Frank-type stacking faults (FSFs) are among the most important extended defects in 4H-SiC, yet their crystallographic classification, transformation mechanisms, electronic structures, and optical properties remain incompletely understood. Here, we present a comprehensive investigation of FSFs in 4H-SiC through the integration of high-angle annular dark-field high-resolution scanning transmission electron microscopy (HAADF HR-STEM), photoluminescence (PL) mapping and spectroscopy, and density functional theory (DFT) calculations. By rigorously applying Frank’s original crystallographic definition, we resolve long-standing ambiguities in the intrinsic/extrinsic classification of FSFs and demonstrate that the widely discussed (3,2) FSF is intrinsically classified despite involving an insertion-mediated formation process. Direct atomic-scale observations further reveal structural connectivity among the standard (5,2), (4,2), and (4,1) FSFs, providing experimental support for one possible crystallographic evolution pathway linking these faults. Investigations of non-standard FSFs show that identical Zhdanov notations can correspond to either intrinsic or extrinsic fault configurations depending on their crystallographic topology. DFT calculations establish, for the first time, comprehensive stacking-fault energies and electronic band structures for both standard and non-standard FSFs. While most FSFs exhibit conventional 3C-like quantum-well states, the (1,1) and (2,1) FSFs display distinct 2H-like electronic characteristics associated with dominant K-point split-off states. Finally, direct HR-STEM/PL correlation and first-principles calculations identify the characteristic PL emission wavelength of the standard (4,1) FSF as 459 nm, demonstrating that the long-accepted 424 nm assignment is inconsistent with both experimental and theoretical evidence. These results establish a unified crystallographic, thermodynamic, electronic, and optical framework for FSFs in 4H-SiC.
A new dimensionless descriptor for single-phase microstructure prediction in multicomponent alloys (MCA) and high-entropy alloys (HEA) is proposed: the normalised dispersion of binary mixing enthalpies, δH. This descriptor quantifies the internal heterogeneity of chemical interactions among constituent element pairs —a contribution that classical descriptors do not capture, as they rely on weighted averages that mask the coexistence of strongly attractive and repulsive pairs. Combined with the atomic size mismatch parameter δ, the pair δH – δ significantly outperforms the Ω – δ reference criterion established by Yang and Zhang (2012), with an improvement of +3.16 percentage points in cross-validated accuracy (83.16% vs 80.00%) and +0.063 in the Matthews Correlation Coefficient (0.663 vs 0.600), validated on an experimental dataset of 1675 alloys from three independent sources spanning binary to nonary compositions (McNemar test, p = 0.006). Although δH and δ are moderately correlated at the global level (Spearman ρ = 0.27), partly because both tend to increase with compositional complexity, the significant improvement of δH – δ over any univariate classifier confirms that δH contributes predictive information that δ alone does not capture. The critical threshold δH ≤ 1.1 has a direct physical interpretation: the solid solution is stable when the heterogeneity of binary chemical interactions does not exceed 1.1 times the mean thermal energy available at the solidification temperature.
Electron Beam Physical Vapor Deposition (EB-PVD) is a critical technique for high-performance coatings, but modeling its full non-equilibrium process chain, i.e., from source evaporation to film evolution, remains a significant challenge. This study presents a comprehensive, integrated Molecular Dynamics (MD) framework that simulates the entire non-equilibrium EB-PVD process for nickel thin films, in which vapor composition, atomic configuration, velocity, incidence angle, and atomic flux obtained from open-boundary evaporation are directly transferred to the deposition model. The emitted vapor is predominantly monomeric, while larger clusters form during subsequent gas-phase transport. Vapor density primarily governs collision and aggregation, whereas vapor temperature controls cluster coarsening and persistence. During deposition, film morphology shifts from cluster-size controlled to substrate-controlled regimes: roughness increases with cluster size on smooth surfaces while this sensitivity is substantially reduced on rough substrates. This work provides critical atomic-level predictive insights for microstructural engineering and performance optimization in EB-PVD systems.
Achieving reliable wide-temperature lubrication remains a fundamental challenge for self-lubricating metal matrix composites. Conventional multi-lubricant strategies often suffer from mechanical degradation and lubricant depletion due to oxidation during thermal cycling. Here, we introduce a single SiC additive in a NiCr matrix to trigger an in-situ reaction during spark plasma sintering. Partial dissolution of Si into Ni lowers the stacking fault energy and promotes the formation of a hard Ni2Si phase, which enhances high-temperature load-bearing capacity and mechanical strength. Simultaneously, it generates nanoscale graphite that ensures low-temperature lubrication without notably compromising mechanical properties. Moreover, Si oxidizes to form a protective SiO2-rich scale that shields graphite from oxidation at elevated temperatures. Consequently, the composite maintains friction coefficients below 0.26 from room temperature to 700 °C and retains lubricity even after 100 h at 700 °C, with a yield strength of 1276 MPa and 16% compressive strain. This work achieves self-adaptive wide-temperature lubrication via a single SiC precursor, overcoming the traditional trade-off between lubrication and mechanical integrity.
