International Journal of Applied Ceramic Technology最新文献

Rare-earth zirconates (REZO) have emerged as next-generation thermal barrier coating materials, owing to their exceptional phase stability, ultralow high-temperature thermal conductivity, and high thermal expansion coefficient. However, their relatively low fracture toughness limits practical implementation. While numerous studies have documented fracture toughness measurements in REZOs at room temperatures, the intrinsic influences of rare-earth element selection and order-disorder phase transitions on fracture mechanisms at various temperatures remain insufficiently explored. This study integrates molecular dynamics simulations with high-throughput calculations and experimental validation to systematically elucidate how rare-earth cation configurations, crack propagation orientations, and order-disorder transition govern fracture toughness and crack evolution in REZO systems. Our findings demonstrate brittle fracture behavior across all crystallographic orientations in REZOs, with maximum critical stress along (100) and minimum along (111). Fracture characteristics correlate not only with surface energy but also with geometric factors at crack tips. Molecular dynamics simulations reveal that structural disorder reduces fracture toughness without altering failure mechanisms. The integration of experimental and computational analyses for Nd₂Zr₂O₇ demonstrates that REZO exhibits lattice softening and reduced fracture toughness at elevated temperatures while maintaining brittle fracture characteristics. These findings establish critical experimental and theoretical foundations for advancing high-toughness, long-lifespan REZO-based thermal barrier coating materials.

B₄C-ZrB₂/B₄C-TiB₂ laminated ceramics (BZBTLCs) were fabricated to systematically study effects of the layer thickness ratio (LTR) on residual stress, microstructure evolution, and mechanical properties, and especially investigate the impact resistance mechanism of the BZBTLCs. The result showed that only residual compressive stress (RCS) was in the B₄C-ZrB₂ (BZ) layer, while only residual tensile stress (RTS) was in the B₄C-TiB₂ (BT) layer, and that their alternate distribution was in accordance with the distribution of the BZ and BT layers. As the LTR increased, the number of microdefects in BZBTLC first decreased and then increased. The flexural strength (FS), overall fracture toughness (OFT), and impact toughness (IT) of the BZBTLC initially increased and then decreased with an increase of the LTR. When the LTR was 4, the BZBTLC exhibited higher FS (711 ± 14 MPa), higher OFT (7.2 ± 0.21 MPa·m^1/2) and higher IT (2.9 ± 0.15 J·cm²). The enhancement of IT was attributed to the RCS-dominated stress offset mechanism and decreased microdefects. This study established a correlation between LTR, residual stress, and IT, offering a valuable reference for improving the IT of B₄C-based ceramics.

Low-rate and high-strain rate Knoop hardness (HK) was determined on Si₃N₄, Al₂O₃, B₄C, and TiB₂ ceramics. Quasi-static hardness was determined between 0.98 to 98 N using a microhardness test unit, while the high-strain rate hardness was evaluated between approximately 5 and 45 N using a modified split Hopkinson pressure bar unit. The hardness data were analyzed and compared using a plot of HK as a function of load, a load-independent HK (LIHK), and a “true” HK using a proportional specimen resistance (PSR HK). The Si₃N₄ hardness/load curves showed the hardness increased with increasing strain rate, while the other three ceramics showed very little change. On the other hand, the LIHK hardness of all but the TiB₂ increased by about 10% while the PSR HK indicated that three of the four ceramics exhibited a hardness decrease. There was no appreciable difference in the damage/cracking around indents at comparable loads but different strain rates. These results will be discussed and compared to previous dynamic hardness data. There generally appears to be a minimal, if any, effect of strain rate on hardness. Attempting to make a comparison between these two indentation methods is a challenge due to the significant differences in dwell time, indenter velocity, and the loading process.

In this work, porous SiNiOC ceramics with enhanced electromagnetic wave (EMW) absorption performance are successfully prepared by the hydrothermal method and the polymer-derived ceramics (PDCs) process. The influence of the annealing temperature on the microstructure and EMW absorption performance of the SiNiOC ceramics is also systematically studied. It is shown that the increased annealing temperature can induce phase separation in SiOC, yielding SiC and SiO₂, while Ni²⁺-catalyzed graphitic carbon promotes the carbothermal reduction of SiO₂ into more SiC. The large amount of SiC generated by the two reactions significantly improves the low dielectric constant of SiOC. After annealing treatment at 1400°C, the porous SiNiOC ceramics exhibit the best EMW absorption performance, achieving a minimum reflection loss of −55.62 dB when the thickness is 1.97 mm and an effective absorption bandwidth of 3.93 GHz when the thickness is 1.33 mm. Such a thin matching thickness in our as-prepared porous SiNiOC ceramics can meet the requirement of future EMW absorbing applications, exhibiting significant potential as a high-performance EMW absorbing material.

Oxygen transport membrane (OTM) is an economic technology for oxygen separation and high-purity oxygen production. To mitigate various issues induced by high temperatures, intermediate temperature OTM technology has been pursued in recent years. However, in certain circumstances, high operating temperatures are unavoidable, such as in situ oxygen production using OTMs for direct oxy-combustion. Nevertheless, the lack of reliable high temperature gas-tight sealing imposes great challenges on OTM technology for such applications. Herein, a novel sealing strategy is developed to obtain a gas-tight bonding/sealing of two different bulk ceramics using ceramic slurry in combination with phase inversion process. The sealing strategy is successfully applied to a model material system of alumina supporting tube-La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) hollow fiber-alumina supporting tube assembly. The utilization of LSCF as the sealing material allows operating temperatures of OTM assembly up to 1200°C, the sintering temperature for LSCF hollow fiber fabrication. A significant enhancement in oxygen flux is revealed at ultra-high temperatures (> 1000°C). Long-term durability and thermal cycling tests demonstrate the excellent robustness and stability of the sealing. This work provides a general sealing strategy for OTM technology upscaling and robust operation in wide temperature conditions.

This study reports the development of translucent-grade aluminum nitride (AlN) ceramics using a spark plasma sintering (SPS) technique for MIR applications. To enhance densification and translucency, a low-melting-point additive, CaF₂, was introduced at varying concentrations. The optimized composition of 97 wt% AlN with 3 wt% CaF₂ yielded translucent-grade ceramics with a relative density of 99% and a hardness of 1289 HV₁. At a sintering temperature of 1800°C, near monolithic AlN ceramics were produced, exhibiting an average grain size of 2.30 µm, a thermal conductivity of 95.2 W/m·K, and a negligible presence of secondary phases and pores. Consequently, the in-line transmission efficiency improved, remaining stable across the 2.5–6.0 µm wavelength range, attributed to well-defined grain boundaries that minimized scattering losses. Moreover, intergranular fracture was predominant in the AlN sintered sample with CaF₂, whereas AlN without the additive underwent oxidation at higher temperatures, which resulted in increased bulk density and predominantly transgranular fracture. In addition, surface machining using the micro laser-assisted machining technique achieved a surface finish of 0.1855 µm. Overall, the developed AlN ceramics, with their obtained optical, thermal, and mechanical properties, demonstrate potential for use as MIR window materials.

This investigation highlights a hybrid composite for bullet and blast protection. The front face of the hybrid composite was made of silicon carbide (SiC), the middle layer of aluminium (Al) Honeycomb and the back face made of para-aramid fibre—polyetherketoneketone polymer composite, and fabricated by using high temperature epoxy adhesive. The bullet and blast energy were absorbed essentially due to the material configuration of the hybrid composite. SiC forms a hard face layer with high temperature resistance, which absorbs blast energy, blunt shrapnels and resists high temperature. Al Honeycomb absorbs a large amount of energy by deforming itself, and the back layer of polymer composite stops shrapnels. For ballistic tests, a single layer of SiC was used. For the blast test, four layers of SiC were used. The experimental results of ballistic tests proved that the material has been successful in stopping a 7.62 mm hard steel bullet with a speed of 710 m/s fired from a distance of 10 m, which conforms to NIJ level III+. The modified hybrid composite has been successfully tested to withstand improvised explosive device blasts up to 10 kg TNT with 10% shrapnels, with a standoff distance of 5 m, conforming to Level 4 protection specified in STANAG 4569.

Application of carbon fiber-reinforced silicon carbide (C/SiC) composites in aerospace structures is increasing due to their high specific strength and thermal resistance. However, limited data are reported on the flexural performance of C/SiC structural members under complex loading modes. This study investigates the mechanical behavior of 2D-C/SiC I-beams under plane-bending, skew-bending, and bending-twist through experiments and finite element (FE) simulations. Fracture loads of 9260, 5782, and 7831 N were recorded for plane bending, skew bending, and bending-twist, respectively. Delamination was the dominant failure mode in all cases, with rupture occurring at the bottom flange. Damage initiation and progression were monitored using strain gauges, and infrared thermal wave imaging confirmed the onset and progression. FE simulations incorporating nonlinear constitutive behavior and Hoffman failure criterion reproduced the strain response and ultimate loads with small deviations (7.6% in plane bending, 4.2% in bending-twist), and a larger error in skew-bending (13%) due to stress interactions. While the study provides validated experimental and numerical insights, it was limited by a small specimen set and a simplified calculation procedure. Future work should refine FE models to include progressive damage and extend the study to cyclic, thermal, and fatigue loadings for aerospace design.

The mechanism of the reliability improvement by alloying Ni internal electrodes of BaTiO₃-based multilayer ceramic capacitors (MLCCs) was studied from two perspectives: electric barrier formation at the electrode-dielectric interface and diffusion of alloying elements into the bulk dielectric layer. In the case of Ni-Sn alloy electrodes, the reliability improvement is due to the formation of a Sn segregation layer at the interface between the internal electrode and the dielectric layer, and the associated formation of a Schottky barrier, which is an electron barrier layer. Therefore, when the dielectric layer is sufficiently thin, this electron barrier layer functions critically, but as the dielectric film thickness increases, the effect of this barrier layer gradually decreases because of an increased number of grain boundaries and the grains in the dielectric layer, which are other factors that determine the insulation. On the other hand, in the case of Ni-In alloy electrodes, In diffuses not only at the interface between the internal electrode and the dielectric, but also into the shell part of the “core-shell” structure of the BaTiO₃ grains in the dielectric layer along with the grain boundaries. Therefore, it was revealed that the reliability improvement continues even if the dielectric thickness increases to a certain extent. The outstanding improvement in the reliability of the Ni–In MLCC could be derived from not only the formation of an electrical barrier at the interface between the internal electrode and the dielectric layer, but also enhanced resistivity provided by a grain boundary barrier layer and an intragranular acceptor region at the shell region of the core-shell structure by the In diffusion.

Regulatory agencies and key stakeholders are increasingly promoting the use of probabilistic approaches in design processes for large corporations. This shift is particularly emphasized in analyzing mechanical properties, such as fatigue and failure prediction. Additionally, the use of probabilistic artificial intelligence represents a transformative advancement in material science that leads to enhanced predictive accuracy and robust decision-making capabilities. These artificial intelligence methods enable more informed decision-making in the design and evaluation of advanced materials by quantifying uncertainty and offering probabilistic assessments, particularly for applications involving extreme environments. High-temperature materials, such as carbon/carbon (C/C) composites, are essential for modern technological applications. However, their vulnerability to oxidation poses a significant barrier, indicating the necessity for effective protective coatings. The application of these coatings to C/C composites is complex and has hindered their widespread use in high-temperature settings. In this study, we utilize finite element analysis (FEA) and machine learning (ML) combined with Bayesian probability to examine the behavior of silicon carbide ceramic-coated cubic C/C composites. The investigation focuses on how stress and strain evolve under varying thermal conditions and cyclic thermal loading from a probabilistic perspective. This work integrates FEA and Bayesian probabilistic-based ML to enhance the predictive power for evaluating ultra-high-temperature materials.