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•Well-developed twinned dendrites are found in wire arc directed energy deposited aluminum alloys.•Formation causes of twinned dendrites are investigated via experiments and ...simulation.•Regular dendrites can grow epitaxially from lateral branch of twinned dendrites.•The evolution of twinned dendrites during deposition is sensitive to remelting depth.
Twinned dendrites have attracted worldwide attention in the past half century due to their unusual orientation and crystallographic symmetry. Successive research has established a basic understanding of them in relatively steady processes like direct chill casting and directional solidification. This work, for the first time, investigated the growth behaviors of twinned dendrites in the wire arc directed energy deposition. The crystallographic characteristics, formation, and evolution laws of the twinned dendrites in the unsteady localized solidification condition are explored via experiments and numerical simulations. Results show that stacking faults are vital in the longitudinal growth of twinned dendrites by adjusting intermittent twin boundaries. During deposition, Mg, Zn, and Cu, which have low stacking fault energy, can promote the growth of twinned dendrites. The molten pool tail has large temperature gradients, crystallization velocities, and sufficient convection, providing advantageous growth conditions for twinned dendrites. Competitive relationships form between twinned and regular dendrites at the molten pool center. However, the twinned dendrites also cooperate with regular dendrites in epitaxial growth via their 〈100〉 lateral branch. With the remelting depth increasing, the twinned dendrite morphology changes from lamellar to isolated unilateral feather shape, then to unchained islands, and finally disappear.
The traditional WE43 magnesium alloy (WE43-Mg) manufacturing process faces challenges in producing large and complex structures. The cold metal transfer wire arc additive manufacturing (CMT-WAAM) ...offers a promising solution due to its flexibility, high deposition efficiency and low heat put. However, energy transfer and mass transfer are highly coupled in the CMT additive manufacturing process. Under different working modes, the local thermal processes are quite different for the same transition metals, which can produce different microstructures and mechanical properties. Therefore, it is necessary to study the effect of working modes on microstructure and mechanical properties. This study successfully deposited single-pass multi-layer WE43-Mg components using four CMT processes: CMT, CMT-Pulse, CMT-Advance, and CMT-Pulse + Advance. The microstructure and mechanical properties of these deposited samples were compared. Results revealed equiaxed grains with uniform sizes in the top and middle regions, with fine-grain regions between layers in the four CMT modes. Compare the microstructure characterization results, the higher the line energy, the narrower the width of the remelted fine grain zone. Four CMT modes deposited components exhibited superior mechanical properties compared to as-cast WE43-Mg. The CMT pulse mode shows the best results due to its low porosity. The average yield strength is 149.0 MPa, tensile strength is 222.9 MPa, and elongation is 6.4 %.
Wire-arc directed energy deposition is promising for manufacturing ultra-high-strength Al-Zn-Mg-Cu alloy components. However, the undesired microstructure and performance of as-deposited alloys make ...the heat treatment a mandatory post-process, which still lacks systematic investigation. This work aims to establish a comprehensive understanding of it. An interplay between second-phase dissolution and defect formation in the single-stage solution of as-deposited Al-Zn-Mg-Cu alloy was found: as solution temperatures increase, the equilibrium proportion of residual phases decreases, but the proportion of pore defects increases significantly. Based on a systematic full-factor solution test, a 430°C/4 h + 450°C/4 h step solution process was proposed, which suppressed the pore defects by about 54.8% while keeping the effect of the residual phase dissolution unchanged. After the step solution and artificial aging, the average yield strength of the alloy reached 475 MPa, and the elongation reached 6.5%, showing 201.6% and 85.7% improvement compared with the as-deposited state, respectively.
Highlights
Achieving ultrahigh energy-storage density (7.19 J cm
−3
) and outstanding storage efficiency (93.8%) at 460 kV cm
−1
in BNT-based relaxor ferroelectric ceramics under a moderate electric ...field.
Superior energy-storage performance accomplished through meticulous regulation of permittivity, enhancement of insulation quality, and strategic domain engineering via chemical formula optimization.
The intricate structure–property relationship elucidated with precision using high-resolution transmission electron microscopy.
The increasing awareness of environmental concerns has prompted a surge in the exploration of lead-free, high-power ceramic capacitors. Ongoing efforts to develop lead-free dielectric ceramics with exceptional energy-storage performance (ESP) have predominantly relied on multi-component composite strategies, often accomplished under ultrahigh electric fields. However, this approach poses challenges in insulation and system downsizing due to the necessary working voltage under such conditions. Despite extensive study, bulk ceramics of (Bi
0.5
Na
0.5
)TiO
3
(BNT), a prominent lead-free dielectric ceramic family, have seldom achieved a recoverable energy-storage (ES) density (
W
rec
) exceeding 7 J cm
−3
. This study introduces a novel approach to attain ceramic capacitors with high ESP under moderate electric fields by regulating permittivity based on a linear dielectric model, enhancing insulation quality, and engineering domain structures through chemical formula optimization. The incorporation of SrTiO
3
(ST) into the BNT matrix is revealed to reduce the dielectric constant, while the addition of Bi(Mg
2/3
Nb
1/3
)O
3
(BMN) aids in maintaining polarization. Additionally, the study elucidates the methodology to achieve high ESP at moderate electric fields ranging from 300 to 500 kV cm
−1
. In our optimized composition, 0.5(Bi
0.5
Na
0.4
K
0.1
)TiO
3
–0.5(2/3ST-1/3BMN) (B-0.5SB) ceramics, we achieved a
W
rec
of 7.19 J cm
−3
with an efficiency of 93.8% at 460 kV cm
−1
. Impressively, the B-0.5SB ceramics exhibit remarkable thermal stability between 30 and 140 °C under 365 kV cm
−1
, maintaining a
W
rec
exceeding 5 J cm
−3
. This study not only establishes the B-0.5SB ceramics as promising candidates for ES materials but also demonstrates the feasibility of optimizing ESP by modifying the dielectric constant under specific electric field conditions. Simultaneously, it provides valuable insights for the future design of ceramic capacitors with high ESP under constraints of limited electric field.
In the last few decades, dielectric capacitors have gotten a lot of attention because they can store more power and charge and discharge very quickly. But it has a low energy-storage density (Wrec), ...efficiency (η), and temperature stability. By adding Pb(Mg1/3Nb2/3)O3 (PMN) and (Bi0·1Sr0.85)TiO3 (BST) to a nonstoichiometric (Bi0·51Na0.5)TiO3 (BNT) matrix, the goal is to change the phase transition properties and make the material more relaxor ferroelectric (RFE) by lowering the remnant polarization Pr and keeping the maximum polarization Pmax. A viscous polymer process (VPP) is used to improve the electric breakdown strength, which is also a key part of being able to store energy. By working together, ceramics with the formula 0.790.85BNT-0.15PMN-0.21BST (BP-0.21BST) are made. The phase structure has been changed from a rhombohedral phase to a rhombohedral-tetragonal coexisted phase. This is beneficial for RFE properties and gives a Wrec of 6.45 J/cm3 and a η of 90% at 400 kV/cm. Also, the energy-storage property is very temperature stable between 30 and 150 °C. These results show that process optimization and composition design can be used to improve the energy storage properties, and that the dielectric ceramic materials made can be used in high-powder pulse dielectric capacitors.
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•Energy storage performance (ESP) was enhanced via phase coexistence design and VPP.•PMN and BST were used to tailor the ESP of BNT-based ceramics.•High Wrec of 6.45 J/cm3 and η of 90% with good temperature stability are achieved simultaneously.
Studying the mechanisms of the spin Hall effect (SHE) is essential for the fundamental understanding of spintronic physics. By now, despite the intensive studies of SHE on heavy metal (HM)/metallic ...magnet heterostructures, the SHE on HM/ferrimagnetic insulator (FMI) heterostructures still remains elusive. Here, we study the mechanism of SHE in the Pt/Tm3Fe5O12 (TmIG) heterostructure. We first tune the crystallinity and resistivity of Pt by an annealing method, and then study the spin–orbit torque (SOT) in the tuned-Pt/TmIG devices. The SOT generation efficiency per unit electric field and spin Hall angle were obtained, which are insensitive to the annealing temperature. We further demonstrate that the intrinsic contribution in the moderately dirty regime is responsible for the SHE in our Pt/TmIG bilayer. Our study provides an important piece of information for the SHE in FMI-based spintronic physics.
•BT-SBT-NdVPP ceramic achieved an ultrahigh Wrec of 4.2 J/cm3 under 460 kV/cm.•High Wrec of 2.6 J/cm3 at 30 ~ 100 °C and 10 ~ 400 Hz under 300 kV/cm.•Two-step strategy provides a universal way for ...fabricating energy storage ceramics.
As the industrial pillar of electronic ceramics, BaTiO3 ceramic is difficult to achieve large energy storing performance due to its high Pr and low dielectric breakdown field strength, making it difficult to satisfy their development requirements of miniaturization and lightweight of power electronic equipment. Therefore, a two-step strategy including adjusting the ratio of chemical elements to modify the microstructures and optimizing the preparation process to enhance electric breakdown strength has been proposed to greatly enhance the energy storing performance of lead-free ferroelectric ceramics, whose effectiveness has been proved within this investigation. Especially, the (Ba0.65Sr0.245Bi0.07)0.99Nd0.01TiO3 (BT-SBT-NdVPP) ceramic prepared by this strategy obtains a superhigh energy storage density of 4.2 J/cm3 under 460 kV/cm, and its temperature (30 ~ 100 °C) and frequency (10 ~ 400 Hz) stabilities under 300 kV/cm are pretty good. In addition, this ceramic has excellent pulse performance under 350 kV/cm between 30 and 150 °C. Therefore, this two-step strategy put forward within this investigation not only significantly improves the energy storage performance of BT-based ceramics but also provides a reference for the preparation of dielectric ceramics with high quality, which could has great potential for the practical industrial application.
Our study investigates the impact of local political uncertainty on public financing costs in China. By examining a series of unexpected turnovers of municipal government leaders, we find that the ...offering yield spreads of municipal corporate bonds increase by around 23 basis points shortly following an anti-corruption investigation and reverse afterward. Indicators show that the anti-corruption investigation escalates the short-term uncertainty about government actions. The pricing effect is stronger for issuers with higher exposure to government policies or lower financial resilience. A transparent information environment alleviates the impact. In contrast, temporary government inefficiency does not explain the increase in yield spreads. Our findings suggest that political uncertainty is a determinant of public financing costs.
•Gas protection improves the forming quality of deposited WE43-Mg by WAAM.•The cooling effect induced by gas protection enhances grain refinement.•Gas protection significantly reduces the content of ...oxides.•Eliminating oxide inclusions and refining grain enhances the mechanical properties.
In this study, WE43 magnesium alloy was successfully fabricated using wire arc additive manufacturing technology, focusing on reducing the common oxide inclusion defects. The implementation of a gas shielding hood significantly improved the grain morphology of the deposited samples and diminished both the quantity and size of oxides. In addition, the cooling effect induced by the shielding gas contributed to the refinement of grain size. The synergistic effect of oxide reduction and grain refinement significantly improves the mechanical properties of the deposited samples. For heat treatable magnesium alloys, minimizing the consumption of rare earth elements is beneficial for optimizing heat treatment mechanical properties.
Abstract
Porous BaTiO
3
‐based relaxor ferroelectric ceramics with lamellar structure were achieved by ice templating method, and the rheological properties of ceramic slurry for freeze casting were ...deeply studied. Epoxy resin was then backfilled to generate ceramic–epoxy resin composites. Ceramic–epoxy composites with a lamellar structure were obtained when using a slurry with a ceramic content of 45 wt.%. The nanoindentation results showed that the introduction of ceramic materials into the epoxy resin can significantly improve the penetration resistance and hardness of the material. The dielectric and ferroelectric properties of the composites were also characterized. The interaction between the highly coupled dipoles in the polymers results in a decrease in the breakdown field strength of the composite. The dielectric constant reached up to ∼800. At 220 kV/cm,
W
rec
= 0.62 J/cm
3
, and
η
was ∼80%. At low frequencies,
W
rec
was ∼0.16 J/cm
3
, which indicated good stability.
