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To increase the electrical conductivity of nickel electrodes used in solar cells, this study investigated the effects of six different alcohol-based brighteners on nickel electrodeposition and elucidated their mechanisms during the deposition process. Nickel electrodeposition was conducted on a single-crystal silicon (c-Si) substrate in a Watts nickel plating bath with the addition of various additives at 1 g/L. Surface analysis and microstructure characterization were employed, alongside density functional theory calculations and molecular dynamics simulations, to analyze the influence of brightener molecule adsorption on metal grain growth and conductivity properties. These results indicate that alcohol-based additives can be automatically absorbed on the surface of the deposit, whereas long-chain polyhydroxy additives result in a smaller energy gap ( Δ E ) and more active adsorption sites than do short-chain additives, facilitating greater reactivity on the Ni surface. This resulted in a preferred orientation shift of the crystal structure from the (200) plane to the (111) plane, along with a refined grain size and conical morphology growth. Among the studied additives, long-chain molecules increased the Ni0 content in the plating layer and increased its conductivity. In particular, sorbitol effectively reduced the resistivity and grain growth rate of the coating, underscoring its potential as an additive for fabricating high-performance electrodes on c-Si substrates. [ABSTRACT FROM AUTHOR]

A Monte-Carlo-assisted phase field model for the simulation of grain growth in metals and alloys is presented. The simulation time in this model is connected to real time through an experimental data-based kinetic model. Site selection probability is introduced to simulate grain structure evolution under non-isothermal conditions. The grain evolutions with temporal and spatial distributions of temperature during the welding process are comprehensively reproduced. The average size and topological texture of the generated grains in the fusion zone and heat-affected zone are examined. The computed results are compared to experimental data for laser-welding two alloys: Fe–6.5 wt.%Si and low-carbon steel. The applications of real-time–temperature based phase field simulation to material processing indicate significant promise for understanding grain structures during the welding process or additive manufacturing processes. [ABSTRACT FROM AUTHOR]

A deep operator network (DeepONet) has been constructed that generates accurate representations of phase-field model simulations for evolving two dimensional metal grain morphology growing from melt. These representations serve as lower resolution, computationally efficient stand-ins for quick parameter space exploration of solutions to the Allen–Cahn equations that dictate the phase-field model simulations. The experimental target for the phase-field model is a uranium casting system cooling a 434 g uranium charge from a maximum temperature of 1400 °C at an average rate of 30 ° C min , traversing the crystallographic phases of the pure metal. Experimental parameters inform the phase-field model, whose higher resolution computational model solutions are used to train the DeepONet in a given parameter space with the aim of developing a faster, more efficient method for predicting the solidifying metal's microstructure at different potential experimental values. The final DeepONet generates high accuracy, lower resolution predictions with cumulative relative approximation error over all timesteps of less than 0.5%, while ensuring solutions remain within physically feasible ranges. These relative error values are comparable with other state-of-the-art DeepONet models for microstructure evolution, while significantly reducing the amount of training data required. Training a convolutional neural network simultaneously with the DeepONet, enforcing realistic values at the complex metal grain boundaries, and mathematically encoding boundary conditions into the structure of the DeepONet improved prediction accuracy and computational efficiency over a standard DeepONet model. [Display omitted] • Developed an ML phase-field model surrogate for solidifying metal grain morphologies. • Predictions have relative errors below 0.5% with low computational overhead. • ML surrogate model allows quick inference for parameter space investigation. [ABSTRACT FROM AUTHOR]

We demonstrate the origin of the modification to the primary Mg 2 Si phase induced by ultrasonic treatment (UST) of a P-modified Al–Mg 2 Si alloy through combined experimental and theoretical investigations. Multicomponent Al–Mg 2 Si alloys contain various secondary phases including primary Mg 2 Si, Q, Si, θ, and Zn phases. Regardless of the cooling rate, applying UST transforms the coarse, irregular dendritic Mg 2 Si phase into a fine, compact phase. High-resolution transmission electron microscopy revealed that in the absence of UST, the Mg 3 P 2 phase acted as a preferential nucleation site for the primary Mg 2 Si phase. By contrast, when UST was applied, the MgO particles were the main nucleation sites for this phase. First-principles calculations confirmed the higher nucleation potency of the MgO phase compared with that of the Mg 3 P 2 phase. UST resulted in the deagglomeration of MgO particles while improving their wettability to molten Al, allowing the more potent MgO particles to act as nucleation sites for the primary Mg 2 Si phase. Our experimental and theoretical results show that UST alters the primary Mg 2 Si nucleation pathway from the Mg 3 P 2 phase to the more potent MgO particles activated by UST, resulting in a significant modification of the primary Mg 2 Si phase in chemically modified Al–Mg 2 Si alloys. [Display omitted] • Multicomponent Al alloy contains various secondary phases (Mg 2 Si, Q, Si, θ, and Zn). • Mg 3 P 2 phase acts as a preferential nucleation site for Mg 2 Si phase in P-modified alloy. • Ultrasonication converts the coarse dendritic Mg 2 Si phase into a fine compact phase. • UST deagglomerated the MgO particles while improving their wettability to molten Al. • UST alters the nucleation pathway of primary Mg 2 Si from Mg 3 P 2 to more potent MgO. [ABSTRACT FROM AUTHOR]

The provisions for a new variational theory of crystal growth in multicomponent metal melts were formulated. The developed theory is the generalization of the previously conducted studies of crystal growth under conditions of deviation from local equilibrium at the phase boundary. The description of the methods of non-equilibrium thermodynamics of interrelated physico-chemical processes occurring in the initial phase, on the interface of phases and inside the growing crystal, was compared with the variational description of the crystal growth as a macrobody. The developed approach made it possible to find the general expression for the crystal growth rate, considering the influence of thermal and diffusion processes, as well as taking into account the influence of nonstationary effects associated with deviation from the local equilibrium on the surface of the growing nucleus. The justification of the new method showed that when the condition of the local equilibrium on the surface of the growing crystal is satisfied, the resulting equations take the form of expressions that can be obtained by constructing the equation of a mass and internal energy balance for the system under consideration. As an example, the problem of crystal growth from a melt of eutectic composition was considered. The equation of the growth rate of the two-component nucleus of the stoichiometric composition was obtained, taking into account the influence of the local non-equilibrium effects on growth. The expressions obtained were compared with the known equations of the solute trapping theory. [ABSTRACT FROM AUTHOR]

Controllable crystallographic texture in copper foils exhibiting enhanced mechanical and electrical properties by pulse reverse electrodeposition. Highly textured and twinned Cu films fabricated by pulsed electrodeposition. 10.1103/PhysRev.26.390 2 Zhan X. Preparation of highly (111) textured nanotwinned copper by medium-frequency pulsed electrodeposition in an additive-free electrolyte. B replying to b C. Lu et al. I Nature Communications i https://doi.org/10.1038/s41467-022-32949-y (2022) In Lu et al.'s comment, the possibility of achieving textured crystal growth on textureless polycrystalline substrates is questioned. [Extracted from the article]

A lot of research has been focused on increasing the specific surface area of adsorbents over a long period of time to remove heavy metal ions from wastewater using the adsorbent. However, porous adsorbents with high specific surface area have demonstrated drawbacks in water purification processes, such as high pressure drop and limitations in the adsorption capacity of heavy metal ions. In recent years, a mechanism-based convergence method involving adsorption/chemical precipitation has emerged as a promising strategy to surmount the constraints associated with porous adsorbents. The mechanism involves amine groups on chelating fibers dissociating OH− ions from water molecules, thereby raising the pH near the fibers. This elevated pH promotes the crystallization of heavy metal ions on the fiber surfaces. The removal of heavy metal ions proceeds through a sequence of adsorption and chemical precipitation processes. An adsorbent based on chelating fibers, integrating adsorption technology with chemical precipitation, demonstrates superior performance in removing significant quantities of heavy metal ions (ca. 1000–2000 mg/g for Cd2+, Cu2+ and Pb2+) when compared to developed porous adsorbents (ca. 50–760 mg/g for same ions). This review paper introduces advanced polymer fibers endowed with the capability to integrate hybrid technology, delves into the mechanism of hybrid technology, and examines its application in process technology for the effective removal of heavy metal ions. The versatility of these advanced fibers extends far beyond the removal of heavy metal ions in water treatment, making them poised to garner significant attention from researchers across diverse fields due to their broad range of potential applications. After further processes involving the removal of templates from chelating polymeric fibers used as supports and the reduction of precipitated heavy metal oxide crystals, the resulting heavy metal crystals can exhibit thin walls and well-interconnected porous structures, suitable for catalytic applications. [Display omitted] • The hybrid method is the convergence of adsorption and chemical precipitation. • High removal capacity of heavy metal ions is achieved by the hybrid method. • Amine-groups immobilized polymeric fibers are good supporters for the hybrid method. • Polymeric fibers serve enough space and surface for the heavy metal crystal growth. • The electric double layer theory is suggested for an isotherm model. [ABSTRACT FROM AUTHOR]

Simulation of the grain growth process, as a function of steel heat transfer conditions, is helpful for predicting grain structures of continuous cast steel products. Many authors have developed models based on numerical methods to simulate grain growth during metal solidification. Nevertheless, the anisotropic nature of grain structures makes necessary the employment of new mathematical methods such as chaos theory, fractals, and probabilistic and stochastic theories of simulation. The problem is significant for steelmakers to avoid defects in products and to control the steel microstructure during the continuous casting process. This work discusses the influence of nodal solidification times and computer algorithms on the dynamic formation of the chill, columnar, and equiaxed zones including physical phenomena such as nucleation and grain growth. Moreover, the model incorporates pre-nucleation and pre-growth routines in the original algorithm. There is a description of the influence of the mathematical parameter criteria and probabilities over the grain morphology obtained after solidification. Finally, an analysis of these algorithms elucidates the differences between these structures and those obtained from models considering only the solidification. [ABSTRACT FROM AUTHOR]

The article focuses on unconventional grain growth suppression in oxygen-rich metal oxide nanoribbons. Topics include the nanograined metal oxides are requisite for diverse applications that use large surface area, and the nanoscale grains are thermodynamically unstable and tend to coarsen at elevated temperatures.

Morphology transformation and crystal growth strategies of metal oxide semiconductors are still extensively studied in material science recently, because the morphology and crystallinity significantly affect the physicochemical characteristics of metal oxide nanomaterials. However, understanding the morphology changes of α-MoO3 induced by annealing is still a challenge. Herein, the nanostructure transition of α-MoO3 induced by the annealing temperature is carefully investigated via the XRD and SEM methods. It can be found that crystallization is highly dependent on the annealing temperature. Interestingly, the MoO3 nanoflowers can change into nanosheets at 500 °C. Afterward, the nanosheets turned into microrods with the increase in annealing temperature due to the continuous growth of MoO3 crystal. On the other hand, the sensing performances of various MoO3 nanostructures are studied toward ethanol gas. Compared to the MoO3 nanoflowers and microrods, the MoO3 nanosheets-based sensor exhibits superior sensing performance to ethanol, and the maximum response value is 8.06. [ABSTRACT FROM AUTHOR]

We build a rigorous statistical framework to provide constraints on the chemical and dust evolution parameters for nearby late-type galaxies with a wide range of gas fractions (⁠|$3{{\ \rm per\ cent}}\lt f_g\lt 94{{\ \rm per\ cent}}$|⁠). A Bayesian Monte Carlo Markov Chain framework provides statistical constraints on the parameters used in chemical evolution models. Nearly a million one-zone chemical and dust evolution models were compared to 340 galaxies. Relative probabilities were calculated from the χ2 between data and models, marginalized over the different time-steps, galaxy masses, and star formation histories. We applied this method to find 'best-fitting' model parameters related to metallicity, and subsequently fix these metal parameters to study the dust parameters. For the metal parameters, a degeneracy was found between the choice of initial mass function, supernova metal yield tables, and outflow prescription. For the dust parameters, the uncertainties on the best-fitting values are often large except for the fraction of metals available for grain growth, which is well constrained. We find a number of degeneracies between the dust parameters, limiting our ability to discriminate between chemical models using observations only. For example, we show that the low dust content of low-metallicity galaxies can be resolved by either reducing the supernova dust yields and/or including photofragmentation. We also show that supernova dust dominates the dust mass for low-metallicity galaxies and grain growth dominates for high-metallicity galaxies. The transition occurs around 12 + log (O/H) = 7.75, which is lower than found in most studies in the literature. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) migration and grain growth in nanocrystalline metals are major obstructions to exploit these materials to their fullest potential, thus limiting their utility as advanced structural materials. Here, we investigate the effect of Zr segregation to a Ni GB on migration and subsequent strengthening during shear deformation and high-temperature bending creep. Specifically, using molecular dynamics simulation, we simulate deformation of a Ni bicrystal specimen having a symmetric ∑5 grain boundary with and without segregated Zr. It is found that GB segregation up to 0.4 at.% pins the CSL boundary resulting in increased shear strength. Similar behavior is also observed in the case of bending creep deformation where the creep resistance increases only up to 0.4 at.%. This study indicates that larger amounts of GB segregation cause destabilization of the local atomic structure and consequently affect the GB stiffness. Moreover, we investigate the effect of Zr segregation on the interaction between the GB and a dislocation. We find that the preexisting dislocation is absorbed in the GB region for both clean and segregated specimens; however, the absorption path of the dislocation is different due to the change in GB stiffness caused by the Zr segregation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A grain growth model during material extrusion-based AM was developed. • Anisotropic sintering behavior was accounted to predict the grain size. • Grain growth kinetics parameters were calibrated to apply for other sintering profiles. Most traditional powder melting-based additive manufacturing (AM) technologies generally yield high-performance parts at the expense of additional cost and energy consumption. As an economical and efficient alternative method, material extrusion (ME) that deploys polymer-based filaments with highly filled metal particles offers the possibility of scalable, low-cost fabrication of metal components. As a critical step, sintering governs the mechanical strength and geometry of the final parts. The grain growth behavior induced during sintering should be well controlled to achieve the parts with the desired mechanical performance. Due to the nature of AM, grain growth kinetics could also involve extremely complex grain boundary migration and atomic diffusion mechanisms caused by the heterogeneous pore distribution. In this work, an analytical model was developed to predict and understand the grain growth behavior of stainless steel (SS) 316L built by ME-based sintering-assisted AM. Such a model accounts for anisotropic viscosity parameters calibrated through a three-dimensional dilatometry test, enabling the prediction of grain size evolution during sintering. Grain growth kinetic parameters were further identified by the grain size data at the heating and holding stages. To validate and generalize the model, we also conducted the grain size evolution prediction under different sintering temperature profiles for as-built SS 316L specimens. This work will provide scientific insights into the grain growth behavior of metal parts built by this AM technique and its understanding can be readily transferred to other sintering-assisted AM processes like binder jetting and ink writing for metal structure creation. [ABSTRACT FROM AUTHOR]

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Bi2O3- and MgO-doped BaTiO3–(Na1/4Bi3/4)(Mg1/4Ti3/4)O3 (BT–NBMT) ceramics were synthesized from a solid-state approach, and then the impacts of Bi2O3 and MgO dosages on the structures and dielectric characteristics were studied. Obvious dual peaks were observed with Bi2O3 dosage to 0.04 and MgO dosage to 0.02. The low-temperature dielectric stability and grain size of the Bi2O3 dopant were improved, while those of the MgO dopant hardly changed with MgO dosage to 0.02, indicating the core/shell microstructure of BT–NBMT was formed following the dissolving-precipitating mechanism of BT systems doped with low-melting-point substances. The low-temperature dielectric stability of the Bi2O3- or MgO-doped BT–NBMT ceramics first improved and then deteriorated with the increase of doping concentrations. High-temperature stability and diffuse-state transition were found in the optimal ceramics. The second phases of Bi2O3 and MgO, magnesium titanium compounds were observed in Bi2O3 and MgO dopants, respectively. Bi2O3-doped and MgO-doped ceramics exhibited a fine-grained microstructure and significant grain growth, respectively, and the core/shell microstructure was responsible for the dielectric temperature stability for Bi2O3 dopants and collapsed to a homogeneous one with remarkable grain growth and the second phases for MgO dopants. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the relationship between the crystallographic structure of Cu-Sn intermetallic grains and Sn whisker growth was investigated. In order to prevent the influence of the elements in the alloy composition and the effect of the soldering process on the formation of the intermetallic layer, 99.99% pure Sn was vacuum evaporated onto Cu substrates. The Sn layer thickness was sub-micron region (∼400 nm in average) to reach considerable and rapid compressive stress on the tin layer originated by the intermetallic formation. The samples were stored at room temperature for 1 month. Different types of whiskers (nodule and filament) and the layer structure underneath were studied with a scanning ion microscopy and transmission electron microscopy. It was found that not only the thickness of the intermetallic layer and shape of the intermetallic grains affects the whisker growth but the crystallographic structure of the intermetallic grains as well. The susceptibility of the Sn layer to whisker development is higher in those regions where the intermetallic layer is composed of monocrystalline grains instead of those regions, where it is composed of polycrystalline grains. This effect can be explained by the higher compressive stress generated by the monocrystalline intermetallics compared to the polycrystalline ones. Graphical abstract Image 1 Highlights • Crystallographic structure of Cu 6 Sn 5 IMC grains effects on Sn whisker growth. • Sn whiskers are more likely over monocrystalline Cu 6 Sn 5 IMC than over polycrystalline. • This effect could be explained by the high elastic anisotropy of the Cu 6 Sn 5 IMC. • Monocrystalline Cu 6 Sn 5 IMC has higher Young's modulus than the polycrystalline. • Compressive stress on Sn layer is higher over monocrystalline Cu 6 Sn 5 IMC than over polycrystalline. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The grain growth behavior of superalloy 718 was investigated using high-temperature compression tests and subsequent heat treatment. Abnormal grain growth (AGG) induced by low plastic strains was observed during thermal processing, which included solution heat treatment, and annealing, causing the matrix grains to coarsen from ∼12 μm to 80 μm in diameter. Both the plastic strain and displacement rate during deformation had large influences on the occurrence of AGG, which was mainly observed in regions of low plastic strain; the plastic strain range where AGG occurred increased with decreasing displacement rate. In particular, deformation at low displacement rates (within the same range as dynamic recrystallization) easily produced grain growth during solution heat treatment. Such grain growth was referred to as irregular grain growth (IGG) to distinguish it from AGG. Both the AGG and IGG processes were initiated when the intragranular misorientation exceeded a critical level, causing an increase in the twin boundary ratio and a decrease in intragranular misorientation. The nuclei of AGG grains were the nucleation of newly recrystallized grains without dislocation. [ABSTRACT FROM AUTHOR]

Abstract Optical and spectroscopic properties of Er3+/Pr3+-codoped Gd 3 Ga 5 O 12 single-crystal grown by Czochralski method have been studied. Absorption spectrum of the crystal was measured at room temperature and Er3+ absorption cross-section spectral distributions were calibrated from it. The Er3+ spectroscopic properties were analyzed on the basis of the Judd-Ofelt theory. Fundamental spectroscopic parameters were obtained that include absorption coefficient, cross-section spectral distribution, electronic transition oscillator strength, Judd-Ofelt parameters, fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency as well. Study shows that Pr3+-codoping results in substantial change of Er3+ spectroscopic properties, in qualitative consistent with the previous fluorescence studying result. In addition, refractive index of the crystal was measured at different wavelengths using prism coupling method, and the Sellmeier equation reported previously for Er3+-only doped Gd 3 Ga 5 O 12 crystal is corrected. Highlights • Juud-Ofelt spectroscopic properties of Er3+/Pr3+:Gd 3 Ga 5 O 12 crystal were studied. • Pr codoping results in substantial increase of the Judd-Ofelt parameters. • Pr codoping induces shortening of Er3+ 2.7 and 1.5 μm lifetimes from ms to sub-ms. • The effect is related to two resonant energy transfers from Er3+ to Pr3+. • Different efficiencies of the two transfers enable to realize 2.7 μm lasing. [ABSTRACT FROM AUTHOR]

Abstract Recently, alluaudite-type cathode materials with two types of large Na tunnels attract considerable attention. Hereby, a compound Na 2 Mn 2 V(PO 4) 3 was synthesized and its high quality single crystals were grown in the NaCl molten-salt media. The single-crystal diffraction data analysis shows that Na 2 Mn 2 V(PO 4) 3 belongs to the typical alluaudite-type structure with unit parameters of a = 12.0533(15) Å. b = 12.5844(16) Å, c = 6.4987(8) Å, β = 114.51(2)˚. The density functional theory calculations based on the nudged elastic band method were used to obtain the migration energy barrier of Na ions in Na 2 Mn 2 V(PO 4) 3 and Na 2 Fe 2 V(PO 4) 3. The results of calculations show that Na 2 Mn 2 V(PO 4) 3 has a better Na+ conductivity than Na 2 Fe 2 V(PO 4) 3. The electrochemical tests also demonstrate that Na 2 Mn 2 V(PO 4) 3 exhibits electrochemical activity operating at an average voltage of 3.5 V (vs. Na/Na+) delivering a capacity of 97 mAh g−1 at 10 mA g−1 rate. Graphical abstract Image 1 Highlights • Na 2 Mn 2 V(PO 4) 3 and Na 2 Fe 2 V(PO 4) 3 crystals were obtained using molten salt method. • Na 2 Mn 2 V(PO 4) 3 and Na 2 Fe 2 V(PO 4) 3 crystallize in the typical alluaudite-type structure. • The DFT calculations show that Na 2 Mn 2 V(PO 4) 3 has better Na+ conductivity. • Na 2 Mn 2 V(PO 4) 3 has 3.5 V average voltage and high capacity. [ABSTRACT FROM AUTHOR]

Abstract The effect of a galia (Ga 2 O 3) addition on the crystallographic phase transformations and the grain growth behavior of yttria stabilized zirconia (YSZ) were investigated regarding powders containing different amounts of galia in the range of 0–25 mol %. Ternary compositions of galia- YSZ sponge-like cryogels were prepared by the sol-gel method combining freeze-drying process and calcination of dried powders at different temperatures for 2 h in air. Crystallographic phase transitions were analyzed via X-ray diffraction (XRD) and exceptional powder particle morphology of internal nano voids derived from the freeze-drying technique was investigated by using Scanning Transmission Electron Microscope (STEM). It was shown that galia supressed the grain growth process in yttria stabilized zirconia and had no effect on the internal voids obtained. Highlights • Galia addition inhibited 8YSZ crystallization and extended the amorphous range. • Galia addition elevated the activation energy for the grain growth process in 8YSZ. • Internal nano-voids were formed via sol-gel synthesis followed by freeze-drying. [ABSTRACT FROM AUTHOR]

Abstract We reported a new layered ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O which crystallizes in two-dimensional (2D) nanosheets morphology in our previous work. Herein, two-dimensional hexagonal ZnCo 2 O 4 nanosheets were synthesized by the thermal transformation of the ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O precursor. Benefiting from this special hexagonal nanosheet morphology, the as-prepared ZnCo 2 O 4 electrode has induced a pseudo-capacitance contribution, leading to a stable discharge capacity of 688 mAh g−1 (at 5.0 A g−1) over 1000 cycles. To the best of our knowledge, the rate performance of ZnCo 2 O 4 for lithium ion batteries (LIBs) is superior to those of previously reported ZnCo 2 O 4 electrodes. Further applied to sodium ion batteries, ZnCo 2 O 4 electrode show fascinating performance with the specific capacity of 463 mAh g−1 after 60 cycles. This study provides a promising strategy for developing high-quality ZnCo 2 O 4 nanosheet electrodes for long-cycle-life and high-power LIBs and sodium ion batteries (SIBs). Graphical abstract Image 1 Highlights • Hexagonal ZnCo 2 O 4 nanosheet has been synthesized from the hydroxide precursor. • Our ZnCo 2 O 4 electrode exhibits high-rate performance for lithium ion battery. • Our ZnCo 2 O 4 electrode show fascinating performance in sodium ion storage. [ABSTRACT FROM AUTHOR]

Abstract Grain size, growth morphology, and grain boundary were considered to affect hardness and fracture toughness of hard coatings. An effective approach is currently developed to improve their hardness and toughness via tailoring their architectures through grain boundary control. V-Al-C coatings consisting of variable architectures were prepared by reactive sputtering V 2 AlC target with different CH 4 flow rates in this study. The results indicated that, when the carbon content increased from 37.32 at.% to 71.4 at.%, the microstructure of V-Al-C coatings was tailored to span a wide changes from coarse columnar grain to fibrous columnar grains and finally to nanocomposite structure consisted of the (V, Al)C nanocrystallites and sp2-rich a-C. Especially, the maximum hardness of 28.74 GPa and the excellent toughness with high H/E value of 0.11 were obtained once the coating displayed fibrous columnar structure, such good mechanical properties benefited the lowest wear rate of 2.8 × 10−16 m3/Nm. Instead, the nanocomposite structure showed the lower fracture resistance due to the dominated amorphous carbon matrix. All coatings with nanocomposite structure exhibited low friction coefficient of ∼0.18, which was attributed to the coupling lubrication originated from both V 2 O 5 Magnéli phases and amorphous carbon formed during friction process. The enhanced mechanical and tribological properties were also discussed in terms of the columnar boundaries evolution as a function of carbon content. Graphical abstract Image 1 Highlights • Significant microstructure changes were tuned with varying the content of a-C. • Coating with fibrous columnar grain rendered enhanced mechanical properties. • The influence mechanism of boundaries on mechanical properties was discussed. • Structure zone diagram with C content was established in this study. • The synergistic lubrication of V 2 O 5 Magnéli phase and amorphous C was observed. [ABSTRACT FROM AUTHOR]

Abstract Pore-grain boundary separation at the final stage of pressureless sintering was successfully suppressed via limiting grain growth in MgAl 2 O 4 ceramics. A pretreatment process by spark plasma sintering (SPS) was utilized to obtain a homogeneous porous body with relative density of 88%, small pores (~28 nm) and uniform grains (~230 nm). The subsequent pressureless sintering results shows that the SPS-ed sample exhibited superior densification with limited grain growth, in contrast to the sample pretreated by pressureless sintering. Coble's model for intermediate stage of sintering was applied to correlate the densification behavior with the instantaneous grain size. It was demonstrated that the densification process could be promoted significantly by maintaining small grain size. In the final stage of sintering, the grain growth mechanism is pore displacement controlled by lattice diffusion. After final densification by hot isostatic pressing, transparent ceramics possessing fine-grained microstructure and acceptable transmittance had been fabricated. Average grain size of the transparent ceramics was 1.9 µm, which enhanced its Vickers hardness (13.9 ± 0.2 GPa). [ABSTRACT FROM AUTHOR]

Abstract In this study, electrospinning was successfully used to fabricate hybrid Carbon-Silicon Carbide (C-SiC) fibers using polyacrylonitrile (PAN) and silicon (Si) nano-particles as precursors. Silicon-to-carbon precursor ratios and heat treatment were optimized to fabricate hybrid nano-fibers with high oxidation resistance. After heat treatment, the nano-fibers showed two-dimensional ordered carbons and SiC nano-phases formation. As a result, a noticeable improvement in mechanical and thermal properties was achieved. Samples with 90 wt% PAN/10 wt% Si showed about four-time improvements in char yield as compared with 100 wt% PAN. In addition, after heat treatment of the fiber at 1250 °C, SiC was formed. The SiC phase played a major role in ordering the carbon phase. The carbon and SiC crystallinities had a great impact on the oxidation and mechanical property improvement of hybrid nanofibers. The determination of crystal size was carried out using X-ray results obtained at different temperatures and holding times. The SiC grain growth was predicted using kinetic model and its exponent was found to be around n = 4 with an activation energy around 35 KJ/mol.K. For such growth, the dominant grain growth mechanism was grain boundary diffusion. [ABSTRACT FROM AUTHOR]

Abstract The effect of manganese (0.1, 0.5 and 1.0 wt%) on the sintering and mechanical properties of alumina was studied. Sintering was carried out by the conventional heating method in a box furnace and in a hybrid multimode microwave furnace. XRD analysis revealed the precipitation of a spinel second phase (MnAl 2 O 4) in manganese-doped samples as a result of manganese limited solubility in the corundum lattice. The addition of 0.1 wt% manganese was most beneficial in enhancing the densification of alumina (97.5% relative density when compared to 94.2% for the undoped sample), hindered grain growth, and improved the hardness of the ceramic when sintered at 1500 °C. The study also revealed that microwave sintering was effective in suppressing grain growth of alumina. In addition, the hardness was dependent on the sintered bulk density and that grain coarsening ensued as the density of the sintered alumina exceeded 95% of theoretical. [ABSTRACT FROM AUTHOR]

Abstract Highly crystalline Ni 1-x Ru x O films have been prepared via a pulsed laser deposition technique using a Q-switching Nd:YAG laser. The impact of the substitution of Ni2+ ions with Ru4+ ions on the lattice constants and sizes of the NiO crystals was explored by the X-ray diffraction. The surface topography and the grain growth at various Ru ion substitutions have been examined by the atomic force microscopy and scanning electron microscopy. The elemental composition was determined by the energy dispersive spectroscopy, while the influence of Ru ions on the Ni-O and O-O vibration modes was studied by the Raman spectroscopy. The optical properties were investigated by the UV–vis spectroscopy. The I-V characteristics, electrical resistivity, hole mobility and carrier concentrations have been measured. The developed films revealed optical transparency exceeding 97% along the visible region. These films showed a decrease of the optical bandgap from 3.4 to 2.8 eV as the Ru ion content increased from 0 to 10 at%. The doping of NiO with 10 at% of Ru ions causes a decrease of the resistivity to 5 × 10−5 Ω cm, an increase of the mobility to 210 cm2 V−1 s−1 and an increase of the carrier concentration to 3.8 × 1020 cm−3. These unique features make Ru-doped NiO films promising for a replacement of n-type ITO and FTO in optoelectronic applications. [ABSTRACT FROM AUTHOR]

Abstract Two-step sintering (TSS) was applied on the M-type Sr-hexaferrite to control grain growth and form a desirable microstructure during the final stage of sintering. The process involved T 1 (temperature in the first sintering stage), t 1 (holding time at T 1), T 2 (temperature in the second sintering stage), and t 2 (holding time at T 2). The effects of each setting parameter on the density, grain growth, degree of orientation and magnetic properties were systematically investigated. The results revealed that T 1 was the main factor that primarily controlled microstructure and magnetic properties. Compared with conventional sintering (CS) process, the magnets with smaller average grain size were achieved by TSS, which suggested that two-step sintering could improve the coercivity of Sr-hexaferrites. It was shown that the high integrated magnetic properties for Sr-hexaferrites, including B r = 440.4 mT, H cj = 328.2 kA/m and (BH) max = 37.6 kJ/m3, were obtained under the optimum processing condition: T 1 = 1200 °C, T 2 = 1000 °C, t 1 = 5 min, and t 2 = 2 h. [ABSTRACT FROM AUTHOR]

Abstract x Nb 2 O 5 –7.5La 2 O 3 -Al 2 O 3 ceramic composites with in-situ-grown columnar Al 2 O 3 crystals were successfully prepared by microwave sintering at 1450–1525 °C using α-Al 2 O 3 , Nb 2 O 5 , and La 2 O 3 powders as raw materials. X-ray diffraction results indicated that the main phases were Al 2 O 3 , LaNbO 4 , and Nb 2 O 5 in the prepared samples. A field emission scanning electron microscope (FESEM) showed that the Al 2 O 3 crystals appeared as columnar in the structure. Moreover, the grain size of the columnar Al 2 O 3 crystals increased with the Nb 2 O 5 content. The ratio of the major axis to the minor axis of the crystals was largest when the Nb 2 O 5 content was 15 vol%. Furthermore, the grain-growth kinetics index (n), growth activation energy (Q), and growth mechanism of the columnar Al 2 O 3 crystals were studied. The results indicated that the Nb 2 O 5 addition could promote formation and growth of columnar Al 2 O 3 crystals, and the grain-growth activation energy indicated that the dissolution process controls the crystal growth. The growth mechanism of the columnar Al 2 O 3 crystals was also studied. The present work demonstrated that Nb 2 O 5 is a good additive for the preparation of Nb 2 O 5 –7.5La 2 O 3 -Al 2 O 3 composite ceramics with columnar Al 2 O 3 crystals. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Continuous transition between vertex-driven and curvature-driven models. • Extensive set of statistics computed. • Several choices of grain boundary energy considered, including the Read-Shockley energy. Abstract We consider a variational model for two-dimensional grain growth that allows for finite mobilities of boundaries and boundary junctions. We use a collocation method to describe the grain boundaries and posit evolution equations that ensure energy dissipation. The resulting algorithm is amenable to parallelization and a GPU implementation described in this work leads to significant reduction in computational time. We benchmark our code against known numerical and analytical solutions in some special cases. We also conduct an extensive analysis of statistics that develop for various parameter regimes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Based on the multi-grain growth phase field model of multi-element single-phase system. • Using the adaptive finite element method to study the morphological evolution during directional solidification. • Investigating the growth of the interface morphology and the transformation mechanism of seaweed tissue. • Quantitatively analyzed the effects of disturbance and anisotropy intensity on the seaweed microstructure. • The larger the system size, the better superiority of the adaptive finite element method. Abstract Based on the multi-grain growth phase field model of multi-element single-phase system, the adaptive finite element method using non-uniform grid is studied to solve the problem. The Al-4wt.%Cu binary alloy is taken as an example to study the planar solidification process and morphological evolution during the initial transition phase of solidification were studied under the condition of large computational domain and thin interfacial layer thickness. The effects of disturbance and anisotropy intensity on the microstructure of the solidification, the influence of physical parameters such as temperature gradient and cooling rate on the interface morphology growth and evolution were quantitatively analyzed. The growth mechanism of the interface morphology during directional solidification and the transformation mechanism of seaweed tissue were discussed. The results show that under the condition of low temperature gradient and high cooling rate, the flat interface is unstable and forms cell or dendrites, and then the tip is continuously split to form seaweed structure morphology. The adaptive finite element method is one order of magnitude lower in computing time and storage space comparing to the finite difference method. When the system size is larger, the superiority of the adaptive finite element method can be better reflected, which facilitates the simulation of the large-scale multi-field coupled phase field model. [ABSTRACT FROM AUTHOR]

Abstract ZnTe crystal is a promising electro-optical crystal materials applied for THz generation and detection. However, there is still a big challenge to obtain large sized high quality ZnTe crystals. In this work, large sized ZnTe bulk crystals with Φ30 mm × 150 mm were grown by the traveling solvent melting zone (TSMZ) method. With the characterization of the optical and electrical properties of as-grown ZnTe crystals, the band gap (2.22 eV), high IR transmittance (around 60%), high resistivity (3.5 × 103 Ω·cm), low density (1.3 × 105 cm−2) and small sizes (3 μm - 5 μm) of Te inclusions in ZnTe crystals, low etch pit densities (1.5 × 105 cm−2), high peak intensity to FWHM ratio (2.5 × 104) of the LO peak in the Raman spectra were obtained. Furthermore, the THz transmission spectra was measured and the maximum transmittance is more than 40% at the range of 0.3 - 3 THz. Based on these results, high quality and large aspect ratio ZnTe bulk crystals can be obtained by the TSMZ technique. Our work has greatly facilitated the application of ZnTe crystals in THz device. Highlights • Large aspect ratio of ZnTe bulk crystals were successfully grown by TSMZ technique under the condition of seedless. • A large number of high purity ZeTe polycrystallines powder was synthesized successfully. • The optical and electrical properties of different parts of the ZnTe ingot were analyzed. • The transmission properties of THz wave in ZnTe crystal were briefly evaluated. [ABSTRACT FROM AUTHOR]

Friction welding (FRW) was used to weld 700-MPa-grade fine-grained steel and the changes in the microstructure state of the joints after low-temperature tempering treatment were analyzed. The results of testing show that it is advantageous to adopt a high current for welding to reduce the width of the heat-affected zone (HAZ) and minimize the size of the grain growth. The microstructures of the weld zone (WZ) and HAZ were finer than those of the base metal (BM), and the size of the grain in the HAZ was 9-11 µm. As the thermal stability of the frictionwelded joints of ultrafine-grained (UFG) welding steel is low, if it is necessary to release the residual stress of joints by tempering after welding, the temperature should not exceed 300 ?. [ABSTRACT FROM AUTHOR]

The effects of sintering temperature and Ti substitution on the microstructure and microwave magnetic properties of Li-Zn ferrites prepared by a ceramic process were investigated. The pure spinel phase of the specimens was observed from X-ray diffraction patterns. The densification and grain growth were enhanced due to the increase of sintering temperature. The grain growth had negative effects on the squareness ratio of high-porosity specimens. Moreover, the magnetic anisotropy constant (K1) was estimated and discussed. The ferromagnetic resonance linewidth (ΔH) values measured at the Ku-band decreased by 18% owing to improved microstructure. The contributions of other linewidths to ∆H were estimated. [ABSTRACT FROM AUTHOR]

Graphical abstract It has been believed that ZrO 2 columnar grains, which contribute to the reduction of oxygen diffusion in the oxide layer, are the result of grain growth, and the subsequent oxidation mechanism of zirconium alloy is also formed and developed on this basis. Here we report an in situ oxidation experiment carried out at 500 ℃ air condition demonstrating that large size ZrO 2 grains were results of the merging of small size grains rather than growth of grains. We further show that original orientation of small size grains and dislocation motion play crucial roles in the merging process of small size grains. Highlights • An in situ TEM oxidation at 500 ℃ air condition was carried out. • An atomic view of microstructure evolution mechanism of the oxide layer of zirconium has been reported. • The role of dislocation, initial orientation and stress in oxide microstructure evolution has been studied. Abstract It has been believed that ZrO 2 columnar grains, which contribute to the reduction of oxygen diffusion in the oxide layer, are the result of growth of small grains, and the subsequent oxidation mechanism of zirconium alloy is also formed and developed on this basis. Here we report an in situ oxidation experiment carried out at 500 ℃ air condition demonstrating that large size ZrO 2 grains was results of the merging of small size grains rather than growth of small grains. We further show that original orientation and dislocation motion play crucial roles in the merging process of small size grains. [ABSTRACT FROM AUTHOR]

The present overview gives a new approach toward developments and recent achievements in severe plastic deformation. The review focuses on several subjects. First, an outline of SPD research status in the world is presented by literature analysis based on the total number of publications, citations, and the contribution of the top-ranked countries. Second, the mechanisms of grain refinement and grain growth during SPD processing are discussed by means of the latest concepts. Third, all SPD methods invented so far are classified based on a new approach. Up to now, the growing tendency of researchers to introduce new SPD techniques results in a large number of SPD methods which can be considered as new or modified techniques or a combination of previous ones. Such a reference can help to prevent the future duplication to introduce the SPD processes, which are technically similar. At the end, the practical applications of ultrafine/nanostructured materials and industrial commercialization of SPD methods are summarized. [ABSTRACT FROM AUTHOR]

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A fully coupled thermo-mechanical model is established to simulate the temperature variations and the material deformations in friction stir welding (FSW) of Ti-6Al-4V. The extracted data are used for further simulation on microstructural evolutions. A multi scale model, which consists of the grain growth model in grain cluster scale and the phase transformation model in one grain scale, is proposed. The nuclei of α and β phases, the recrystallizations and the grain growths are systematically investigated. Comparisons with experimental data and experimental observations can validate the newly proposed microstructural evolution model for Ti-6Al-4V. Results indicate that the volume fractions of α and β phases can be directly determined by the cooling rates in FSW process. With the increase of the rotating speed, the volume fraction of α phase is increased and β phase decreased due to the increase of welding temperature. With the decrease of the translational speed, the volume fraction of α phase gets bigger and β phase smaller. The acicular α grain can be generated on the β grain boundaries and grows along <1 1 0> direction on β substrate. The average length of α grain can be increased with longer cooling time and decreased with lower rotating speed or higher translational speed. [ABSTRACT FROM AUTHOR]

In this work, model α-Fe 2 O 3 catalysts with different morphologies were synthesized to investigate crystal plane effects on soot oxidation. The results revealed that the electron-rich state of Fe 2 O 3 {113} planes conferred them more surface O x − and thus better catalytic performance than the {014} and {012} planes. Surface grafting of a polycrystalline CeO 2 layer onto Fe 2 O 3 gave rise to Fe 2 O 3 @CeO 2 catalysts with drastically increased oxygen utilization. More importantly, by loading Ag nano-particles on the surface of Fe 2 O 3 @CeO 2 , a tandem oxygen delivery route was opened, resulting in strong O x - generation/regeneration ability and superior low temperature soot oxidation activity. These Ag/Fe 2 O 3 @CeO 2 catalysts overwhelmed the nano-cubic Ag/CeO 2 in both catalyst cost and activity, making them very promising for application in catalyzed gasoline particulate filters (CGPFs). [ABSTRACT FROM AUTHOR]

Abstract Domain structure plays a critical role in the functionality of ferroelectrics. In this work, the domain structure and local domain switching behaviors of a (001) C -oriented 0.38Bi(Zn 2/3 Nb 1/3)O 3 -0.62PbTiO 3 single crystal with high Curie temperature (~ 430 °C) and high tetragonality (c / a > 1.04, where c and a represent the lattice parameters of the tetragonal crystal), were studied by polarized light microscopy (PLM) and piezoresponse force microscopy (PFM). Local polar domains with typical sizes from several nanometers to micrometers were observed by PFM in the crystal. The local domain switching was realized by applying a voltage, indicating the ferroelectricity of the crystal. This work provides a better understanding of the micro-/nanodomain structure and related phenomena in ferroelectrics of complex perovskite structure. [ABSTRACT FROM AUTHOR]

Abstract In this work, (K 0.5 Na 0.5)(Ta 0.3 Nb 0.7)O 3 (KNNT) powders synthesized by the microwave-hydrothermal method were sintered under different oxygen partial pressure (P O2 = 0, 0.498, 0.995 atm) atmospheres. Effects of P O2 on the phase composition, microstructure, piezoelectric properties, and defects in the KNNT ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Ultraviolet-visible diffuse reflectance spectroscopy (UV–Vis DRS). Results indicated that P O2 had almost no effect on the phase structure and grain morphology of KNNT ceramics. Abnormal grain growth was observed with increasing P O2 ; simultaneously, the density of the ceramics decreased. However, the d 33 value reached its maximum of 205 pC/N when sintered at the highest P O2 , and k p showed a similar trend. TEM observations indicated that the microscopic domains had the most regular domain orientation at a P O2 of 0.998 atm. These phenomena were due to the different oxygen vacancy concentrations caused by varying P O2. UV–Vis DRS revealed that the defect concentration decreased with increasing P O2 ; moreover, the oxygen vacancy concentrations were determined by XPS to be 23.5%, 21.1%, and 19.1% corresponding to P O2 values of 0, 0.498, and 0.995 atm, respectively, indicating that oxygen-enriched sintering can reduce defects and enhance piezoelectric properties. [ABSTRACT FROM AUTHOR]

Abstract Spherical and uniform CuAlMn shape memory foams (SMFs) with quasi-oligocrystalline microstructure and various foam structures were manufactured by the silica-gel beads infiltration method. The strut architecture was quantitatively characterized by strut node size N , strut length L and L/N , and the oligocrystalline degree of foams was characterized by grain size d over N (d/N) for the first time. d/N is found to increase linearly with L/N due to the constricted effect of complex strut architecture on two-dimensional grain growth. The coupling effect of strut sizes and oligocrystalline degree on properties of the SMFs was explored. Too thin struts (smaller N) result in higher quenching rate and consequently more quenched-in vacancies, hindering the thermal-induced martensitic transformation and low-amplitude martensite damping. The peak damping becomes more dependent on d/N and tends to increase with increasing d/N , while the high-amplitude martensite damping improves linearly with d/N. The compression recovery strain also increases linearly with d/N under certain porosity, although higher porosity tends to compromise the favorable effect of higher d/N. The results demonstrate that higher d/N, which corresponds to higher oligocrystalline degree and lower grain constraints, favors the boundary mobility and martensite accommodation and thus improves the damping and compression recovery properties of Cu-based SMFs. Graphical abstract Image 1 Highlights • Oligocrystalline degree of SMFs was quantitatively characterized for the first time. • The strut architecture influences the grain growth and oligocrystalline degree. • Too thin struts hinder the thermal-induced M transition and low-amplitude M damping. • Damping and recovery ability increase linearly with d/N for lower grain constraints. • Relatively high recovery strain remains in high porosity foams with higher d/N. [ABSTRACT FROM AUTHOR]

Two Ce 3+ doped sodium strontium (calcium) silicates, Na 2 SrSi 2 O 6 :Ce 3+ and Na 2 CaSi 2 O 6 :Ce 3+ , were prepared by high temperature solid state reaction. They both crystallize in trigonal crystal system with space group R 3 ¯ m. Substitution of three independent Ca 2+ sites for Ce 3+ ions yields blue emission when excited by UV light (λ e x  = 352 nm). Accordingly, Ce 3+ ions occupying two distinct Sr 2+ sites generate UV to blue light under 300-nm UV excitation. A series of Na 2 Ca 1- x Sr x Si 2 O 6 :Ce 3+ ( x  = 0–1) were prepared. All the samples form solid solutions and are isotypic confirmed by Rietveld refinements. Increasing Sr 2+ content leads to asymmetrical blue shift of PL spectra. Refinement results clarify preferable site occupancy of Sr 2+ in Na 2 CaSi 2 O 6 compound which results in the irregular shift. The migration of Ce 3+ ions between M3 and M4 sites is the key point of this phenomenon. This mechanism could be a guideline to optimize the emissions of emitting centers with multiple sites. [ABSTRACT FROM AUTHOR]

To improve the thermoelectric properties of as-grown electrodeposited films, their crystallinity should be increased by promoting crystal growth and suppressing formation of micro-pores. Here, we prepared as-grown bismuth telluride (Bi 2 Te 3 ) electrodeposited films using sputtered Bi 2 Te 3 seed layers (AES films) on a glass substrate. The seed layers were thermally annealed in advance and the as-grown electrodeposited Bi 2 Te 3 films were formed under galvanostatic conditions in nitric acid-based solution. The in-plane thermoelectric properties of the AES films were measured at approximately 300 K, and the properties of the electrodeposited films alone were calculated from the measured values. The maximum power factor of the as-grown electrodeposited film was 4.2 μW/(cm·K 2 ), which was approximately eight times higher than that of the electrodeposited films grown using a standard method (without the use of the seed layer) mainly because of the significant increase in electrical conductivity. Surface scanning electron microscopy revealed that the AES films consisted of nano-sized crystal grains with densification in the morphology, thus presenting a smooth, homogeneous surface. However, the electrodeposited films obtained using standard methods exhibited dendritic crystals on the top surface, and a large area of micro-pores on the bottom surface of the film after detachment from the substrate. X-ray diffraction analysis clearly showed peaks of the rhombohedral phase of Bi 2 Te 3 in the AES film, indicating that crystal growth also occurred in the electrodeposited film. Therefore, we concluded that the thermoelectric properties of the as-grown electrodeposited Bi 2 Te 3 films increased because of the improved crystallinity and the suppressed micro-pores in the films. [ABSTRACT FROM AUTHOR]

The grain growth kinetics and mechanical properties of graphene platelets(GPLs) reinforced ZrO 2 /Al 2 O 3 (ZTA) composites prepared by microwave sintering were investigated. The calculated grain growth kinetics exponent n indicated that the GPLs could accelerate the process of the Al 2 O 3 columnar crystal growth. And the grain growth activation energy of the Al 2 O 3 columnar crystal indicated that the grain growth activation energy of the GPLs doped ZTA composites is much higher than those of pure Al 2 O 3 and ZTA in microwave sintering. The optimal mechanical properties were achieved with 0.4 vol% GPLs, whose relative density, Vickers hardness and fracture toughness were 98.76%, 18.10 GPa and 8.86 MPa m 1/2 , respectively. The toughening mechanisms were crack deflection, bridging, branching and pull-out of GPLs. The results suggested that GPLs-doped are good for the Al 2 O 3 columnar crystal growth in the ZTA ceramic and have a potentially improvement for the fracture toughness of the ceramics. [ABSTRACT FROM AUTHOR]

Coarse grain growth has conventionally been induced by high temperature and pressure during the sintering of ZrC ceramic. Even under the harsh sintering conditions, the microstructure contained inhomogeneous grain sizes and residual pores. To reduce the agglomeration of grains during sintering, we focused on inducing lattice strain. Mechanical milling was carried out to induce high strain in the lattice of ZrC, with the amount of strain varying during milling. This could slow down the grain growth, eventually producing homogeneous grain sizes of sintered ZrC ceramic. The sintered grain size decreased at the maximum strain, with 10 h of milling, while it started to increase significantly after 10 h. This study demonstrates that the sintering conditions could be optimized to obtain the lattice strain for fully dense sintered ceramic. [ABSTRACT FROM AUTHOR]

SiC–BN composites were fabricated by conventional hot-pressing from β-SiC and h-BN nanopowders with 2 vol% yttria as a sintering additive. Electrical and thermal properties of the composites were investigated as a function of initial BN content. Owing to the nanosize of the starting powders, the grain-growth-assisted N-doping of the SiC lattice was significantly enhanced during liquid-phase sintering, yielding the highest-reported electrical conductivity of ~124 (Ω cm) −1 for a SiC–4-vol% BN composite. The typical values of electrical resistivity and thermal conductivity of the SiC–4-vol% BN composite at room temperature were 8.1 × 10 −3 Ω cm and 92.4 W m −1 K −1 , respectively. [ABSTRACT FROM AUTHOR]

Commercial Mg extrusions usually develop various types of basal textures, affecting the formability and mechanical properties. The mechanisms for the formation of basal texture variations were systematically investigated for the first time based on the twinning and dynamic recrystallization (DRX) during extrusion using electron back-scatter diffraction (EBSD) characterization. The results indicate that {10 1 ¯ 2} extension twins with various variants played a key role in the formation of [10 1 ¯ 0] fiber texture, while twin-induced DRX mechanism associated with {10 1 ¯ 1} twins made a limited contribution to overall texture evolution. The microstructure developed consecutively as a result of continuous DRX (CDRX) and discontinuous DRX (DDRX) after twinning with different nucleation of new orientations. In the unDRXed region, new DRXed grains with 30° [0001] GBs preferentially nucleated via CDRX, forming preferred selection of [2 1 ¯ 1 ¯ 0] fiber orientation. Consequently, [10 1 ¯ 0] fiber texture became weakened with [2 1 ¯ 1 ¯ 0] fiber component strengthening, progressively leading to the development of [10 1 ¯ 0]-[2 1 ¯ 1 ¯ 0] double fiber texture. In the DRXed region, DDRX further occurred along the serrated grain boundaries and at the triple junctions of the parent grains by bulging, forming fresh DRXed grains without preferred orientation selection. Thus, the [10 1 ¯ 0]-[2 1 ¯ 1 ¯ 0] double fiber texture became randomized and gradually transformed into non-fiber texture at the late stage of extrusion. Besides, typical nucleation sites for DRX and subsequent grain growth were also discussed in this study. These findings unveil that basal texture variations are attributed to the twinning and DRX mechanisms during extrusion, which leads to new insight to design new wrought Mg alloys with high performance by grain refinement and texture modification. [ABSTRACT FROM AUTHOR]

Abstract Engineering components operating at high temperature often fail due to the initiation and growth of cracks in the heat-affected zone (HAZ) adjacent to a weld. The size and morphology of the prior austenite grains (PAGs) in the HAZ of a tempered martensite steel weld can have a strong influence on the final martensitic microstructure. However, there are few available models to predict PAG size in the HAZ of martensitic steel welds. In this work two approaches are examined to predict PAG growth in the HAZ of a martensitic steel (P91) weld. Phase field (PF) methods, which explicitly represent the changing morphology of a representative volume of martensite grains, and approximate analytical solutions for grain growth at high temperature are examined. The predicted grain growth kinetics and final grain diameter using a two term analytical solution is shown to agree well with experimental data and with the validated PF simulation. The two term analytical model provides a versatile tool to analyse PAG growth at low computational costs. In addition, a simplified equation for predicting the final PAG diameter in the HAZ of P91 welds is proposed for engineering applications. The methods have been used to estimate the final grain diameter in the HAZ of a single bead-on-plate weld. Highlights • Three methodologies for prediction of prior austenite grain growth in HAZ of a martensitic steel have been proposed. • Combined PF and FEM has been used for analyzing the relationship of process and microstructural evolution in welding. • A modified macroscale grain growth model is proposed to account for the precipitate dissolution in welding of P91 steel. • A near closed-form equation for calculating the grain size is proposed and validated. • The effect of welding thermal history on grain growth kinetics has been quantitative studied. [ABSTRACT FROM AUTHOR]

The volumetric growth rate of individual grains as a function of their number of sides, as well as the average normalized volumetric growth rate for a given topological class are studied based on large-scale phase-field simulations of normal grain growth. For all cases, where different initial grain size distributions are considered, the same averaged normalized volumetric growth rate for a given topological class was obtained with the averaged normalized volumetric growth rate approximately zero for grains with F o ≈ 15 sides. The normalized average grain size as a function of topological class becomes constant within the transient regime and the relation in the transient and steady-state regime is similar and independent of initial grain structure. The relation does however not match Mullins' analytical model [W. Mullins, Acta Metall. 37 (1989) 2979–2984]. The effect of the average number of sides of the neighbouring grains on the average volumetric growth rate for a given topological class is analyzed, as well. Moreover, tracking of the evolution of four grains suggests that the normalized volumetric growth rate of a grain is strongly linked with the number of sides of the grain at the given time. [ABSTRACT FROM AUTHOR]

The evolution of the microstructure of P92 steel during heat processing has a significant effect on the final performance of steel products and is thus an area of critical interest. Accordingly, the grain growth behavior of austenite and δ-ferrite changes in P92 steel is comprehensively investigated in this study through thermodynamic calculations and physical simulation. The results show that the AC1, AC3 and γ-δ transformation temperatures of P92 steel are 841 °C, 878 °C and 1095 °C, respectively, which are comparable to the measured values of 850 °C, 879 °C and 1175 °C, respectively. When the temperature exceeds the AC1 temperature, the austenite grain size increases with increasing temperature and longer holding times, and the growth rate of austenite grains increases with higher temperatures but decreases with holding time at a certain temperature. A model that shows the austenite grain growth kinetics is established: Dn − D0n =  2.03 × 1016exp(− 498,770/RT)t, in which the time exponent n decreases from 4.52 to 2.11 with an increase in temperature from 1000 °C to 1200 °C due to the reduced pinning effect resultant of the dissolution of precipitates, M23C6, VX and NbX at 887 °C, 1073 °C and 1200 °C, respectively. The formation of δ-ferrite at 1200 °C when held for 600 s and 1300 °C when held for 60 ~ 600 s causes a smaller austenite grain size. The relationship between the evolution of the microstructure of P92 steel and the mechanical properties is also studied. The results show that the prior austenite grain size has an inverse relationship with impact energy and ultimate tensile strength at 620 °C, while the presence of soft δ-ferrite leads to a reduction in the microhardness, impact energy and ultimate tensile strength at 620 °C. [ABSTRACT FROM AUTHOR]