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.
The quest for ceramic oxides with ultra-low phonon conductivity and high infrared spectrum reflectance is crucial for the development of advanced thermal insulation materials. While there are various methods to manipulate phonon thermal conductivity to achieve extremely low values, strategies for suppressing radiative conductivity at high temperatures remain limited. In this study, we propose a hierarchical defect coupling approach for Nd(2-2x)/3CaxTiO3 ceramics to tailor both phonon and radiative conductivity. After characterizing the microstructure, we observe dense twin grain boundaries in all samples, a natural phenomenon in perovskite-type Nd(2-2x)/3CaxTiO3 oxide ceramics. Through defect engineering, in situ generation of a nano-chessboard structure was achieved in the Nd0.6Ca0.1TiO3 by introducing varying concentrations of cation vacancies into CaTiO3. The emergence of a strain field is observed surrounding the nano-chessboard structure, and this surrounding strain field significantly contributes to the enhanced stability of the Ca-depleted zones. This approach results in a hierarchical defect coupling, ranging from 0-dimensional point defects to 2-dimensional heterogeneous interfaces, in Nd(2-2x)/3CaxTiO3. Nd0.6Ca0.1TiO3 exhibits high infrared reflectance due to refractive index fluctuations, promoting scattering between multiple interfaces and photons, thereby suppressing the radiant energy from directly penetrating the entire material. Simultaneously, phonon thermal conductivity gradually decreases with increasing cation vacancy concentration and boundaries of nano-chessboard structure, leading to a glass-like phonon thermal conductivity with high infrared reflectance in Nd0.6Ca0.1TiO3. Atomistic simulations confirm a strong scattering probability between 0-dimensional point defects and phonons, effectively hindering phonon transport. Consequently, we successfully achieve the coupling of both low thermal conductivity and infrared spectrum shielding ability in cation-deficient Nd0.6Ca0.1TiO3 through hierarchical defect coupling. Our findings offer an innovative and practical strategy for tuning materials with low thermal conductivity and outstanding infrared spectrum shielding properties.
This work quantitatively investigates the γ′ precipitation behaviour and mechanical properties of the Alloy 925 (UNS N09925) material system to elucidate its resilience to compositional variations and aging treatments. Using advanced characterisation techniques, it is shown that both composition and aging parameters have a distinct influence on the volume fraction and size of γ′ precipitates during production-relevant heat treatments, including one-step aging at 720–760°C and subsequent second aging steps at 621–635°C. Quantitative analysis of the γ′ volume fraction, implementing a novel analysis procedure for high-energy X-ray diffraction data proposed in this work, shows that minor changes to the Ti and Al contents result in changes of up to 2 vol.% in the γ′ phase during aging. In addition, the introduction of a second aging step at lower temperatures increases the γ′ fraction by approximately 2.5 vol.%. Small-angle X-ray scattering captures not only the progressive coarsening with increasing temperature and time during one- and two-step aging, resulting in precipitate diameters ranging from 4 to 22 nm, but also the compositional effect on precipitate size. The experimentally obtained quantitative data for the γ′ precipitates allow the prediction of the yield strength increase associated with precipitation strengthening as well as the validation of precipitation kinetics modelling. Comparison with the results of hardness measurements reveals a strong correlation between the γ′ precipitation behaviour and the mechanical properties due to order-type strengthening associated with the weakly coupled dislocations mechanism.
Amorphous alloys offer unique opportunities for tailoring microstructures via non-equilibrium processing; however, precise control of nanoscale crystallization during rapid solidification remains challenging without post-solidification heat treatments. Herein, we demonstrate that in-situ precipitation of FCC-Al nanocrystals in an Al88Ni10MM2 (MM: Ce-rich misch metal) metallic glass can be effectively controlled solely by tuning the cooling rate during melt-spinning. By systematically varying the wheel speed from 40 m/s to 10 m/s, corresponding to cooling rates from 2.5 × 10⁶ K/s to 4.0 × 10⁵ K/s, we achieve a substantial increase in the number density of FCC-Al nanoprecipitates from 2.15 × 10²¹ to 1.55 × 10²² m⁻³, while maintaining a nearly constant nanocrystal size (∼5–6 nm). To elucidate the governing nucleation kinetics, nucleation delay times were quantified using flash differential scanning calorimetry and employed to construct Time-Temperature-Transformation and Continuous-Cooling-Transformation diagrams. Statistical analysis of nucleation temperatures enables direct estimation of nucleation rates under different cooling conditions, revealing that reduced cooling rates significantly enhance nucleation kinetics, leading to dense in-situ precipitation. In contrast, crystal growth remains strongly diffusion-limited under rapid solidification conditions, thereby constraining precipitate coarsening. Consequently, we establish a cooling-rate-dependent framework for decoupling nucleation and growth during melt-spinning, enabling high-density nanocrystal formation without significant size evolution. Mechanical testing, including ribbon bending and cyclic tensile experiments, confirms that such controlled in-situ nanocrystallization simultaneously enhances both tensile strength and plasticity, addressing one of the long-standing challenges in metallic glass research. This work provides a processing strategy for cooling-driven microstructural design in metallic glasses, offering a pathway to bypass conventional annealing treatments while achieving enhanced mechanical performance.
