Changchun Ge

We have systematically analyzed the solution and aggregation characteristics of yttrium (Y), lanthanum (La), lutetium (Lu) and potassium (K) on symmetrically inclined tungsten (W) grain boundary (GB) Ʃ5(310)/[001] by first principles calculation. Furthermore, the influence mechanism of Y, La Lu and K on the strength of W GB was analyzed. K/La and Y/Lu exhibit two different evolution characteristics in the W GB region. The calculation results show that Y/Lu preferentially occupies the substitution site (V₀) on the W GB plane, and the solution energy of Y/Lu at the substitution site increases with distance from the W GB plane. However, the most stable occupation sites of La/K in the W GB region are the sites (V₁) nearest to the W GB plane. The electronic structure analysis showed that the segregation energies of Y, La Lu and K on the W GB were positively correlated with the number of electron transfer. The existence of K/La in the W GB region promotes the dissolution of subsequent atoms, while the existence of Y/Lu atoms has little effect on the dissolution of subsequent atoms. In terms of mechanical properties, the addition of alloying elements significantly improves the fracture energy of W GB, and the Y and Lu effectively increase the fracture energy to 5.602 J/m² and 5.687 J/m², which is higher than the 5.185 J/m² of clean W GB. This strengthening mechanism is mainly attributed to the strong metal bond between W-Y and W-Lu. Although the fracture energy of La and K is also higher than that of clean W GB—5.465 J/m² and 5.335 J/m², respectively—the strength improvement mainly depends on the action of La-La and K-K metal bonds.

Si₃N₄ ceramics with a YF₃-MgSiN₂ binary additive system were fabricated by hot pressing (HP) and spark plasma sintering (SPS) at 1500–1700 °C, followed by annealing at 1850 °C for 6 h. The effects of sintering route and temperature on phase transformation, microstructure evolution, thermal conductivity, and mechanical properties were systematically investigated. SPS significantly accelerated the α→β phase transformation compared with HP, and the β-Si₃N₄ content in SPS samples exceeded 94% at 1600 °C. After annealing, all samples were completely transformed into β-Si₃N₄, accompanied by obvious grain growth. Thermal conductivity was closely related to both grain size and relative density. Grain growth reduced grain-boundary phonon scattering, whereas density loss and residual porosity deteriorated heat transport. The mechanical properties were jointly governed by β-Si₃N₄ content, grain morphology, and porosity. Elongated β-Si₃N₄ grains promoted crack deflection and crack bridging, thereby improving fracture toughness, while excessive porosity reduced flexural strength. These results demonstrate that optimizing the balance between phase transformation, grain growth, and densification is essential for tailoring the thermal and mechanical performance of Si₃N₄ ceramics containing non-oxide sintering additives.

The main method for large-scaled preparing powder superalloys in the production process is inert gas atomization, particularly vacuum-induced gas atomization (VIGA). A novel technique called electrode-induced gas atomization (EIGA) with a crucible-free electrode was proposed to prepare non-inclusion superalloy powders. In this study, a Ni-based superalloy of FGH4096 powder was prepared using both the VIGA and EIGA methods, while blanks were prepared through direct hot isostatic pressing (as-HIPed) near-net-forming method. The particle size, morphology, microstructure, and mechanical properties of the powders and blanks were compared via a laser particle size analyzer, SEM, TEM, and room-temperature and 650 °C tensile tests. The results indicated that EIGA-prepared powders exhibited a finer particle size and better surface quality than the one prepared via VIGA, which showed reduced satellite powders. However, the as-HIPed blank of EIGA-prepared powders had a lower secondary γ’ ratio and slightly reduced strength compared to the as-HIPed blank of VIGA-prepared powders due to its slightly lower secondary γ’ phase ratio and less effective inhibition of dislocation movement. Furthermore, the overall performance of the two samples did not differ significantly due to the similar microstructural characteristics of the powders. However, the variation in particle size affects heat conduction during the HIP process, resulting in slight differences in blanks’ properties.

Carbon nanotubes (CNTs)-reinforced copper-based composites (CNT/Cu) have been extensively investigated due to their exceptional theoretical electrical, thermal, and mechanical properties. However, the actual performance of these composites has consistently fallen short of theoretical expectations. This discrepancy primarily arises from the inability to achieve direct chemical bonding between copper and carbon nanotubes or to alloy them effectively. Consequently, this leads to interference in electron and phonon transmission at the interface between the two materials, adversely affecting their electrical and thermal conductivity as well as other properties. In recent years, research has increasingly focused on optimizing and regulating the interfacial interactions between carbon nanotubes and the copper matrix to enhance overall performance while also exploring potential applications. This article reviews recent advancements from an interface regulation perspective, summarizing typical interfacial characteristics such as physical interfaces, chemical bonding, and metallurgical bonding along with their respective preparation methods and effects on performance enhancement. Furthermore, a novel microstructural design of CNT/Cu is put forward, where amorphous CNTs (aCNTs) were utilized as the reinforcing phase to form a nanoscale networked composite interface. This not only enables Cu to adhere to the aCNTs’ sidewall but also fills the sidewall within them, with the aim of significantly strengthening the interfacial bonding strength of CNT/Cu and achieving comprehensive improvement of the composite material properties.

Digital light processing (DLP) 3D-printed Si₃N₄ ceramics, known for their exceptional performance, offer distinct advantages in meeting the high-strength and complex structural demands of industries such as aerospace, semiconductors, healthcare, automotive, energy, and machinery. However, due to Si₃N₄’s strong chemical stability, low diffusion rate, low self-sintering ability, and high melting point, achieving densification under conventional sintering conditions is challenging. As a result, sintering additives are essential to promote the sintering process, lower the sintering temperature, improve densification, and enhance performance. In this study, 45 vol% Si₃N₄ slurries were prepared using DLP 3D printing technology, incorporating nine different combinations of sintering additives, including aluminum oxide (Al₂O₃), yttrium oxide (Y₂O₃), and aluminum nitride (AlN), in various ratios with Si₃N₄. The slurries were then sintered at 1800 °C for 2 h under a 1 MPa N₂ atmosphere. Additionally, the phase composition, microstructure, grain distribution, and crack propagation of the materials. The results showed that a Si₃N₄ to Al₂O₃ and Y₂O₃ ratio of 95:2.5:2.5 produced elongated β-Si₃N₄ grain structures and enhanced density, achieving a maximum Vickers hardness of 12.88 ± 0.52 GPa. Additionally, the synergistic toughening effect of the rod-like β-Si₃N₄ grains and sintering aids significantly improved the fracture toughness of the Si₃N₄ ceramic matrix, with a flexural strength of 540.63 ± 10.05 MPa and a fracture toughness of 4.92 ± 0.07 MPa·m^1/2. This study lays the foundation for the future application of 3D-printed Si₃N₄ ceramics, optimization of sintering aid combinations at different ratios, and performance enhancement in extreme environments.

Photocatalytic antimicrobials, as emerging advanced oxidative antimicrobial materials, have the advantages of low price and long-lasting antimicrobial properties. Nevertheless, with catalysts increasingly trending toward nanoscale dimensions, the environmental challenge of catalyst recycling becomes more pronounced. In this paper, we propose utilizing one-dimensional carbon fiber as a substrate, employing the nucleating agent method to induce Titanium dioxide (TiO2) growth on the fiber surface. Furthermore, the material's band gap underwent modification through hydrogen calcination, thus resulting in the attainment of hierarchical black TiO2/carbon fiber composites with visible light-driven capabilities. The characterization of the materials was conducted via scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results revealed that when the black hydrogenated TiO2 was composited with carbon fiber, the Schottky heterojunction was formed, and thus effectively improved the photocatalytic effect of the composites. Notably, the degradation rate of methylene blue achieved 96.25% within 150 min when utilizing black TiO2/carbon fiber composites, while the inactivation rate of Escherichia coli (E. coli) reached 97.58% within 0.5 h and attained complete inactivation within 60 min.

Oxide inclusions in Ni-based superalloys play a crucial role in determining their mechanical properties, oxidation resistance, and corrosion resistance at high temperatures. In this paper, the source and formation mechanism of different types of oxide inclusions in a high-aluminum Ni-based superalloy were systematically studied. An automatic field emission scanning electron microscope equipped with an energy dispersive spectrometer and a self-designed superalloy inclusion analysis standard was utilized to quantitatively reveal the oxide inclusion characteristics of the high-aluminum Ni-based superalloy prepared via vacuum induction melting (VIM) and vacuum induction remelting (VIR) processes. The experimental results indicate that the typical oxide inclusions in the Ni-based superalloy before the VIR process are irregular MgO·Al₂O₃ inclusions with sizes of less than 2 μm. After the VIR process, the typical oxide inclusions in the Ni-based superalloy are also MgO·Al₂O₃ inclusions. However, these oxide inclusions can be classified into three categories: (i) endogenous irregular MgO·Al₂O₃ inclusions, less than 4.3 μm in size, inherited from the master alloy; (ii) several hundred-micron film-like MgO·Al₂O₃ inclusions generated as interface reaction products between the MgO crucible and melts; and (iii) millimeter-scale MgO·Al₂O₃ inclusions and several tens of microns of MgO inclusions from the exfoliation of the MgO crucible matrix.