Due to the depletion of hydrocarbon resources worldwide, intensive research is being conducted to identify alternative energy carriers. Hydrogen has emerged as a promising candidate due to its high energy density and environmentally friendly nature. However, large-scale implementation of hydrogen energy is hindered by the lack of safe, efficient, and cost-effective storage methods. Among the various materials studied for solid-state hydrogen storage, boron nitride (BN)-based compounds have attracted significant attention owing to their high thermal stability, tunable morphology, and potential for physisorption-based storage. This review focuses on recent advances in the synthesis, functionalization, and structural optimization of BN-based materials, including nanotubes, nanosheets, porous frameworks, and chemically modified BN. Although other boron-containing hydrides such as LiBH₄, Mg(BH₄)₂, and closo-borates are briefly mentioned for comparison, the primary emphasis is placed on BN-related systems. This paper discusses various modification strategies aimed at enhancing hydrogen uptake and reversibility, offering insights into the future potential of BN-based materials in hydrogen storage technologies.

Thermal-sprayed WC–Co–Cr coatings are widely used to improve the wear and corrosion resistance of steel components operating under severe service conditions. This study investigates WC–Co–Cr coatings deposited by detonation spraying (DS), high-velocity oxy-fuel (HVOF), and atmospheric plasma spraying (APS) before and after ultrasonic nanocrystal surface modification (UNSM). The coatings were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), together with microhardness, tribological, abrasive, erosive, impact-abrasive, cavitation, corrosion, oxidation, and valve endurance tests. The results demonstrate that the deposition technology strongly affects the coating structure and performance. UNSM produced a pronounced increase in microhardness, reaching 1468 HV for DS + UNSM, 1596 HV for HVOF + UNSM, and 1561 HV for APS + UNSM. Ultrasonic treatment also reduced material loss under abrasive, erosive, impact-abrasive, and cavitation conditions. APS + UNSM demonstrated the best performance in the principal laboratory wear tests, with the lowest abrasive mass loss (0.42–0.45 mg), erosive mass loss (0.55–0.60 mg), impact-abrasive mass loss (0.75–0.85 mg), and cavitation mass-loss rate (0.33–0.38 mg/h). In tribological testing, APS + UNSM exhibited the lowest coefficient of friction (0.28), compared with 0.32 for HVOF + UNSM and 0.36 for DS + UNSM. In valve endurance testing, HVOF + UNSM showed the lowest plunger displacement growth rate (0.050 mm/h) and the longest calculated time to reach the 2 mm displacement criterion (22 h). Overall, the combination of thermal spraying and UNSM improves the mechanical and service performance of WC–Co–Cr coatings, while the optimal coating condition depends on the specific degradation mechanism and operating conditions.

Al-Cu-Fe quasicrystalline coatings were deposited on AISI 321 stainless steel substrates by high-velocity oxy-fuel (HVOF) spraying at oxygen pressures of 3.0, 3.5, and 4.0 bar. The influence of oxygen pressure on the phase composition, microstructure, porosity, corrosion behavior, thermal stability, and microhardness of the coatings was investigated using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS), ImageJ porosity analysis, electrochemical corrosion testing in 3.5 wt.% NaCl solution, simultaneous thermal analysis (TGA/DSC), and microhardness measurements. XRD analysis revealed the formation of quasicrystalline-related intermetallic phases together with Al, Fe₃Al₁₃, FeAl, Fe₃O₄, CuFe₂O₄, Cu₂O, and CuO phases. The coating deposited at 3.5 bar exhibited the lowest porosity (5.37%), the most homogeneous microstructure, and the largest residual coating thickness after corrosion testing. SEM and EDS analyses indicated that corrosion preferentially initiated at pores, splat boundaries, and phase interfaces, while the coating produced at 3.5 bar demonstrated the most stable surface condition after exposure to a 3.5 wt.% NaCl solution. Thermal analysis showed that all coatings remained stable up to 900 °C. Sample (a) exhibited the lowest mass loss and the highest thermal stability, whereas sample (b) demonstrated the most favorable combination of structural integrity, phase ordering, coating density, corrosion-related performance, and thermal stability. Microhardness values of the coatings ranged from 754 to 778 HV, significantly exceeding that of the AISI 321 substrate. The results demonstrate that oxygen pressure is a critical parameter controlling the microstructure and functional properties of HVOF-sprayed Al-Cu-Fe coatings, with 3.5 bar providing the most balanced set of properties.

This study examines the effect of spark plasma sintering (SPS) temperature on the phase composition, microstructure, densification, and microhardness of cobalt-free WC–Fe and WC–Fe–Ni hard alloys. Increasing the sintering temperature from 1250 °C to 1300 °C improved densification in both alloy systems. Residual porosity decreased from 13.2% to 12.7% in the WC–Fe–Ni alloy and from 13.8% to 12.0% in the WC–Fe alloy, while the density increased from 12.39 g/cm³ to 12.46 g/cm³ and from 12.15 g/cm³ to 12.40 g/cm³, respectively. The WC–Fe -Ni alloy exhibited a more homogeneous microstructure and higher microhardness, increasing from 708 $\pm$ 10 HV_0.2 to 823 ± 15 HV_0.2, whereas the WC–Fe alloy showed an increase from 630 ± 15 HV_0.2 to 770 ± 5 HV_0.2. X-ray diffraction analyses identified Fe₃W₃C, FeNi₃, and (Fe, Ni) solid-solution phases formed during SPS. The results indicate that both the sintering temperature and binder composition influence densification, phase evolution, and mechanical performance. Among the investigated materials, the WC–Fe–Ni alloy showed better microstructural stability and hardness than the WC–Fe alloy. These findings suggest that Fe–Ni binders are promising candidates for cobalt-free cemented carbides, although additional studies on fracture toughness and wear resistance are required before practical cutting-tool applications can be fully assessed.