adjusted using NaOH solution followed by calcination to obtain bismuth vanadate (BiVO₄) photocatalysts. During synthesis, pH directly influenced the formation and structure of the gel network. Therefore, the effects of pH on the microstructure and photocatalytic activity of BiVO₄ were investigated. At pH 3, the sample consisted of microspheres formed by tightly packed small particles. At pH 5, the microspheres transformed into aggregated flakes. Photocatalytic performance was evaluated through methylene blue (MB) degradation, revealing the sample prepared at pH 7 (7-BVO) demonstrated the highest efficiency. The electronic band structure, bandgap, and band edge positions of 7-BVO were probed by density functional theory (DFT) and UV-vis absorption spectra. Furthermore, photoluminescence spectroscopy, electrochemical measurements, active species trapping experiments and liquid chromatography mass spectrometry technique collectively revealed the possible mechanistic pathways for MB photodegradation by 7-BVO.