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The flow behavior of the solution-treated Mg-3.2Bi-0.8Ca (BX31, wt.%) alloy was systematically investigated during hot compression at different deformation conditions. In the present study, the strain-related Arrhenius constitutive model and dynamic recrystallization (DRX) kinetic model were established, and the results showed that both two models had high predictability for the flow curves and the DRX behavior during hot compression. In addition, the hot processing maps were also made to confirm a suitable hot working range. Under the assistance of a hot processing map, the extrusion parameters were selected as 573 K and 0.5 mm/s. After extrusion, the as-extruded alloy exhibited a smooth surface, a fine DRX structure with weak off-basal texture and good strength–ductility synergy. The newly developed strong and ductile BX31 alloy will be helpful for enriching low-cost, high-performance wrought Mg alloy series for extensive applications in industries.

CH₄–CO₂ replacement technology has broad application prospects in reducing CO₂ emission and developing natural gas hydrate (NGH) resources. It is of great significance to study the mechanism of CH₄–CO₂ replacement. In this paper, the effect of H₂O on CH₄–CO₂ displacement behavior is studied by molecular dynamics (MD) simulation and quantum mechanics calculation. The interactions between the host and guest in cages of CH₄ hydrate are calculated using the symmetry-adapted perturbation theory method. The contribution of physical components of binding energy can be determined. The result indicates that the electrostatic interaction of H₂O–H₂O and H₂O–gas is a key factor of the CH₄–CO₂ replacement mechanism. Additionally, the microconfigurations and microstructure properties are analyzed by MD simulation in the systems containing a gas layer (CO₂ or CH₄) and a CH₄ hydrate layer. The results showed that the movement and the arrangement of H₂O molecules influence the hydrate structure due to the interaction of H₂O–gas during the replacement process. The molecular simulation suggests that the change of electrostatic interaction with H₂O molecules could improve the CH₄–CO₂ replacement efficiency, which can be favorable for the investigation of CH₄ replacement technology in NGH with CO₂ injection.

To evaluate the influences of ceramic phase content and its morphology on the mechanical properties of MgO–C refractories, pre-prepared Si powder-phenolic resin loaded with Fe2O3 was introduced to prepare MgO–C refractories via catalytic nitridation. The effects of nitriding temperature and Fe2O3 content on the phase composition, microstructure evolution and properties of MgO–C refractories were studied and compared. The results show that the increase of the nitriding temperature was conducive to the in-situ formation of the ceramic phases, and a new phase of Mg2SiO4 was formed at temperatures ≥1450 °C. Both the increase in nitriding temperature and the addition of catalyst could inhibit the growth of α-Si3N4 to promote the formation of β-Si3N4 and MgSiN2. In addition, the formation of excessive ceramic phases caused samples after nitriding to expand violently and form more porous, thereby reducing the physical properties of MgO–C refractories.

In this paper, the growth behavior of brain-like SnO2 microspheres synthesized by a tetrahydrofuran (THF) solvothermal method was studied. Unlike water or ethanol as the solvent, THF is a medium polar and aprotic solvent. Compared with other common polar solvents, the THF has no strong irregular effects on the growth process of SnO2. In addition, the viscosity of THF also helps the SnO2 to form a regular microstructure. The growth behavior of the brain-like SnO2 microspheres is controlled by changing the synthesis temperature of the reaction. The SEM and TEM results reveal that the SnO2 forms particles first (125 °C/3 h), and then these nanoparticles connect to each other forming nanowires and microspheres (diameter ≈ 1–2 μm) at 135 °C for 3 h; finally the microspheres further aggregate to form double or multi-sphere structures at 180 °C for 3 h. In this paper, the brain-like SnO2 microspheres obtained at 125 °C for 3 h were selected as sensitive materials to test their gas sensing performance at different operating temperature (50 °C and 350 °C). The H2S was tested at 50 °C which is the lowest operating temperature for the sensor. The combustible gas (H2/CH4/CO) was measured at 350 °C which is the highest temperature for the sensor. They all have extremely high sensitivity, but only H2S has excellent selectivity.

To solve the problem of the high cost of ZrN as a raw material, nanoscale c-ZrN powders were synthesized by molten-salt nitridation at 1100 °C and introduced into low-carbon MgO–C refractories. The effect of ZrN content on the microstructure and properties of the refractories was investigated. The results indicated that the addition of ZrN significantly promoted the reaction, and there was a certain degree of chemical bonding between ZrN and the formed ceramic phases. As the content of ZrN increased, the formation of more ceramic phases was promoted, especially the formation of a larger amount and larger size of flake-like Mg2SiO4, which greatly improved the mechanical properties of the MgO–C refractories. Finally, the mechanism of ZrN in the MgO–C refractories was clarified.

Concrete is often used in building, bridges, dams, roads and other infrastructures. However, the porosities and natural hydrophilicity of concrete often induce the damage of the concrete architecture or other disasters. Endowing the concrete with superhydrophobicity can effectively improve the antifreeze–thaw, anti-corrosion and anti-icing properties and expand the application prospect of concrete in the modern construction industry. Despite all this, the compressive strength of superhydrophobic concrete is not high enough, limiting its application. Here, we maintained superhydrophobic concrete for 28 days and improved the compressive strength for 3.5 times from 10 MPa to 34.48 MPa. The main mechanism is that calcium silicate hydrate structures grow with the increase in maintenance time and make the inside microstructures connected more closely. In addition, XPS spectra were also collected to investigate the chemical compositions of the superhydrophobic concrete. A series of tests were carried out on superhydrophobic concrete and indicated that the superhydrophobic concrete after maintenance had high surface robustness, anti-corrosion property and high anti-icing and deicing capacity, showing the application value.

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios. The effects of spinning parameters on the forming accuracy of ellipsoidal heads have been studied, and optimized spinning parameters have been obtained. The microstructure evolution of a workpiece is usually very complicated in the spinning process. In this work, the influence of spinning parameters on the microstructures of two-pass spun ellipsoidal heads is studied. It is found that the forming angle and feed rate of the first pass, angle between passes, and feed rate of the second pass significantly affect the microstructures. Meanwhile, the evolution rule of the microstructures near the inner and outer surfaces of the spun parts is almost consistent. A large forming angle, large angle between passes, or large feed rate of the second pass are beneficial to obtain uniform microstructures. A small or large feed rate of the first pass reduces the microstructure uniformity. To improve the microstructure uniformity between the inner and outer surfaces, the optimized spinning parameters are determined.

Two kinds of MgO–C refractories were separately prepared by carbon-embedded method and high-temperature nitridation. The phase compositions, microstructures and physical properties of heat-treated samples were investigated. Specially, the relationship between interface bonding and physical properties was mainly studied. Compared with the carbon-embeded burnt samples, the nitrided samples showed higher porosity, but exhibited better mechanical properties. And a direct chemical bonding interface was formed between Si3N4 and flake graphite in the nitrided samples, which enhanced the driving force between the molecules. Based on the fact, the molecular dynamics simulation of the interface between Si3N4 and flake graphite was carried out by the Material Studio software, and the interface phase relationship was β-Si3N4 (1 1 0)//graphite (1 0 0).

Severe plastic deformation and lateral flow during machining of pure iron surface resulted in relatively serious tool wear and poor surface quality. Although several methods proposed could improve machinability of pure iron to some extent, poor wettability and high plasticity of pure iron cannot be changed, and further improvement of surface quality may be therefore restrained. In this paper, we propose a new machining method using atmospheric pressure plasma jet to adjust material properties of pure iron during precision turning process. The influence mechanism of plasma jet on surface wettability of pure iron is investigated by plasma modification experiment, scanning electron microscope, and X-ray photoelectron spectroscopy. On the basis of the influence mechanism, precision turning experiments are performed under different lubricating conditions. The experimental results indicate that plasma jet can effectively improve pure iron surface wettability by changing surface composition while not influencing surface microstructures. Under plasma atmosphere, surface roughness and cutting force are obviously reduced, and tool wear is effectively alleviated.

International audience; Cracks play an essential role in the degradation of the thermomechanical behavior of ceramic matrix composites. However, characterizing their complex 3D geometries within a complex microstructure is still a challenge. This paper presents a series of procedures, based on X-ray tomographic images, to evaluate the applied 3D strains, including their through-thickness gradients, and to detect and quantify the induced crack networks in ceramic matrix composites. Digital volume correlation and some dedicated image processing algorithms are employed. A novel method is proposed to estimate the opening, orientation and surface area of the detected cracks. The proposed procedures are applied to the images of a SiC/SiC composite tube that has been tested in situ under uniaxial tension with synchrotron X-ray computed tomography.

Wettability patterns have significant application potential in liquid transportation and water collection. Plasma hydrophilization is high-efficient and less-destructive, and has been widely used for preparing wettability patterns. However, the plasma-treated surfaces tend to recover to its original wettability, causing invalidation of the patterns. As a green treatment method, boiled water treatment could construct nanostructures, which is favorable for hydrophilicity-retaining; while the hydrophilization effect of plasma treatment would promote the reaction. Therefore, it should be possible to combine plasma and boiled water treatments to prepare long-lasting wettability patterns. In this paper, superhydrophobic aluminum surfaces were modified by plasma jet followed by boiled water treatment. The time stability, microstructures and chemical compositions of the treated surfaces were investigated by testing contact angles, scanning electron microscope, X-ray diffractometer, and X-ray photoelectron spectroscopy. The surfaces treated by plasma jet and boiled water could retain superhydrophilicity for a long time under various storage conditions, including normal ambient, high temperature or high humidity. On the basis of this technique, long-lasting patterns could be prepared on different metal substrates. The green method proposed is expected to have promising application potential in fabricating wettability patterns and lab-on-chip devices, especially for those used in severe conditions.

In the present work, a Co-substituted LiZnTiBi (Li0.43Zn0.27CoxTi0.13Fe2.167-xBi0.003O4) ferrite with equivalent permeability and permittivity was prepared by a low-temperature sintering method. In detail, the LiZnTiBi ferrite with high permeability was obtained by a solid phase method. Next, different mass of Co2O3 (x = 0.100, 0.125, 0.150, 0.175 and 0.200) were added to reduce permeability (μr’) and enhance cut-off frequency (fr) of the ferrite. Results indicated that the Co-substituted LiZnTiBi ferrite with equivalent permeability and permittivity (μr’ = er’ = ∼12.3) was obtained when additive amount of Co2O3 (x) is around 0.150. Meanwhile, the cut-off frequency (fr) of the ferrite is more than 500 MHz. Also, the influences of Co2O3 additive on the microstructure and phase structure of the LiZnTiBi ferrite have been investigated and discussed. SEM images indicated that the Co-substituted LiZnTiBi ferrites possess uniform and compact grains (average grain size is ∼1 μm). XRD patterns demonstrated that the LiZnTiBi ferrite material has a pure spinel structure. Rietveld refinement of XRD proved that Fe3+ is substituted by Co3+. And energy dispersive spectrometer (EDS) result indicated that the Co element is existed in ferrite grains. Such a low-temperature sintering ferrite substrate material with equivalent permeability and permittivity at high frequency (@500 MHz) should also be an alternative material for microwave devices, especially for miniature antenna.

The microstructural variation and high-temperature flow features of a Ti-55511 alloy in the β region are studied by utilizing double-stage compression with a stepped strain rate. The results demonstrate that the stresses in the latter stage of hot compression markedly reduce as the strain at the previous stage or the strain rate at the previous/latter stage drops. Moreover, the annihilation/interaction of substructures is promoted, and the distinct refinement of the dynamic recrystallization (DRX) in the β grain can be found. However, the coarsening of the β grain and the consumption of dislocation substructures are accelerated at high temperatures. Furthermore, the principal DRX nucleation mechanism of the Ti-55511 alloy during double-stage compression with a stepped strain rate in the β region is discontinuous DRX. Additionally, by using the microstructural variation characteristics related to the forming parameters, a physical mechanism equation is modeled to forecast the forming features, the DRX fraction, and the size of the β grain in the investigated alloy. The forecasted results are in accordance with the tested results, indicating that the established model can accurately forecast the microstructure variation and flow features of the studied alloy.

This study proposed a dynamic forming mechanism development of the negative Poisson’s ratio elastomer molds—plate to plate (P2P) forming process. To dynamically stretch molds and control the microstructural shape, the proposal is committed to using the NPR structure as a regulatory mechanism. The NPR structural and dynamic parallel NPR-molds to control microstructure mold-cores were simulated and analyzed. ANSYS and MATLAB were used to simulate and predict dynamic NPR embossing replication. The hot-embossing and UV-curing dynamic NPR P2P-forming systems are designed and developed for verification. The results illustrated that the dynamic forming mechanism of the negative Poisson’s ratio elastomer molds proposed by this study can effectively control microstructure molds. This can effectively predict and calculate the geometrical characteristics of the microstructures after embossing. The multi-directional dynamic NPR microstructural replication process can accurately transfer microstructures and provide high transfer rate-replication characteristics.

A novel type of inorganic high-temperature adhesive that can be cured at room temperature and applied to a high-temperature furnace was prepared using alumina and micro-silica as materials, liquid aluminum dihydrogen phosphate as a binder, and then sintered at a high temperature. To evaluate the mass ratio of Al2O3:SiO2 and the optimal sintering system, the physical properties of the adhesive after sintering were tested, and the phase and microstructure were characterized. The results revealed that the physical properties of the adhesive at 1300–1600 °C were better at a mass ratio of Al2O3:SiO2 = 5:1. When the sintering temperature was 1300 °C, columnar mullite was formed. At 1500 °C, the adhesive had a high shear strength.

The methane hydrate formation and the methane hydrate dissociation behaviors in montmorillonite are experimentally studied. Through the analyses of the microstructure characteristic, the study obtains the porous characteristic of montmorillonite. It is indicated that methane hydrate in montmorillonite forms the structure I (sI) crystal. Meanwhile, molecular dynamics simulation is carried out to study the processes of the methane hydrate formation and the methane hydrate dissociation in montmorillonite. The microstructure and microscopic properties are analyzed. The methane hydrate formation and methane hydrate dissociation mechanisms in the montmorillonite nanopore and on the montmorillonite surface are expounded. Combining the experimental and simulating analyses, the results indicate the methane hydrate formation and methane hydrate dissociation processes have little influence upon the crystal structure of porous media from either micro- or macro-analysis. It is beneficial to the fundamental researches on the exploitation and security control technologies of natural gas hydrate in deep-sea sediments.

Generally, well wear resistance corresponds to low friction coefficient. While, well wear resistance and high friction coefficient are needed in brakes for short braking distance and long serving life. Ceramics possess high hardness which correspond well wear resistance. Cobalt is often used as bond phase of tungsten carbide ceramic, which will increase the toughness of tungsten carbide. While, the stiffness of WC-Co will decrease after cobalt is introduced into tungsten carbide, which will lead to the decrease of friction coefficient. To increase the stiffness and the friction coefficient of WC-Co, nano WC particles were introduced into cobalt binder phase which formed WC-(nano WC-Co). In this work, WC-(nano WC-Co) coatings were prepared through high velocity oxygen fuel (HVOF) spray on the vermicular iron substrate in order to increase friction coefficient and wear resistance simultaneously. The microstructure, mechanical property and wear performance of the coating were investigated. It was found that the microhardness of WC-(nano WC-Co) coatings had the highest hardness of 1393 ± 13 HV with 50% nano WC-10Co-4Cr. Meanwhile, its friction coefficient was obviously increased to 0.7, which was three times higher than that of the vermicular cast iron and higher than both of the micro-sized and nano sized WC-Co. Its wear mass loss of WC-(nano WC-Co) coating was much lower than that of the vermicular cast iron and lower than both of the micro-sized and nano sized WC-Co. The friction coefficient and wear resistance of WC-(nano WC-Co) were increased simultaneously.

The carbon coated core-shell C@Fe3C/Fe nanocomposites were prepared by plasma arc-discharging method. The core-shell and graphite network structures were obtained, which could improve the absorbing properties by optimizing the impedance matching and increase the internal reflections of the propagated microwave. By varying the coating thickness from 1.0 to 5.0 mm, the reflectivity of C@Fe3C/Fe nanocomposites prepared in 30% CH4 is less than −20 dB nearly in the whole range of 2–18 GHz. The minimum reflection loss value reaches −32.9 dB at 14.2 GHz and the effective bandwidth (

International audience; Damage initiation is an important issue to understand the mechanical behavior of ceramic matrix composites. In the present work, a braided SiC/SiC composite tube was studied by FFT simulation tightly linked with micro-computed tomography (µCT) observations performed during an in situ uniaxial tensile test, which provide both the real microstructure, with a good description of local microstructural geometries, and location of cracks at the onset of damage. The FFT method was proven applicable to tubular structures and efficient to complete the large-scale simulation on a full resolution µCT scan (~6.7 billion voxels) within a short time. The edge effect due to the numerical periodic boundary conditions prescribed on the real and not rigorously periodic microstructure was quantified. The obtained stress field was compared to the cracks detected by the in situ µCT observations of the same composite tube. This one-to-one comparison showed that cracks preferentially initiated at tow interfaces, where sharp edges of macropores are mostly located and generate stress concentrations.

The failure of a convection tube used in an ethylene cracking furnace after service for >6 years was analyzed by various characterizing techniques. Cracks were found on the second convection tube located under the straight tube section. Severe bulging deformation was found around the cracking area. Stereoscopic inspection revealed that the main crack has penetrated through the tube wall, while a circumferential crack network was formed on the failed tube surface. Chemical composition analysis confirmed that the failed tube material belong to the 304H stainless steel family. SEM analysis on the fractured surface showed that the cracking mechanism was mainly intergranular brittle fracture. Microstructure observation found that grains within the cracked area experienced severe growing compared with intact area. Besides, more coarsened chromium carbides distributed within grains and along grain boundaries around cracked area, where voids were also occurred at grain boundaries. Based on the above inspection and analysis, the crack of the convection tube were confirmed to be caused by the localized overheating. The root cause for such localized overheating may due to inadequate steam flow and uneven heat distribution within the convection tube during service.

The microstructure and mechanical properties of high-entropy alloy (HEA) coatings by plasma cladding on Ti substrate are studied by the analysis of a series of FeCoCrNiNbX (X = 0.25, 0.6, 0.8) HEA coatings, to reveal the additional elemental Nb effects. The results show that the HEA coatings exhibit typical dendritic structure, and consist of BCC and FCC structures. The wear resistances of FeCoCrNiNbX HEA coatings increase firstly and then decrease with the increase of Nb content, agreeing with the hardness of coatings. Compared with the other HEA coatings from the previous work, the friction coefficients of the FeCoCrNiNbX HEA coatings are relatively lower and more stable, indicating the potential applications, such as for wear protection films of gear. The FeCoCrNiNb0.6 HEA coating shows high hardness and good wear resistance due to the reasonable volume fraction between BCC and FCC phases. The volume fraction of BCC and FCC structures in HEA coating are predicted not only using the valence electron concentration (VEC), but also by calculating parameters of Δ H mix and δ depending on the mixing enthalpy and the atomic size difference.

The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca (TZX621) (mass fraction, %) alloy was investigated. It is found that incomplete dynamic recrystallization (DRX) took place in as-extruded TZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXed grains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particles and fine Mg2Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation of as-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%, 17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.

High entropy alloy attracts great attention for its high thermal stability and corrosion resistance. A CoCrFeNiMn high-entropy alloy coating was deposited on grey cast iron through plasma transfer arc cladding. It formed fine acicular martensite near the grey cast iron, with columnar grains perpendicular to the interface between the grey cast iron substrate and the cladding layer as well as dendrite in the middle part of the coatings. Simple FCC solid solutions present in the coatings which were similar to the powder’s structure. The coating had a microhardness of 300 ± 21.5 HV0.2 when the cladding current was 80 A for the solid solution strengthening. The HEA coating had the highest corrosion potential of −0.253 V when the plasma current was 60 A, which was much higher than the grey cast iron’s corrosion potential of −0.708 V. Meanwhile, the coating had a much lower corrosion current density of 9.075 × 10−7 mA/cm2 than the grey cast iron’s 2.4825 × 10−6 mA/cm2, which reflected that the CoCrFeNiMn HEA coating had much better corrosion resistance and lower corrosion rate than the grey cast iron for single FCC solid solution phase and a relatively higher concentration of Cr in the grain boundaries than in the grains and this could lead to corrosion protection effects.

The evolution of helium bubbles in a newly developed Fe9Cr1.5W0.4Si alloy that is an important candidate used as fuel claddings in the Lead-cooled fast reactors was in-situ investigated by transmission electron microscopy during 30 keV He+ irradiation at 500 °C and subsequently annealed at 600 °C. Meanwhile, the evolution of dislocation loops was in-situ researched in the initial stage of irradiation. Two mechanisms including the absorption of irradiation defects and the combination of dislocation loops induced the loop growth. Both He+ irradiation and subsequently annealing induced the initiation, migration, aggregation, and growth of helium bubbles, and changed their shape from spherical to preferential faceted. But it was more obvious under the annealing condition. Helium bubbles would preferentially nucleate and grow at dislocation lines and grain boundaries and had large size. The bubble lines formed at dislocation line during helium irradiation, and annealing made them more obvious and larger. A denuded zone with few helium bubbles appeared near grain boundary, but its width decreased with the increase of helium fluence and annealing time. Meanwhile, annealing would lead to the appearance of super large helium bubbles at grain boundaries. The irradiation hardening and swelling were increased with the increase of helium fluence. The corresponding mechanism was analyzed based on in-situ experimental observation.

High strength steel products with good ductility can be produced via Q&P hot stamping process, while the phase transformation of the process is more complicated than common hot stamping since two-step quenching and one-step carbon partitioning processes are involved. In this study, an integrated model of microstructure evolution relating to Q&P hot stamping was presented with a persuasively predicted results of mechanical properties. The transformation of diffusional phase and non-diffusional phase, including original austenite grain size individually, were considered, as well as the carbon partitioning process which affects the secondary martensite transformation temperature and the subsequent phase transformations. Afterwards, the mechanical properties including hardness, strength, and elongation were calculated through a series of theoretical and empirical models in accordance with phase contents. Especially, a modified elongation prediction model was generated ultimately with higher accuracy than the existed Mileiko’s model. In the end, the unified model was applied to simulate the Q&P hot stamping process of a U-cup part based on the finite element software LS-DYNA, where the calculated outputs were coincident with the measured consequences.

The effect of Sn content on the mechanical properties and corrosion behavior of Mg-3Al-xSn alloys was investigated by SEM-EDXS, XRD, electrochemical measurements, and scanning Kelvin probe force microscopy (SKPFM). The results showed that when the Sn content was 1.4 wt%, Sn dissolved in the α-Mg matrix and then precipitated as an intermetallic compound (Mg2Sn). The combined results of mass loss, hydrogen evolution, and electrochemical measurements indicated that Mg-3Al-1Sn had a low corrosion rate. The SKPFM results showed that the Volta potential of Mg2Sn particles, Al-Mn, and β-Mg17Al12 phases were 100, 80, and 50 mV higher than the matrix, respectively. Therefore, the Mg2Sn phase that formed in Mg-3Al-xSn served as a local cathode due to its high potential, which accelerated microgalvanic corrosion along with the secondary local cathode (Al-Mn). The Sn solution strengthening and secondary phase strengthening (fine Mg2Sn particles) improved the mechanical properties of the Mg-3Al-xSn alloys.

Rare-earth-oxide Tb2O3-doped Ga2O3–B2O3–SiO2–GeO2 (GBSG) glasses with different B2O3 concentrations were prepared and studied. The Verdet constant of the GBSG glasses was measured, and it was found that the Verdet constant increased greatly when the content of Tb4O7 is fixed but the B2O3 concentration increases. The X-ray photoelectron spectrometry and electronic paramagnetic resonance spectrums show that the ratio Tb3+/Tb4+ increases with the increase of B2O3. The self-reduction of Tb4+ occurred. According to the Fourier transform infrared and MAS-NMR spectrums, when the B2O3 concentration increased, the depolymerization of the boron groups occurred. The [BO4]-based high polymeric network decomposed into the lower ones containing [BO3], which caused the reduction in which the diamagnetic Tb4+ gradually reduces to the paramagnetic Tb3+. This is the basic reason why the Verdet constant increases with the B2O3 concentration. Finally, the schematic illustration of the position of Tb ions and the electron tra...

A medium carbon alloy steel is processed by austenizing at 900 °C for 30 min, then rapid quenching into a patented quenching liquid and holding at 170 °C for 5 min, finally isothermally holding at 250 °C for different times. The morphology and mechanical properties are performed by using optical microscopy and scanning electron microscopy. A multiphase microstructure characterized by a mixture of lenticular prior martensite (PM), fine needle bainitic ferrite and filmy retained austenite (RA) is obtained. It is found that the PM formed firstly upon quenching can accelerate the subsequent bainitic transformation and promote refinement of multiphase colonies. The results show that an optimum mechanical property of a 4000.9 MPa bending strength and a 2030 MPa tensile strength is achieved at 250 °C for 120 min, which is attributed to the multiphase microstructural characteristics and a high product of the volume fraction of RA and the carbon content of austenite.

Natural gas hydrate (NGH) formation behavior in porous sediment influences the investigation of the reservoirs and the exploitation of NGH. However, its molecular mechanisms of NGH formation in the porous sediment remain unclear. In this work, we present the CH4 hydrate formation in the smectite system through molecular dynamics simulation. The microstructure molecular configurations and properties are analyzed. The results find the pure H2O solution and the CH4-H2O homogeneous solution in the initial configuration of the smectite layer reveal the different influence on the hydrate formation. The gas–water ratio (ri) affects the molecular diffusion and the hydrate formation. In the smectite layer, the two types of arrangements of cages are present: the semi-cage arrangement and the link-cage arrangement. The silicon-oxygen ring of the smectite surface connecting with the two types of arrangements of cages has the stable effect for the hydrate formation in the smectite.

Although the parts produced by selective laser melting (SLM) are reported to possess comparable or better mechanical properties than the traditionally processed counterparts, the SLM-produced parts demonstrate slightly unfavorable corrosion resistance properties compared with their traditional counterparts. This work shows that, in addition to rapid manufacturing of parts, SLM can effectively refine the grains of eutectic Al-12Si alloy. The SLM-produced Al-12Si shows an ultrafine-grained microstructure and improved corrosion resistance, which provides an innovative and efficient approach to refine the silicon particles in eutectic Al-12Si alloy. Unlike the microstructured Al-12Si alloy manufactured by traditional casting, the SLM-produced Al-12Si alloy contains ultrafine-grained eutectic silicon particles distributing in the aluminum substrate. Importantly, it is found that the SLM-produced Al-12Si alloy possesses superior corrosion resistance than the cast Al-12Si alloy in terms of the results from electrochemical methods and weight loss test. The favorable corrosion resistance of SLM-produced Al-12Si is attributed to these ultrafine silicon particles, which prominently benefits for the formation of the oxide film. The influence of the microstructure with regard to eutectic silicon particles size on the corrosion resistance has also been discussed in depth. Keywords: Selective laser melting, Corrosion resistance, Eutectic Al-12Si alloy, Ultrafine microstructure

Electrochemical measurements and microstructural studies were carried out to investigate the corrosion behaviour of the different planes for the Al-12Si alloy produced by selective laser melting (SLM). The electrochemical results demonstrate that the building direction plane (XZ-plane) of the SLM-produced alloy exhibits better corrosion resistance in comparison with the building plane (XY-plane) in 3.5 wt% NaCl solution. The relatively inferior corrosion resistance of the XY-plane is ascribed to that the grown corrosion products extrude the deep and small-bore Si shells on the aluminum substrate, thereby causing the crack of Si shells. Without such a cover of the Si shells, the Cl− would continuously penetrate into the aluminum substrate and ultimately induce occurrence of the severe pitting. As for the XZ-plane, the corrosion products cannot grow and deposit in its shallow and large-bore Si shells, instead of transferring to the testing solution. The undamaged Si shells and formed oxide film constitute a protective layer to protect the aluminum substrate from the attack of Cl−, thereby displaying superior corrosion behaviour for the XZ-plane.

NbOx@NbN microcomposite particles with enhanced photocatalytic and electrochemical properties were synthesized through in situ partial oxidation from a NbN precursor by annealing in air. Thermal treatment optimization is carried out accompanied by extensive investigation on the formation of NbOx with TEM and XPS analysis. The as-prepared NbOx@NbN composite inherited the layer-like structure from the pre-annealed NbN powders and grew with mixed niobium oxides. The sample exhibited a 17-fold increase in photocatalytic hydrogen production and a 1.8 times enhancement of the specific capacity as an anode material for lithium-ion batteries compared with commercial Nb2O5. An illustrative scheme of the sample formation and photo-driven reaction was proposed. Due to the escape of nitrogen during heating, the mesopore-containing microstructure and increased specific surface areas are advantageous for electron mobility and interfacial reactions. By analyzing the positive effect of the optical and electrical properties from NbOx and the improved light absorption from the presence of NbN, the functional properties of the NbOx@NbN heterostructure in terms of both photocatalytic and electrochemical applications are revealed for the first time.

In this work, the microstructure, precipitations, crystal orientation and texture of an Inconel 718 superalloy manufactured by selective laser melting (SLM) are investigated by performing post heat treatment. Horizontal and vertical reference faces are examined in the as-built condition, solution conditions for 0.5 and 1 h, and aging condition, respectively. In the as-built condition, Inconel 718 superalloy exhibited cellular and columnar dendrites, a large amount of the fine Laves phase, and several γ′ phases. During post treatment, the grain size on the horizontal face is changed, which is ranged from 502.23 to 523.55 μm2 per grain. Meanwhile, grains coarsened distinctly on the vertical face. The average area of the grain is 739.48 μm2 in the as-built condition and increases to 898.19 μm2 in the aging condition. Additionally, the amount of MC carbides, γ′, and γ″ strengthening phases increased as well during the post heat treatment process, while that of the Laves phase decreased after solution treatment. The preferred orientation on the horizontal face was 〈111〉//X, 〈001〉//Y in the as-built condition, and 〈101〉//Z in the solution and aging conditions. The preferred orientation on the vertical face was 〈001〉//X, 〈101〉//Y in the as-built condition, 〈101〉//Y in the solution condition, and 〈001〉//X in the aging condition. The orientation distribution function (ODF) analysis showed that the main textures in the as-built and solution conditions were {110}〈110〉 and {110}〈112〉, respectively, which transformed to {001}〈100〉 and {001}〈110〉 during aging. The values of multiples of uniform density (mud) in both horizontal and vertical reference faces the aforementioned preferred orientation and texture increased during post heat treatment. Application of post heat treatment can lead to an ideal microstructure Inconel 718 superalloy manufactured by SLM.

In this work, a systematic study of the influences of CuO nanoparticle on the crystal structure, morphological characteristics and magnetic parameters of LiZnTi ferrite is present. The CuO-substituted LiZnTi ferrites (Li0.43−x/2Zn0.27Ti0.13CuxFe2.17−x/2O4; 0 ≤ x ≤ 0.25) are synthesized through solid-phase sintering process. XRD results suggest that there is only spinel structure (space group Fd-3m), meaning the CuO nanoparticle has no effect on phase structure. And the phenomenon that left shift of the diffraction peaks is due to larger Cu2+ ions substitution. SEM images show that the ferrites have uniform and compact grain, which indicates the Cu2+ ions substitution does not deteriorate microstructure. Moreover, the relationships between magnetic properties and Cu2+ ions content have been discussed in detail. Finally, a spinel structure LiZnTi ferrite with uniform grain and optimized magnetic parameters (4πMs = 3904.3 G, Br/Bs = 0.87, Hc = 241.2 A/m and Bs = 306.2 mT) is obtained when Fe3+ ions are replaced by Cu2+ ions (i.e., x = 0.15).

The reversible/irreversible recovery of mechanical properties, and the microstructure characteristics of a typical hot-stamped steel B1500HS have been studied under different conditions of hydrogen permeation. Initially, all tested specimens were permeated by hydrogen atoms through an electrochemical hydrogen charging scheme. Then, the comparisons between different currents and charging time were performed. The influence of different storage time was compared as well. Additionally, the effect of the plastic strain introduced by pre-stretching was also investigated. The experimental results showed that the negative impact of hydrogen embrittlement was altered from reversible to irreversible as the magnitude of the charging current increased. The hydrogen blistering and the hydrogen charging-induced cracks were both observed and inspected in the tested samples regarding the irreversible situation. Moreover, the adverse influence of hydrogen embrittlement was enhanced by plastic pre-straining or extending the charging period. At the micro-level, hydrogen charging-induced cracks generally were generated at defect locations, such as the prior austenite grain boundaries and lath martensite interfaces. Particularly, crack direction occurred perpendicular to the orientation of lath martensite, and transgranular fracture occurred at the prior austenite grains.

The influence of W and Al on the solidus and liquidus temperatures, microstructure and stress-rupture property at 980 °C/250 MPa was investigated in three Re-free experimental Ni-based single crystal superalloys. The results indicated that the solidus temperature increased for 14.0 °C and 9.8 °C by adding 0.84 wt.% W only and adding 0.45 wt.% Al and 0.44 wt.% W to the base alloy, respectively. The γ′ morphology changed from nearly cuboidal in the base alloy to cuboidal by adding 0.45 wt.% Al and 0.44 wt.% W. The volume fraction of γ′ precipitates increased, while the γ channel width decreased after adding Al and W. The additions of Al and W improved the stress-rupture life at 980 °C/250 MPa because of higher γ′ volume fraction, narrower γ matrix channel and more complete rafting structure.

The classical homogenization method has been widely adopted to capture the effective behaviors of heterogeneous materials. However, when the characteristic length of the microstructure of the heterogeneous material is comparable to the size of the structure, the classical homogenization method is mathematically no longer valid. In this paper, a new substructure-based homogenization approach is proposed to predict the mechanical responses of systems with periodic microstructures of comparable sizes. A substructure element is developed to reconstruct the system with periodic microstructure of comparable size. It is verified that this substructure-based homogenization approach can accurately predict the mechanical responses of the system. Comparing with the full finite element analysis, the computational scale is dramatically decreased. After that, a simplified substructure element is developed by using less surface nodes in the “full” substructure element. The numerical results show that, with further significantly reduced computational cost, the third-order simplified substructure element can provide a good prediction of the responses of the system with periodic microstructure of comparable size.

Magnesium alloys are the most promising implant materials due to their excellent biodegradability. However, their high degradation rate limits their practical application. In this study, we produced a calcium-phosphate (Ca-P) coating and a calcium-phosphate-silicon (Ca-P-Si) coating via one-step and two-step micro-arc oxidation processes, respectively. The microstructure and chemical composition of the MAO coatings were characterized using SEM, XRD and EDS. The degradation behaviors of the MAO coatings and the substrate were investigated using electrochemical techniques and immersion tests in simulated body fluid (SBF). The results show that the silicate was successfully incorporated into the Ca-P coating in the second MAO step, and this also increased the thickness of the coating. The Ca-P-Si coatings remarkably reduced the corrosion rate of the Mg alloy and Ca-P coating during 18 days of immersion in SBF. In addition, the bone-like apatite layer on the sample surface demonstrated the good biomineralization ability of the Ca-P-Si coating. Potentiodynamic polarization results showed that the MAO coating could clearly enhance the corrosion resistance of the Mg alloy. Moreover, we propose the growth mechanism of the MAO coating in the second step.

Microneedle (MN) offers an attractive, painless and minimally invasive approach for transdermal drug delivery. Polymer microneedles are normally fabricated by using the micromolding method employing a MN mold, which is suitable for mass production due to high production efficiency and repeat-using of the mold. Most of the MN molds are prepared by pouring sylgard polymer over a MN master to make an inverse one after curing, which is limited in optimizing or controlling the MN structures and failing to keep the sharpness of MNs. In this work we describe a fabrication method of MN mold with controlled microstructures, which is meaningful for the fabrication of polymer MNs with different geometries. Laser micro-machining method was employed to drill on the surface of PDMS sheets to obtain MN molds. In the fabrication process, the microstructures of MN molds are precisely controlled by changing laser parameters and imported patterns. The MNs prepared from these molds are sharp enough to penetrate the skin. This scalable MN mold fabrication method is helpful for future applications of MNs.

Magnesium-based alloys exhibit biodegradable, biocompatible and excellent mechanical properties which enable them to serve as ideal candidate biomedical materials. In particular, their biodegradable ability helps patients to avoid a second surgery. The corrosion rate, however, is too rapid to sustain the healing process. Alloying is an effective method to slow down the corrosion rate. However, currently magnesium alloys used as biomaterials are mostly commercial alloys without considering cytotoxicity from the perspective of biosafety. This article comprehensively reviews the status of various existing and newly developed degradable magnesium-based alloys specially designed for biomedical application. The effects of critical alloying elements, compositions, heat treatment and processing technology on the microstructure, mechanical properties and corrosion resistance of magnesium alloys are discussed in detail. This article covers Mg–Ca based, Mg–Zn based, Mg–Sr based, Mg–RE based and Mg–Cu-based alloy systems. The novel methods of fabricating Mg-based biomaterials and surface treatment on Mg based alloys for potential biomedical applications are summarized.

The effects of samarium (Sm) on the microstructure and corrosion behavior of AZ91 magnesium alloy treated by ultrasonic vibration were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electrochemical measurements. The results showed that the addition of Sm resulted in the formation of Al2Sm, which reduced the volume fraction of the &beta, Mg17Al12 phase and changed its morphology to fine granular. The AZ91&ndash, Sm alloys treated by ultrasonic vibration revealed relatively lower weight loss, hydrogen evolution, and corrosion current density values compared to the ultrasonic-treated AZ91 alloy prepared without Sm. Locally, a coarse &beta, phase in the ultrasonic-treated AZ91 alloy accelerated the possibility of micro-galvanic corrosion growing into the matrix. In the prepared AZ91&ndash, Sm alloys treated by ultrasonic vibration, the fine &beta, and Al2Sm phases reduced the probability of micro-galvanic corrosion growth and, therefore, formed a uniform corrosion layer on the surface of the alloys.

Promoting grain growth and optimizing microstructure are valid strategies for enhancing gyromagnetic and microwave dielectric properties of low-temperature sintered ferrite materials. Here, a modified low-temperature sintering technique was attempted for the synthesis of LiZnTi ferrites that have compact microstructure and improved performances. Trace amounts of CuO-Bi2O3 mixtures (0.50 wt%) were adopted as sintering additives to promote grain growth and to reduce the sintering temperature. Meanwhile, Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles (∼21.9 nm) were synthesized using a sol-gel auto-combustion method and were used to optimize the microstructure and to restrain abnormal grain growth. XRD Rietveld refinement and SEM images revealed that uniform and dense LiZnTi ferrites with single-phase spinel structure were obtained. Results demonstrated that co-doping of Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and CuO-Bi2O3 mixtures allows low-temperature sintering (900 °C) to be achieved and also promotes grain growth and densification. In particular, LiZnTi ferrites that were modified with 5.00 wt% Li0.42Zn0.27Ti0.11Fe2.2O4 nanoparticles and 0.50 wt% CuO-Bi2O3 sintering additives exhibited narrow ferromagnetic resonance linewidth (ΔH, ∼145 Oe) and low dielectric loss tangent (tanδe, ∼2.45 × 10−4) at ∼9.50 GHz, high saturation flux density (Bs, ∼364 mT), and high squareness ratio (Br/Bs, ∼0.89). Such a modified sintering technique at a low sintering temperature, as reported in this work, provides a reference for other advanced ferrites.

A paraxial powder-feeding system by employing a quasi-continuous fiber laser machine was established to repair non-weldable nickel-based K447A alloy. In the present study, the duty cycle (DC) of the pulsed-wave laser was chosen to reveal the influence on hot cracking. The results showed that the total length of hot cracking on the 10.5 mm-length longitudinal section of the cladding zone reduces from 3.263 mm to 0.092 mm with the decline of DC from 80% to 30%. The intermittent occurrence of the laser beam induced the ripple microstructure in the cladding layer (CL). It is the high cooling rate in laser extinguishment process that caused the fine dendrite zone which provides more resistance for hot cracking propagation in the CL. The liquid film in the heat-affected zone (HAZ) mainly results from the M5B3/γ, γ′/γ, and MC/γ constitutional liquation successively among 1200–1300 °C. Heat input is the main factor affecting hot cracking in the HAZ. With the decrease of DC, the dendrite spacing of the fine dendrite zone decreases in the CL, and the depth of liquefaction zone decreases in the HAZ, as a result, the length of hot cracking in the CL and HAZ both decreases.