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We present a novel Hall magnetohydrodynamics (HMHD) numerical simulation of a three-dimensional (3D) magnetic flux rope (MFR) -- generated by magnetic reconnections from an initial 3D bipolar sheared field. Magnetic reconnections during the HMHD evolution are compared with the MHD. In both simulations, the MFRs generate as a consequence of the magnetic reconnection at null points which has not been realized in contemporary simulations. Interestingly, the evolution is faster and more intricate in the HMHD simulation. Repetitive development of the twisted magnetic field lines (MFL) in the vicinity of 3D nulls (reconnection site) is unique to the HMHD evolution of the MFR. The dynamical evolution of magnetic field lines around the reconnection site being affected by the Hall forcing, correspondingly affects the large-scale structures., Accepted for publication in Physica Scripta

Third generation γ-titanium aluminides with nominal compositions Ti–45Al–5Nb–0.2B–0.2C and Ti–45Al–10Nb–0.2B–0.2C were investigated to identify the phase transformation and their morphological stability with temperature. Electron microscopy and differential scanning calorimetry were employed for the characterization of phases and for recording the corresponding transformations, respectively. It has been inferred that the order–disorder transformation temperatures α2 → α increased with increasing Niobium (Nb), while the α-transus temperature decreases. The stability of the microstructure for both alloys with temperature were also investigated. Mass change measured for the heating rates 20 °C s−1 and 30 °C s−1 reveals that the alloy Ti–45Al–10Nb–0.2–0.2C shows stability up to 1100 °C, and the alloy Ti–45Al–5Nb–0.2B–0.2C is stable up to 900 °C. The orientation relationship between the phases indicates that with the change in shape of the α phase from lamellar to equiaxed, it deviates from the Blackburn orientation relationship.

The evolution of microstructure and texture during selective laser melting (SLM) of silver alloy—sterling silver 925 (AM Ag925) has been investigated and analyzed vis-a-vis cast sterling silver (AC Ag925). The microstructure of AM Ag925 was characterized by a single-phase silver-rich face-centered cubic solid solution with dendritic morphology, along with some locally distributed micro-segregated copper–germanium (Cu–Ge)-rich regions. Each adjacent dendritic feature consists of Ag–Cu-rich and Ag–Ge-rich regions and appears as alternate dark and bright regions. On the other hand, the as-cast AC Ag925 microstructure comprises Ag and Cu phases. Specific heat treatment was employed, which led to an equiaxed microstructure in AM Ag925 with Cu distributing along grain boundaries while the microstructure of AC Ag925 had Cu precipitates inside the matrix. Bulk texture studies revealed that the solidified textures were very weak for AM Ag925, and a random texture is observed. On the other hand, for the AC Ag925 specimens, a typical fiber texture is observed. Both AC Ag925 and AM Ag925 showed significant deviation from $$\left\langle {100} \right\rangle$$ solidification texture and influences the mechanical properties.

An anomalous deformation texture evolution has been observed in high-stacking-fault-energy pure platinum during cold rolling. A maximum of 98% thickness reduction, equivalent to a true strain of 3....

Metal additive manufacturing processes offer unique opportunities for the biomedical industry owing to their ability to produce custom-designed implants with near-net shape and intricate geometry. Co–Cr alloys are among the most popular metallic biomaterials due to their excellent resistance to both corrosion and wear. Several studies have been reported in recent years on studying the processing-structure–property relationships in additively manufactured Co–Cr alloys. However, there is a significant gap in knowledge of critical issues such as the microstructural features and properties of additively manufactured parts as well as the role of the processing parameters and post-manufacturing treatments. The performance of the additively manufactured Co–Cr alloys for biomedical applications such as fatigue, wear, corrosion, and the biological response is poorly characterized as yet. This article presents an overview of the existing literature available on additively manufactured Co–Cr alloys and identifies challenges and opportunities for their use in biomedical implants.

The alloy Ti6Al7Nb with the in situ reinforcement of TiB has been processed by selective laser melting (SLM). Premixed Ti6Al7Nb-xTiB2 powders were used for the powder bed. The microstructure of the Ti6Al7Nb alloy was characterized by martensite (αʹ), while the addition of TiB2 led to a bimodal microstructure with refined features as a result of in situ formation of fine TiB phase. A prismatic ││BD fiber texture was evident in all samples, though the texture formation was found to be affected by the change in the phase transformation pathway due to the formation of TiB. Higher hardness and yield strength (YS) in the composites as compared to the base material are attained. The examination of corrosion response revealed a lower corrosion current (Icorr) value for all the specimens in simulated body fluid (SBF) in comparison to Ti6Al4V alloy. The improved mechanical behavior and better corrosion resistance indicate the potential of SLM-processed Ti6Al7Nb/TiB composite as a suitable replacement for Ti6Al4V alloys for bio-implants.

The role of shear strain and deformation temperature on the microstructure and texture evolution in commercially pure (CP) titanium was investigated in the present study. CP titanium samples were s...

This study investigates heterogeneity in the deformation of an annealed sheet of commercially pure titanium (cp-Ti), its variation with loading direction and its influence on dwell fatigue response...

Thermo-mechanical softening forms the basis for hot working of metallic materials. In materials with hierarchical microstructures such as martensite, softening processes can be mediated or restricted by interfaces. In the present study, the operation of three distinct softening mechanisms in P91 martensitic steel during thermo-mechanical processing (TMP) has been investigated. The softening in the present case is found to arise from the interplay between microstructural strain, texture, and phase transformation. Further, softening characteristics vary with the TMP parameters. The manifestation of softening has been explored at the macroscopic, mesoscopic, and microscopic length scales. It has been found that each softening mechanism is differently mediated by the interfaces and is governed by local crystallographic orientation. Thermo-mechanical softening of martensite proceeds through orientation-dependent dynamic recrystallization. The role of specific interfaces in impeding this mechanism has been highlighted. In contrast, TMP of austenite proceeds through interface-mediated softening, combining the phenomena of recrystallization and phase transformation.

The potassium dihydrogen phosphate (KDP) is a popular nonlinear optical material. Optically good quality LiCl doped KDP crystals have been grown by slow solvent evaporation method at room temperatu...

Microstructure evolution and texture development during cold rolling of a Ti15333 alloy were systematically investigated in the present work. Texture was simulated using mean-field [Visco-Plastic Self-Consistent (VPSC) and Taylor] models. Evolution of crystallographic texture was also simulated using the Visco-Plastic Fast Fourier Transform (VPFFT) model. The as-received samples (in the hot-forged and hot-rolled condition) were cold rolled unidirectionally up to 20, 40, 60 and 80 pct thickness reductions. Increase in the cold-rolling reduction resulted in changes in the crystallographic texture as well as grain morphology. The initial hot-rolled sample consisted of in-grain shear bands that were aligned approximately ± 35 to 40 ° with respect to the sample rolling direction. Shear band density gradually increased with the increase in cold-rolling reduction, and these bands usually represent narrow zones of intense strain. α (RD//〈110〉) and γ (ND//〈111〉) fibers were observed in all the cold-rolled samples. The volume fraction of both these fibers was found to be highest for the 80 pct deformed sample. For mean-field simulations, the normalized difference of the texture index (normalized TIdiff) was found to be a good criterion to represent the match between the simulated and experimental texture. The affine model (VPSC) was found to give a good match with the experimental texture compared to the Taylor models. The γ-fiber and α-fiber were always overestimated in mean-field VPSC simulations. Extensive shear band formation could be the possible reason for mismatch between the simulated and experimental texture. For VPFFT simulations, the general texture evolution involved the intensification of the γ-fiber and α-fiber texture. Simulated texture was reasonably well predicted quantitatively with VPFFT, analyzed based on the volume fraction of the different texture fibers/components.

Hot deformation and softening response for the titanium aluminide Ti–48Al–2V–0.2B has been investigated. The deformation response to softening mechanisms has been examined. Deformation experiments were carried out in the strain rate range 0.01–10 s−1 keeping the temperature constant at 1200 °C and in the temperature range 1000–1200 °C at the strain rate 1 s−1. With an increase in strain rate, the microstructural changes associated with the softening mechanism include breaking of the lamellae, spheroidization of the broken laths and dynamic recrystallization. For the strain rate 1 s−1, deformation in the (α2 +γ) phase field leads to fine recrystallized grains, remnant lamellae and cavitation along the grain boundaries (for temperatures 1000 and 1100 °C). Deformation in the (α +γ) phase field leads to dynamic recrystallization at the shear bands, within the lamellae, breaking and rotation of the α phase during the continuous increase in the deformation strain.

The prediction of precipitated graphite nodules size and distribution in a large industrial casting is critical to understand the mechanical behavior of cast iron components used in heavy vehicles. An accurate prediction of the graphite nodules requires a validated and integrated macro-micro modeling framework, which forms the motivation behind the present study. Classical theories in the literature (Lesoult et al. in Acta Mater 46:983–995, 1998) proposed two stages of graphite growth: in (i) liquid stage, after encapsulation by the austenite grain, and in (ii) solid stage, surrounded by only austenite phase. In this work, a new stage of graphite growth was proposed, where a graphite nodule was in direct contact with the liquid metal, existing in the presence of an austenite grain separated from the nodule. The resulting three-stage graphite growth in a microscopic control volume was formulated using a volume-averaged micro-model. This was made to evolve with the help of a macroscopic temperature field obtained from finite-element-based numerical simulation and thus creating a comprehensive modeling framework. Further, for the first time, a diffusion-based deforming-grid micro-model was developed to obtain the exact nature of a single graphite nodule growth based on the position of individual phases in the microscopic control volume. The model predictions were validated with experimental results from the step-casting experiments in the present study, as well as with the observations of single nodule growth from in situ synchrotron X-ray tomography (Bjerre et al. in Model Simul Mater Sci Eng 26:085012, 2018; Azeem et al. in Acta Mater 155:393–401, 2018). The proposed models captured, faithfully, the experimental patterns of graphite growth evolution, number density of the nodules, and the size distribution as a function of cooling rate. This integrated multi-scale modeling approach is envisaged to be effective for determining exact graphite growth behavior of a single nodule and volume-averaged graphite growth in a large casting.

The present study investigates the structural, electronic and thermoelectric properties of Uranium Monocarbide using Density Functional Theory based on first principles calculation. The electronic structure of UC was calculated using the Quantum Espresso code and the Thermoelectric properties were evaluated using the BoltzTrap code based on the semiclassical Boltzmann transport theory. The dependence of strain on the thermoelectric properties such as electrical and thermal conductivity, Seebeck coefficient and thermoelectric figure of merit (ZT) is calculated. At room temperature, the Thermoelectric figure of merit (ZT) decreases under compressive strain whereas it increases over tensile strain.

The electronic and optical properties of rare-earth based half-Heusler ErPdSb compound are investigated by the using of first-principle density functional theory. The generalized gradient approximation (GGA) with spin–orbit coupling (SOC) and Hubbard parameter (U) have been used for exchange and correlation effect. Our calculations of electronic band structure show the half metallic nature of ErPdSb compound. The majority spin (up) states found semiconductor nature with a narrow indirect band gap 0.25 eV. While minority spin (down) states found metallic with no gap. The optical properties are investigated via optical conductivity, reflectivity along with other related optical constants such as absorption coefficient and refractive index.

Silica plays an important role in aluminium-based materials. However, role of silica in aluminium matrix composite is not clear so far. In the present study, pure silica was successfully extracted from rice husk by thermal and chemical treatments. The extracted silica had undergone FESEM, FTIR, and XRD for characterizing the purity of silica particles. The results showed that the obtained silica particles were highly pure. The rice husk-extracted pure silica was used as reinforcement in graphite/aluminium matrix hybrid composites. Composites were made using powder metallurgy process followed by sintering. Reinforcements of silica and graphite in aluminium matrix composites were done at different compositions to control the hardness in order to improve machinability. The aluminium matrix hybrid composites had shown excellent physical, mechanical, and thermal properties in terms of surface strength along with light mass as well as controlled thermal conductivity. The hardness of the hybrid composites had increased significantly compared to the single phase aluminium and also was controlled by the combined effect of added silica nanoparticle and graphite flake as reinforcements. Beside mechanical properties, these hybrid composites showed significantly desired thermal properties, particularly lower thermal expansion than that of pristine aluminium. Hence, the newly developed rice husk-extracted pure silica reinforced graphite/aluminium matrix hybrid composites can be used as potential materials for various advanced applications including microelectronic devices, engine piston, and automobile components.

In the present investigation, the evolution of texture and microstructure during incremental sheet forming was investigated. Hot-rolled sheets of commercially pure titanium were subjected to single-point incremental forming to obtain truncated pyramid geometries. It was observed from texture measurements that there was splitting of basal poles along the transverse direction. Moreover, a significant number of twins was observed in the deformed microstructure with the fraction of extension twins being highest compared to other variants. The crossing of deformation twins, formation of twin lamellar structure and formation of secondary extension twins within primary contraction twins were additionally observed. The state of deformation in the pyramid walls was analyzed via finite element method which in turn was used as input for carrying out crystallographic texture simulations via visco-plastic self-consistent simulations. It was observed that the state of deformation in the wall regions is plain strain compression plus through-thickness shear.

A stochastic reaction–diffusion drift model is used to simulate the time kinetics of interface and bulk oxide traps responsible for bias temperature instability (BTI), stress-induced leakage current (SILC), and time-dependent dielectric breakdown (TDDB) in MOSFETs. Trap generation and passivation are calculated using dissociation and repassivation of trap precursors and simultaneous diffusion and/or drift of atomic, molecular, and/or ionic species. The average of multiple stochastic simulations is used to qualitatively explain the measured BTI and SILC data. The difference in BTI and SILC time kinetics, variation in SILC time kinetics across reports, and oxide thickness dependence of TDDB Weibull slope variation are also qualitatively explained.

CuFe2O4/β–SiC and CuFe2O4/SiO2 catalysts were prepared by wet impregnation method, following the high temperature solid state route and their catalytic performance is evaluated in the SO3 decomposition reaction of the Sulfur–Iodine (S–I) cycle for hydrogen production. The synthesized catalysts are characterized by XRD, FT–IR, TGA, XPS, N2–BET, TEM, HR–TEM, FESEM–EDS and elemental mapping. CuFe2O4/β–SiC catalyst shows higher activity and stability while sintering is observed in the spent CuFe2O4/SiO2 whose activity decreased during the reaction time on stream. Kinetic studies were performed over CuFe2O4/β-SiC in the temperature range of 800–900 °C using wide range of space time, 6.54–44.40 kg h kmol−1. A heterogeneous kinetic model was developed based on the product distribution and the reaction rates determined by the model fitted well with the experimental rates at different temperatures.

Asphaltenes are a class of high molecular weight aromatic compounds found in crude oil. They adsorb onto toluene-water interfaces and induce a spontaneous emulsification phenomenon, whereby stable water-in-oil emulsions form without the need of an external energy input. This work aims to control and understand the factors affecting spontaneous droplet formation in the presence of asphaltene adsorption. This is particularly useful for crude oil refining, where the presence of a stable emulsion hampers the efficiency of downstream processing operations. We explore the effect of the addition of copolymers designed as crude oil flow improvers as a means to control the extent of emulsion formation. We find that the polymers competitively adsorb onto the toluene-water interface and diminish spontaneous emulsification. We also conduct fluorescence microscopy experiments and measurements of the interfacial energy to determine the mechanism of spontaneous emulsification in asphaltene systems. We conclude that an emulsion forms via the diffusion of molecular water into the oil phase and subsequent binding with asphaltene aggregates, leading to the nucleation of micrometer-sized water droplets. We find that the polymer forms complexes with the dissolved asphaltenes, possibly hampering the ability of diffused water to bind to the asphaltenes and reducing the extent of spontaneous emulsification. Finally, we investigate the role of interfacial shear and dilatational viscoelasticity to better understand which fundamental interfacial properties are important in the emulsification of asphaltene-laden systems. We find that the rate of formation of an interfacial microstructural network is inversely correlated with the extent and rate of spontaneous emulsification.

In this investigation, the superalloy IN718 has been prepared by additive manufacturing (AM) following a selective laser melting technique, and the post-AM heat treatments have been optimized. The microstructure of additively manufactured (AM) IN718 is characterized by the presence of dendritic and cellular features with large spatial heterogeneity along and across the build plane. Along the build direction, the fiber texture dominates. Heat treatment involving two-step solution treatment, and subsequently, two-step aging treatment was specifically designed to facilitate the precipitation of d phase at the grain boundaries to make the material resistant to grain boundary sliding (GBS). The AM IN718 showed dynamic strain aging (DSA) at three different temperatures, while the critical strain for the onset of serration was extended to a higher value after the heat treatment.

Ti-Nb-based low modulus metastable β-titanium alloys are popular choice for orthopedic implant materials. The performance of these materials could be affected by variation in crystallographic texture developed during processing. In the present study, texture evolution during unidirectional rolling and multi-step cross-rolling of the alloys Ti-34Nb-2Ta-3Zr-0.5O (TNTZO) and Ti-34Nb-2Ta-0.5O (TNTO) (in wt pct) has been studied. In both the alloys, the rolling texture is characterized by the absence of RD∥〈110〉 fiber, and cross-rolling leads to a stronger texture than unidirectional rolling. However, the prominent texture components in the cross-rolled condition are different for the two alloys. The TNTZO alloy shows the formation of a strong γ-fiber (ND∥〈111〉) along with {001}〈110〉 components while in TNTO, the texture is dominated by strong {001}〈110〉 component. These experimental results have been analyzed by simulations using viscoplastic self-consistent model and further validated by microstructural analysis using electron back scattered diffraction (EBSD). The deformation texture evolution has been attributed to a predominantly $$ \left\{ {11\overline{2} } \right\}\left\langle {111} \right\rangle $$ slip. The simulated texture of Ti-34Nb-2Ta-0.5O alloy shows a minor deviation from the experimental texture, which can be related to the reduced stability of this alloy due to the absence of Zr.

The formation of shear bands during hot deformation of a two-phase (α2 + γ) titanium aluminide and its consequences on dynamics softening has been investigated. The starting material consists of a colony of lamellar grains along with the segregated vanadium and niobium which was subjected to hot deformation in the temperature range 1000–1175 °C at the strain rate 10 s−1. Microstructures of the deformed samples indicate that, with increase in the deformation temperature, the orientation of shear bands changes. Moreover, the extent of dynamic recrystallization also increases with deformation temperature. The softening behaviour and crystallographic orientation change within lamellae during hot deformation have been explored. The nucleation of newly recrystallized grains has been observed at twin–parent grain boundary and within the twined γ phase. Lamellae of the γ and α2 phase have been also observed to be twisted and tilted, leading to the band formations under the load, whose mechanisms have also been explored in the present study.

The evolution of deformation texture and microstructure in commercially pure Al (cp-Al) and two Al–Mg alloys (Al–4Mg and Al–6Mg) during cold rolling to a very large strain (true strain et ≈ 3.9) w...

The implementation and commercialization of perovskite solar cells (PSCs) are hindered due to the presence of toxic lead. Metal phthalocyanines (MPc) have been studied extensively as charge transport layers (CTLs) in PSCs due to their desirable properties such as thermal and chemical robustness, and low production cost. In the present work, a theoretical study of the effect of phthalocyanine-based CTLs on a non-leaded KSnI3-based PSC is carried out using SCAPS software. The defect concentration of the layers and the interfaces, doping density and thickness of the layers, shunt, and series resistance of the device is optimized. Carbon is suggested as an affordable alternative to the state of art back contact material, gold. The stability of this device with temperature is also established. The optimized solar cell showed an excellent fill factor (FF) of 86.51% with a power conversion efficiency (PCE) of 11.91% and an excellent quantum efficiency (QE) ranging from 99.42%(400 nm) to 72.02%(660 nm) in the visible region. The present study highlights the enhanced performance parameters of leadless KSnI3-based PSC with phthalocyanine-based CTLs as compared to the state-of-art CTLs, TiO2 and Spiro-OMeTAD reported in previous literature with a PCE and FF of 9.776% and 36.139% respectively.

Research was conducted on the microstructural evolution and ensuing mechanical response from high-pressure torsion (HPT) processing of Ti-6Al-4V alloy in the as-cast and β-forged conditions with and without 0.1 wt.% boron addition. The boron addition produces refinement of the prior β grains and the (α+β) colonies and introduces an additional TiB phase but this affects the deformation response and the microstructural evolution only at low strains of 0.5 to 5 rotations. In the initial condition the orientation of the (α+β) colonies significantly affects the deformation response and leads to differences in substructure formation in both the as-cast and β-forged conditions. This orientation dependence counts on the initial microstructural differences between the unmodified and the boron modified alloys. At higher strains, there is a similar deformation response and microstructure evolution all the alloys. The hardness variation with equivalent strain is similar for the unmodified and boron modified alloys in as-cast and β-forged conditions and represents various deformation regimes in HPT-processing. Strength modelling confirms a simultaneous contribution from microstructural refinement and increased dislocation density towards the hardness increment during HPT processing. Overall, the as-cast and β-forged Ti-6Al-4V-0.1B alloys possess identical deformation response to the β-forged unmodified Ti-6Al-4V alloy in the initial and intermediate stages. At high levels of straining, all alloys respond in an equivalent manner, thus ruling out any possible effects from additional TiB phase or microstructural refinement for the boron-modified alloys.

We combine the first-principle calculations, based on the density functional theory, and Boltzmann transport theory to investigate the structural, electronic and thermoelectric of narrow gap RNiSb (R = Gd, Er and Lu) half Heusler (HH) compounds. Coulomb corrected generalized gradient approximation (GGA + U) has been employed which is the most competent method to treat rare earth compound. We find spin up/down Ni-3d and spin down R-4f states as main contributors to the total density of states (DOS) near Fermi energy (EF). All the investigated compounds exhibit the indirect narrow energy gaps (0.246–0.279 eV) that are in agreement with the corresponding experimental values. We obtained fairly high values of the Seebeck coefficient (S) in agreement with available experimental data. The calculated value of total S (from spin-up and spin-down channels), using two current models, increases from 50 to 202 µV/K at 300 K when Gd with half-filled f-states is replaced by Lu with completely filled f-states in these RNiSb HH compounds. We also find the maximum value of ZT is 0.32 and 0.76 at 800 K for Gd and Er compounds, whereas 0.68 is the maximum ZT for Lu compound at 450 K. We obtained favorable and stable ZT values (ZT > 0.7) for a wide temperature range only in ErNiSb compound in agreement with the experiment. This proposes ErNiSb as a promising candidate for thermoelectric applications.

In this study, mechanical properties and microstructural investigation of Ti64 at high strain rate are studied using a split-Hopkinson pressure bar method under compression for temperatures up to 800 °C. Flow softening in the mechanical response of material to such loading conditions hints at instability in compression, which increases with an increase in temperature. Microstructural characterization of the deformed material is characterized using the electron-backscattered diffraction technique. It reveals the presence of instabilities in Ti64 in the form of a fine network of shear bands. The shear band width grows with an increase in temperature along with the area fraction of shear band in the material, displaying its improved capacity to contain microstructural instabilities at higher temperature. After a detailed microstructural investigation, a mechanism for shear band widening is proposed. Based on this mechanism, a path generating nuclei within shear bands is discussed.