Advanced Powder Materials最新文献

Powder-based laser direct metal deposition (DMD), one of the directed energy deposition, was applied in air and underwater to repair pre-machined NV E690 steel plates. Systematic investigations on the effects of underwater environment and ambient pressures (0.01–0.35 MPa) on the microstructure evolution, phase transformation, and mechanical properties were conducted. The water quenching effect refined the grain size and increased the dislocation density and lath martensite content. The theoretical models of the underwater pressurized nitriding process and the precipitation kinetics of (Ti, V)N particles were established. Moreover, the microstructure evolution and the mechanical properties of other underwater DMD repaired samples did not show obvious relation with the underwater ambient pressures. This investigation not only provides a candidate for the underwater restoration technique but also bridges marine engineering and emerging DMD technology.

The morphology and distribution of silicides in α/α+β type titanium alloys impress on their properties. Nevertheless, the types of silicide precipitates and their formation mechanisms remain unclear in β-type Ti–Nb–Zr–Ta alloys. In this study, we report the precipitation behavior of silicides formed upon aging treatment of a laser powder bed fusion (LPBF)-fabricated β-type Ti–34.5Nb–6.9Zr–4.9Ta–1.4Si (wt%, TNZTS) alloy. We further discuss their underlying formation mechanism and silicide selection-oriented mechanical properties tailoring for LPBF-fabricated TNZTS alloy. Two novel silicide precipitates were formed: a supersaturated Si–rich β–Ti matrix in the form of a network that can further transform into the (Ti, Zr)₂Si (S2) phase with the increase of aging temperature; and a short, rod-like S2 precipitate adjacent to pre-existing dot-shaped S2. The former results from the aggregation of Si solute atoms towards to the dislocation walls/microbands and the subsequent precipitation reaction, while the latter arises from the considerable micro-strain around the phase boundary between the dot-shaped S2 and β-Ti owing to the large difference in their thermal expansion coefficients. The aging-treated TNZTS alloy exhibits a good combination of tensile strength (1083 ​± ​5 ​MPa) and fracture strain (5.6% ​± ​1.0%), which is attributed to precipitation strengthening, grain-boundary strengthening, and discontinuous intergranular silicide derived from phase selection. The obtained results provide a basis for the design and fabrication of biomedical Si-containing β-type Ti alloys with excellent mechanical properties.

Despite the importance of temperature distribution in spark plasma sintering of metallic glasses, its quantification has been experimentally laborious. This work proposes an experimental strategy to determine the sintering temperature by establishing a quantitative relationship between the temperature-thermal signal. We reproduced the thermal profiles of spark plasma sintering by isothermal annealing and found a correlation between annealing temperature and isothermal crystallization time. This strong correlation indicates the temperature-dependent structural evolution of glassy powders. Using isothermal crystallization time as the measuring gauge, we correlated the annealing temperature to the sintering temperature and obtained the sample temperature map. The sample temperature is at least 19 ​°C higher than the nominal temperature of 425 ​°C measured by the thermocouple. Meanwhile, the sample temperature shows a hump-shaped pattern closely correlated with the current density. The maximum temperature of 453 ​°C occurs on the sample/punches contact surfaces. Temperature heterogeneity within the sample induces diverse microstructures and porous structures. We elucidate that the temperature inhomogeneity is intrinsic, given the presence of contact interfaces. Contact resistances affect the current distribution and heat transfer, resulting in a larger temperature gradient than the traditional powder metallurgy process.

Although the Ostwald ripening approach is often utilized to manufacture single hollow metal oxide, constructing hollow binary oxide heterostructures as potent photoelectrochemical (PEC) catalysts is still obscure and challenging. Herein, we reveal a general strategy for fabricating hollow binary oxides heterostructures (Co₃O₄-δ-MnO₂ and Co₃O₄–SnO₂) utilizing Ostwald ripening. Hollow Co₃O₄-δ-MnO₂ nano-network with the structure evolution process was systematically explored through experimental and theoretical tools, identifying the origin of hollow binary oxides due to the interfaces acting as landing sites for their growth. In addition, the structural evolution, from hollow Co₃O₄-δ-MnO₂ to Co₃O₄-α-MnO₂, can be observed when the time of secondary hydrothermal reaches 96 ​h due to the topotactic layer-to-tunnel transition process. Notably, optimized Co₃O₄-δ-MnO₂-48 exhibits a superior PEC degradation efficiency of 96.42% and excellent durability (20,000 ​min) under harsh acid conditions, attributed to the massive hollow structures' vast surface area for high intently active species. Furthermore, density functional theory simulations elucidated the Co₃O₄-δ-MnO₂’ electron-deficient surface and high d-band center (Co₃O₄-δ-MnO₂, -1.06; Co₃O₄-α-MnO_2, -1.49), strengthening the interaction between the catalyst's surface and active species and prolonging the lifetime of active species of •O₂⁻ and ¹O₂. This work not only demonstrates superior PEC degradation efficiency of hollow Co₃O₄-δ-MnO₂ for practical use but also lays the cornerstone for constructing hollow binary oxides heterostructures through Ostwald ripening.

Nanoprecipitation strengthening has been widely adopted as an effective way to design high-strength alloys, which generally leads to the loss of ductility. Here we unveil the unique bifunctionality of L1₂-structured nanoprecipitates in a FeCoNiAlTi-type high entropy alloy , enabling the combined increase of tensile strength and ductility. Results show that as-quenched precipitate-free matrix alloys undergo thermally-induced martensite transformation and form the body-centered cubic martensite phase with limited tensile ductility. In strong contrast, when introducing the dense coherent L1₂-type nanoprecipitates, the face-centered cubic matrix is temporarily stabilized, which in turn promotes the microbands-induced plasticity associated with stress-induced martensite transformation upon deformation. This allows us to achieve significantly improved work hardening capability and excellent plastic deformation stability at a high-strength level. These new findings reshape our understanding of the precipitation strengthening and could provide useful guidance for developing high-performance alloys by regulating the coherent nanoprecipitate and martensitic phase transformation.

Calcium bismuth niobate (CaBi₂Nb₂O₉) is regarded as one of the most potential high-temperature piezoelectric materials owing to its highest Curie point in bismuth layer-structured ferroelectrics. Nevertheless, low piezoelectric coefficient and low resistivity at high temperature considerably restrict its development as key electronic components. Herein, markedly improved piezoelectric properties and DC resistivity of CaBi₂Nb₂O₉ ceramics through Na⁺ and Sm³⁺ co-doping are reported. The nominal compositions Ca_1-2x(Na, Sm)_xBi₂Nb₂O₉ (x ​= ​0, 0.01, 0.025, and 0.05) ceramics have been prepared via the conventional solid state method. An optimum composition of Ca_0.95(Na, Sm)_0.025Bi₂Nb₂O₉ is obtained, which possesses a high Curie point of ∼949 ​°C, a piezoelectric coefficient of ∼12.8 ​pC/N, and a DC electrical resistivity at 500 ​°C of ∼4 ​× ​10⁷ ​Ω ​·cm. The improved d₃₃ is probably ascribed to the reduction in domain size and the increase in domain wall density caused by the reduced grain size. More importantly, after annealing at 900 ​°C for 2 ​h, the piezoelectric coefficient still maintains about 90% of the initial d₃₃ value, which displays a significant improvement compared to pure CaBi₂Nb₂O₉ ceramic with only 44% of the initial d₃₃ value. This work exhibits a feasible approach to simultaneously obtain high piezoelectric property and thermal stability in CaBi₂Nb₂O₉ ceramics by Na⁺/Sm³⁺ co-doping.

Advanced photovoltaics, such as ultra-flexible perovskite solar cells (UF-PSCs), which are known for their lightweight design and high power-to-mass ratio, have been a long-standing goal that we, as humans, have continuously pursued. Unlike normal PSCs fabricated on rigid substrates, producing high-efficiency UF-PSCs remains a challenge due to the difficulty in achieving full coverage and minimizing defects of metal halide perovskite (MHP) films. In this study, we utilized Al₂O₃ nanoparticles (NPs) as an inorganic surface modifier to enhance the wettability and reduce the roughness of poly-bis(4-phenyl) (2,4,6-trimethylphenyl) amine simultaneously. This approach proves essentials in fabricating UF-PSCs, enabling the deposition of uniform and dense MHP films with full coverage and fewer defects. We systematically investigated the effect of Al₂O₃ NPs on film formation, combining simulation with experiments. Our strategy not only significantly increases the power conversion efficiency (PCE) from 11.96% to 16.33%, but also promotes reproducibility by effectively addressing the short circuit issue commonly encountered in UF-PSCs. Additionally, our UF-PSCs demonstrates good mechanical stability, maintaining 98.6% and 79.0% of their initial PCEs after 10,000 bending cycles with radii of 1.0 and 0.5 ​mm, respectively.

Flexible lithium metal batteries with high capacity and power density have been regarded as the core power resources of wearable electronics. However, the main challenge lies in the limited electrochemical performance of solid-state polymer electrolytes, which hinders further practical applications. Incorporating functional inorganic additives is an effective approach to improve the performance, including increasing ionic conductivity, achieving dendrite inhibiting capability, and improving safety and stability. Herein, this review summarizes the latest developments of functional inorganic additives in composite solid-state electrolytes for flexible metal batteries with special emphasis on their mechanisms, strategies, and cutting-edge applications, in particular, the relationship between them is discussed in detail. Finally, the perspective on future research directions and the key challenges on this topic are outlooked.

Surface charge localization and inferior charge transfer efficiency seriously restrict the supply of reactive hydrogen and the reaction dynamics of CO₂ photoreduction performance of photocatalysts. Herein, chemically bonded BiVO₄/Bi₁₉Cl₃S₂₇ (BVO/BCS) S-scheme heterojunction with a strong internal electric field is designed. Experimental and density function theory calculation results confirm that the elaborated heterojunction accelerates the vectorial migration of photogenerated charges from BiVO₄ to Bi₁₉Cl₃S₂₇ via the interfacial chemical bonding interactions (i.e., Bi-O and Bi-S bonds) between Bi atoms of BVO and S atoms of BCS or Bi atoms of BCS and O atoms of BVO under light irradiation, breaking the interfacial barrier and surface charge localization of Bi₁₉Cl₃S₂₇, and further decreasing the energy of reactive hydrogen generation, CO₂ absorption and activation. The separation efficiency of photogenerated carriers is much more efficient than that counterpart individual in BVO/BCS S-scheme heterojunction system. As a result, BVO/BCS heterojunction exhibits a significantly improved continuous photocatalytic performance for CO₂ reduction and the 24 ​h CO yield reaches 678.27 ​μmol·g⁻¹. This work provides an atomic-level insight into charge transfer kinetics and CO₂ reduction mechanism in S-scheme heterojunction.

The effect of scanning strategy on the microstructure and properties of GH3536 Ni-based superalloy prepared by Laser Powder Bed Fusion was investigated, for the purpose of building high quality hydrocyclone part. The results show that the strength of Z67° (a zone with 67° hatch angle strategy) specimen is the highest among the four scanning strategies (0°, 67°, 90°and Z67°), with yield strength and tensile strength of 681 ​MPa and 837 ​MPa, respectively. Selective orientation of crystals occurs during the forming process because the longitudinal section of the specimen exhibits a high texture strength in (001). As the stretching proceeds, the plastic deformation mechanism of the specimen gradually changes from slip to twin-dominated, a substantial amount of twinning is observed in the region where the deformation of the specimen reaches 80%. The additive manufacturing simulation suite: Ansys Additive is used to simulate the stress and deformation of the part during the process, and the displacement results are consistent with the experimental phenomena. According to the simulation results, the structure design is optimized and the surface quality of the part is improved. The results show that the support of the part is more reasonable when the overhang angle is 45°.