Driven by the demand for electronic system miniaturization, the development of dielectric energy storage materials characterized by high energy storage density, high efficiency, and excellent temperature stability has been necessitated to overcome the energy density limitations of dielectric ceramic capacitors. In this study, we focus on lead-free strontium barium niobate (SBN) ceramics of the unfilled Tungsten Bronze structure. We introduce Bi3+/Na+ ion pairs at the A site, utilizing the lone pair effect of Bi3+ to enhance the polarization response, while compensating for crystal lattice distortion with Na+; at the B site, we substitute Nb5+ with Ta5+ and, through a high-temperature solid-state reaction process, prepare the ceramic (Sr0.42u2013x/2Ba0.53u2013x/2Bix/2Nax/2La0.05)(Nb1.95u2013xTaxSn0.05)O6(BNTx) via high-temperature solid-state reaction process. The study found that moderate doping induced the formation of weakly coupled polar nanodomains, reducing the relaxation activation energy to 0.058 eV and significantly lowering the dipole reversal barrier. The grain refinement and increased grain boundary resistance resulting from doping effectively suppressed leakage current. Ultimately, the BNT0.1 ceramic achieved an energy storage density of 5.45 Ju00B7cmu20133 and an ultra-high energy storage efficiency of 95.61% at 500 kVu00B7cmu22121, with current and power densities reaching 1508.5 Au00B7cmu22122 and 211.2 MWu00B7cmu22123, respectively.
Magnesium aluminate spinel (MgAl2O4) is a technologically important transparent ceramic with a broad optical window, high hardness, excellent thermal stability, and good chemical durability, making it attractive for infrared windows, transparent armor, and related optoelectronic components. However, pressureless densification of spinel remains difficult because the diffusion of Mg2+ and Al3+ ions is intrinsically sluggish, so conventional sintering typically requires long dwell times or pressure-assisted routes such as hot pressing and hot isostatic pressing. In this work, pressureless ultrafast high-temperature sintering (UHS) was employed to densify MgAl2O4 spinel ceramics. Starting from a green compact with an initial relative density of about 55%, the samples were rapidly heated to 1750 u2103 at rates exceeding 1000 u2103u00B7min-1, held for only 5 s, and then cooled in vacuum. The sintered body retained a single cubic spinel phase, with no detectable secondary phases in XRD. Archimedes measurements gave a relative density of 98.2%, corresponding to a low residual porosity of 1.8%. The microstructure consisted of fine equiaxed grains with an average size of 0.62 u00B1 0.13 u03BCm, together with a small amount of residual pores located mainly at grain boundaries and triple junctions. After polishing to a thickness of about 1 mm, the specimen exhibited an in-line transmittance of 64.7% at 5.3 u03BCm and showed a monotonic increase in transmittance with wavelength, consistent with residual pore scattering in the mid-infrared region. The enhanced densification achieved by UHS is attributed to two coupled effects. First, the extremely fast heating schedule suppresses the low-temperature stage dominated by surface diffusion, thereby limiting unnecessary grain coarsening and preserving a high sintering driving force at the peak temperature. This fine-grain retention is critical because the densification rate in grain-boundary-diffusion-controlled sintering depends strongly on grain size. Second, the severe thermal shock associated with UHS may freeze grain boundaries into high-energy, non-equilibrium states, which could accelerate grain-boundary diffusion and facilitate pore elimination, although this mechanism is presently supported only by indirect evidence and requires direct atomic-scale verification in future work. For comparison, a conventional pressureless sintering schedule of 10 u2103u00B7min-1 to the same peak temperature followed by a 5 s hold produced a much lower relative density of 74.2% and a coarser grain size of about 2.31 u03BCm. These results demonstrate that UHS provides a powerful pressureless route for rapidly densifying diffusion-limited spinel ceramics and offers a viable basis for the preparation of small-sized transparent MgAl2O4 components.
Ceramic-based dispersed matrix fuel(CDM)takes advantage of the excellent thermal conductivity and irradiation resistance of SiC materials,which can further enhance the operational safety of TRISO(Tristructural-isotropic)pellets and meet the requirements of higher temperatures and fuel consumption in reactors.In this work,the mechanical properties of the TRISO pellets coating and its interfacial bonding properties with the SiC matrix in CDM with zirconia simulated core were studied.The Young's modulus and Vickers' hardness of each coating,as well as the fracture toughness of the SiC coating and the SiC substrate,were tested by the micrometer indentation method.Furthermore,the bonding force of the relevant interfaces was evaluated by using the push-out method and the indentation method,and the crack propagation behavior at each coating and interface was investigated with microstructure characterization.The results show that considering the bonding force of each interface of the CDM sample and the strength of each coating area itself,the relatively loose Buffer layer and the core/Buffer interface with weak bonding are prone to damage and failure.The study has proposed feasible testing methods and analytical approaches for the characterization of the mechanical properties and interfacial bonding of fuel microsphere-coated coatings,providing an important reference for the improvement of the sample processing technology of TRISO and CDM.
The proposed aluminum-plated LaMA dual ceramic thermal barrier coating life extension strategy significantly enhances the coating's high-temperature oxidation resistance through aluminum deposition on the LaMA coating surface.The coating was fabricated using a composite technique of plasma spraying and arc ion plating.Detailed characterization of the coating's phase composition,surface morphology,and cross-sectional structure was performed via X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy-dispersive X-ray spectroscopy(EDS).Findings revealed that the aluminum plating treatment significantly reduced microcracks and pores on the coating surface,improved coating density,and enhanced oxidation resistance.In oxidation kinetics testing,the weight gain rate of the aluminum-coated LaMA coating was 4.84±0.23 mg/cm2,significantly lower than the 8.39±0.12 mg/cm2 of the uncoated sample,indicating that the aluminum layer effectively reduced weight gain under high-temperature oxidation.Further analysis of TGO layer evolution revealed that the aluminum-coated layer effectively retards rapid TGO thickening and mitigates interfacial stress accumulation during oxidation.This demonstrates the significant advantage of aluminum coating in enhancing high-temperature oxidation resistance.These findings provide an effective technical solution for ensuring the long-term reliability of dual-ceramic thermal barrier coatings in high-temperature environments.
The next-generation aero-engines impose increasingly stringent demands on the high-temperature resistance,lightweight nature,and long service life of hot-section components.Continuous silicon carbide fiber-reinforced silicon carbide(SiCf/SiC)ceramic matrix composites have emerged as core candidate materials owing to their excellent comprehensive performance.However,the efficient densification of complex-shaped components remains a critical bottleneck restricting their engineering applications.The combined chemical vapor infiltration(CVI)and precursor infiltration and pyrolysis(PIP)process,by synergistically leveraging the advantages of CVI in fabricating a SiC matrix with high crystallinity and few defects and the characteristics of PIP in efficient pore filling and near-net shaping,provides an optimal technical pathway to address the issues of low densification efficiency,high cost,and unbalanced performance associated with single processes.This paper focuses on the synergistic mechanism of the CVI+PIP combined process.It systematically analyzes the parameter optimization strategies for key processing steps,including fiber preform fabrication,interphase tailoring,initial CVI densification,deep PIP filling,and post-treatment.The core advantages of this combined process in enhancing material density,optimizing microstructure,shortening the fabrication cycle,and reducing cost are elaborated in depth.Furthermore,the application examples and performance of the process in typical hot-section components such as combustor liners,turbine guide vanes,and exhaust nozzles are reviewed in detail.Finally,considering current technical challenges including process optimization,precise microstructural control,and the development of durable environmental barrier coatings,future research directions are proposed.This paper provides important theoretical support and technical references for the scale-up fabrication of high-performance SiCf/SiC composite hot-section components and the performance leap of aero-engines.
