Single-phase Domains Research Articles

The Influence of Thermomechanical Conditions on the Hot Ductility of Continuously Cast Microalloyed Steels.

Continuous casting is the most common method for producing steel into semi-finished shapes like billets or slabs. Throughout this process, steel experiences mechanical and thermal stresses, which influence its mechanical properties. During continuous casting, decreased formability in steel components leads to crack formation and failure. One reason for this phenomenon is the appearance of the soft ferrite phase during cooling. However, it is unclear under which conditions this ferrite is detrimental to the formability. In the present research, we investigated what microstructural changes decrease the formability of microalloyed steels during continuous casting. We studied the hot compression behaviour of microalloyed steel over temperatures ranging from 650 °C to 1100 °C and strain rates of 0.1 s-1 to 0.001 s-1 using a Gleeble 3800® (Dynamic Systems Inc, Poestenkill, NY, USA) device. We examined microstructural changes at various deformation conditions using microscopy. Furthermore, we implemented a physically-based model to describe the deformation of austenite and ferrite. The model describes the work hardening and dynamic restoration mechanisms, i.e., discontinuous dynamic recrystallisation in austenite and dynamic recovery in ferrite and austenite. The model considers the stress, strain, and strain rate distribution between phases by describing the dynamic phase transformation during the deformation in iso-work conditions. Increasing the strain rate below the transformation temperature improves hot ductility by reducing dynamic recovery and strain concentration in ferrite. Due to limited grain boundary sliding, the hot ductility improves at lower temperatures (<750 °C). In the single-phase domain, dynamic recrystallisation improves the hot ductility provided that fracture occurs at strains in which dynamic recrystallisation advances. However, at very low strain rates, the ductility decreases due to prolonged time for grain boundary sliding and crack propagation.

Continuous dynamic recrystallization behaviors in a single-phase deformed Ti-55511 alloy by cellular automata model

In this study, the continuous dynamic recrystallization (CDRX) behaviors of a hot-deformed Ti-55511 alloy are investigated in β single-phase domain. CDRX is found to play a dominant role in the microstructure evolution during thermomechanical forming of the Ti-55511 alloy. In order to quantitatively and visually simulate the hot forming process, a probabilistic cellular automata (CA) method is established. This CA technology integrates the dislocation evolution model, subgrain nucleation rate model, misorientation evolution model, grain boundary (GB) migration model, and topology deformation model. The results of a systematic study of both microstructural evolution and macroscopic mechanical response at various strains, strain rates, and temperatures are presented. The average absolute relative error (AARE), correlation coefficient (R), and root-mean squared error (RMSE) values between the experimental and simulated stresses are 4.63 %, 0.9963, and 3.81 MPa, respectively. The deviation values of subgrain size range from 1.27 % to 17.25 %, when the temperatures varies from 920 to 980 °C. The predicted results well agree with the measured results, demonstrating the transition from a coarse and static recrystallized structure to a refined and continuous dynamic recrystallized structure. A low Zener-Hollomon (Z) parameter can effectively enhance the progress of CDRX. Higher temperatures and lower strain rates result in a larger volume fraction of CDRX. Quantitative analyses confirm that the incubation period for CDRX is significantly longer than that for subgrain formation, indicating a sustained transformation from the low-angle grain boundaries (LAGBs) to the high-angle grain boundaries (HAGBs) through the absorption of dislocations.

Intrusion of liquids into liquid-infused surfaces with nanoscale roughness.

We present a theoretical study of the intrusion of an ambient liquid into the pores of a nanocorrugated wall w. The pores are prefilled with a liquid lubricant that adheres to the walls of the pores more strongly than the ambient liquid does. The two liquids are modeled as a binary liquid mixture of two species of particles, A and B. The mixture can decompose into a liquid rich in A particles, representing the ambient liquid, and another one rich in B particles, representing the liquid lubricant. The wall is taken to attract the B particles more strongly than the A particles. The ratio w-A/w-B of these interaction strengths is changed in order to tune the contact angle θ_{AB} formed by the A-rich/B-rich liquid interface between the two fluids and a planar wall, composed of the same material as the one forming the pores. We use classical density functional theory in order to capture the effects of microscopic details on the intrusion transition, which occurs as the concentration of the minority component or the pressure in the bulk of the ambient liquid is varied, moving away from bulk liquid-liquid coexistence within the single-phase domain of the A-rich bulk ambient liquid. These liquid structures have been studied as a function of the contact angle θ_{AB} and for various widths and depths of the pores. We also studied the reverse process in which a pore initially filled with the ambient liquid is refilled with the liquid lubricant. The location of the intrusion transition, with respect to its dependence on the contact angle θ_{AB} and the width of the pore, qualitatively follows the corresponding shift of the capillary-coexistence line away from the bulk liquid-liquid coexistence line, as predicted by a macroscopic capillarity model. Quantitatively, the transition found in the microscopic approach occurs somewhat closer to the bulk liquid-liquid coexistence line than predicted by the macroscopic capillarity model. The quantitative discrepancies become larger for narrower cavities. In cases in which the wall is completely wetted by the lubricant (θ_{AB}=0) and for small contact angles, the reverse transition follows the same path as for intrusion; there is no hysteresis. For larger contact angles, hysteresis is observed. The width of the hysteresis increases with increasing contact angle. A reverse transition is not found inside the domain within which the ambient liquid forms a single phase in the bulk once θ_{AB} exceeds a geometry-dependent threshold value. According to the macroscopic capillarity theory, for the considered geometry, this is the case for θ_{AB}>54.7^{∘}. Our computations show, however, that nanoscale effects shift this threshold value to much higher values. This shift increases strongly if the widths of the pores become smaller (below about ten times the diameter of the A and B particles).

Computational development, synthesis and mechanical properties of face centered cubic Co-free high entropy alloys

The search for Co-free high entropy alloy (HEA) matrix for Stellite (Co-Cr) substitution in nuclear applications is addressed by computational and experimental investigations conducted within the Cr20-(Fe-Mn-Ni)80 system at 1100 °C. Calphad method is employed using Thermo-Calc and TCHEA3 to determine the single phase domain of the face centered cubic (FCC) solid solution. For each composition of this domain, the intrinsic lattice strength is calculated using two models from literature, namely Varvenne and Walbrühl. Then, four alloys of the Cr20-(Fe-Mn-Ni)80 plane, with atomic compositions Cr20Fe35Ni45, Cr20Fe30Mn5Ni45, Cr20Fe35Mn5Ni40, Cr20Fe30Mn10Ni40 are elaborated by arc-melting. Thermo-mechanical treatments (homogenization at 1100 °C, 80% cold-rolling reduction and annealing/recrystallization at 900 °C) are performed to obtain equiaxed recrystallized microstructures and different grain sizes for each alloy. As expected from thermodynamic calculations, all samples of all alloys are confirmed to be face centered cubic (FCC) by X-Ray Diffraction. Hall-Petch law parameters are established from tensile tests and intrinsic lattice strength are deduced. Experimental results are discussed regarding other HEAs and Co-Cr FCC alloys and intently compared to predictions from Varvenne and Walbrühl models. Results indicate that Co-free HEA from the Cr-Fe-Mn-Ni alloy system with intrinsic lattice strength similar or superior to the classical Cantor alloy may be identified.

Enhanced Single-Phase Phase Locked Loop Based on Complex-Coefficient Filter

Complex coefficient filters (CCFs) are widely used for phase-locked loop (PLL) in three-phase power systems, while its usage is largely sparse in the single-phase domain. Single-phase CCF-PLLs so far reported in the literature do not yield satisfactory performances at off-nominal frequency conditions, which is a crucial PLL attribute. Whether they are a suitable filtering technique of choice for single-phase PLL is yet to be formally documented in a methodological way. In this regard, this article derives an enhanced version of the single-phase CCF-PLL (ECCF-PLL), which is able to provide accurate estimation of grid parameters in dynamically changing grid frequency environment. The proposed ECCF-PLL is then numerically and experimentally compared with few other single-phase PLLs to gauge its efficacy and suitability. The test shows the advantage of harmonic robustness from ECCF-PLL, which is specifically useful in a weak grid.

Coupling Stokes Flow with Inhomogeneous Poroelasticity

Summary We investigate the behaviour of flux-driven flow through a single-phase fluid domain coupled to a biphasic poroelastic domain. The fluid domain consists of an incompressible Newtonian viscous fluid while the poroelastic domain consists of a linearly elastic solid filled with the same viscous fluid. The material properties of the poroelastic domain, that is permeability and elastic parameters, depend on the inhomogeneous initial porosity field. We identify the dimensionless parameters governing the behaviour of the coupled problem: the ratio between the magnitudes of the driving velocity and the Darcy flows in the poroelastic domain, and the ratio between the viscous pressure scale and the size of the elastic stresses in the poroelastic domain. We consider a perfusion system, where flow is forced to pass from the single-phase fluid to the biphasic poroelastic domain. We focus on a simplified two-dimensional geometry with small aspect ratio and perform an asymptotic analysis to derive analytical solutions. The slender geometry is divided in four regions, two outer domains that describe the regions away from the interface and two inner domains that are the regions across the interface. Our analysis advances the quantitative understanding of the role of heterogeneous material properties of a poroelastic domain on its mechanical response when coupled with a fluid domain. The analysis reveals that, in the interfacial zone, the fluid and the elastic behaviours of this coupled Stokes—poroelastic problem can be treated separately via (i) a Stokes–Darcy coupling and (ii) the solid skeleton being stress free. This latter finding is crucial to derive the coupling condition across the outer domains for both the elastic part of the poroelastic domain and the fluid flow. Via specification of heterogeneous material properties distribution, we reveal the effects of heterogeneity and deformability on the mechanics of the poroelastic domain.

Experimental Study on the Phase Relations of the SiO2-MgO-TiO2 System in Air at 1500\xb0C

We investigated the phase relations of the SiO2-MgO-TiO2 system in air at 1500°C using the high-temperature isothermal equilibration/quenching technique, followed by x-ray diffraction measurements and direct phase analysis using scanning electron microscopy coupled with x-ray energy dispersive spectrometry. One single liquid phase domain, five two-phase domains (liquid-TiO2, liquid-cristobalite, liquid-MgO·SiO2, liquid-2MgO·SiO2, and liquid-MgO·2TiO2), and five three-phase regions (liquid-TiO2-MgO·2TiO2, liquid-MgO·SiO2-cristobalite, liquid-TiO2-cristobalite, liquid-MgO·SiO2-2MgO·SiO2 and liquid-2MgO·SiO2-MgO·2TiO2) were observed. We constructed a 1500°C isothermal phase diagram based on the experimentally measured liquid compositions. We compared simulations using MTDATA and FactSage thermodynamic software and their databases with the experimental results obtained in this study. These results can be used to provide guidelines for updating the MTDATA and FactSage titania-bearing thermodynamic databases by reassessing the thermodynamic properties of the phase with new experimental data.

Efficient Ternary Polymer Solar Cells with Tunable Crystallinity and Phase Separation of Active Layers via Incorporating GHK-Cu.

The crystallinity of a nonfullerene small-molecule acceptor plays an important function in the bimolecular recombination and carrier transfer of polymer solar cells (PSCs). However, because of the competition between the donor (PBDB-T) and acceptor (ITIC) in processes of phase separation and crystallization, the PBDB-T preferentially forms a crystalline network, which limits the molecular diffusion of ITIC and leads to the weak crystallinity of ITIC, eventually restricting the photoelectric conversion efficiency (PCE) of PSCs. Therefore, in our work, a small-molecule biomaterial, Gly-His-Lys-Cu (SMBM GHK-Cu), is incorporated into binary PBDB-T:ITIC to construct a PBDB-T:ITIC:GHK-Cu ternary system. The addition of GHK-Cu increases ITIC crystallinity and promotes the formation in continuous single-phase domains of PBDB-T and ITIC, which creates an optimized bicontinuous network path to increase and balance charge transmission in PSCs. Meanwhile, GHK-Cu makes energy transfer from GHK-Cu to PBDB-T appreciably efficient, improving the photon capture and exciton-generation rate of PBDB-T. Moreover, it can form a complementary absorption spectrum with PBDB-T and ITIC, which enhances the PCE of ternary devices. Excitingly, the PCE of PSC-based PBDB-T:ITIC is enhanced from 10.28% to 12.07% via incorporating 0.1 wt % GHK-Cu into PBDB-T:ITIC, in which the enhanced open voltage (VOC) is 0.92 V, the short-circuit current (JSC) is 17.87 mA/cm2, and the fill factor (FF) is 73.4%. Meanwhile, the PCE of PSC-based PM6:Y6 is also enhanced from 15.21% for a binary PSC to 17.11% for ternary PSC-based PM6:Y6:0.1 wt % GHK-Cu. This work shows that the cheap and environmentally friendly GHK-Cu has great potential for application in tuning the crystallinity and phase separation of the active layer.

NMR Study of LiCo0.96Al0.04O2 As a Positive Electrode Material for Li-Ion Batteries: Homogeneity and Role of Doping on Mechanisms

LiCoO2 (LCO) is one of the most widely used positive electrode materials in lithium-ion batteries due to its high volumetric energy density which can be further improved by charging at high voltages. However, working at high potential (above 4.3 V vs. Li+/Li) causes a deterioration in cycling performance induced by structural instabilities, electrolyte oxidation and Co dissolution. Extensive studies have been devoted to increasing energy density by increasing the cutoff voltage. The substitution of cobalt with various metals is one of the classic methods, the choice of aluminum as dopant for example is based on several criteria: low cost and non-toxicity, a similar radius for Al3+ compared to Co3+ (0.535 Å vs. 0.545 Å) facilitates the replacement of the latter and maintains the structure leading to the complete solid solution LiCo1-yAlyO2.We will focus here on LiCo0.96Al0.04O2, synthesized by the solid route and characterized by 7Li, 27Al and 59Co Nuclear Magnetic Resonance (NMR) and synchrotron X-Ray Diffraction (XRD). In addition to the characterization of the mean structure by XRD, the NMR allows us to study the local environments of the different nuclei. 27Al MAS NMR and synchrotron XRD studies revealed that the Al-doping in this material is homogeneous. 7Li MAS NMR indicates that its stoichiometry (Li/M=1.00) is ideal. The electrochemical study has shown that the phase transitions occurring during delithiation of LiCoO2, were partially eliminated by aluminum doping even with a low doping amount and the high potential mechanisms appear to be different. In order to better understand the role of Al-doping on the mechanisms involved during cycling, several phases LixCo0.96Al0.04O2 were prepared by electrochemical deintercalation and studied by 7Li, 59Co, and 27Al NMR and by XRD.During lithium deintercalation, Co3+ is oxidized to Co4+ then one unpaired electron is generated in the t2g band of Co atoms (t2g 5eg 0). For 0.8 ≤ x ˂ 1.00 the 7Li MAS NMR shows that the system behaves locally as two phase domain: domain with localized electrons and domain with delocalized ones on Con+ ions (Knight shift), even for very low amount of deintercalation (x=0.98), thus the XRD results confirm the existence of the biphasic domain. Whereas, a single phase domain is observed for the deintercalated materials with 0.4 ≤ x ≤ 0.8 and also at the NMR time of scale a single signal (Knight shift) is observed. This signal increases in intensity at the expense of 0 ppm and shifts to the higher isotropic displacement values up to x=0.5 then decreases, thus the evolution of the chex lattice parameter is correlated with the signal shift. For x = 0.3 and x = 0.2: a new broad signal appears probably due to formation of new Li environment in stacking faulted layers (O1 type). These different contributions will be more detailed on the presentation.

Numerical Study on the Tandem Submerged Hydrofoils Using RANS Solver

This paper is presented on the tandem two-dimensional hydrofoils with profiles NACA4412 in single-phase and two-phase flow domains for different submergence depths and different distances in a various angle of attack (AoA). Also, supercavitation is studied at σ = 0.34 by the Zwart cavitation model. Reynolds-averaged Navier–Stokes (RANS) with the shear stress transport (SST) K-ω is employed as a turbulence model in transient analysis of Ansys FLUENT software. The numerical results show that, by increasing depth, the drag coefficient increases for both hydrofoils 1 and 2 as well as the lift coefficient. The drag coefficient of hydrofoil 2 is bigger than hydrofoil 1 for all depths; moreover, it was found that the flow pressure behind the hydrofoil 1 had affected the upper and the lower surface of the hydrofoil 2 at each distance or AoA. These effects are observed in the hydrofoil 2 lift coefficient as well as the flow separation. However, the maximum lift-to-drag ratio is observed at AoA = 8 ° and 3.5c distance. Also, single-phase results reveal that the value of pressure and the hydrodynamic coefficient are very different from the two-phase flow results, due to the elimination of the free surface. So, a two-phase flow domain is recommended for increasing the accuracy of results. In addition, the investigation of supercavitation shows a growth in cavity occurrence on the surface by raising AoA.

Synthesis of carbon-supported bimetallic palladium\u2013iridium catalysts by microemulsion: characterization and electrocatalytic properties

Carbon (Vulcan XC-72)-supported bimetallic Pd–Ir catalysts with different Pd/Ir proportions (5–50 mol% Ir, 2 wt% Pd) were prepared by “water-in-oil” microemulsion method (w/o) using solutions of low (0.02 M, L series) and high concentration (0.2 M, H series) of the metals precursors (PdCl2 and IrCl3). The bimetallic particles were examined in terms of nanoscale phase properties (extent of Pd–Ir alloying, phase separation), surface composition (Pd and Ir fractions) and electrocatalytic performance for the formic acid oxidation reaction. Structural characterization was performed using XRD, SEM and HRTEM techniques. Electrochemical characterization allowed estimating the PdH formation ability and the surface composition of Pd–Ir particles what was confirmed by XPS data. The Pd–Ir nanoparticles of similar average size (ca. 4 nm), close to that of Ir (3.8 nm) and below that of Pd (6.2 nm) were formed regardless of the Pd/Ir proportion and the concentration of the metals precursors in the w/o. In contrast to the largely alloyed PdIr nanoparticles with the Pd-rich surface formed at low concentration of the metals precursors (0.02 M), the particles of almost closed surface and bulk Pd/Ir ratios composed mostly of randomly distributed single-phase domains were formed at high concentration (0.2 M). At the lowest bulk Ir content, 5 mol%, the particles have Ir-rich surface regardless of the preparation method. The catalytic studies involving formic acid electrooxidation reaction showed the activity enhancement for the L series catalysts with respect to monometallic Pd/C (twofold TOF increase) and H series counterparts. The Pd85Ir15/C catalyst of the Pd–Ir alloyed and the surface composition expressed by the Pd/Ir atomic ratio near to 6 displayed the highest activity which was 2.9-times higher relative to that of Pd.Graphic abstract

Mastering of Particle Size and Morphology of the Puckered Layer γ’-V2O5 Polymorph for Enhanced Na Electrochemical Properties

Due to the cost and low availability of Li sources, Na-ion batteries (NIBs) are attracting considerable interest as tomorrow’s world batteries. Compared to LIBs, the number of electrode materials for NIBs are limited but progress in Na intercalation grows very rapidly [1]. Layered materials with Van der Waals interlayer spacing constitute ideal frameworks for intercalation reactions of guest cationic species from which high discharge-charge rate and minimum structural distortions can be expected. While orthorhombic α-V2O5 was identified in the 70’s as a promising cathode material for secondary Li batteries [2], it is only very recently that Na insertion was addressed in this oxide at room temperature [3]. An alternative way to identify new attractive stable V2O5 polymorphs consists in considering the chemical removal of metallic species from vanadium pentoxide bronzes MxV2O5. Such approach allows taking advantage of the availability of new types of structure with various original layer stacking. This strategy was successfully applied in the 90s’ to obtain the puckered layer γ’-V2O5 polymorph synthesized from the topotactic chemical removal of Li from γ-LiV2O5 by means of strong oxidizing agent [4]. The electrochemical behavior of γ’-V2O5 was shown to explain the enhancement of the cell potential of Li//V2O5 [4] and a recent work has demonstrated the potentialities of this polymorph toward Li insertion [5]. Here we report the interesting capability of γ’-V2O5 toward electrochemical sodium insertion. Nearly one Na+/ mole involving the V5 +/V4 + redox couple can be inserted between the puckered layers of the γ’-V2O5 structure (see inset in Figure 1). As a result, an attractive initial discharge capacity of 145 mAh g-1 is obtained at a high working potential of 3.3 V vs. Na+/Na (Fig.1 curve a). Nevertheless, strong kinetic limitations are evidenced during the first charge process, with a 50% efficiency at RT (Fig.1 curve a). Further cycles exhibit an excellent capacity retention (stable value of 70 mAh g− 1 available after 70 cycles at C/10) [6]. To solve the charge efficiency issue, a downsizing approach was performed using planetary ball milling on the as prepared γ’-V2O5 platelets-like powder. While the platelet morphology is kept, the mean crystallite size is reduced by a factor 3 (90 nm for the as prepared sample vs. 35 nm for the ball-milled γ’-V2O5-BM). As shown in Fig.1 curve b, a strong effect of the crystallite size reduction is observed both on the shape of the voltage-composition curve and on the first charge efficiency that is strongly improved for the ball-milled powder. Indeed, a charge capacity of 127 mAh g-1 corresponding to a 90% efficiency is recovered for γ’-V2O5-BM. A detailed structural study by X-ray diffraction (XRD) and Raman spectroscopy reveals a greatly modified phase diagram by reducing the dimensions of the particle. The nanosize effect promotes a wide single phase domain at the expense of diphasic region and is also responsible for an easier sodium extraction process in the ball milled compound, leading to a genuine electrochemical and structural reversibility. A mastering of the particle morphology has also been conducted : γ’-V2O5 was synthesized from a home-made α-V2O5 precursor obtained through polyol process, leading to pure, fine and coral-like porous powders with homogeneous grain size distribution [7]. This peculiar morphology drastically increases the available surface for sodium diffusion, leading to a quantitative charge process at a high working voltage of 3.4 V vs. Na+/Na (Fig.1 curve c). Furthermore, enhanced rate capability performance and excellent cycle life are achieved, with 130 mAh g-1 still available after 60 cycles at C/10. Raman and XRD measurements demonstrate the high structural reversibility of the sodium insertion-extraction reaction in γ’-V2O5. References 1- N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, Chem. Rev. 114 (2014) 11636. 2- M.S. Whitthingham, Chem. Rev. 104 (2004) 4271. 3- D. Muller, R. Baddour-Hadjean, M. Tanabe, L.T.N. Huynh, M.L.P. Le, J-P. Pereira-Ramos, Electrochim. Acta 176 (2015) 586. 4- J. M. Cocciantelli, P. Gravereau, J-P. Doumerc, M. Pouchard, P. Hagenmuller, J. Solid State Chem., 93 (1991) 497. 5- R. Baddour-Hadjean, M. Safrany Renard, J-P. Pereira-Ramos, Acta Mater. 165 (2019) 183 6- M. Safrany Renard, N. Emery, R. Baddour-Hadjean, J-P. Pereira-Ramos, Electrochim. Acta 252C (2017) 4. 7- N. Emery, R. Baddour-Hadjean, D. Batyrbekuly, B. Laïk, Z. Bakenov, J-P. Pereira-Ramos, Chem. Mater 30 (2018) 5305. Figure 1. First discharge-charge curve of a γ’-V2O5 composite electrode made of the following active material: (a) as-prepared platelet-like powder/ crystallite size 90 nm (b) ball-milled powder / crystallite size 30 nm (c) coral-like powder. C/10 rate. NaClO4 1M/PC electrolyte, 2% vol. FEC. Inset: crystal structure of γ’-V2O5. Figure 1

Phase segregation of metastable quenched liquid mixtures and the effect of the quenching rate

ABSTRACTThe effect of the quenching rate on the phase separation of partially miscible liquid mixtures is studied, showing that it may influence the growth rate of single-phase domains. In particular, the phase separation of metastable binary mixtures in the presence of strong emulsifiers appears to be heavily retarded. These effects constitute an important limitation to the phase transition extraction process introduced by the authors in previous works, which is based on the fact that phase separation of unstable mixtures is rapid, even in the presence of surface active compounds.

Exploration of the NaxMoO2phase diagram for low sodium contents (x≤ 0.5)

Phase diagram in the NaxMoO2system (x≤ 0.5) determined using electrochemistry andin situX-ray powder diffraction.

The NaxMoO2 Phase Diagram (1/2 ≤ x &lt; 1): An Electrochemical Devil’s Staircase

Layered sodium transition metal oxides represent a complex class of materials that exhibit a variety of properties, for example, superconductivity, and can feature in a range of applications, for example, batteries. Understanding the structure–function relationship is key to developing better materials. In this context, the phase diagram of the NaxMoO2 system has been studied using electrochemistry combined with in situ synchrotron X-ray diffraction experiments. The many steps observed in the electrochemical curve of Na2/3MoO2 during cycling in a sodium battery suggest numerous reversible structural transitions during sodium (de)intercalation between Na0.5MoO2 and Na∼1MoO2. In situ X-ray diffraction confirmed the complexity of the phase diagram within this domain, 13 single phase domains with minute changes in sodium contents. Almost all display superstructure or modulation peaks in their X-ray diffraction patterns suggesting the existence of many NaxMoO2 specific phases that are believed to be characteri...

Realization of Absolute‐Phase Unwrapping and Speckle Suppression in Laser Digital Holography

In this paper, an absolute‐phase unwrapping and speckle suppression approach to reconstruct a three‐dimensional (3‐D) image of an object with laser digital holography is described. This method offers three advantages to enhance the performance of the phase reconstruction technique. First, both speckle suppression and phase unwrapping are processed in the complex amplitude domain rather than in the single phase or amplitude domain. With this approach, the phase details of the object are better preserved upon phase reconstruction. Second, the proposed algorithm requires no threshold determination and thus achieves self‐adaptive speckle suppression and robust phase unwrapping, in contrast to other methods. Finally, an improved dual‐domain image denoising method is applied to further remove speckle‐remnant‐induced phase distortion. Ideal 3‐D phase reconstruction results are obtained both theoretically and experimentally for the first time.

Electrochemical Zinc Intercalation in Lithium Vanadium Oxide: A High-Capacity Zinc-Ion Battery Cathode

Rechargeable zinc-ion batteries (ZIBs) with high energy densities appear promising to meet the increasing demand for safe and sustainable energy storage devices. However, electrode research on this low-cost and green system are faced with stiff challenges of identifying materials that permit divalent ion-intercalation/deintercalation. Herein, we present layered-type LiV3O8 (LVO) as a prospective intercalation cathode for zinc-ion batteries (ZIBs) with high storage capacities. The detailed phase evolution study during Zn intercalation using electrochemistry, in situ XRD, and simulation techniques reveals the large presence of a single-phase domain that proceeds via a stoichiometric ZnLiV3O8 phase to reversible solid–solution ZnyLiV3O8 (y > 1) phase. The unique behavior, which is different from the reaction with lithium, contributes to high specific capacities of 172 mAh g–1 and amounts to 75% retention of the maximum capacity achieved in 65 cycles with 100% Coulombic efficiency at a current density of 133 ...

Progress in the Understanding of the Microstructure Evolution of Direct Laser Fabricated TiAl

With the introduction of TiAl in aircraft jet engines, there is an increasing demand for the evaluation of novel processing routes for gamma titanium aluminides such as additive manufacturing (AM). A Ti-47Al-2Cr-2Nb powder material has been used as feedstock for laser fabrication of 3D samples by means of “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD). A number of processing parameters including laser power, laser scan rate, powder feed rate, have been varied to evaluate their effects on the material soundness. Optimised conditions can significantly reduce the crack sensitivity for this relatively low ductility material. In particular, crack-free experimental conditions have been identified by using additional heating strategies, thus limiting built-up residual stresses during fast cooling. The different samples have been examined using optical and scanning electron microscopy in the as-built condition. The non-equilibrium cooling conditions generate ultra-fine and metastable structures exhibiting high microhardness values. A range of post-heat treatments have been performed to relieve the residual stresses and to tailor more uniform microstructures. Conventional heat treatments in the α+γ two-phase domain or in the α single phase domain have been successfully used to fully restore homogeneous microstructures either duplex or fully lamellar. A comparison is made with microstructures of both laser treated materials and of conventionally processed materials.

Thermally and Electrochemically Driven Topotactical Transformations in Sodium Layered Oxides NaxVO2

Phase diagrams and structural transformations in the complex NaxVO2 system have been studied using electrochemical (de)intercalation and in situ and operando high resolution synchrotron powder diffraction. Starting from O′3-Na1/2VO2 obtained by sodium electrochemical deintercalation of O3-NaVO2, the structural details of irreversible and reversible thermally driven transformations to P′3 and P3 type structures are presented. Subsequently, these P′3-NaxVO2 phases provide a platform for operando studies exploring the NaxVO2 phase diagram as a function of sodium electrochemical (de)intercalation. In this system, three single phase domains have been found: a line phase P′3-Na1/2VO2, one solid solution for 0.53 ≤ x ≤ 0.55 characterized by an incommensurate modulated structure, and a second solid solution for 0.63 ≤ x ≤ 0.65 with a defective structure resulting from a random stack of O′3 and P′3 layers. With further sodium intercalation (x > 0.65), the structure irreversibly transforms to the starting parent ph...

Mean field modelling of dynamic and post-dynamic recrystallization during hot deformation of Inconel 718 in the absence of δ phase particles

Dynamic and post-dynamic recrystallization kinetics were investigated during hot-working of Inconel 718 as a function of temperature, strain and strain rate in the single phase domain. The post-dynamic evolution was found to be extremely fast and impacting significantly the grain size. A two-site mean field model including both dynamic and post-dynamic evolution was used to predict the recrystallized fraction, the average grain size and the stress–strain curves in different thermomechanical conditions.