Journal of Composites Science

In this paper, the relationship between the temperature regimes of spark plasma sintering (SPS), the evolution of the phase composition, the local atomic structure, and the mechanical properties of high-entropy ceramics of equiatomic composition (V,Nb,Ti,Ta,Zr)C has been established, and the temperature interval of complete cation homogenization has been determined. A series of samples was obtained by SPS in the temperature range of 1700–2100 °C; the evolution of the structure and properties was traced by a set of complementary methods—XRD with Rietveld refinement, XPS, EXAFS, NEXAFS, SEM-EDS, dilatometry, and hardness measurements. It is shown that cation homogenization proceeds non-monotonically and does not coincide in temperature with the densification of the powder body. The shrinkage kinetics indicate that the liquid-phase densification mechanism, caused by the presence of residual metallic niobium in the initial NbC powder, is realized at 1470–1550 °C and is completed already by 1760–1790 °C, whereas further heating up to 2100 °C serves exclusively for the diffusion mixing of cations. According to EXAFS, the nearest carbide environment of niobium stabilizes already at 1800 °C and does not change substantially with a further increase in the sintering temperature. At 2100 °C, according to XRD, a single cubic carbide phase of the NaCl type forms. Changes in the XPS chemical shifts and in the parameters of the local environment of Nb according to EXAFS are consistent with a rearrangement of the cation sublattice but do not allow one to unambiguously establish a completely random distribution of cations. At 1900 °C, a local maximum of microstrains of the NbC-like phase and the largest positive shift in the carbide component of Ta 4d_5/2 are observed. The competition of two strengthening mechanisms has been revealed: solid-solution strengthening increases monotonically with temperature, reaching a maximum microhardness of HV0.2 = 2896 at 2100 °C, whereas the maximum hardness HV30 = 2930 was recorded at 1800 °C due to the contribution of interphase boundaries in the still multiphase structure; the fracture toughness in all regimes remains low (K₁C < 1 MPa·m^1/2), and the fracture character changes from radial Palmqvist cracks to local chipping as the interphase boundaries disappear. The results obtained show that densification and cation homogenization in high-entropy carbides are kinetically and temperature-separated processes, and the choice of the SPS technological regime should be determined not by the maximum achievable temperature, but by the temperature-time resource sufficient for the completion of cation diffusion after the end of shrinkage.

Previous research on material-extruded soy hull fiber (SHF)/polylactic acid (PLA) has emphasized feedstock development, leaving the joint effects of composition, raster architecture, and filament production history on compression insufficiently characterized. This study addressed that gap through a factorial comparison of 192 coupons spanning four SHF contents (0, 10, 20, and 30 wt.%), four raster sequences, and three filament production positions, without compatibilizers or plasticizers. Build-direction tests measured apparent modulus, 0.2% offset yield stress, and stress at 10% toe-corrected crosshead strain. Literature benchmarking included printed polymers, printed and molded biocomposites, and furniture woods. Relative to neat PLA, 10SHF approximately retained apparent modulus, reduced yield stress by 11.1%, and increased stress at 10% strain by 9.9%; corresponding reductions at 30SHF were 25.0%, 59.9%, and 15.3%. Stress at 10% strain was below offset yield in every 0SHF coupon but above it in every 20SHF and 30SHF coupon. Raster rankings depended on composition and response; some production-position modulus differences exceeded raster contrasts. All twelve 10SHF cell mean yield stresses exceeded six wood benchmarks from one study; apparent modulus means exceeded the compiled printed natural fiber composite values. These findings support partial PLA replacement and further evaluation of short, stocky furniture components under axial compression.

In this study, superhydrophobic coatings based on a zinc composite with micro- and nanosized aluminum oxide particles were obtained. Electrodeposition of the composite was used to achieve the required polymodal roughness of the metal surface, and stearic acid was used as a surface energy-reducing agent. Metal crystallite microstructures were formed during zinc deposition. To obtain submicrostructures in the coating, Al₂O₃ nanoparticles with a size of ~40 nm were introduced into the electrolyte. However, to achieve a sufficient density of nanostructures on the surface, the concentration of Al₂O₃ nanoparticles should be greater than 10 g/L, which inevitably led to the formation of large agglomerates (>1000 nm) even with intensive stirring. To break up the agglomerates, larger Al₂O₃ particles with a size of ~10 μm and at a higher concentration were used. It was assumed that, having a greater mass than loose agglomerates, microparticles would act as grinding bodies, colliding with agglomerates during mixing and breaking the latter into smaller agglomerates (<250 nm) and individual particles. Composite coatings Zn-Al₂O₃ demonstrated high anticorrosion properties; they retained superhydrophobic properties (θ_c > 150°) for at least 100 h in the corrosive conditions of neutral salt mist. To evaluate the mechanical properties of the obtained superhydrophobic Zn-Al₂O₃ coatings, they were put to a water jet test and remained superhydrophobic for 10 min of testing.