Semi-coherent Interface Research Articles

Nano-Phase and SiC-Si Spherical Microstructure in SiC/Al-50Si Composites Solidified under High Pressure.

The formation of coarse primary Si is the main scientific challenge faced in the preparation of high-Si Al matrix composites. The SiC/Al-50Si composites are prepared by high pressure solidification, which allows the primary Si to form a SiC-Si spherical microstructure with SiC, while the solubility of Si in Al is increased by high pressure to reduce the proportion of primary Si, thus enhancing the strength of the composites. The results show that the high melt viscosity under high pressure makes the SiC particles almost "fixed" in situ. The SEM analysis shows that the presence of SiC in the growth front of the primary Si will hinder its continued growth and eventually form SiC-Si spherical microstructure. Through aging treatment, a large number of dispersed nanoscale Si phases are precipitated in the α-Al supersaturated solid solution. The TEM analysis shows that a semi-coherent interface is formed between the α-Al matrix and the nanoscale Si precipitates. The three-point bending tests shows that the bending strength of the aged SiC/Al-50Si composites prepared at 3 GPa is 387.6 MPa, which is 18.6% higher than that of the unaged composites.

Size dependence for mechanical properties of Ti/Cu multilayered nanowire with a semi-coherent interface

Metallic multilayered nanowires have a wide application prospect in micro-nano devices because of their superior physical and chemical properties and microstructure designability. Size effects on the tensile behaviors of Ti/Cu multilayered nanowires are investigated by molecular dynamic simulations. Aspect ratios of 1:4, 1:3, 1:2, 1:1, 1:0.75, and 1:0.67 and sectional dimensions of 3, 4, 5, 6, and 7 nm are adopted to construct nanowires with different sizes. Simulation results indicate that the strength of Ti/Cu nanowires decreases with the decrease of aspect ratio in the large aspect ratio range (>1:2) and all simulated sectional dimension ranges, showing a reverse Hall-Petch effect. The Hall-Petch law can only be satisfied in a small aspect ratio range (<1:2). Deformation mechanism transition is found in the critical aspect ratio of 1:2. When the aspect ratio is larger than 1:2, crystalline phases of Ti and Cu layers dominate the plastic deformation of Ti/Cu nanowires. Crystal phases and interface both bear plastic deformation when the aspect ratio is smaller than 1:2. Interface is an important factor in the strength and deformation of Ti/Cu nanowires. The variation of interface fraction and interaction between interface and dislocation motion determine the tendency of strength variation for Ti/Cu nanowires.

0D/2D/1D Ag@Ni(OH)2/La(OH)3 heterojunction with semi-coherent interface derived from perovskite La1-xAgxNiO3 self-assembling with g-C3N4 for boosting photocatalytic hydrogen evolution

Interfacial electron transfer plays an important role in the boosting photoactivity of heterojunction under sunlight irradiation. Here, the lattice oxygen migration etching Ag-doped perovskite induced self-assembly ternary heterojunction 0D/2D/1D Ag@Ni(OH)2/La(OH)3 via hydrothermal treatment. The LaNiO3 controlled self-assembled into Ni(OH)2/La(OH)3 heterojunctions at the interface and constructed a semi-coherent interface. Furthermore, it became reinforced quaternary heterojunction 0D/2D/1D/2D Ag@Ni(OH)2/La(OH)3/g-C3N4 by electrostatic self-assembly with g-C3N4. The novel constructed Z-scheme heterojunction Ag@Ni(OH)2/La(OH)3/g-C3N4 promotes the effective separation of photogenerated carriers. The semi-coherent interface between Ni(OH)2/La(OH)3 promotes the transfer of photogenerated carriers. At the same time, the silver nanoparticles on Ni(OH)2 nanosheets act as electron trapping sites to further improve the photocatalytic performance. In this way, the synthesized photoexcited quaternary heterojunction Ag@Ni(OH)2/La(OH)3/g-C3N4 showed an outstanding hydrogen production rate from photocatalytic water splitting (the yield of hydrogen was 1633 μmol/g/h) under simulated sunlight. It is comparable to many g–C3N4–based photocatalysts known at present.

Microstructures and oxidation behavior of PM Ni-based superalloy FGH97 with in-situ carbide precipitates

FGH 97 alloy (FG) and its composite with TiC addition (FT) were prepared by spark plasma sintering. The TiC particles were dissolved into the alloy matrix during ball milling, but precipitated out in-situ as MC solid solution with semi-coherent interface after sintering, leading to a homogeneous and fine microstructure. After exposure to 900 °C for 300 h, its grain size grew by only 31%. The fine microstructure promoted selective oxidation of Al and ensured high oxidation resistance of the composite FT. The precipitated carbides increased oxidation resistance of FT and endows its oxide scale with self-healing ability for long-term oxidation.

Overcome strength and toughness trade-off in Cu-decorated carbon nanotubes reinforced magnesium matrix composites by chemical reaction interface and grain refinement

The trade-off of strength and toughness limits the development of magnesium matrix composites. In this paper, the strong interface bonding and uniform dispersion of carbon nanotubes (CNTs) were achieved in CNTs reinforced magnesium matrix (CNTs/Mg) composite through electroless copper plating of CNTs, ball milling, sintering and extrusion. The composite was characterized by SEM, HRTEM, tensile test, etc. The structure characterization shows that the CuMg2 interfacial phase, with coherent and semi-coherent interface, forms by the reaction between the decorated copper of CNTs and the magnesium matrix, thus improving the interfacial bonding. Furthermore, CNTs are uniformly distributed at the grain boundary, which hinder the process of discontinuous dynamic recrystallization and play the role of grain refinement. As a result, the strengthening and toughening efficiency of CNTs/Mg composite reach 325% and 264%, respectively, by adding only 0.125 vol% of CNTs. The calculation model of its strength is established.

Microstructure and mechanical properties of 7075 composites reinforced with TiO2-coated carbon nanotubes

Microstructure and mechanical properties of 7075 aluminum matrix composites (AMCs) reinforced with TiO2-coated carbon nanotubes (TiO2@CNTs) prepared by high energy ultrasonic assisted casting were investigated. In this paper, a novel method was developed to increase interfacial bonding by coating TiO2 on the surface of CNTs. The results showed that high-energy ultrasound can effectively promote the uniform dispersion of TiO2@CNTs in the melt, and the TiO2@CNTs can refine the α-Al phase. The optimal addition of TiO2@CNTs was 0.9wt.%, and the optimal ultrasonic time was 10 min. The yield strength, ultimate tensile strength, and microhardness of the as-cast composites prepared under the optimal parameters were 201.22 MPa, 261.79 MPa, and 126.02 HV, respectively, which increased by 40.9%, 32%, and 32.2% compared with those of the matrix, respectively. The semi-coherent interface was formed at the TiO2/α-Al interface and well-bonded interfaces between the CNTs and the matrix were formed. The fine grain strengthening, thermal mismatch strengthening, Orowan strengthening, and direct bearing strengthening were considered as four strengthening mechanisms that occurred simultaneously, leading to excellent mechanical properties of as-cast 7075-TiO2@CNTs composites.

Strength-plasticity transition mechanism after the solution treatment of GH3230 superalloy fabricated via laser powder bed fusion

Owing to their unique microstructure, GH3230 superalloys prepared using laser powder bed fusion (LPBF) exhibit high strength but low ductility, which limits their functional performance in engine combustion chambers. In this study, the process parameters were optimized to obtain LPBF GH3230 with minimal defects, and solid-solution treatment (ST) was conducted to modulate its inhomogeneous microstructure and mechanical properties. The results revealed that ST eliminated the substructure of as-printed (AP) samples and transformed nano-M23C6 into micron and submicron M6C/M12C in situ. Significant amounts of M6C/M12C promoted Orowan strengthening, but the quasi-continuous semi-coherent lattice interface between M6C/M12C and the matrix was a weak zone for cracking, resulting in reduced plasticity owing to the presence of micron carbide. The increased solid solution temperature causes the carbide to remelt, triggering a strong plastic transformation. The impact of carbide size on strength and plasticity conversion rate was more significant than that of carbide content. Final, LPBF-GH3230 samples containing micron carbides were obtained in ST below 1230 °C with an ultimate tensile strength (UTS) comparable to that of forgings. Further increase in the ST temperature to 1280 °C eliminated the carbides, a LPBF-GH3230 that fulfilled the strength standard for cast parts (647 ± 23 MPa) with an excellent elongation (39.4 ± 1.7%) was obtained. This study provides a theoretical basis for the practical application of the LPBF GH3230 superalloy in the aerospace industry and offers guidance for improving post-treatment methods to ensure high plasticity.

In-situ formation of magnetic sodium ferric silicate/ferric oxide S-scheme heterojunction with efficiently removing tetracycline in photo-Fenton-like reaction

The improvement of Fe(III)/Fe(II) conversion efficiency and facilitation for recycling of Fe-based catalyst have dual economic and green benefits in the field of photo-Fenton-like for wastewater treatment. To achieve those purposes, we have designed and fabricated an S-scheme catalyst by in-situ growing magnetic sodium ferric silicate/ferroferric oxide-ferric oxide (SFS/M-FO) heterojunction. Our results demonstrated the mechanism of heterogeneous interface formation and S-scheme charge transportation between NaFeSi2O6 and α-Fe2O3 in the composite. Meanwhile, the semi-coherent interface in heterojunction could effectively reduce the charge transfer resistance. The incorporation of magnetic ferroferric oxide (Fe3O4) not only ensured high recoverability of the catalyst, but also facilitated charge transfer and improved light absorption capacity. The improved catalytic activity was derived from the combination of the S-scheme NaFeSi2O6/α-Fe2O3 heterojunction and Fe3O4 electronic conductor. Therefore, the SFS/M-FO composite showed excellent tetracycline removal rate of 91.8% within 50 min in the photo-Fenton-like reaction. The ternary composite also held excellent performance, reusability and structural stability. The produced intermediates and three degradation pathways of tetracycline were identified by liquid chromatograph-mass spectrometer. This study offers a convenient way for combining high performance and magnetical retrievability by in-situ growth method for wastewater treatment.

Effect of in-situ phase transition of (MgCoNiCuZn)O high-entropy oxides on microstructure and performance of Ag-based electrical contact materials

Reducing arc corrosion on the surface of electrical contact is beneficial for the stability of electrical systems. For improving the anti-arc erosion performance of composites, a reinforcement with good arc extinction and thermal stability is still a need. In this work, by annealing the as-prepared single-phase (MgCoNiCuZn)O high-entropy oxides (SHEO) reinforced Ag composites at 700 °C, the reinforcement was in-situ transformed in multi-phase (MgCoNiCuZn)O high-entropy oxides (MHEO) consisting of ZnCo2O4, CuO, and non-equiatomic (MgCoNiCuZn)O high-entropy oxides (NHEO). In this process, a semi-coherent interface is formed between CuO (firstly precipitated) and NHEO, and a coherent interface is formed between ZnCo2O4 (secondary precipitated) and NHEO. During arcing, the endothermic phase transformation from MHEO to SHEO reduced arc energy. A comparative study of the composites was carried out with 12 wt% reinforcement. Ag-MHEO possessed exceeded hardness than that of Ag-SnO2 and electrical conductivity similar to Ag-SnO2. Under the DC load of 24 V/8A, Ag-MHEO exhibited 60% less mass loss and 26% less burning arc energy than Ag-SnO2In2O3 during 10,000 times contacts. Compare with Ag-SHEO and Ag-SnO2In2O3, the arc corrosion on Ag-MHEO surface was the weakest after the mentioned contact. This study paves a feasible way to improve anti-arc erosion performance by in-situ reversible endothermic phase transformation.

High entropy alloy thin films on SS304 substrates: Evolution of microstructure and interface modulated by energetic condensation in nanoscale

High entropy alloys (HEAs), as a novel material in the 21st century, possess several advantages, such as excellent corrosion & oxidation resistance and high mechanical properties. HEA thin films show these favourable properties with lower material costs than their bulk counterparts. Studying the HEA film-substrate interface represents challenges but is of extreme importance for the understanding of growth mechanisms with important implications for film adhesion. However, most HEA films were deposited on monocrystalline silicon substrates with limited practical applicability. Further, where commercial stainless steel, aluminium or titanium alloy substrates were used, the microstructure and chemistry at the interface were neglected. Here, we deposited AlCrFeCoNiCu0.5 HEA thin films on stainless steel 304 (SS304) substrates using cathodic arc deposition with different substrate biases. The crystallography and microstructure were investigated using an X-ray and electron-microscopy based chatacterization. A transition of an incoherent to semi-coherent interface was observed from 0 V to -50 V of the substrate bias. Energy dispersive spectroscopy demonstrated a transition of Cr2O3 to aluminum oxide across the interface. The nanoindentation tests revealed the significant improvement of mechanical properties of SS304 with HEA coatings. High-strength HEA (8.0 ± 0.2 GPa) thin films with semi-coherent interfaces were manufactured on SS304.

How Coherent and Semi‐Coherent Interfaces Govern Dislocation Nucleation in Lamellar TiAl Alloys

γ/γ interfaces drive plastic deformation in lamellar TiAl alloys. Due to the ordering and resulting tetragonal nature of γ phase, γ/γ twin interfaces exist as different variants, some of which exhibit coherency stresses or semicoherent interface structures. While geometric parameters, such as the lamella spacing and orientation, are explored extensively in experiments, the isolation of individual influence of different interfaces in a nanolamellar microstructure remains a challenge. Herein, the range of γ/γ interface states is modeled using bilayers of the coherent γ/γTrueTwin, and the coherent or semicoherent γ/γPseudoTwin, and their deformation behavior is compared. It is shown that residual coherency stresses arise due to misfit accommodation in coherent γ/γPT specimens, which causes early preferential nucleation in one γ layer. Similarly, semicoherent specimens show preferential nucleation from misfit dislocations at the interface, which obeys Schmid's rule. In contrast, coherent γ/γTT specimens show no preferential nucleation and therefore exhibit higher strength. Thus, it is demonstrated that the presence of rotational γ/γ interfaces with misfit is responsible for localized and early plasticity, that lowers the strength of a lamellar microstructure. The interface type, which considers the coherency state, is used as a criterion for alloy microstructure design in the future.

Electrical insulation improvement from interface regulation for high-temperature thin-film sensors on superalloy substrate

The stability and durability of insulation structure is crucial for the operation of thin-film sensors, especially at high temperature. However, it still faces great challenges in practical applications owing to the insulation failure during thermal cycles. In this study, an ALD Al2O3 film was introduced into the traditional TGO-sputtered Al2O3 insulation structure for interface regulation. After five thermal cycles up to 1000 °C, the modified insulation structure survived, while the control structure failed. The ALD Al2O3 layer could form denser equiaxed crystal during high-temperature crystallization, thereby preventing the propagation of cracks in sputtered Al2O3 due to volume shrinkage in phase transition. Furthermore, the ALD Al2O3 acted as a transition layer by forming semi-coherent interface with TGO Al2O3, stabilizing the multilayer insulation structure. Finally, Pt-PtRh thin-film thermocouples were fabricated on the modified insulation structure, which exhibited outstanding thermoelectric performance and stability at high temperature. Therefore, the interface regulation strategy proposed in this work could provide significant guidance for the development of high-temperature electrical insulation.

Photocatalytic Production of Syngas from Biomass.

ConspectusAs a renewable solar energy and carbon carrier, biomass exploration has received global attention. Photocatalytic valorization of biomass into fuels and chemicals is a promising and sustainable method for future chemical production. Photocatalysis has the potential to accomplish reactions under ambient conditions due to the unique reaction mechanisms involving photoinduced charge carriers and has recently been recognized as an efficient and feasible technology for biomass conversion. Biomass is widely used as sacrificial agent to scavenge holes in photocatalytic hydrogen evolution, and the carbon is eventually degraded to CO2 with a minor amount of CO. The generation of CO instead of CO2 is more economical and promising but also a challenge under photoreforming conditions.This is a new research direction, while until now there has still been the lack of a comprehensive review article to summarize and provide prospects for this topic. This Account will highlight our contributions in the research direction of the photocatalytic reforming of biomass into syngas (CO + H2). In 2020, we first reported the photocatalytic conversion of biopolyols and sugars into syngas by employing a defect-rich Cu-TiO2 nanorod photocatalyst and found that formic acid is a key intermediate to CO. Further study revealed that a facet-dependent electron-trapping state on anatase TiO2 will affect the photocatalytic dehydration activity for formic acid intermediates by regulating the electron transfer process during the reaction, and the selective generation of FA or CO from photocatalytic biomass reforming was achieved via exposing the (100) or (101) facets, respectively. Visible light-driven syngas generation was further achieved over a CdS-based photocatalyst. Sulfate modification of CdS ([SO4]/CdS) was constructed as the proton acceptor, thus efficiently facilitating the proton-coupled electron transfer process. Besides, we put forward an oxygen-controlled strategy to increase the CO generation rate without a significant decrease in CO selectivity via controlling the O2/substrate ratio. Based on this system, a Z-scheme CdS@g-C3N4 core-shell structure and CdO-CdS semicoherent interface were created to facilitate charge transfer and enhance the O2 activation, thus increasing the CO generation rate. Moreover, we also developed a photoelectrochemical approach to separately produce CO and H2 from biomass. Nitrogen doping of a hexagonal WO3 nanowire array was used to produce the photoanode. The built-in electric field generated via nitrogen doping promoted charge transfer, hence improving the efficiency of PEC reforming of biopolyols and sugars. This Account will systematically analyze the challenges in this research direction, the reaction route in the photocatalytic biomass reforming, and the factors affecting CO selectivity and give insight into the design of efficient photocatalytic systems.

Bimetal-organic layer-derived ultrathin lateral heterojunction with continuous semi-coherent interfaces for boosting photocatalytic CO2 reduction

Current heterojunction photocatalysts suffer from sluggish charge transfer due to the discontinuous interfaces at an atomic level. Herein, we report a NiO–Co3O4 ultrathin lateral heterojunction using NiCo-based bimetal–organic layers as precursors. The atomic-resolution images display a unique continuous semi-coherent interface between NiO and Co3O4. The experimental results confirm that the continuous semi-coherent interfaces effectively expedite the electron transfer from NiO to Co3O4. Concomitantly, the electron transfer raises d-band center of Co3O4 in NiO–Co3O4 toward Fermi level, as revealed by the density functional theory calculations. As a result, the *COOH intermediate can be strongly bound on cobalt reactive centers. The successful modulation of charge transfer and intermediate binding by continuous semi-coherent interfaces leads to a remarkable gas yield of 22.67 mmol h−1 from photocatalytic CO2 reduction over NiO–Co3O4. This work highlights the crucial roles of interface engineering in regulating carrier kinetics and surface reactions.

Hydrogen Embrittlement and its Prevention in 7XXX Aluminum Alloys with High Zn Concentrations

7xxx aluminum alloys are representative high-strength aluminum alloys; however, mechanical property degradation due to hydrogen hinders further strengthening. We have previously reported that hydrogen embrittlement in 7xxx alloys originates from trapped hydrogen at the MgZn2 precipitate interface, providing high hydrogen trapping energy. We propose the dispersion of Mn-based second-phase particles as a novel technique for preventing 7xxx aluminum alloy hydrogen embrittlement. In this study, the deformation and fracture behaviors of high hydrogen 7xxx alloys containing 0.0% Mn and 0.6% Mn are observed in situ using synchrotron radiation x-ray tomography. Although no significant differences appear between the two alloys regarding the initiation of quasicleavage cracks, the area fractions of final quasicleavage fractures are 16.5% and 1.0% for 0.0% Mn and 0.6% Mn alloys, respectively; this finding indicates that Mn addition reduces hydrogen-induced fractures. The obtained macroscopic hydrogen embrittlement is quantitatively analyzed based on hydrogen partitioning in alloys. Adding 0.6% Mn, generating second-phase particles with high hydrogen trapping abilities, significantly suppresses hydrogen-induced quasicleavage fracture. The results of an original hydrogen partitioning analysis show that the dispersion of Mn-based particles (Al12Mn3Si) with high hydrogen trapping abilities reduces the hydrogen concentration at the semicoherent MgZn2 interface and suppresses hydrogen embrittlement.

Vacuum brazing TiAl intermetallic to K4169 alloy using amorphous filler metals Ti56.25–xZrxNi25Cu18.75

A series of Ti56.25–xZrxNi25Cu18.75 (x = 0–25, at.%) filler metals were designed based on a cluster-plus-glue-atom model to vacuum braze TiAl intermetallic to K4169 alloy. The impact of Zr content on the interfacial microstructure and shear strength of joints was examined. And the relationship between the interfacial lattice structure and the fracture behavior of the joint was investigated. The findings reveal a sectionalized characteristic with three reaction zones (Zone I, Zone II and Zone III) in the microstructure of the TiAl intermetallic to K4169 alloy joint. As the Zr content in filler metals increased, the diffusion of Ti transitioned from long-distance to short-distance in Zone I, changing the initial composition from TiNi3/TiNi/NiNb/(Cr, Fe, Ni)SS to NiCrFe/(Cr, Fe, Ni)SS/TiNi. In Zone II, the initial composition altered from TiNi3/TiNi to TiNi/Ti2Ni/TiNi3/TiCu/TiNi. The interface between Zones II and III altered from a non-coherent and semi-coherent interface of TiNi/TiAl/Ti3Al with significant residual stress to a semi-coherent interface of TiNi/TiNi3/TiAl2/Ti3Al with a gradient distribution. The shear strength of the joint initially decreased and then increased. When the Zr content of filler metal was 25 at.%, the shear strength of the joint reached 288 MPa. The crack initiation position changed from non-coherent TiNi/TiAl interface with high angle grain boundaries (HAGBs) and lattice mismatch of 65.86 at.% to a semi-coherent Ti3Al/TiAl2 interface with a lattice mismatch of 20.07 at.% when the Zr content increased. The brittle fracture was present on the fracture surfaces of all brazed joints.

Vacancies-mediated atomic diffusion controlled by the interfacial structure of FCC/BCC HEA multilayers

The radiation-induced segregation is one of the major concerns for nuclear materials, as it can damage the service performance of the material. Eutectic high entropy alloy (HEA) multilayer is considered a potential nuclear material for improving the irradiation tolerance of materials, due to its outstanding irradiation tolerance and mechanical properties. Abundant heterogeneous interfaces in eutectic HEA multilayer can interact with irradiation-induced vacancies, thus resulting in changes in the behavior of atomic diffusion and segregation. In the current work, to explore the effects of the heterogeneous interfacial structure on atomic diffusion and segregation, we have investigated the evolution of the elemental distribution in FCC/BCC HEA multilayers with coherent and semicoherent interfaces under vacancy flow in detail. It is found that the segregation and atomic diffusion behaviors of eutectic HEA multilayer are sensitive to the heterogeneous interfacial structure. The semicoherent interface promotes the interface diffusion and interface segregation due to the vacancy annihilation at interface and the intrinsic excess volume of interface. Whereas, the coherent interface is benifcial to the intragranular diffusion because it is transparent for the diffusion of vacancy.

Effects of dispersoid preforming via multistep sintering of oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy

• A newly designed ODS manufacturing process, multi-step sintering process, consisting of a dispersoid preforming heat treatment followed by sintering to achieve the dispersoid refinement in HEA matrix was suggested. • An atypical form of Y 2 O 3 , FCC-Y 2 O 3 , formed adjacent to the dislocation inside the matrix grain during the dispersoid preforming heat treatment of multi-step sintering process with a cube-on-cube orientation relationship with the matrix. • The FCC-Y 2 O 3 formed in the multi-step sintered bulk acts as an effective obstacle to grain boundary and dislocation movement resulting in a microstructure refinement and the increment of mechanical strength. • In the bulk prepared by the conventional ODS manufacturing process, coarsened dispersoids consisting of a complex structured oxide with BCC-Y 2 O 3 as the core were predominantly formed along the grain boundary. • Cr-C-O region with a crystal structure of Cr 23 C 6 formed in the HEA matrix serves as an oxygen-supplying reservoir for dispersoids, promoting coarsening of the dispersoids. Dispersoid formation and microstructural evolution in an oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy (HEA) using a newly designed multistep sintering process are investigated. The proposed multistep sintering consists of a dispersoid preforming heat treatment of as-milled 0.1wt% Y 2 O 3 -CoCrFeMnNi high-entropy alloy powders at 800°C, followed by sintering at 800–1000°C under uniaxial pressure. In the conventional single-step sintered bulk, the coarsened BCC Y 2 O 3 dispersoids mainly form with an incoherent interface with the HEA matrix. In contrast, finer FCC Y 2 O 3 dispersoids, an atypical form of Y 2 O 3 , are formed in the matrix region after multistep sintering. Nucleation of FCC Y 2 O 3 dispersoids is initiated on the favorable facet, the {111} plane of the austenitic matrix, with the formation of a semi-coherent interface with the matrix during the dispersoid preforming heat treatment and it maintains its refined size even after sintering. It is found that dispersoid preforming prior to sintering appears promising to control the finer dispersoid formation and refined grain structure.

Engineering semicoherent interface with O–Fe–Se coordination for boosting the capacity and rate capability of a battery-type supercapacitor anode

The low capacity and rate capability of the battery-type supercapacitor anode prevent its widespread application. In this paper, we construct a semicoherent heterojunction of Fe2O3/FeSe2 as an advanced battery-type supercapacitor anode to overcome the bottleneck. A series of characterization and first-principles calculations confirm that the special heterointerface manipulation automatically generates a stronger inherent electric field, thereby enhancing the electron transport rate and the OH− adsorption capacity. In addition, it facilitates additional redox reactions between the active materials and OH− and makes the reaction system easier to execute. Taking advantage of these benefits, the prepared anode has a high specific capacity of 199.2 mA h g−1 (1 A g−1) and retains 90.2% of its initial capacity after 5000 cycles at 105.8 mA h g−1 (10 A g−1). In addition, an asymmetric supercapacitor device is fabricated with the prepared Fe2O3/FeSe2 as the anode, which provides a maximum energy density of 52.55 W h kg−1 at 0.8 kW kg−1 and a capacity retention of 91.2% even after 15,000 cycles. In our work, a novel strategy for the optimal design of a battery-type supercapacitor anode with a large capacity and superior rate capability is conceived, significantly advancing the widespread application of transition metal compounds in energy storage systems.

Achieving grain refinement of α-Al and Si modification simultaneously by La‒B‒Sr addition in Al‒10Si alloys

As-cast Al‒Si alloys always face low ductility because of coarse α-Al grains and large lamellar eutectic Si. Although B-containing refiners and Sr modifiers could refine the α-Al grains and eutectic Si respectively, simultaneous addition leads to an invalid effect of Sr because B-containing refiner has a poisoning effect (PE) on Sr modifier in the Al‒10Si‒B‒Sr alloys. The present work achieves both refinement of α-Al grains and modification of Si merely by the addition of 500 ppm La in Al‒10Si‒0.02B‒0.015Sr alloy, which greatly enhances the ductility and tensile strength. Sr‒B interaction in the Al‒10Si‒0.02B‒0.015Sr melt results in a consumption of Sr by forming Sr‒B intermetallic compound. CALPHAD-type calculations reveal that Sr concentration in liquid before eutectic reaction becomes a key parameter to estimate the alloying modification effect. The addition of La forms LaB6 and thereby releases Sr to protect the Sr modification effect. First-principles calculations illustrate that both Sr and La are beneficial to the formation of twin boundaries in Si particles due to their negative formation energy of twin boundaries. The formed LaB6 has a semicoherent interface with α-Al with the orientation relationship of [11¯0]LaB6//[11¯0]Al and (11¯1)LaB6//(11¯1)Al, demonstrating that LaB6 is an efficient nucleation site for α-Al, which contributes to the refinement of α-Al in the Al‒10Si‒0.05La‒0.02B‒0.015Sr alloy. Our findings reveal the micro-mechanism of refinement during the solidification process and develop an effective and simple way to obtain high-performance Al alloys.