Journal of the American Ceramic Society最新文献

Fiber-reinforced ceramic matrix composites (CMCs) are used in structural components of gas turbines and fusion reactors due to their high toughness and ability to withstand ultra-high temperatures. The enhanced fracture toughness of CMCs arises from the complex interactions between mechanical damage and their microstructures that involve fiber bridging, fiber pull-out, crack deflection, and sliding at the fiber-matrix interfaces. However, there is a lack of microstructure-resolved models that enable direct simulation of these damage processes. This study introduces a phase-field model that explicitly accounts for microstructure-level cracking and interface sliding in CMCs. Simulations are performed to investigate the effects of fiber diameter, orientation, length, density, and interface sliding resistance. Fiber bridging and fiber pull-out are successfully simulated. In particular, the simulation results demonstrate the critical role of interface sliding in fiber bridging. Parametric studies suggest that thicker fibers, longer fibers, and lower interface sliding resistance can lead to enhanced performance of CMCs when fiber bridging dominates the damage processes. This model has demonstrated its capability to serve as a valuable tool for quantitative understanding of CMC damage processes and for guiding design of the microstructures for next-generation CMCs.

Novel applications in the foldable electronics market require flexible substrates, notably ultra-thin glass (UTG). While conventional UTG is known for its high robustness and resilience, its brittle characteristics commonly lead to cracks, breakages and other field failures. This study introduces super-flexible and ion-exchangeable glass for foldable displays, achieved by lowering the Young's modulus of the glass. Effective reduction of Young's modulus from 72 to 53 GPa was achieved when SiO₂ was substituted with B₂O₃ and P₂O₅. Indentation and two-point bending tests examined the bending characteristic of the glasses. The obtained low modulus glasses showed enhanced flexibility, including a high level of fracture toughness and resistance to flaw formation as well as decreased bending repulsive force, implying smaller folding radius. The enhanced flexibility of the glass, which makes it suitable for various foldable devices, was discussed based on structural changes induced by composition.

A systematic investigation was conducted on the densification and grain growth of 170 and 260 nm tetragonal BaTiO₃ (BTO) powders during high-temperature sintering. Densification and grain growth were uniquely analyzed using Python-based computational modeling of dilatometer data and scanning electron microscopy (SEM), respectively. The findings revealed that the 260 nm powder exhibited higher activation energies for both densification and grain growth. While a high-fidelity master sintering curve (MSC) provided an excellent fit at lower temperatures (R² > 0.99), its predictive capability diminished above 1200°C. This unprecedented observation was correlated with a decrease in the densification activation energy during the final sintering stage, which will be further discussed along with its link to prominent abnormal grain growth and the limitations of the MSC method.

Flexoelectricity, an intrinsic electromechanical coupling phenomenon, has shown great potential in advanced ceramic. However, the typically low flexoelectric coefficients of bulk materials severely limit their practical applications, especially for single crystals. Surprisingly, recent advances have demonstrated that room-temperature dislocation engineering can effectively modulate functional properties. In this study, we employ the cyclic indentation method to introduce controlled surface dislocations into single-crystal SrTiO₃ with (100), (110), and (111) orientations. Precise regulation of indentation cycles enables tunable flexoelectric coefficients with pronounced orientation dependence. Comprehensive characterization reveals a direct correlation between surface dislocation configurations and bulk flexoelectric response. These results demonstrate an effective and controllable strategy for the controlled modulation of flexoelectric properties in single crystals, providing a foundation for further development of high-performance flexoelectric-based novel electromechanical devices.

We investigated the ferroelectric properties of 10 nm BaTiO₃ (BTO) nanocubes formed by dispersing them on the surface of an Nb-doped SrTiO₃ (Nb:STO) substrate. The microwave synthesis procedure produced BTO nanocubes with a size of approximately 10 nm, and the BTO nanocubes were dispersed in ethanol before being spin coated on the surface of the Nb:STO substrate. From the piezoelectric d₃₃ hysteresis loops measured by a piezoresponse force microscope, it was confirmed that the 10 nm BTO nanocubes exhibited canonical ferroelectric properties. External voltages were applied to switch the polarization of the 10 nm BTO nanocubes, providing further evidence of their ferroelectric behavior. In particular, it was experimentally confirmed that the BTO nanocubes with a size of about 10 nm can be utilized as tunnel ferroelectric junction memory devices.

Glass ceramics have gained research attention for use in scintillator applications. In this work, Eu₂O₃-doped lithium gallium silicate glass and its glass ceramics were synthesized, and the luminescence characteristics were investigated. To fabricate glass ceramics, the Eu₂O₃-doped lithium gallium silicate glass was heated for 3 h at 740°C or 763°C. A transparent glass ceramic with a high transmittance of approximately 70% at 650 nm was obtained by the heat treatment at 740°C. Luminescence derived from the electronic transition of 4f→4f levels in Eu³⁺ ions appeared under visible light (530 nm) or X-ray. It was found that the scintillation intensity was improved due to the formation of crystalline phases in the silicate glass host matrix during the heat treatment at 740°C. According to the Judd–Ofelt theory, the Eu³⁺ luminescent ions might be present mainly in a glass phase of the transparent glass ceramic, and the enhancement of the scintillation intensity should be derived from the improvement of the energy transfer efficiency in the host matrix.

This study investigates the effects of dry and wet air oxidation on the tensile behavior of unidirectional SiC/BN/SiC minicomposites, with a particular focus on how environmental conditions and pre-cracking influence strength retention and failure modes. The pristine minicomposites exhibit high strength and failure strain, attributed to effective fiber coatings and preservation of fiber strength throughout processing. Oxidation at 1000°C without pre-cracking in dry air causes only minor degradation and is associated with a transition from transverse matrix cracking with distributed fiber fracture to a shear-driven failure mode. In wet air, the same shear-driven mode occurs but with a significantly lower failure strain. The most severe degradation is observed when pre-cracking precedes oxidation; bonding between fibers and with the matrix eliminates interfacial sliding, resulting in a dramatic reduction in failure strain. The work identifies three distinct fracture regimes controlled by the interplay of fiber waviness, oxidation conditions, and mechanical loading history.

The development of high-performance glass fibers for applications such as wind turbine blades demands materials with superior mechanical properties, particularly a high Young's modulus. To this end, the structure and Young's modulus of CaO‒MgO‒Al₂O₃‒SiO₂ glasses with varying MgO/CaO ratios were investigated by experiments and molecular dynamics simulations in this study. It was observed that as the MgO/CaO ratio increased, the density of the glass samples gradually decreased, while the Young's modulus significantly increased. The trends of structural and performance changes derived from MD simulations were found to be in good agreement with experiments, revealing the underlying structural origin. Owing to the weaker charge-balancing capacity of Mg²⁺ compared to Ca²⁺, the formation of high coordinated aluminium ([AlO₅]) and tri-coordinated oxygen (O[3]) is promoted with the replacement of CaO by MgO. This process strengthens the glass network by converting bridging oxygen (O[2]) into a combination of O[3] and non-bridging oxygen (O[1]). Furthermore, the distribution of O[3] among the five oxygen atoms within [AlO₅] was examined. The [AlO₅] unit containing two O[3] is the most possible form of existence. Most importantly, a strong linear correlation (R² = 0.93) was identified between the concentration of [AlO₅] and Young's modulus, establishing [AlO₅] as a key structural descriptor for stiffness in these glasses.

Air-plasma-sprayed thermal barrier coating analysis faces three key challenges: informational complexity from overlapping defect morphologies, semantic ambiguity from gradient boundaries, and data scarcity from asymmetric feature distribution. Conventional segmentation approaches struggle particularly with distinguishing unmelted from melt-solidified regions. This research proposes TBC-HybridNet, a confidence-guided feature-fusion architecture combining the specialized UnmeltedSegNET with generic deep convolutional neural networks through hierarchical fusion. UnmeltedSegNET employs multiscale modules to extract contextual information, integrating large receptive fields for structural integrity with small receptive fields for edge preservation, outperforming human annotators with 97.8% accuracy in boundary detection. The framework implements a confidence-guided fusion strategy that dynamically adjusts model weights, addressing data imbalance while maintaining sensitivity to rare defects without computationally intensive retraining. The system achieves 97.9% accuracy for unmelted regions, 91.8% overall accuracy, and an 88.3% F1 score for cracks. It enables real-time quantification of critical quality metrics, including unmelted volume fraction and crack density. With 96.6% crack continuity detection and 71.1% unmelted boundary fidelity, these capabilities establish precise correlations between spray processes and microstructure, improving coating durability prediction in aerospace applications and directly impacting turbine engine performance and service life.

The effect of mechanically induced surface damage layers on the crystal structure and ferroelectric properties was systematically investigated in lead-free 0.99(0.67BiFeO₃−0.33BaTiO₃)−0.01BiMnO₃ ceramics. The surface damage layer formed by mechanical polishing was identified through diffraction peak broadening, increased lattice strain, and reduced remanent polarization. The damage layer was eliminated by thermal annealing at 800°C, which resulted in sharp diffraction peaks, reduced lattice strain, and complete recovery of polarization. Structure refinement confirmed that Bi³⁺ off-centering was suppressed by polishing, whereas Bi³⁺ displacement and nanoscale domain activity were restored by annealing. Phase-field simulations revealed that the damage layer functioned as a ferroelectrically inactive region and that the recovery of Bi³⁺ off-centering was essential for polarization restoration. It was demonstrated that the degradation and recovery of ferroelectric properties in BiFeO₃-based ceramics depended on the formation and relaxation of mechanically induced surface damage layers. These findings provide a clear processing–property relationship and establish a strategy to optimize the performance of lead-free piezoelectric ceramics for electronic and energy applications.