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Continuous cooling transformation diagrams in synthetic weld heat-affected zone (SH-CCT diagrams) show the phase transition temperature and hardness at different cooling rates, which is an important basis for formulating the welding process or predicting the performance of welding heat-affected zone. However, the experimental determination of SH-CCT diagrams is a time-consuming and costly process, which does not conform to the development trend of new materials. In addition, the prediction of SH-CCT diagrams using metallurgical models remains a challenge due to the complexity of alloying elements and welding processes. So, in this study, a hybrid machine learning model consisting of multilayer perceptron classifier, k-Nearest Neighbors and random forest is established to predict the phase transformation temperature and hardness of low alloy steel using chemical composition and cooling rate. Then the SH-CCT diagrams of 6 kinds of steels are calculated by the hybrid machine learning model. The results show that the accuracy of the classification model is up to 100%, the predicted values of the regression models are in good agreement with the experimental results, with high correlation coefficient and low error value. Moreover, the mathematical expressions of hardness in welding heat-affected zone of low alloy steel are calculated by symbolic regression, which can quantitatively express the relationship between alloy composition, cooling time and hardness. This study demonstrates the great potential of the material informatics in the field of welding technology.

The ultrahigh electrostrain and piezoelectric constant (d33) in relaxor piezoelectric PMN-30PT single crystals are closely related to the coexistence and transition of multiple phases at the morphotropic phase boundary (MPB). However, the key mechanisms underlying the stability of the phases and their transitions are yet to be fully understood. In this work, we undertake a systematic study of the influences of phase transitions on the electrostrictive and piezoelectric behaviors in ⟨001⟩-, ⟨011⟩-, and ⟨111⟩-oriented PMN-30PT single crystals. We first classify the various phase transitions within the quasi-MPB in electric field-temperature phase diagrams as either dominated by the electric field or by temperature. We find that the electrostrain reaches a maximum at each phase transition, especially in the electric-field-dominated transitions, whereas d33 only peaks at specific phase transitions. In particular, the electrostrain in the ⟨001⟩ crystal reaches a maximum of S = 0.52% at 55 °C under an external electric field with E = 15 kV/cm, primarily due to a joint contribution of the electric field-dominated rhombohedral-monoclinic and monoclinic-tetragonal phase transitions at the quasi-MPB. An ultrahigh d33 (∼2460 pC/N) only occurs at the rhombohedral-monoclinic phase transition in the ⟨001⟩ crystal and at the rhombohedral-orthorhombic transition in the ⟨011⟩ crystal (d33 ∼ 1500 pC/N) due to the lower energy barriers. The temperature-dominated phase transitions also contribute toward minor peaks in electrostrain and/or d33. This work provides a deeper and quantitative understanding of the microscopic mechanisms underlying electrostrictive and piezoelectric behaviors relevant for the design of high-performance materials.

As a close relative of ferroelectricity, antiferroelectricity has received a recent resurgence of interest driven by technological aspirations in energy-efficient applications, such as energy storage capacitors, solid-state cooling devices, explosive energy conversion, and displacement transducers. Though prolonged efforts in this area have led to certain progress and the discovery of more than 100 antiferroelectric materials over the last 70 years, some scientific and technological issues remain unresolved. Herein, we provide perspectives on the development of antiferroelectrics for energy storage and conversion applications, as well as a comprehensive understanding of the structural origin of antiferroelectricity and field-induced phase transitions, followed by design strategies for new lead-free antiferroelectrics. We also envision unprecedented challenges in the development of promising antiferroelectric materials that bridge materials design and real applications. Future research in these directions will open up new possibilities in resolving the mystery of antiferroelectricity, provide opportunities for comprehending structure-property correlation and developing antiferroelectric/ferroelectric theories, and suggest an approach to the manipulation of phase transitions for real-world applications.

High-entropy alloys (HEAs) open up a new horizon for discovering un-explored mechanical properties and deformation mechanisms. Local chemical fluctuations (LCFs) in HEAs were found to have significant influences on their mechanical performance, however, the underlying origins remain unclear. In this work, direct dynamic observation of the interaction between LCFs and dislocations was captured by in situ transmission electron microscopy in a ductile body-centered-cubic (BCC) HfNbTiZr HEA under loading. The observed dislocation pinning induced by LCFs contributes to the increment not only in the strength but also in the ductility due to strongly promoted dislocation interaction. The observed local double cross-slips caused by the LCFs distribute dislocations onto various atomic planes homogenously, which is also beneficial for ductilization in HfNbTiZr. Our findings not only shed light on the understanding of deformation mechanisms of HEAs, but also provide a new perspective to design ductile BCC HEAs.

ZrO2/TiO2 composites with an ink-bottle mesoporous structure were synthesized by a mild solvothermal method without high-temperature calcination. Many caves in this ink-bottle structure can adsorb organic groups, making them suitable for catalytic materials. The effects of ZrO2 additions and particle size on the morphology and catalytic performance of composite powders were investigated. Comparative experiments on changing the particle size and the content of ZrO2 show that the TiO2-10 wt% ZrO2 composite has outstanding photocatalytic performance under simulated sunlight, especially when the particle size of as-prepared ZrO2 is on the submicron scale. By mixing two different n-type semiconductors of ZrO2 and TiO2, a new heterostructure is formed to hinder the autonomous recombination of excited electron-hole pairs, improving photocatalytic activity.

Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity. To mitigate these issues, free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites (Si/C-ZIF-8/CNFs) are designed and synthesized by electrospinning and carbonization methods, which present greatly enhanced electrochemical properties for lithium-ion battery anodes. This particular structure alleviates the volume variation, promotes the formation of stable solid electrolyte interphase (SEI) film, and improves the electrical conductivity. As a result, the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mA h g−1 at 0.2 A g−1 with a capacity retention of 64% for 150 cycles, and exhibits a reversible capacity of 538.6 mA h g−1 at 0.5 A g−1 over 500 cycles. Moreover, the full cell composed of a free-standing Si/C-ZIF-8/CNFs anode and commercial LiNi1/3Co1/3Mn1/3O2 (NCM) cathode shows a capacity of 63.4 mA h g−1 after 100 cycles at 0.2 C, which corresponds to a capacity retention of 60%. This rational design could provide a new path for the development of high-performance Si-based anodes.

The stems of living trees in upland forests might contribute to the global methane (CH4) source, but the contribution is poorly understood. We investigated CH4 concentration in the heartwood of living trees in dominant upland forests using field campaign and subsequently evaluated the importance of stem CH4 emission in the context of the global total. We found that only 0%, 9.8%, and 1.8% of stems of living trees had substantial CH4 concentration in heartwood of ≥ 10,000 μL L–1 in the boreal, temperate, and tropical and subtropical upland forests investigated, respectively. CH4 concentration in heartwood depended mainly upon tree species and subsequently soil moisture. Relationships fitted indicate that CH4 concentration followed a power function with respect to water content in heartwood, whereas nitrous oxide (N2O) or carbon dioxide (CO2) concentration linearly increased with water content in heartwood. Stem CH4 emission was estimated at approximately 0.2–2 Tg yr–1 globally, corresponding to less than 0.4% of the global total including all natural plus anthropogenic sources. Water content in heartwood is positively associated with soil water content. Soil water content rarely exceeds 40% v/v in upland forests, indicating stem CH4 emission occurs mainly in the areas of low-lying upland forests with occasionally moist soils. More attentions should be paid on low-lying upland forests and forested wetlands in future when stem CH4 emission needs to be estimated in all forests.

Hydrogen embrittlement (HE) substantially deteriorates the mechanical properties of metals. The HE behavior of nanograined (NG) materials with a high fraction of grain boundaries (GBs) may significantly differ from those of their coarse-grained counterparts. Herein, molecular dynamics (MD) simulations were performed to investigate the HE behavior and mechanism of NG α-Fe under creep loading. The effects of temperature, sustained stress, and grain size on the creep mechanism was examined based on the Mukherjee-Bird-Dorn (MBD) equation. The deformation mechanisms were found to be highly dependent on temperature, applied stress, and grain size. Hydrogen charging was found to have an inhibitory effect on the GB-related deformation mechanism. As the grain size increased, the HE mechanism transitioned from H-induced inhibition of GB-related deformation to H-enhanced GB decohesion. The current results might provide theoretical guidance for designing NG structural materials with low HE sensitivity and better mechanical performance.

In this letter, we briefly summarize experimental and theoretical findings of formation and characterization of short-range orderings (SROs) as well as their effects on the deformation behavior of high-entropy alloys (HEAs). We show that existence of SROs is a common yet key structural feature of HEAs, and tuning the degree of SROs is an effective way for optimizing mechanical properties of HEAs. In additional, the challenges concerning about formation mechanism and characterization of SROs in HEAs are discussed, and future research activities in this regard are also proposed.

Continuous exploration of high-temperature structural materials is being driven by the needs of gas-turbine engines capable of withstanding the high-temperature environment. Relatively low melting points of currently applied superalloys restrain the further improvement of service temperatures. With higher melting temperatures above 2000 °C, Mo-Si-B alloys are regarded as a new generation of ultrahigh-temperature structural materials. However, oxidation is a concern for the industrial application of Mo-Si-B alloys. Therefore, an in-depth understanding of the oxidation mechanisms may contribute to solving this issue, whereas relevant reviews about their recent advances are lacking. In the current work, a comprehensively systematic review about the oxidation behaviors of Mo-Si-B alloys is described for this purpose.

Nanograined materials have much denser grain boundary (GB) networks than their coarse-grained counterparts, thereby the hydrogen (H) diffusion and trapping behaviors in nanograined materials, which are strongly influenced by GBs, may differ greatly from those in coarse-grained materials. In the present research, the grain-size dependent hydrogen diffusion coefficient in nanograined Fe is studied by theoretical analysis and molecular dynamics (MD) simulations. A theoretical model based on thermodynamics is developed. The GB-related material parameters required by the model are then obtained by fitting the MD simulation results. Finally, the grain-size dependent diffusion coefficients are compared with model predictions to evaluate the validity of the model. It is found that the trapping effect of triple junctions that usually ignored in coarse-grained materials becomes increasing important as grain size and temperature decrease. Due to the strong trapping effect of GBs in nanograined Fe, H diffusion is slowed down by the GBs.

All-solid-state sodium-ion batteries that utilize inorganic superionic conductors show great potential in energy storage applications. However, suitable Na superionic conductors with desirable high ionic conductivities and cross-linked diffusion networks are still in their infancy. In this work, we systematically studied the structural stabilities and Na ion transport mechanisms of the halide-based Na superionic conductors with different phase structures using first-principle calculations and data mining techniques. The iodide-based Na3YI6 with C2/m, Pm1, and P1c space groups possess fcc and hcp anion sublattices with stable octahedral Na occupations, differing from the reported fast-ion transport mechanism in the sulfide bcc anion ones with tetrahedral Na occupations. The Oct–Tet–Oct diffusion pathway and Na-site weighted phonon vibrational frequencies play crucial roles in the synergistic Na-ion transport capabilities, leading to Na ionic conductivities of 0.35, 0.18, and 9.1 × 10−3 mS cm−1 at room temperature and corresponding activation energies of 315.5, 351.1, and 454.0 meV for C2/m-Na3YI6, Pm1-Na3YI6, and P1c-Na3YI6, respectively. Restricted by the decisive diffusion triangle, P1c-Na3YI6 shows deficient Na-kinetic performance with one-dimensional blocked ion transport channels. The phase-structure-dependent ion transport networks involving Oct–Tet and Oct–Oct pathways broaden the diffusion channels and provide rational guidance for the experimental design of halide-based Na superionic conductors.

Antiferroelectric materials are proposed as a potential solution to achieve multi-state memories, but the fundamental physical mechanism underlying the memory effect still needs to be clarified. Here, we study the memory effect in a typical antiferroelectric ceramic of Pb0.99Nb0.02[(Zr0.6Sn0.4)0.95Ti0.05]0.98O3 by systematically analyzing various hysteresis loops of polarization intensity and current density vs. electric field, where the kinetic behaviors are concerned about for the first time. The parallel pre-poling electric field reduces the critical electric field of antiferroelectric-ferroelectric phase transition, while the antiparallel field increases it. The memory behavior is significantly enhanced with the increasing of pre-poling time, but exhibits a remarkable weakening with the relaxation time increasing. It is a combined effect of electric-field-induced preferentially oriented antiferroelectric domains and internal bias electric field. This work not only improves comprehending in memory effect in antiferroelectric materials, but also enlightens the deeper understanding of other physical properties related to field-induced phase transitions.

Due to the lack of plastic strain accommodation and work-hardening capability, brittleness still dominates dynamic deformation in most bulk metallic glass composites (BMGCs). Herein, we present a series of Zr-based BMGCs characterized with a unique combination of fracture strain of ~15%, ultimate strength of ~1550 MPa and unusual two-stage work-hardening behavior upon dynamic loading. The strain-induced martensitic transformation occurred, not only homogenizes the dynamic plastic flow, but also compensates the amorphous work-softening. Our work highlights a novel route for developing high-performance BMGCs for high-speed applications, and sheds new insights on the deformation mechanisms of BMGCs.

We introduce and adopt the concept of a phenomenological parameter, microstructure entropy, S*, to understand the yield strength in alloy systems with bimodal grain size distribution obtained from large sets of experimental data. 60 groups of bimodal grain size distribution data was obtained through the application of an ingenious concept involving severe cold deformation to obtain dislocation cell-type of martensite, followed by annealing when martensite reverts to austenite by shear or diffusion mechanism, with the aim to obtain ultrafine grain size. Six factors emerged from statistical data analysis through EBSD studies in terms of grain size and grain numbers from 60 sets of data. Microstructure entropy (S*) was obtained from the bimodal structure data in a self-similar regime. Inverse of the square root of microstructure entropy ( 1 S * ) and yield strength exhibited a linear relationship. The proposed conceptual methodology has wide acceptance for any grain size distribution to obtain microstructure entropy (S*) of a specific grain structure and predict yield strength. A generic equation similar to Hall-Petch relationship, but involving microstructure entropy is proposed to predict and understand yield strength of metallic systems characterized by grain size distribution or microstructural evolution.

Summary Understanding and controlling pressure-related structural transformations, which can be utilized to tune functional and mechanical properties of materials, is one of the most important research themes in materials science. However, the underlying mechanism governing pressure-driven phase transformations in high-entropy alloys (HEAs) remains poorly understood. By combining an in situ high-energy X-ray diffraction (XRD) technique and ab initio calculations, we reveal that the face-center-cubic (fcc) phase, rather than the hexagonal-close-packed (hcp) phase, is thermodynamically stable in the MoxCrFeCoNi HEA system under atmospheric conditions. However, a fcc to hcp transformation was identified under pressure, resulting from a pressure-induced electronic redistribution. Remarkably, the valence electron concentration has been further demonstrated as a critical factor for regulating this transformation, the reduction of which by Mo doping can encourage the hcp transformation. Our studies provide new insights into the physical processes underlying the allotropic transformation that enables customized alloy design of high-performance HEAs.

A new kind of WO3-coated TiO2 heterostructure with higher photocatalytic activity was prepared via a novel two-step alcohothermal synthesis process. The effects of the WO3 addition on the TiO2/WO3 products were systematically studied, including analysis of the phases, observation of the morphologies and calculation of the band gaps. Under illumination, the conduction band electrons of TiO2 are excited and accompanied by the generation of positive holes. In this heterostructure, the conduction band electrons of WO3 occupy the nearest valence band of TiO2 and then combine with the internal holes, inhibiting the flow of the electrons transferred from the conduction band of TiO2. Compared with anatase TiO2, the WO3-coated TiO2 heterostructure (weight ratio of WO3:TiO2 = 1:2) with a finer grain size exhibits excellent photocatalytic performance.

Lithium (Li) metal with high theoretical capacity and low electrochemical potential is the most ideal anode for next-generation high-energy batteries. However, the practical implementation of Li anode has been hindered by dendritic growth and volume expansion during cycling, which results in low Coulombic efficiency (CE), short lifespan, and safety hazards. Here, we report a highly stable and dendrite-free Li metal anode by utilizing N-doped hollow porous bowl-like hard carbon/reduced graphene nanosheets (CB@rGO) hybrids as three-dimensional (3D) conductive and lithiophilic scaffold host. The lithiophilic carbon bowl (CB) mainly works as excellent guides during the Li plating process, whereas the rGO layer with high conductivity and mechanical stability maintains the integrity of the composite by confining the volume change in long-range order during cycling. Moreover, the local current density can be reduced due to the 3D conductive framework. Therefore, CB@rGO presents a low lithium metal nucleation overpotential of 18 mV, high CE of 98%, and stable cycling without obvious voltage fluctuation for over 600 cycles at a current density of 1 mA·cm−2. Our study not only provides a good CB@rGO host and pre-Lithiated CB@rGO composite anode electrode, but also brings a new strategy of designing 3D electrodes for those active materials suffering from severe volume expansion.

Superelasticity associated with martensitic transformation has found a broad range of engineering applications, such as in low-temperature devices in the aerospace industry. Nevertheless, the narrow working temperature range and strong temperature sensitivity of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. Here, we scrutinized the phase transformation behavior and mechanical properties of multicomponent B2-structured intermetallic compounds. Strikingly, the (TiZrHfCuNi)