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The twin boundaries and inherent lattice strain of five-fold twin (5-FT) structures offer a promising and innovative approach to tune nanocrystal configurations and properties, enriching nanomaterial performance. However, a comprehensive understanding of the nonclassical growth models governing 5-FT nanocrystals remains elusive, largely due to the constraints of their small thermodynamically stable size and complex twin configurations. Here, we conducted in situ investigations to elucidate the atomic-scale mechanisms driving size-dependent and twin configuration-related aggregation phenomena between 5-FT and other nanoparticles at the atomic scale. Our results reveal that surface diffusion significantly shapes the morphology of aggregated nanoparticles, promoting the symmetrical formation of 5-FT, especially in smaller nanoparticles. Moreover, the inherent structural characteristics of 5-FT mitigate the dominance of surface diffusion in its morphological evolution, retarding the aggregation evolution process and fostering intricate twin structures. These findings contribute to advancing our capacity to manipulate the configuration of twinned particles, enabling more predictable synthesis of functional nanomaterials for advanced engineering applications. The mechanisms underlying the nonclassical growth of penta-twinned gold nanocrystals remain unclear. Here, the authors elucidate the atomic-level processes that drive size-dependent and twin configuration-related aggregation phenomena. [ABSTRACT FROM AUTHOR]

The α variant selection and microstructure evolution in a new metastable β titanium alloy TB17 were studied in depth by DTA, microhardness, XRD, SEM, and EBSD characterization methods. Under the rapid cooling rate conditions (150 °C/min–400 °C/min), only a very small amount of granular αWM (α Widmanstatten precipitates within the grains) precipitated within the grains. The secondary α phase precipitated in the alloy changed from granular to fine needle-like at moderate cooling rates (15 °C/min–20 °C/min). When continuing to slow down the cooling rates (10 °C/min and 1 °C/min), the αGB (α precipitates along the β grain boundaries), αWGB (α Widmanstatten precipitates that developed from β grain boundaries or αGB) and αWM grew rapidly. Moreover, the continuous cooling transformation (CCT) diagram illustrated the effect of cooling rate on the β/α phase transition. EBSD analysis revealed that the variants selection of α near the original β grain boundary is mainly divided into three categories. (i) The double-BOR (Burgers orientation relationship) αWGB colonies within neighboring β grains grow in different directions but have the same crystallographic orientation. (ii) The double-BOR αWGB colonies within neighboring β grains have different growth directions and different crystallographic orientations. (iii) The double-BOR αWGB colonies within the same grain have the same growth direction, but different crystallographic directions. And these double-BOR αWGB colonies correspond to two variants of the given {0001}α//{110}β. [ABSTRACT FROM AUTHOR]

Given the highly temperature-sensitive nature of the polymorphic phase boundaries, attaining excellent piezoelectric coefficient with superior temperature stability in lead-free piezoceramics via direct compositional design remains a formidable challenge. We demonstrate the synergistic improvement of piezoelectric coefficient and thermal stability in lead-free piezoceramics via atomic-scale local ferroelectric structure design. Via modulation of the local Landau energy barrier at doping sites, we effectively mitigate fluctuations in piezoelectric d33. Our approach achieves an impressive d33 of ~430 pC/N with a minimal temperature fluctuation range (△d33 ~ 7%) across the room temperature to 100 °C in potassium sodium niobate ceramics. Further optimization through annealing extends this temperature up to 150 °C (△d33 ~ 8%) while maintaining a high d33 of ~380 pC/N, rivaling the performance of classic temperature stable lead zirconate titanate. This work establishes a framework for addressing the dilemma between high piezoelectric coefficient and inadequate temperature stability in lead-free piezoceramics. The authors reveal that the incorporation of doping elements with varying electronic structures and ionic radii alters the atomic-scale configuration, thereby affecting the local energy barrier associated with polarization rotation. [ABSTRACT FROM AUTHOR]

Directed energy deposition (DED) provides the possibility of high-throughput synthesis by controlling the multi-channel powder feeders. However, the compositional accuracy of the targeted alloy is of concern due to the difficulty of adjusting the proportions. In this work, we present a method to improve the adjustment accuracy of the high-throughput DED technology by replacing the elemental powder with pre-alloyed powder, and binary Al–Mn alloys with different compositions were synthesized with a composition step of 1 wt.%. The effect of Mn content on the microstructure and mechanical properties of the alloys was characterized and analyzed, and the relationship between the Al6Mn phase and the yield strength was established. The results showed that the microstructures of DED-ed Al–Mn alloys are composed of Al and Al6Mn phases with Mn contents in the range of 2–10 wt.%. The Al–Mn alloy reaches a tensile strength of 165 MPa and maintains an elongation of 9% at Mn content of 4 wt.%. The improved controlling accuracy of composition step to 1 wt.% by pre-alloyed powder in this work provides a paradigm for high-throughput discovery of high-performance alloys. [ABSTRACT FROM AUTHOR]

N and Ti co-doped Fe45Mn35Co10Cr10 alloys were prepared by Laser-Directed Energy Deposition (L-DED). We find that precipitate reinforcement of TiN particles introduced by harnessing N solid solution can result in a microstructure featuring attached MnO and TiN composite nanoparticles. Co-doped samples exhibit a notable 69% increase in yield strength compared with that of the free-doped, rising from 310 MPa to 533 MPa, maintaining 44.5% elongation. Even at 77 K, the co-doped alloy displays ultra-high strength, approximately 1400 MPa. These findings on metastable high entropy alloys through additive manufacturing open new avenues for their application in various fields. [ABSTRACT FROM AUTHOR]

Three types of solution treatment and aging were designed to reveal the α' decomposition and its effect on the mechanical properties of near-α Ti-80 alloy, as follows: solution at 970 °C then quenching (ST), ST + aging at 600 °C for 5 h (STA-1), and ST + aging 600 °C for 24 h (STA-2). The results show that the microstructures of the ST samples were mainly composed of equiaxed αp and acicular α', with a large number of dislocations confirmed by the KAM results. After subsequent aging for 5 h, α' decomposed into acicular fine αs and nano-β (intergranular β, intragranular β) in the STA-1 specimen, which obstructed dislocation motion during deformation, resulting in the STA-1 specimen exhibiting the most excellent yield strength (1012 MPa) and maintaining sufficient elongation (8.1%) compared with the ST (898 MPa) and STA-2 (871 MPa) samples. By further extending the aging time to 24 h, the size of acicular αs and nano-β gradually increased while the density of dislocations decreased, which resulted in a decrease in strength and an increase in plasticity. Based on this, a microstructures–properties correlation model was proposed. This study provides a new method for strength–plasticity matching of near-α titanium alloys through α' decomposition to acicular αs+nano-β. [ABSTRACT FROM AUTHOR]

Carbon‐free aluminum electrolysis is crucial for achieving the low‐carbon development and carbon neutrality in the future aluminum industry. NiFe2O4‐based cermet is the potential candidate of inert anode, benefiting from the satisfactory corrosion resistance and high‐temperature conductivity. Herein, complex‐shaped 25(Cu–20Ni)/(NiFe2O4–10NiO) cermets were fabricated via a plastic shaping method using the polyformaldehyde (POM)‐based granular feedstock. The feedstock showed uniform microstructure with evenly dispersed powders wrapped in polymers, which exhibited shear‐thinning behavior during molding. Roles of the feedstock with different powder loadings in the morphology and bending strength of the cermets were investigated. High‐precision gear parts exhibited no deformation, a high relative density over 98%. Investigation of different powder loadings revealed that parts prepared with a 56 vol% loading demonstrate the excellent performance, and possessed an impressive flexural strength of 178.4 MPa. This achievement provided a foundation for the future utilization of complex‐shaped inert anode material components in industrial applications. [ABSTRACT FROM AUTHOR]

"Perovskite/carbon" interface is a bottle‐neck for hole‐conductor‐free, carbon‐electrode basing perovskite solar cells due to the energy mismatch and concentrated defects. In this article, in‐situ healing strategy is proposed by doping octylammonium iodide into carbon paste that used to prepare carbon‐electrode on perovskite layer. This strategy is found to strengthen interfacial contact and reduce interfacial defects on one hand, and slightly elevate the work function of the carbon‐electrode on other hand. Due to this effect, charge extraction is accelerated, while recombination is obviously reduced. Accordingly, power conversion efficiency of the hole‐conductor‐free, planar perovskite solar cells is upgraded by ≈50%, or from 11.65 (± 1.59) % to 17.97 (± 0.32) % (AM1.5G, 100 mW cm−2). The optimized device shows efficiency of 19.42% and open‐circuit voltage of 1.11 V. Meanwhile, moisture‐stability is tested by keeping the unsealed devices in closed chamber with relative humidity of 85%. The "in‐situ healing" strategy helps to obtain T80 time of >450 h for the carbon‐electrode basing devices, which is four times of the reference ones. Thus, a kind of "internal encapsulation effect" has also been reached. The "in situ healing" strategy facilitates the fabrication of efficient and stable hole‐conductor‐free devices basing on carbon‐electrode. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium‐ion batteries (LIBs). Na3V2(PO4)2F3 (NVPF) as a common cathode of SIBs, features the merits of high operating voltage, small volume change and favorable specific energy density. However, it suffers from poor cycling stability and rate performance induced by its low intrinsic conductivity. Herein, we propose an ingenious strategy targeting superior SIBs through cross‐linked NVPF with multi‐dimensional nanocarbon frameworks composed of amorphous carbon and carbon nanotubes (NVPF@C@CNTs). This rational design ensures favorable particle size for shortened sodium ion transmission pathway as well as improved electronic transfer network, thus leading to enhanced charge transfer kinetics and superior cycling stability. Benefited from this unique structure, significantly improved electrochemical properties are obtained, including high specific capacity (126.9 mAh g−1 at 1 C, 1 C = 128 mA g−1) and remarkably improved long‐term cycling stability with 93.9% capacity retention after 1000 cycles at 20 C. The energy density of 286.8 Wh kg−1 can be reached for full cells with hard carbon as anode (NVPF@C@CNTs//HC). Additionally, the electrochemical performance of the full cell at high temperature is also investigated (95.3 mAh g−1 after 100 cycles at 1 C at 50 °C). Such nanoscale dual‐carbon networks engineering and thorough discussion of ion diffusion kinetics might make contributions to accelerating the process of phosphate cathodes in SIBs for large‐scale energy storages. [ABSTRACT FROM AUTHOR]

The µW‐level power density of flexible piezoelectric energy harvesters (FPEHs) restricts their potential in applications related to high‐power multifunctional wearable devices. To overcome this challenge, a hierarchical design strategy is proposed by forming porous piezoceramics with an optimum microstructure into an ordered macroscopic array structure to enable the construction of high performance FPEHs. The porous piezoceramic elements allows optimization of the sensing and harvesting Figure of merit, and the array structure causes a high level of effective strain under a mechanical load. The introduction of a network of polymer channels between the piezoceramic array also provides increased device flexibility, thereby allowing the device to attach and conform to the curved contours of the human body. The unique hierarchical piezoceramic array architecture exhibits superior flexibility, a high open circuit voltage (618 V), high short circuit current (188 µA), and ultrahigh power density (19.1 mW cm−2). This energy density value surpasses previously reported high‐performance FPEHs. The ultrahigh power flexible harvesting can charge a 0.1 F supercapacitor at 2.5 Hz to power high‐power electronic devices. Finally, the FPEH is employed in two novel applications related to fracture healing monitoring and self‐powered wireless position tracking in extreme environments. [ABSTRACT FROM AUTHOR]

The service conditions of high temperature and heavy load of aero-engine require high-temperature self-lubricating composites with high strength, low wear and long life. Hence, the high-level objective of this study is to regulate the interface between the substrate and hexagonal boron nitride (h-BN) lubricant in GH4169 nickel-based high-temperature self-lubricating composites to improve the interfacial bonding strength and the overall performance. Electroless plating method was adopted to coat nickel on h-BN, and the dense high-temperature self-lubricating composites were fabricated through hot-pressing sintering. The effects of nickel coating on h-BN on the microstructure, mechanical properties and high-temperature tribological behaviors of composites were analyzed in detail, and the lubrication mechanism was also elucidated. The results illustrate the Ni@h-BN/GH4169 composites with addition of chemically modified lubricant particles have excellent mechanical properties and lubrication and wear reduction properties, compared to h-BN/GH4169 composites. This is mainly due to the introduction of nickel coating contributed to the distribution uniformity of h-BN in the matrix, and the wettability between h-BN and the substrate together with interfacial bonding strength were enhanced as well. This work provides an insight to overcome the challenges facing the technology when using GH4169 nickel-based self-lubricating composites in manufacturing of mechanical components in aerospace. [ABSTRACT FROM AUTHOR]

The dynamic spheroidization mechanism and its orientation dependence in Ti-6Al-2Mo-2V-1Fe alloys during subtransus hot deformation were studied in this work. For this purpose, hot compression tests were carried out at temperatures of 780–880 °C, with strain rates of 0.001–0.1 s−1. Based on SEM, EBSD and TEM characterization, the results showed that the aspect ratio of the α phase decreased with increasing deformation temperatures and decreasing strain rates. At 880 °C/0.001 s−1, the aspect ratio of the α phase was the smallest at 2.05. The proportion of HAGBs decreased with increasing temperatures and strain rates, which was different from the trend of the spheroidization; this indicated that the formation of HAGBs was not necessary for the spheroidization process. Furthermore, the formation of the α/α interface was related to the evolution of dislocations and twin boundaries at high (880 °C) and low temperatures (780 °C), respectively. Moreover, the dependence of lamellar spheroidization on the crystallographic orientation tilt from the compression direction (θ) was clarified: when θ was between 45° and 60°, both the prism slip and basal slip systems were activated together, which was more favorable for spheroidization. This study could provide guidance for titanium alloy process designs and microstructure regulation. [ABSTRACT FROM AUTHOR]

Fast reaction between organic salt and lead iodide always leads to small perovskite crystallites and concentrated defects. Here, polyacrylic acid is blended with organic salt, so as to regulate the crystallization in a two‐step growth method. It is observed that addition of polyacrylic acid retards aggregation and crystallization behavior of the organic salt, and slows down the reaction rate between organic salt and PbI2, by which "slow‐release effect" is defined. Such effect improves crystallization of perovskite. X‐ray diffraction study shows that, after addition of 2 mm polyacrylic acid, average crystallite size of perovskite increases from ≈40 to ≈90 nm, meanwhile, grain size increases. Thermal admittance spectroscopy study shows that trap density is reduced by nearly one order (especially for deep energy levels). Due to the improved crystallization and reduced trap density, charge recombination is obviously reduced, while lifetime of charge carriers in perovskite film and devices are prolonged, according to time‐resolved photoluminescence and transient photo‐voltage decay curve tests, respectively. Accordingly, power conversion efficiency of the device is promoted from 19.96 (±0.41)% to 21.84 (±0.25)% (with a champion efficiency of 22.31%), and further elevated to 24.19% after surface modification by octylammonium iodide. [ABSTRACT FROM AUTHOR]

The globularization of the lamellar α phase by thermomechanical processing and subsequent annealing contributes to achieving the well-balanced strength and plasticity of titanium alloys. A high-throughput experimental method, wedge-shaped hot-rolling, was designed to obtain samples with gradient true strain distribution of 0~1.10. The samples with gradient strain distribution were annealed to obtain the gradient distribution of globularized α phase, which could rapidly assess the globularization fraction of α phase under different conditions. The static globularization behavior under various parameters was systematically studied. The applied prestrain provided the necessary driving force for static globularization during annealing. The substructure evolution and the boundary splitting occurred mainly at the early stage of annealing. The termination migration and the Ostwald ripening were dominant in the prolonged annealing. A backpropagation artificial neural network (BP-ANN) model for static globularization was developed, which coupled the factors of prestrain, annealing temperature, and annealing time. The average absolute relative errors (AARE) for the training and validation set are 3.17% and 3.22%, respectively. Further sensitivity analysis of the factors shows that the order of relative importance for static globularization is annealing temperature, prestrain and annealing time. The developed BP-ANN can precisely predict the static globularization kinetic curves without overfitting. [ABSTRACT FROM AUTHOR]

Weight reduction is often considered the primary goal in the development of structure materials. A new Ti-8Al-1Cr-1V-0.5Fe-0.1Si (wt.%) alloy with a low-density and a high-strength was developed in this work. The microstructures and mechanical properties of the alloy were investigated in hot-rolled and solution-aging (STA) treatment conditions. The microstructures of the alloy in both states consist of the spherical αp phase, acicular αs phase, and a small amount of β phase. Attributed to such heterogeneous microstructures, the hot-rolled alloy exhibits an outstanding tensile strength of 1046.1 MPa, a total elongation of ~8.3%, and an impressive low density of 4.23 g/cm3. After heat treatment, the alloy also exhibits a similar strength and ductility. A detailed analysis of the deformation modes shows that the numerous dislocations slippages and deformation twinning in the αp phase are the main reasons for the high ductility, and the acicular αs phase provides the alloy with high strength after heat treatment. This newly developed alloy is a potential material for various structural applications. [ABSTRACT FROM AUTHOR]

Due to the unique electromechanical energy conversion capability of ferroelectric materials, they have been at the forefront of materials science for a variety of applications such as sensors, actuators and energy harvesting. Researchers have focused on exploring approaches to achieve improved ferroelectric performance, and to ensure that the available material systems are more environmentally friendly. This comprehensive review summarizes recent research progress on porous ceramics and highlights the variety of factors that are often ignored, namely the influence of porosity on the Curie temperature, and applications of porous ferroelectric materials with adjustable Curie temperature. Finally, the development trends and challenges of porous ferroelectric materials are discussed, aiming to provide new insights for the design and construction of ferroelectric materials. [ABSTRACT FROM AUTHOR]

In this work, the anisotropic microstructure and mechanical properties of selective laser melted (SLMed) Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy before and after aging treatment are investigated. Owing to the unique thermal gradient, the prior columnar β grains with {001} texture component grow in the building direction, and the mechanical properties of the as-fabricated Ti-55511 alloy exhibit slight anisotropy. Aging treatment creates uniform precipitation of the α phase at the boundaries as well as the interior of β grains. Due to the microstructure of the aged samples with a weak texture, the mechanical properties exhibit almost isotropic characteristics with an ultimate tensile strength of 1133 to 1166 MPa, yield strength of 1093 to 1123 MPa, and elongation from 13 to 16%, which meet the aerospace allowable specification very well. By XRD and EBSD analyses, the total dislocation density of the aged samples (~134.8 × 1013 m−2) is significantly lower than that of the as-fabricated samples (~259.4 × 1013 m−2); however, the aged samples exhibit a higher geometrically necessary dislocation (GND) density (~28.5 × 1013 m−2) compared with the as-fabricated samples GND density (~2.9 × 1013 m−2). Thus, a new approach to strengthening theory for estimating the anisotropic mechanical properties of AM alloys is proposed. [ABSTRACT FROM AUTHOR]

Additive manufacturing provides alternative solutions for complex geometry and design freedom for the customization of aluminum alloys, while the unique microstructure as well as the complex solidification behavior is of great concern due to the severe thermal stress in the layer-by-layer accumulated process. In this work, the effects of laser power, laser scanning speed, and hatch spacing on the microstructure and mechanical properties of a laser powder bed fusion (LPBF) fabricated thermal conductive aluminum alloy 6063 (AA6063) were studied. The relationship between processing parameters and metallurgical defects was investigated. The element distribution and misorientation between grains around the crack were characterized. The results revealed that the majority of cracks were parallel to the building direction. The crack density was suppressed by increasing the scanning speed. The orientated cracks lead to the anisotropy of mechanical properties. The strength and ductility of the vertical samples are both higher than those of the horizontal samples. After aging treatment, an ultimate tensile strength of 241 MPa, yield strength of 215 MPa, and elongation of 4.9% were obtained in the vertical specimen of the LPBF processed AA6063. It was demonstrated that cracks tend to stretch along the high-angle grain boundaries because of the concentration of local thermal stress at the final stage of solidification. This work provides guidance for defects suppression and mechanical properties optimization in additively manufactured AA6063 and other aluminum alloys. [ABSTRACT FROM AUTHOR]

A strong temperature-dependent effect in the range from 25°C to 700°C in the nanomechanical behaviour has been found in a single-crystal nickel-base superalloy. The hardness of this alloy gradually increases from 25°C to 400°C and then rapidly decreases, in contrast to the peak tensile yield strength which occurs at around 700°C. The nanomechanical response is strongly dependent on the indentation load over a wide range of temperature, which is rationalised by its unique γ/γ' dual-phase microstructure. The experimental measurements show that the hardness is position-sensitive owing to its unique solidified dendrite microstructure when the indentation marks span 640 μm. [ABSTRACT FROM AUTHOR]

Capacitor dielectrics with high energy density are urgently needed in power electronics and pulsed power system applications. To date, the most explored ceramic/polymer nanocomposites still suffer from the common challenge of a contradictory relationship between permittivity and the electric breakdown strength due to the overloading of nanofillers. Orientated films are considered the most prospective and scalable manufacturing option to overcome the above problems. Herein, a series of stretched PVDF polymer films were fabricated, and they demonstrated a substantial and concurrent increase in both electric displacement and breakdown strength (e.g. 16.10 μC cm−2 at 798.8 kV mm−1) by tuning its crystallization behavior in multiaspects. The phase transition and crystal orientation led to enhanced electric polarization, while the high strain-induced enhancement of Young's modulus and suppression of leakage current brought significant improvement in electric breakdown strength. Particularly, the effects of crystalline morphologies and orientations on the electric polarization behavior and stress distribution under high electric fields have been revealed by theoretical simulation, for the first time. As a consequence, the stretched PVDF films at a high strain of 500% (R = 5) almost presented the highest discharge energy density of 34.90 J cm−3 among dielectric polymers, along with a high energy efficiency of 68.2%, based on the solid-state drawing process. This work provides a feasible and paradigmatic approach to developing high-performance dielectrics for electrostatic energy storage applications. [ABSTRACT FROM AUTHOR]

Alloys used as bearings in aircraft landing gear are required to reduce friction and wear as well as improve the load-carrying capability due to the increased aircraft weights. Cu-15Ni-8Sn-0.8Nb alloy is well known for possessing good mechanical and wear properties that satisfy such requirements. In this study, the microstructure, mechanical properties, and grease-lubricated sliding wear behavior of Cu-15Ni-8Sn-0.8Nb alloy with 0.8 wt% Nb are investigated. The nanoscale NbNi3 and NbNi2Sn compounds can strengthen the alloy through the Orowan strengthening mechanism. A Stribeck-like curve is plotted to illustrate the relationship among friction coefficient, normal load, and sliding velocity and to analyze the grease-lubricated mechanism. The wear rate increases with normal load and decreases with sliding velocity, except at 2.58 m/s. A wear mechanism map has been developed to exhibit the dominant wear mechanisms under various friction conditions. When the normal load is 700 N and the sliding velocity is 2.58 m/s, a chemical reaction between the lubricating grease and friction pairs occurs, resulting in the failure of lubricating grease and an increase in wear. [ABSTRACT FROM AUTHOR]

Accurate flow stress data are essential for the design and optimization of thermo-mechanical processes for a wide range of metallic materials. Hot compression testing is generally used to establish the dependence of flow stress on temperature, strain and strain rate. Flow stress measurements have mostly used cylindrical specimens of different sizes. While the data has been corrected for friction and adiabatic heating, the measurements assume idealized uniform deformation in the test specimen when obtaining the flow stress data from the measured load and displacement. In this paper, it is shown that there is significant non-uniform deformation in the test specimen under practical testing conditions, and a methodology is developed to correct the flow stress data. This correction is generally more significant than the correction due to friction or adiabatic heating and is necessary to obtain more accurate flow stress data. The effect of specimen geometry is also investigated, and a geometry which results in more uniform strain distribution than a cylindrical specimen is used. Measurements are conducted for a prototype powder metallurgy nickel-base superalloy at a low strain rate over a deformation temperature range. Constitutive equations are constructed with the measured flow stress data. Finite element modeling of the tests using the corrected data provides a better agreement with the measured loads. The grain microstructures vary with the test parameters and are used to correlate the flow behavior. [ABSTRACT FROM AUTHOR]

Ferroelectric nanolaminates have drawn wide attention due to the process convenience of atomic layer deposition (ALD) method and their superior performance. In this work, HfO2/ZrO2 nanolaminates were prepared by alternately depositing HfO2 and ZrO2 single layer with ALD technology. The crystal structures and electrical properties were comprehensively investigated and analyzed. Compared with HfZrO4 solid solution, HfO2/ZrO2 nanolaminates showed much lower leakage current density and similar ferroelectricity, which was beneficial for the improvement of device life. The highest remnant polarization of 17.7 μC cm−2 was achieved in HfO2/ZrO2 nanolaminates with a ratio of 12:12, exhibiting a good endurance of exceeding 5 × 109 cycles. The effects of film thickness and laminated structure on the electrical properties and fatigue performance were also discussed. The differences in ferroelectricity and leakage current were originated from the different grain sizes. The small roughness, fine grains and enough crystallization are essential for the better ferroelectric properties. This work provides a comparison between doped films and laminated films and reveals the thickness dependence on the ferroelectric properties of HfO2/ZrO2 nanolaminates. [ABSTRACT FROM AUTHOR]

To solve the poor sinterability and wettability between TiN ceramic and pure metal via using coated composite powders, dense TiN‐Ni cermets with uniform microstructure and fine grains were developed at a low sintering temperature of 1300℃ in this work. TiN powders were firstly activated in a strong acid solution, in order to achieve a step‐like surface; Ni‐coated TiN powders showed an uniform and controllable morphology. Two types of TiN‐Ni cermets based on conventional milled powders and Ni‐coated TiN composite powders were fabricated by spark plasma sintering (SPS), and used for the comparison concerning the sintering behavior, microstructure and related mechanical properties. Results showed that Ni‐coated TiN composite powders helped to improve the sinterability between ceramic and metal, which is rather beneficial to obtain dense TiN‐Ni cermets with homogeneous microstructure and high mechanical properties. Compared to those of conventional TiN‐Ni, the relative density, Rockwell hardness and fracture toughness increased from 84.9% to 96.6%, 80.2 to 84.3, and 10.2 MPa·m1/2 to 14.7 MPa·m1/2, with a rather low sintering temperature of 1300 ℃, respectively. [ABSTRACT FROM AUTHOR]

Selective detection of dopamine is still a challenge due to the strong interference from ascorbic acid (AA). A hybrid dopamine electrochemical sensor was fabricated by boron-doped diamond (BDD) film co-modified with gold nanoparticles and graphite-coated nickel nanoparticles (Au-C@Ni/BDD). Highly sensitive and selective detection toward dopamine was achieved by multiple electrochemical anodic polarization treatment (EAPT) with relatively mild voltage (+ 1.6 V vs. Ag/AgCl) on Au-C@Ni/BDD electrode. Specifically, the oxidation peak separation between ascorbic acid and dopamine reached 166 mV, and the limit of detection of dopamine was as low as 0.015 μM in a linear concentration range of 0.05–100 μM with the sensitivity up to 1.99 μA μM−1 cm−2 even in the presence of interference of high-level AA. These could be ascribed to the electrocatalytically active sites and functional oxygen-containing groups of the hybrid electrodes produced by the EAPT and the excellent catalytical activity of gold nanoparticles. [ABSTRACT FROM AUTHOR]

In vivo tracking or in vitro real sample analysis by electrochemistry is one of the most straight and useful methods in biosensor field. However, surface biofouling of electrodes by non-specific protein adsorption is inevitable and usually leads to a decrease in sensitivity. Here, we developed a Nafion-coated porous boron-doped diamond (NAF/pBDD) electrode with hydrophobic nanostructures to minimize the biofouling effect and selectively detect dopamine (DA). Larger active area was obtained by this procedure compared to a bare diamond electrode. The as-prepared electrode shows excellent antifouling property and enrichment capacity toward selective detection of dopamine (DA). The low background current of the BDD electrode and the enhanced signals enables a lower detection limit, 42 nmol L−1, and a wider linear range, 0.1–110 μmol L−1, for determination of DA in human serum. Additionally, the facile modified electrode demonstrated renewable property and long-term stability due to the fact that the antifouling nanostructures belong to its own. [ABSTRACT FROM AUTHOR]

The working atmosphere greatly affects the melting and solidification processes in powder-based additive manufacturing. In this work, pure tungsten components were fabricated by selective laser melting (SLM) under argon and nitrogen, respectively. The effects of the atmosphere and processing parameters on densification, microstructures, and phases were investigated. Tungsten processed under nitrogen exhibited a higher density, lower roughness, and superior mechanical performance than that processed under argon. The high dynamic viscosity of liquid tungsten in argon induced balling and pore formation during the laser melting process, leading to relatively low density and poor mechanical properties of the SLM-processed tungsten that was manufactured in argon. The results help to promote the practical application of SLM for complicated tungsten components in the nuclear and military industries. [ABSTRACT FROM AUTHOR]

Electrospinning has received tremendous attention in terms of the design and fabrication of 1D nanofibers for oxygen electrocatalysis in fuel cells and metal‐air batteries, owing to their high surface area, short charge transport path, superior chemical stability, etc. In this review, a brief introduction is given for fuel cells, metal‐air batteries, and the operation principle of electrospinning. After that, the recent progress of the noble‐metal‐free electrocatalysts prepared through electrospinning, mainly containing heteroatoms‐doped electrospun carbon nanofibers (ECNFs), ECNFs functionalized with transition metal nanoparticles and their compounds (alloy, oxides, carbides, nitrides, sulfides, phosphides), and unique nanostructured transition metal‐nitrogen‐ECNFs (including single‐atom catalysts) are summarized. In this section, electrospun electrodes with self‐standing peculiarity are emphasized. Next, other kinds of electrospun nanofibers based on oxides, nitrides, and carbides as electrocatalysts or their hybrid materials are also discussed. Finally, the prospects and possible future research direction of electrospun NFs‐based oxygen electrocatalysts are also presented. This comprehensive review is anticipated to be valuable and helpful in the context of understanding the design and fabrication of advanced energy conversion and storage devices. [ABSTRACT FROM AUTHOR]

The different unzipping levels of carbon nanotubes (CNTs) reinforced CuCr matrix composites were fabricated by flake powder metallurgy. The strengthening effect of the different unzipping levels of CNTs in the metal matrix was investigated through scanning electron microscopy, transmission electron microscopy, and tensile tests. When the CNTs were unzipped to the proper level, the unzipped-CNTs/CuCr composite presented primarily enhanced an ultimate tensile strength of 373.7 MPa and a fracture elongation of 18.6%, respectively. The formation of sufficient interface contact areas and interfacial adhesion between unzipped CNTs and CuCr matrix, which were responsible for trade-off in the strength-ductility of the composites. This work provides an insight to understand the strengthening behaviors of unzipped CNTs in the metal matrix composites. [ABSTRACT FROM AUTHOR]

In this study, open‐cell Ni–Sn–P alloy foams were prepared by electroless plating. The influence of tin content on the surface morphology and properties of Ni–Sn–P alloy foams were investigated. The surface structure of Ni–Sn–P alloy foams became more uniform and compact with the increase of Sn content. The X‐ray diffraction result showed that Ni–Sn–P alloy foams gradually transformed from an amorphous structure into crystallization with the increase of heat‐treatment temperature. The introduction of Sn significantly enhanced the corrosion resistance of Ni–P coatings in 3.5 wt% NaCl solution, the corrosion current density decreased from 5.022 to 0.805 μA/cm2 and the corrosion potential shifted positively from −0.423 to −0.294 V after adding 5.96 wt% Sn to Ni–P coatings. However, the corrosion resistance of Ni–Sn–P foams was deteriorated after heat treatment. Adding Sn to the Ni–P system slightly weakened the compressive strength of Ni–P binary foams. Nevertheless, significant improvement in the antioxidant performance of Ni–Sn–P alloy foams was indicated by the reduction of the mass change rate in that the mass change rate of Ni–P foams obviously reduced from 5.15% to 0.25% after adding 5.96 wt% Sn. [ABSTRACT FROM AUTHOR]

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d33≈10–16 pC N−1, and pyroelectric coefficient of p≈25.8 μC m−2 K−1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of ϵ33σ≈ 6.3. [ABSTRACT FROM AUTHOR]

We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d33≈10–16 pC N−1, and pyroelectric coefficient of p≈25.8 μC m−2 K−1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of ϵ33σ≈ 6.3. [ABSTRACT FROM AUTHOR]

In this paper, graphite/copper composites with high performance were fabricated by a novel two-steps electroless plating and spark plasma sintering. The interfacial characterization and modification mechanism of nickel coating in the composites were analyzed. Effects of sintering temperature and Ni volume fraction on the mechanical properties and microstructure of composites were also systematically investigated. The results showed that the introduction of Ni coating could significantly improve the interfacial bonding between Cu matrix and graphite and led to the uniform distribution of graphite particles in Cu matrix. Moreover, the mechanical properties of composites increased obviously with the increase of Ni coating content from 0 vol.% to 10 vol.%. When the Ni content was 10 vol. %, the relative density, hardness, and compressive strength of the composites reached to 99.8%, 67.8 HB and 314 MPa, respectively. [ABSTRACT FROM AUTHOR]

Due to the special shape of cutting or grinding tools used nowadays, hot filament (HF)-substrate distance is usually unavoidable during the process of diamond deposition by hot filament chemical vapor deposition (HFCVD), which will lead to difficult deposition process for nanocrystalline diamond (NCD). Based on this problem, the coupling effects of different CH4/H2/Ar gas ratios and HF-substrate distances on the growth of NCD films are systematically studied. SEM and Raman are used to analyze the surface morphology and sp3/sp2 contents of the diamond films deposited on different areas of each specimen. The results indicate that the proper increase of HF-substrate distance and concentration of CH4 or Ar encourage the growth of NCD. Under the condition of lower concentration of CH4 or Ar, NCD with uniform grain size can also be realized at a certain range of HF-substrate distance. A graph that shows the growth conditions of MCD, MCD/NCD and NCD is creatively presented by summarizing the deposition parameters and experimental results. This work provides a path to coat NCD onto the special-shaped cutting or grinding tools by HFCVD. [ABSTRACT FROM AUTHOR]

Electroless plating was adopted to produce Ni-P-coated graphite powder which was subsequently used to prepare nickel/graphite composites via spark plasma sintering (SPS). Effects of sintering parameters on the microstructure and mechanical properties of the composites were investigated. Sintering temperature has a significant effect on the distribution of nickel, and coarsening of Ni3P precipitations occurs with the extension of holding time. Fully dense nickel/graphite composite with the interpenetrating network was achieved by SPS at 750°C for 10 min as optimal conditions. The network consists of nickel and fine Ni3P particles. The flexure strength and hardness of the composite containing 68.2 vol.% graphite reached up to 157 MPa and 57.8 HV, respectively. The tribological properties of the composite obtained at optimal condition were characterized. Under applied load of 30–50 N and sliding speed of 1.55 m/s, the composite exhibited very low wear rate in the order of 10−8 mm3·N−1 m−1 and stable friction coefficient from 0.12 to 0.18. The wear mechanism involved is delamination wear, oxidation wear and abrasive wear. [ABSTRACT FROM AUTHOR]

The Cu–15Ni–8Sn alloy with high strength and toughness is a common bearing alloy, while it is often subjected to premature failure in service due to corrosion and wear. Therefore, the corrosion and wear behaviors of an ultra‐high‐strength and toughness Cu–15Ni–8Sn (wt%) alloy fabricated by hot isostatic pressing were investigated in this study. The results indicated that intergranular corrosion and pits were observed when the studied alloy was immersed into seawater for 30 days. When the Cu–15Ni–8Sn alloy slid in seawater, there was a synergistic effect between corrosion and wear. With the increase of normal load, the synergistic effect weakened initially and then enhanced the interaction between corrosion and wear changed from negative to positive, and the main wear mechanisms transferred from abrasive wear into delamination. [ABSTRACT FROM AUTHOR]

Duplex aging is one of the common heat treatments in titanium alloys. The microstructure introduced in the first-step aging has an effect on the growth/dissolution of α in the second-step aging. In the present work, a β + αacicular microstructure is preset in Ti–55531 (Ti-5Al-5Mo-5V-3Cr-1Zr wt%) alloy. The isochronal and isothermal phase transformation kinetics in the second-step aging is studied by combining the dilatometer test with microstructure characterization and local composition mapping. The phase transformations and corresponding temperature ranges are determined as β → αacicular [643–845 K] and αacicular → β [845–1130 K] by isochronal annealing. A TTT diagram for isothermal transformation kinetics is plotted based on the transformed phase fraction and reproduced by Johnson–Mehl–Avrami theory. The calculated kinetic curves are in good agreement with experiment ones. The C-shaped TTT curves verify the classical nucleation and growth of α in the second-step aging. In comparison with Ti–55531 alloy with preset β + αlath microstructure (in authors' previous work), the α precipitation exhibits prolonged incubation period and slowed average transformation rate, which is evidenced by a right shift of C-curves for the α precipitation portion along the time axis. However, the C-curves of α dissolution show a left shift on the TTT diagram. The precipitation kinetics of α aciculae from dilatometry is synchronous with that obtained from the diffusion of Al detected in STEM mapping, while the diffusion of slow-diffusion elements lags behind the structural transformation. The TTT diagram and the dataset of microstructure features obtained in the present work can be employed to optimize processing in duplex aging. [ABSTRACT FROM AUTHOR]

Tribological behaviors of an ultrahigh strength Cu–15Ni–8Sn–0.2Y alloy sliding against TC6 titanium alloy in deionized water and seawater under various normal loads and sliding speeds were evaluated. The friction coefficient and wear rate of the studied alloy in deionized water were higher than those in seawater. Seawater played cooling, lubricating, and corrosive roles during the friction process. A friction model for calculating ploughing component was established, which could explain the influence mechanism of the normal load on the friction coefficient and wear rate. Chloride ions easily penetrated the passive film and damaged it due to the wear, causing increased corrosion and corrosive products. The corrosive products such as Mg(OH)2 and CaCO3 played important roles in reducing friction and wear. [ABSTRACT FROM AUTHOR]

Core‐rim structure, concerning its interface structure and internal stress, plays an important role in mechanical performance of Ti(C,N)‐based cermets. Four types of cermets containing equimolar TaC, VC, ZrC, and NbC were fabricated, in order to reveal the synergetic relationship between core‐rim structure and mechanical properties. VC and ZrC effectively inhibited the grain growth, while TaC and NbC favored for coarser core‐rim grains. A thin distortion layer at the rim‐binder interface was confirmed, formed during the solidifying stage. Compared to the TaC, ZrC and NbC, VC shrunk the lattice parameters of rims and effectively decreased the lattice misfit of the distortion zone from around 4.0%‐0.8%. Cermets containing VC showed satisfactory bending strength of 2099 MPa and toughness of 10. 3 MPa m1/2, owing to the strengthened rim‐binder interface. TaC and NbC exhibited the similar roles in cermets with comparable mechanical properties, while addition of ZrC increased the lattice misfit of core‐rim structure, resulting in poor mechanical performance. Decreased lattice misfit of rim‐binder interface changed the fracture mode of cermets from intergranular to transgranular fracture, with in‐situ formed dimples. [ABSTRACT FROM AUTHOR]

Although great achievements have been made in realizing ferroelectricity in HfO2-based films by the ALD method, the performance is strongly constrained by film thickness and dopant types. This study was the first to realize ferroelectric properties in undoped HfO2 films by the chemical solution deposition method, which broke the above restrictions while using the ALD method. The evolution of ferroelectricity in pure HfO2 films was studied over a wide range of thickness from 34 nm to 136 nm, without doping any other metallic elements. The HfO2 film with a thickness of 136 nm exhibited a large remnant polarization (Pr) of 22.56 μC cm−2 after a wake-up process of 105 cycles, and could endure up to 107 switching cycles. Residual carbon from the incomplete decomposition of organic matter in films and growth disruption of grains through layer-by-layer thermal treatment could lead to the reduction in grain size, which was beneficial to the formation of the metastable ferroelectric o-phase. Oxygen vacancies existing at the interfaces between the TiN bottom electrode and HfO2 film could be rearranged during electric field cycling, thus inducing the appearance of ferroelectricity. The movement of domains under different tip bias by a piezo force microscope verified the existence of ferroelectricity in the undoped HfO2 films. This report therefore provides an inexpensive and feasible way to gain ferroelectricity in pure HfO2 films and paves the way toward other sensor applications beyond thickness limitations and doping systems. [ABSTRACT FROM AUTHOR]

A significant improvement of permittivity and energy density will enable the miniaturization of dielectric capacitors and promote integration for applications in electrical power and defense systems. In this work, lamellar composite architectures are fabricated from aligned barium titanate (BaTiO3) in an epoxy resin using the freeze casting method. Due to the continuous coupling effect originating from the interconnected and highly oriented BaTiO3 particles, these composites exhibit an extremely high permittivity (εr = 1408) at 1 kHz, which is the highest value achieved in BaTiO3/polymer composites reported so far and fits well to the parallel mode of the mixing rule. A finite element model is used to investigate the local electric field distributions in the BaTiO3 lamellae under the applied electric field parallel and perpendicular to the freezing direction, respectively. A high ratio value of discharge energy density per electric field, Udis/E, ∼0.033, is achieved due to a high electric displacement of D = 15.11 μC cm−2 and a discharge energy density of Udis = 19.6 × 10−2 J cm−3 is achieved at a low electric field (6 kV mm−1). This work provides an effective strategy of designing a ceramic–polymer composite to realize high permittivity and energy density of capacitors for modern electrical and electronic industries. [ABSTRACT FROM AUTHOR]

We report carbon nanotube-encapsulated cobalt as an efficient oxygen reduction electrocatalyst (onset potential of 0.94 V and half-potential of 0.84 V). Calculation results firstly reveal that Co protected by graphitic-N-doped carbon holds more negative charge (−1.22 eV) and has an energy barrier (0.56 eV) lower than that of pyridinic-N-doped carbon (−1.11 eV; 0.78 eV), which is responsible for the ORR activity. The corresponding Zn–air batteries deliver an excellent gravimetric energy density of 837 W h kg−1. [ABSTRACT FROM AUTHOR]

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area. [ABSTRACT FROM AUTHOR]