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In this paper, undoped and Cr-doped VO2 thin films were fabricated and deposited onto Al2O3 substrates using a sol-gel method. Then, the effects of Cr-doping on the thermochromic, and optical properties of the thin films were investigated. Doping with Cr ions gradually increased the metal-insulator transition (MIT) temperature of the films, while the luminous transmittance (Tlum) and the sol modulation efficiency (ΔTsol) gradually decreased. Additionally, Pt/VO2/ITO devices and Cr-doped VO2 devices were prepared to study their threshold switching (TS) properties. For devices fabricated with Cr-doped VO2 films, both the threshold voltage (Vth+) and the OFF-state current decreased as the amount of Cr doping increased. In contrast, the ON/OFF ratio increased from 104 to 105. These results provide insight into the potential for using VO2 in thermochromic, optical, and TS applications.

ZrCo2 and HfCo2 Laves phases were found and characterized in γ-γ′ Co-base superalloys using high-energy X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy. They formed during casting and are stable during long-term annealing at 900 °C. The ZrCo2 phase with a cubic MgCu2-type structure exhibits numerous nano-twins and stacking faults, while HfCo2 has a hexagonal MgNi2-type structure instead of MgCu2-type in contrast to literature. Their chemical compositions strongly deviated from stoichiometry and significant amounts of Al and W are contained in these phases. These could affect the atomic radius ratio and valence electron concentration and thus change the structure of the Laves phases.

This study investigates the creation of heterogeneous martensitic transformation field in shape memory alloy structures with geometrical nonuniformity through experiments and finite element computational analysis. Geometrically graded superelastic NiTi thin plates with series and parallel design configurations with respect to the loading direction have been created. The nonuniform transformation evolutions within these structures are presented by thermal images captured by an infrared camera during tensile experimentation. It is found that the transformation propagation is along the loading direction in a sample with the series design configuration unlike that in a sample with the parallel design configuration. Also, the geometrically graded structures exhibit stress gradient over stress-induced transformation. The transformation propagation and the deformation behaviour of these structures are presented by numerical modelling which is in good agreement with experimental data.

Three Ni-base powder metallurgy superalloys have been developed recently, and tensile tests at temperatures ranging from room temperature (RT) to 815 °C were conducted on them. The results conformed their excellent tensile properties, in comparison with several other existed polycrystalline superalloys. In this work, by means of microstructure characterization, thermal dynamic calculations, and theoretical modeling, different strengthening mechanisms including precipitation strengthening, grain boundary strengthening, solid solution strengthening, and Orowan strengthening, were found to contribute to the yield strength in different degrees, which would help to further enhance the tensile properties of these alloys through composition design and processing optimization thereafter.

Sm2O3–NiO (Sm–Ni) heterojunction was prepared by the sol-gel route for the photo-Fenton degradation of RhB in visible light region. In contrast with single phase Sm2O3 and NiO, the enhanced photocatalytic activity was achieved by Sm–Ni composites. Among the Sm–Ni composites, Sm1–Ni2 with the Sm/Ni molar ratio of 1:2 and the average dimeter of 70 nm exhibited the best photocatalytic activity. •O2− radical plays a vital role in the photocatalytic activity of Sm1–Ni2 composites. The reduced band gap energy of Sm1–Ni2 composites is favorable for the visible-light harvesting, and the tight interface of Sm2O3 and NiO strengthen the transfer and mobility of charge carries, leading to the high resistance to the recombination of photo-produced electron-hole pairs.

The effects of Co on the Cu-Ni-Co-Si alloys' microstructure and mechanical properties were investigated. The Cu-1.5Ni-1.0Co-0.6Si and Cu-1.5Ni-1.5Co-0.6Si alloys with combined aging and 40–80% cold rolling were also investigated. The hardness, electrical conductivity, and microstructure were characterized, complemented by X-ray diffraction analysis and transmission electron microscopy. At 450 °C alloys aging, the aging precipitated phases are β-Ni3Si and Co2Si. Specifically, the orthorhombic (Ni, Co)2Si precipitates were found, which have the same crystal structure as the Ni2Si precipitates. The crystal orientation relationship between the matrix and the precipitates is: [112]Cu//[112]β//[012]p, ( 1 1 ¯ 1 ) Cu// ( 1 1 ¯ 1 ) β//(021)p; [001]Cu//[001]β//[001]p, (220)Cu//(110)β//(100)p. With the increasing Co content, the properties of the alloy were degraded. However, Co can promote the growth of the precipitates and accelerate precipitation during the aging process. After aging at 500 °C for 2 h, the hardness and conductivity of the Cu-1.5Ni-1.0Co-0.6Si alloy with 40% deformation were 250 HV and 43% IACS, respectively.

Different contents of carbon element (0-3 at.%) was added into CoCrFeMnNi high entropy alloys (HEAs) to prepare carbide-reinforced CoCrFeMnNi matrix composites. The effects of carbon on microstructures and mechanical properties were systematically studied. The CoCrFeMnNi HEA sheet without carbon showed fine recrystallized grains with a grain size of approximately 5 μm and contained Cr-rich sigma phase. The CoCrFeMnNiCx HEA sheets with 1.0 at.% and 3.0 at.% C presented fine recrystallized grains and a small fraction of elongated grains. A large number of nano-scaled carbides were observed in the carbon-containing HEA sheets. With the carbon content increasing from 0 at.% to 3.0 at.%, the strengthening of the α-fiber texture is more obvious, and tensile yield strength increased from 371 MPa to 792 MPa, however, the elongation decreased from 54% to 11%, respectively. The CoCrFeMnNiC1 HEA sheet with a volume fraction of 2.9% nano carbides showed excellent balanced mechanical property, with tensile yield strength of 634 MPa and elongation of 38%. The increase of yield strength for the CoCrFeMnNiC1 HEA was mainly ascribed to the combined effects of precipitation Orowan strengthening and dislocations strengthening. Precipitation Orowan strengthening is the primary strength contributor, with a value of approximate 157 MPa.

MXenes is one of the most promising flexible electrode materials for supercapacitor. However, the nanosheets in the MXenes electrode by vacuum filtration are prone to restack during preparation, which largely hinders the full utilization of their surfaces and active sites. In this contribution, the self-restacking of MXene nanosheets (prepared by etching with HCl + LiF) could be prevented effectively by introducing MXene nanoparticles (prepared by etching with HF) as interlayer spacers. The Ti3C2Tx-10 flexible (the electrode with 10% mass fraction nanoparticles) exhibits an excellent specific capacitance of 372 F g−1 at 1 A g−1 which is much higher than that of Ti3C2Tx film, and an impressive cycling stability up to 95% capacitance retention after 5000 cycles. The significant improvement in electrochemical performance is mainly due to that the open sandwich-like structure of the flexible electrode based on multi-scaled Ti3C2Tx provides huge surface area and more active sites.

Recently, high-entropy alloys (HEAs) reinforced with ceramic particles have attracted increasing attentions due to their excellent hardness, strength and wear resistance. In this study, AlCoCrFeNi-xNbC high-entropy alloy (HEA) coatings (x = 10, 20, 30 wt%) were prepared by laser cladding. The phase constituents, microstructure and mechanical properties of the HEAs were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), transmission electron microscope (TEM), microhardness and wear resistance tests. Due to the high entropy effect, the AlCoCrFeNi HEAs composites comprise only simple BCC and FCC structure phases. The addition of NbC particles results in a decrease in the fraction of the FCC phase. NbC particles are mainly distributed at the grain boundary in the HEAs with the addition of NbC. NbC particles have an advantage on the inhibition of HEA grain growth due to a strong pinning effect. The microhardness and the wear resistance of HEA composite improved significantly with the addition of NbC particles. A good comprehensive mechanical properties was obtained at the HEA with the addition of 20 wt% NbC particles. For the 20 wt% NbC-adding HEA, the average Vickers hardness is 525 HV, the average friction coefficient value is 1.023 and the mass loss is 1.05 mg.

The phase stability, γ′ precipitate morphology and element partitioning behavior in dependence on temperature and alloying composition have been systematically investigated in Co-9Al-9W-2X alloys using electron microscopy, energy-dispersive X-ray spectroscopy (EDX) and high-energy X-ray diffraction (HEXRD). The results show that the decomposition of the γ′ phase is promoted by adding some quaternary elements which increase the γ′ solvus temperature (except V). A larger lattice misfit in the Mo, V, Ti, Nb or Ta containing alloys can explain that coarser γ′ particles with a more cuboidal morphology were found in these alloys. Additional alloying elements and the annealing temperature show a stronger influence on the partitioning behavior of W between the γ and γ′ phases compared to that of Co and Al. The partitioning tendency towards the γ′ phase decreases with increasing temperature for all investigated alloying elements except Cr.

In practice, the poor formability and high degradation rate of Mg-based alloys are perceived as two major limitations for their more extensive applications in the biomedical field. Selective laser melting (SLM), as one of the advanced additive manufacturing techniques, is potential for the manufacturing of customized Mg-based implants with improved formability and corrosion resistance. Moreover, the integration of bioactive glass (BG) into Mg-based alloys could endow the materials with further enhanced corrosion resistance and favorable biological performance. In the current work, biomedical Mg-based biodegradable composites (ZK30/xBG, x = 0, 5, 10, 15 wt%) with ZK30 alloy as the matrix and BG (45S5) as the reinforcement were fabricated by SLM. The results showed that the BG particles homogeneously distributed in the matrices of SLM-fabricated ZK30/xBG composites. Meanwhile, the introduction of the BG particles led to improved microhardness of the composites. When immersed in simulated body fluid (SBF), more precipitations (primary Ca–P compounds and partial Mg(OH)2) formed on ZK30/10BG and ZK30/15BG surfaces compared to ZK30 and ZK30/5BG group. The hydrogen evolution and electrochemical polarization tests showed that corrosion resistance of various specimens was in the following order: ZK30/10BG > ZK30/5BG > ZK30/15BG > ZK30. In addition, the in vitro cell viability results showed that ZK30/10BG and ZK30/15BG were more cytocompatible than ZK30 and ZK30/5BG. Overall, these results indicate that the combination of SLM technique and BG integration could be used to manufacture ZK30/xBG composites with enhanced corrosion resistance and favorable formability. Moreover, the ZK30/10BG composite is promising for orthopedic applications considering its combination of favorable bioactivity, corrosion resistance and cytocompatibility.

In this work, effects of scandium on microstructure and mechanical properties of RR1000 were studied. The addition of scandium effectively refines the grain and modifies the morphology of primary γʹ at grain boundary. In the meantime, Sc doping starkly affects the evolution behavior of γʹ during aging, resulting in an inhomogeneous precipitate distribution. Moreover, scandium has a good affinity to oxygen, which consumes deleterious element in the matrix, leading to a stronger grain boundary. As the results, both strength and elongation at room temperature increase gradually with increasing Sc content in the range of 0–0.098 wt % addition.

WO3-SnO2 nanosphere (NS) composites with different structures and morphologies are successfully synthesized by a facial hydrothermal method. Two kinds of gas sensors were fabricated from WO3-SnO2 NS composites of hollow structure with average diameter of 360 nm and solid structure with average diameter of 42 nm by varying the synthesis temperature. The as-prepared composites were annealed at 500 °C for 4 h in atmosphere before the characterization and sensing performance test. The crystalline structures, morphologies and surface compositions of the annealed WO3-SnO2 NS composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photo-electron spectroscopy (XPS) techniques, respectively. The results of gas sensing tests show that WO3-SnO2 NS composites with hollow structure exhibit the superior sensing behavior, including sensitivity, response-recovery rate and selectivity, as compared to the composites with solid structure. The WO3-SnO2 NS composites presented in this work shows a high sensitivity, fast response and selectivity towards acetone. The surface conductivity changes of WO3-SnO2 NS induced by the surface gas adsorption and desorption is proposed to responsible for the corresponding sensing behaviors. The WO3-SnO2 NS composites with hollow structure presented in this study have potential practical applications in the field of gas sensor devices.

The effects of Ce and Y addition on microstructure evolution and precipitation of Cu-Mg alloy hot deformation were investigated by hot compression test in the 500–850 °C temperature range and the 0.001–10 s−1 strain rate range. The influence of rare earth elements on true stress-true strain curves and microstructure evolution of Cu-Mg alloy were obtained, the deformation mechanism under various conditions was defined, and the critical strain of Cu-Mg, Cu-Mg-Ce, and Cu-Mg-Y alloys and the resulting precipitates were determined. Dynamic recrystallization dominated the deformation process at high temperature and low strain rate. Ce and Y significantly delayed dynamic recrystallization and improved flow stress and activation energy of Cu-Mg alloy. The critical strains for Cu-Mg, Cu-Mg-Ce, and Cu-Mg-Y alloys deformed at 700 °C and 0.1 s−1 were calculated to be 0.075, 0.1, and 0.14, respectively. Precipitates appeared in the Cu-Mg-Ce and Cu-Mg-Y alloys deformed at 850 °C and 0.001 s−1, which were determined to be Cu2Mg. In addition, CuP2 phase was found in both Cu-Mg-Ce and Cu-Mg-Y alloys deformed at 800 °C and 0.01 s−1. Precipitates caused dislocation and grain boundary pinning. Furthermore, a large number of twins appeared in the Cu-Mg-Ce and Cu-Mg-Y alloys, which increased the number of grain boundaries and furthered grain refinement.

A hierarchical MnOx@polyvinylidene fluoride (PVDF)/multiwalled carbon nanotubes (MWCNTs) tree-like nanofiber membrane (TLNM) was developed for dye degradation under natural sunlight irradiations, which was prepared by in situ hydrothermal growth of MnOx nanoflakes on the electrospun PVDF/tetrabutylammonium chloride (TBAC)/MWCNTs TLNM. The specific surface area of the MnOx@PVDF/MWCNTs composite catalyst was significantly enhanced by the tree-like structure and MnOx nanoflakes and the catalyst presented good absorption of both ultraviolet light and visible light. Noticeably, the MnOx@PVDF/MWCNTs TLNM exhibited excellent catalytic activity for several different dyes under sunlight and even in the dark condition. Electron spin resonance (ESR) technology and reactive oxidative species scavenging experiments demonstrated that superoxide radicals ( O2−) was the major active ingredient during catalytic degradation process. More importantly, the capacity of manganese with three oxidation states (II/III/IV) could massively enhance the electron transfer and the synergistic oxidation of O2− and Mn(IV) accelerated the degradation of dyes. Meanwhile, MWCNTs act as electron transfer channels which could effectively facilitate the catalytic efficiency. This study will supply a new scheme for construction of new catalysts with enhanced catalytic activity in pollutant degradation under both sunlight and dark conditions.

Refractory high-entropy alloys (RHEAs) are promising high-temperature structural materials due to their high melting point and extraordinarily high yield strength. However, their industrial application is greatly restricted due to their limited room-temperature ductility. In the present investigation, a ductile and strong single-phase NbTaTiV RHEA was synthesized by powder metallurgy method. Effects of the sintering temperature on the phase formation, microstructural evolution and the mechanical properties of the NbTaTiV RHEA were characterized. The results show that the NbTaTiV RHEA sintered at 1700 °C has an equiaxed single bcc phase microstructure, no obvious porosity and compositional segregation can be observed. The alloy exhibits a relatively high hardness of 510 HV, yield strength of 1.37 GPa, and compressive fracture strength of 2.19 GPa with a high fracture strain of 23% at room temperature. Typical strain softening and steady state flow occur during compressive deformation at high temperatures. During deformation at 1000 °C, the alloy still exhibits high yield strength of 437 MPa with a compression strain over than 40%. The outstanding mechanical properties is mainly attributed to the homogeneous and fine microstructures, and solid solution strengthening effect. It can be concluded that the powder metallurgy is a promising way for preparing ductile RHEAs with outstanding comprehensive mechanical properties.

Shape memory alloys exhibit unique thermomechanical properties, e.g., the shape memory effect and the pseudoelasticity. By proper geometrical gradient design, these alloys can be made to exhibit different and more intricate thermomechanical behaviour to enable innovative applications. This paper reports the design of geometrically gradient NiTi and characterisation of its complex and nonuniform transformation and deformation fields. The study investigated two designs, with one using multiple pseudoelastic NiTi strips of different lengths in parallel arrangement to create a discrete geometrical gradient in the direction perpendicular to the loading axis and the other a tapered plate to give a continuous length gradient in the lateral direction for comparison with the former. The geometrically gradient structures exhibited partial stress gradient during stress-induced transformation. A maximum stress window of 520 MPa was achieved, giving an expanded stress interval for shape memory actuation control. Finite element modelling was applied to characterise the deformation behaviour of such structures under tensile loading and to reveal the complex propagation of the stress-induced transformation in such structures.

Te-doped Li4Ti5O12 (LTO) was prepared by a ball milling-assisted solid-state method in air. The as-prepared powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. Li4Ti4.95Te0.05O12 powder sintered at 850 °C presented improved ionic and electronic conductivities of 2.20×10-7 S·cm-1 and 2.40×10-9 S·cm-1 at room temperature, respectively, an order of magnitude higher than those of intrinsic LTO. Electrochemical analysis showed that the discharge specific capacities of Li4Ti4.95Te0.05O12 in Li half cells at 1 C and 5 C were 162.49 mAh·g-1 and 143.5 mAh·g-1, respectively, with capacity retention rates of 98.8% and 98.2% after 100 cycles. The Li4Ti4.95Te0.05O12/LiNi0.5Mn0.3Co0.2O2 full cells also showed a good specific capacity of 101.8 mAh·g-1 at 1 C and delivered good temperature adaptability. This study provides an effective strategy for the preparation of high-performance LTO anodes for lithium-ion batteries.

Recently, SnSe of orthorhombic phase has attracted much attention due to its excellent performance in thermoelectricity, yet the thickness-dependent thermoelectric properties were poorly studied. We have investigated the thermoelectric transporting properties of few-layered (from 1 L to 4 L) and bulk SnSe by using density functional theory plus Boltzmann transport theory. We employed the electron-phonon Wannier method to obtain the accurate transporting parameters, i.e., carrier mobility as well as relaxation time, in contrast to those derived from deformation potential theory. Our results reveal that the band gap decreases from 0.91 eV (1 L) to 0.59 eV (bulk) as the thickness increases, and meanwhile the effective charge mass increases slightly. As bulk SnSe is thinned to the monolayer, the high frequency modes are stiffened while the low frequency modes are softened, and meanwhile the acoustic velocities become larger. At 300 K, the thermal conductivity of bulk SnSe takes 1.52, 0.80 and 0.41 W m−1 K−1 for κa, κb and κc respectively, in good agreement with the experimental values. Thermal conductivity of few-layered SnSe decreases slightly from 2.45 to 1.61 W m−1 K−1 for κa, and from 1.81 to 1.02 W m−1 K−1 for κb as the layer number increases from 1 L to 4 L. The EPW calculations reveal that the electron mobility of n-type films increases rapidly from 24.4 cm2/V s (1 L) to 179.6 cm2/V s (4 L) and the hole mobility of p-type films increases from 47.2 cm2/V s (1 L) to 1211.1 cm2/V s (4 L) at 300 K as the thickness increases. Compared with the monolayer, thicker film of SnSe has larger carrier mobility as well as lower thermal conductivity, which leads to better thermoelectric performance. At 700 K, the figure of merit is enhanced from 0.22 (1 L) to 0.58 (4 L) for n-type films in electron density of −0.55 × 1013/cm2. Our research casts some light on the future thermoelectric applications based on few-layered SnSe.

Hexagonal WO3 (h-WO3) nanorod-cluster films were controllably synthesized by a facile template-free hydrothermal technique. The pH value and the amount of urea in the precursor have critical influences on the crystal form and morphology of the WO3 film. The obtained uniform WO3 films feature a porous structure of clusters composed of h-WO3 nanorods with diameter of 6–10 nm and length of up to several hundred nanometers. Due to the novel microstructure and crystalline phase, the high electrochromic performance in NIR range with a high optical modulation of 46% in 1600 nm, fast switching speed (2.4 s for coloration and 3.6 s for bleaching), high coloration efficiency (106.1 cm2 C−1 in 1600 nm), and an excellent cycling stability (more than 96% charge capacity retained after 1000 cycles) was achieved.

Quaternary alloys CoMnCrAl, CoFeCrAl and their ternary counterpart Co2CrAl are studied experimentally and theoretically to explore the effects of the substitution of Mn or Fe atoms for part of Co atoms in Co2CrAl. It is found that CoMnCrAl or CoFeCrAl has a magnetization 0.92 μB/f.u. or 1.96 μB/f.u. respectively in agreement with the Slater–Pauling (SP) rule, different from the parent ternary alloy Co2CrAl whose magnetization significantly deviates. The combination of experimental and theoretical results suggests that the formation of Co-Cr antisite defect is suppressed by partially substituting Mn or Fe for Co. The main disorder defects in CoMnCrAl are Cr-Al and Mn-Cr antisites, Fe-Cr and Cr-Al antisites in CoMnCrAl. Since these antisite defects only have small effect on the minority band structure, the half metallicity of CoMnCrAl or CoFeCrAl is expected to have much better tolerance for atomic disorder, compared with Co2CrAl. A negative temperature coefficient of resistance for a long temperature range about 10–273 K has been found exclusively for CoMnCrAl compound. Quaternary alloy CoMnCrAl or CoFeCrAl is found to be compensated ferrimagnetism with a relative low magnetization but a Curie temperature (TC) significantly higher room temperature (RT), whose magnetization are relatively low, but TC higher than the ternary alloy Co2CrAl. Considering their low magnetization, decently high TC and the robust half metallicity, these two quaternary alloys may have important applications in spintronic devices.

High entropy alloys (HEAs) have five or more principal elements with four core effects: high entropy, sluggish diffusion, severe lattice distortion, and cocktail effects. These effects lead to some distinct properties of HEAs. Some HEAs are promising for high temperature applications and have the potential to replace Ni-base superalloys as the next generation high-temperature materials, such as high entropy superalloys (HESAs) and refractory HEAs. The microstructures of HESAs consisting of γ and γ′ phases are similar to that of Ni-base superalloys. Refractory HEAs contain refractory elements with high melting temperatures. Thus, a number of aspects of HESAs and refractory HEAs are reviewed and discussed in the present paper, including microstructure, density, room-temperature mechanical properties, high-temperature strength, creep behavior, and oxidation resistance. Furthermore, a number of future research topics are suggested, emphasizing on developing high-performance high-temperature materials.

The FeOOH has been a hotspot in the field of electrochemical research over recent years owing to its typical channel-type nanoporous structure and high theoretical specific capacitance. However, the poor electrical conductivity limits the applications in supercapacitors. In this investigation, the nanocomposites with amorphous FeOOH on Ti3C2Tx nanosheets were one-step chemically synthesized by using FeCl3·6H2O, NH4HCO3, and Ti3C2Tx(MXene) at room temperature. The nanocomposite samples have been characterized by XRD, SEM, TEM, XPS, cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The results show that the capacitive performance is remarkably improved by introducing highly conductive Ti3C2Tx and being composited with amorphous FeOOH. The specific capacitance of the as-prepared nanocomposite reaches 217 F g−1 at current density of 1 A g−1 which is much higher than that of amorphous FeOOH. It also exhibits good rate performance and high charge-discharge cycling stability. The enhancement in electrochemical performance is mainly attributed to the open layered structure with amorphous FeOOH nanoparticles uniformly distributed on Ti3C2Tx nanosheets, which has the enlarged electrode-electrolyte interface area, the shortened diffusion path of ions, and the improved electrical conductivity provided by the conductive Ti3C2Tx frame.

High temperature compressive deformation behaviors of a carbon-containing FeCoCrNiMn high entropy alloy (HEA) was investigated at temperatures ranging from 700 °C to 1000 °C, and strain rates from 0.001s−1 to 1s−1. The microstructure mainly consists of fcc solid solution. The data obtained from the flow curves was employed to develop the constitutive equation, and the apparent activation energy (Q) was determined to be 385.43 kJ/mol. The size of the dynamically recrystallized grains decreased with the increasing value of Zener-Hollomon (Z) parameter. At high Z condition, dislocation cross slip can act as the main deformation mechanism. At intermediate Z condition, dislocation cross slip accompanied by discontinuous dynamic recrystallization (dDRX) becomes the main deformation mechanisms. At low Z condition, continuous dynamic recrystallization (cDRX) becomes the dominant softening mechanism. Nano carbides can be precipitated at intermediate Z and low Z condition, which prevent grain from growing up and promote the nucleation of DRX.

The microstructure, thermal and mechanical stability of Ni-based single crystalline superalloys depend strongly on the alloying elements and their concentrations. Alloying has been the main design strategy for stabilizing the compositions, microstructures and thermal-mechanical properties. This article presents a review on the effects of some common alloying elements on the microstructural and mechanical property stability control of Ni-based superalloys. The various alloying elements are divided into four categories according to their main effects on these properties, comprising base elements, mechanical strengthening elements, long term stability elements and the oxidation resistance elements. The mechanical strengthening elements can further be divided into precipitation, solid solution and grain boundary segregation elements. The precipitation elements strengthen the alloys by forming the L12 structured γʹ phase. The solid solution elements strengthen primarily the γ phase, by increasing the solidus temperatures and decreasing the stacking fault energy, which in turn influences the thermal stability of the phases and the resistance of dislocation movement. The grain boundary elements strengthen the alloys by the formation of carbides and borides along the grain boundaries during solidification, which help to prevent the formation of casting pores and hot tearing and to strengthen low angle boundaries. The long-term stability elements inhibit the precipitation of topologically closed-packed phases causing deterioration of the mechanical properties. The oxidation resistance element, mainly Al, promotes the formation of protective Al2O3 surface layer.

Microstructure and mechanical properties of Ti48Zr18V12Cu5Be17 bulk metallic glass composite were investigated. The research shows that the microstructure mainly consists of amorphous matrix and β-Ti phase. However, the β-Ti phases are inhomogeneous distribution in glass matrix, which relates to composition hardly, but highly dependent to the comprehensive effects of fluid flow, thermal field and free grains. Upon the quasi-static compression, the amorphous composite shows high yield strength about 2016 MPa and a plastic strain about 10.91%. In addition, the deformation mechanisms of the BMGCs were also experimentally and theoretically explored.

TiC reinforced titanium matrix composites are promising for advanced applications. Generally, the relative density of the composites and the interfacial bonding between the matrix and reinforced particles may have a great influence on the mechanical properties. This study presented the fabrication of the full-densified Ti-15Mo-xTiC (x = 1.5, 3.0, 4.5 wt%) composites through in-situ reactive sintering of Ti, Mo, and MoC powders and hot swaging process. Experimental results show the formation of TiC and the absence of MoC in the fabricated composites. After hot swaging, the TiC particles showed aligned distribution along the swaging direction, and exhibited well bonding with the β-Ti matrix. Increasing the TiC content leads to increase tensile strength and Young's modulus but decrease elongation. Ti-15Mo-4.5TiC offers and outstanding combination: ultimate tensile strength = 1290 MPa, yield strength = 1075 MPa, Young's modulus = 89 GPa, and tensile elongation = 3.1%. The strengthening effect is attributed to Mo solid solution in Ti matrix, β-Ti grain refinement, and TiC particle reinforcement. The specific contribution of each mechanism is quantitatively calculated, showing good agreement with the experimental data.

Transparent GaN doped SnO2 thin films were deposited on glass substrates by e-beam evaporation with GaN:SnO2 targets of various GaN weight ratios. The effects of doping level and annealing temperature on the optoelectronic properties of GaN codoped SnO2 thin films were investigated. A conversion from n-type conduction to p-type was observed for GaN doped thin films upon annealing at 440 °C regardless doping level. However, it converted back to n-type conduction at various higher temperatures depending on GaN doping levels. Hole concentration for p-type GaN:SnO2 thin films could be achieved as high as 1.797 × 1019 cm−3 because of the codoping of Ga and N. Hall measurements showed that upon proper thermal treatments, Ga3+-Sn4+ and N3−-O2− substitution reactions occurred in the thin films, which regulated the polarity of conduction and carrier concentration. The formation of No substitutions in the GaN:SnO2 thin films and decomposition of them at certain higher temperature were mainly responsible for the n-p-n conduction transition.

The effect of fabrication methods on microstructures, mechanical properties, and strengthening mechanisms of high-entropy alloys has been systematically studied. In this work, a non-equiatomic Fe0.25CrNiAl medium-entropy alloy (MEA) was selected and fabricated by arc-melting, spark plasma sintering (SPS), and hot-press sintering (HPS). The results indicate that the fabrication method has little effect on the main phase compositions of Fe0.25CrNiAl MEA while marked impacts on microstructures, mechanical properties, and strengthening mechanisms. All alloys mainly consist of a disordered body-centered cubic (BCC) phase and an ordered body-centered cubic (B2) phase. However, the arc-melted alloy possesses a typical dendritic structure, while a speckle-like microstructure for the SPS-ed and HPS-ed alloys. Particularly the grain is refined dramatically by powder metallurgical methods of SPS and HPS. The yield strength of powder metallurgical alloys is over 400 MPa higher than that of arc-melted alloy, and without sacrificing the ductility (~30%). The strengthening mechanism analysis demonstrates that precipitate strengthening plays a significant role for arc-melted alloy while grain boundary strengthening is the dominant strengthening mechanism for powder metallurgical alloys. The Fe0.25CrNiAl MEAs by powder metallurgy achieve a trade-off between high strength and strain-to-failure, which suggests that the method is available for improving the mechanical properties of high-entropy alloys.

The electrical and thermal properties of thermoelectric performance can be decoupled by devising low-dimensional metal-semiconductor nanotechnology, which results to higher thermoelectric performance. In this work, 0D–2D (0 Dimension-2 Dimension) Au-SnSe nanocomposites with intensive interface barriers and beneficial phonon scattering were designed. Au NDs (nano dots) distributed on the surface of SnSe nanoplates, thereby forming the 0D–2D Au-SnSe nanocomposites. The Au NDs with abundant electrons were introduced to improve the electrical transportation properties while the 0D–2D nanostructure grain interfaces were designed to reduce phonons transportation property in comparison with the pure SnSe matrix. The interface barriers between Au NDs and SnSe nanoplates can effectively filter low energy holes and scatter mid and long wavelength phonons. As a consequence, the electrical conductivity of 1 mol% Au/SnSe nanocomposite is 2211.1 Sm−1 at 773 K, increasing by 174.2% with respect of that of pure SnSe, and, meanwhile, the thermal conductivity is 0.363 Wm−1 K−1, reducing by 11.2%. Attributed to the large enhancement in electrical transport and the diminution in thermal conductivity, a much higher ZT value of 0.6 is obtained for 1 mol% Au/SnSe nanocomposite at 773 K, which is in good contrast to 0.16 for pure SnSe nanoplates.

Dielectric Sr0.88Bi0.08TiO3 (SBT) and Sr0.88Bi0.08TiO3/TiO2 (SBT/TiO) thin films were fabricated via sol-gel and spin-coating method with various annealing temperatures ranging from 450 °C to 600 °C. The XRD results show that the SBT thin films can crystallize at a lower temperature due to introducing a TiO2 layer. The SEM results reveal that the annealing temperatures have impact on the surface morphology. Moreover, the absorbed water was closely related with annealing temperature. When the temperature rises to 550 °C, the reduction of absorbed water limited the formation of the aluminum oxide insulating layer between the Al electrode and the thin films, decreasing the breakdown strength. The finite element simulation showed the effect of the aluminum oxide insulating layer on enhancing the dielectric breakdown strength of the samples. The excellent energy storage performance was achieved in the SBT/TiO films annealed at 450 °C with the recoverable energy storage density of 31.3 J/cm3 and ultrahigh efficiency of 96%, which is almost 2 times that of SBT thin films (12.4 J/cm3). Additionally, the samples possess a high dielectric constant (107) and a low dissipation factor (~0.035) at 1 MHz. Therefore, This work could provide a novel and simple way to develop high-performance dielectric capacitor devices.

In this study, seven AlSi10Mg bulks with different construction angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) were fabricated by selective laser melting (SLM). The effects of different construction angles on the microstructure and mechanical properties of AlSi10Mg alloys were investigated. Increasing the construction angle changed the laser track segments from an ellipse to a semi-ellipse and then to fish-scale, specifically again from a semi-ellipse to an ellipse, due to the decrease of the laser radiation area. Meanwhile, the grains in the vertical planes changed from columnar grains to irregularly arranged grains, and then to equiaxed grains. The 45° sample exhibited the highest hardness of 154.44 HV0.1. The 60° sample had a good combination of strength and plasticity with a tensile strength of 463.54 MPa, yield strength of 283.37 MPa, and elongation of 9.25%. The observed mechanical property anisotropy of the current AlSi10Mg alloy was a result of the pores, equiaxed grain structure, ultra-fine equiaxed sub-grains, and working hardening. In addition, the difference in the sample microstructures was attributed to the construction angles and deposited layer area.

High-entropy alloys (HEAs) have attracted tremendous attention in various fields due to unique microstructures and many excellent properties. For particular applications, an in-depth understanding of the essence is important to further developing new HEAs with promising properties. In present paper, the recent development of HEAs was reviewed, including the phase formation and microstructures, various properties, and multi-scale modeling aided composition design. Materials informatics employ machine learning (ML) method to map the relationship between a targeted property and various materials descriptors, providing new avenues to accelerate the discovery of new materials. Particularly with the aid of machine learning approach, reliable composition-properties features can be offered which can act as guides for tuning composition design in HEAs. Eventually, potentials of utilizing machine learning combined multi-scale computation in materials science and the future prospects of HEAs are put forward.

A thermodynamic model was developed based on the first principles to describe the thermal stability in the phase-separated alloy systems. The distributions of the solute atoms in the nanocrystalline system were predicted for the heating process, using the typical phase-separating system of W-Cr alloy as an example. The effects of the re-dissolution and grain-boundary segregation processes on the thermal stability of the nanograin structure were investigated, based on which the critical conditions of grain size and solute concentration for controlling destabilization of nanostructure at high temperatures were proposed. The transformation of solute distribution from phase separation to grain-boundary segregation was described in detail by the present model without introducing any empirical parameters. The calculations indicated that the stabilization mechanisms are distinct for the single- and double-phase states of the nanocrystalline alloys even at the same composition. Thus the approach to inhibit nanograin growth is flexible by adjusting the solute distribution to reach either the thermodynamically stable or the meta-stable state. This study advanced the understanding of the doping effect and facilitated precise design of nanocrystalline alloys with high stability during high-temperature heat treatment.

With the rapid developments of electric vehicles and smart grids, the ever-growing demands for lithium-ion batteries (LIBs) and their further application will probably be impeded by limited lithium resources. In this context, sodium-ion batteries (SIBs) have been regarded as highly promising alternatives for LIBs due to the abundant sodium resources and similar electrochemical properties of this element. As promising electrode materials for SIBs, carbon nanotube (CNT)-based nanomaterials have received considerable attention because of their superior characteristics, such as their unique 1D nanostructure, large specific surface area, high conductivity, excellent flexibility and chemical stability. This article reviews recent advances in CNT-based electrode materials, including cathode materials and anode materials for SIBs. In addition, strategies to improve their electrochemical performance are concluded and discussed. Finally, challenges and prospects for future development of CNT-based electrode materials for SIBs are proposed.

The plastic deformation of FeCuNi ternary alloys of BCC nanocrystalline subjected to compressive or tensile loading is considered via molecular dynamics (MD) simulations at low temperature, to reveal the solid solution effect on BCC metals. Deformation mechanisms at nanoscale have been well revealed for FCC nanocrystalline structure, however, it remains unanswered for BCC nanocrystalline structure. The increase of solute concentration promotes the nucleation of partial dislocation due to the reduction of stacking fault energy, and suppresses the motion of dislocation owning to the severe lattice distortion, which is beneficial to improving the strength and ductility of FeCuNi alloys. There is a critical solute concentration to determine the strengthening or the softening of FeCuNi alloys. Interestingly, the deformation twinning mechanism, instead of traditional dislocation mechanism, dominates the plastic deformation of BCC ternary alloys. In addition, it is clear to observe the phase transformation from BCC to HCP, full dislocation slipping, cross-slip, grain growth, and grain boundary (GB)/twinning boundary (TB) motion. Fracture behaviors of FeCuNi alloys reveal that the addition of Cu and Ni elements results in the larger fracture toughness.