A fundamental understanding of how magnetic fields govern phase stability is crucial for the design and processing of metallic materials. This study develops a thermodynamic model to quantify the non-linear migration of the A3 phase line in Fe-C alloys under high magnetic fields. The model employs a temperature-dependent power-law formulation, incorporating two physical parameters that separately quantify the intensity and functional shape of the field effect. It thereby captures the curvature transition of the A3 phase line and enables the direct calculation of equilibrium carbon concentration of gamma phase along the A3 phase line and the phase fractions of gamma or alpha phase for arbitrary temperature and magnetic field conditions. Its predictive accuracy was experimentally verified using a eutectoid Fe-0.77 wt% C alloy under a 7 T magnetic field: the calculated proeutectoid ferrite volume fraction agrees well with the experimentally measured value obtained from isothermal transformation experiments.

The magnetic field, along with temperature, significantly affects the mechanism of phase transformation, requiring detailed quantitative analysis. In this study, the influence of a magnetic field on the gamma-alpha (austeniteferrite) isokinetic phase transformation process of an Fe-1wt% Cu alloy was quantitatively analyzed through kinetics analysis by in-situ magnetization measurement. The kinetic calculation results demonstrate that the magnetic field accelerates the gamma-alpha phase transformation, leading to shorter transformation time, increased transformation rate, and grain refinement. Quantitative analysis of Avrami exponent, driving force, nucleation barrier and activation energy directly indicates that the magnetic field induces a shift from a site saturation nucleation mode to a continuous nucleation mode, increases the driving force of phase transformation, and reduces the nucleation barriers and activation energy, ultimately resulting in a higher nucleation rate, faster phase transformation rate, and more uniform and finer grain structure. Simultaneously, the magnetic field alters the impingement mode during isokinetic phase transformation, shifting it from anisotropic growth impingement to randomly dispersed nuclei impingement.

The non-equilibrium solidification behavior of deeply undercooled Co-Sn binary alloys (hypoeutectic Co79.5Sn20.5 at.%, eutectic Co76Sn24 at.% and hypereutectic Co72Sn28 at.%) has been investigated by the glass fluxing method under high magnetic fields up to 12 T. Analysis of the results showed that anomalous eutectics consistently manifest in the terminal microstructure of Co-Sn binary alloys regardless of whether a magnetic field is applied. The application of a high magnetic field reduces the critical undercooling for the formation of anomalous eutectics without changing the primary solidification pathway. It was found that at low undercoolings, regular eutectics formed preferentially with a mutual transformation between regular and anomalous eutectics subsequently. At large undercoolings, regular and anomalous eutectics formed nearly simultaneously, further analysis revealed that the two eutectic phases can transform from either coupled or uncoupled growth states into anomalous eutectics. The present research reveals the microstructural evolution characteristics of Co-Sn binary alloys and explains the origin of anomalous eutectics. It enriches the theory of high magnetic field effects on alloy solidification and offers practical guidance for optimizing the microstructures of eutectic alloys.

A phase transformation model based on magnetization is proposed in this paper, which accurately tracks the change in the phase transformation volume fraction with time/temperature f-T/t by analyzing phase transformation magnetization curves under a magnetic field. This allows for the determination of kinetic parameters related to the nucleation and growth processes such as the phase transformation rate df/dt-T/t and Avrami exponent n, enabling quantitative analysis of phase transformation kinetics under magnetic field effects. Additionally, the phase transformation magnetization under a magnetic field can be accurately fitted by combining the volume fraction calculation model with the Johnson–Mehl–Avrami equation, thus also obtaining the kinetics parameters. The aforementioned two models are applied to study the isothermal and isokinetic transformations of austenite (γ) to ferrite (α) in Fe-1 wt. %Cu alloys, demonstrating the effects of external conditions through variations in kinetic parameters.

Immiscible alloys possess broad industrial applications, but the presence of immiscible gaps makes them highly susceptible to the formation of segregated microstructures, thus, a new method for obtaining a uniform distribution of fine minor separated phases needs to be explored. The present work focuses on the evolution mechanism of a CuCo immiscible alloy with a core-shell microstructure during semi-solid isothermal processing under a high magnetic field. The results showed that the microstructure changes from the core-shell structure of the initial sample to homogeneous microstructure after semi-solid treatment, regardless of whether a magnetic field is applied. The mechanism of microstructure evolution of the alloy during semi-solid treatment was revealed through in-situ experiment, in which Ostwald ripening and coalescence mechanisms led to grain coarsening, grain boundary remelting caused grain dissociation, and ultimately the grains underwent spheroidization. However, as a high magnetic field was applied, the average radius of the Co-rich particles decreased, and the particles were aligned in the direction of the magnetic field, forming a chain-like microstructure due to dipole-dipole interactions between the grains. The CuCo immiscible alloy with a uniform microstructure after semi-solid treatment exhibited a higher microhardness and saturation magnetization. This study offers a novel perspective for designing immiscible alloys with homogeneous microstructures as well as chain-like microstructures by utilizing semi-solid treatment combined with a magnetic field.

It has been claimed that graphite hosts superconductivity at room temperature, although all efforts to isolate it have been vain. Here we report a separation method that uses magnetic field gradients to sort the superconducting from normal grains out of industrial graphite powders. We have obtained a concentrate of above room temperature superconducting particles. Electrical resistance measurements on agglomerates of sorted grains of three types of graphite show transition temperatures up to T_c_onset∼ 700K with zero resistance up to ∼ 500K. Magnetization measurements confirm these values through jumps at T_c in the zero field cooled curves, and by the occurrence diamagnetic hysteretic cycles shrinking with temperature. Our results open the door towards the study of above room temperature superconducting ill-stacked graphite phases.

Non-equilibrium solidification experiments were conducted on Cu50Co50 alloys under different magnetic field intensities to investigate the orientation, microstructure evolution, and magnetic properties of the Co-rich phase. The results revealed that the phase-separated rod-like Co-rich phase can realize the alignment morphology and can be oriented with the 〈111〉 crystal direction along the direction of the 5 T high magnetic field (HMF). In contrast, the orientation of the Cu-rich phase, which underwent secondary liquid−liquid phase separation, was not significantly affected by the HMF. The alloy solidified at 0 T showed near-magnetic isotropic behavior, while the alloy solidified at 5 T displayed magnetic anisotropic behavior. The saturation magnetization of the alloy increased slightly, and the coercivity decreased correspondingly, which were strictly dependent on the orientation evolution of the Co-rich crystal.

Systematic understanding on the magnetic field intensity dependent microstructure evolution and re -crystallization behavior in a Co-B eutectic alloy under a constant undercooling ( 6,T approximate to 100 K) were carried out. Absent of the magnetic field, the comparable size of divorced FCC-Co and Co3B eutectic ellipsoidal grains coexist with a few regular lamellas. When the magnetic field is less than 15 T, the elongated primary FCC-Co dendrites parallel to the magnetic field with the dispersed FCC-Co nano-particles em-bedded within the Co3B matrix occupy the inter-dendrite regions. Once the magnetic field increases to 20 T, the FCC-Co/Co2B anomalous eutectic colonies dominate. The formation mechanism of Co2B phase is discussed from several aspects of the competitive nucleation, the chemical redistribution induced by the thermomagnetic-induced convection and magnetic dipole interaction, and the strain-induced trans-formation. Furthermore, the application of magnetic field is found to promote recrystallization, proved by the lower density of misorientation, the appearance of FCC-Co annealed twins and more Co3B sub-grains. This work could further enrich our knowledge about the magnetic-dependent microstructure evolution and recrystallization process in the undercooled Co-B system and provide guidance for controlling the microstructures and properties under extreme conditions.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The magnetic field induced instability patterns have been observed in an undercooled immiscible Co–Cu alloy by an in situ magnetization measurement of the supercooled alloy melt. With the increase in magnetic field intensity and gradient, the undercooled immiscible melt experienced a transition from a core-shell structure to a layered structure at a lower field intensity and then a typical normal field instability pattern with the applied higher magnetic field gradient. Due to the different magnetic response ability of the separated phases in the presence of a magnetic field gradient, the transition of the morphology was complex, and its detailed investigations can provide important insight for better understanding of the ferrofluid and the creation of functional material. Furthermore, under an appropriate field gradient condition, it can achieve the subtle transitions between the diverse morphologies in an immiscible alloy.

In this study, ternary Cu52Co24Fe24 immiscible alloys are prepared with varying undercoolings and under a high magnetic field. The microstructure evolution and properties of the alloys are investigated. The temperature range of the immiscible gap is determined using CALPHAD. According to the excess Gibbs free energy of liquid, the addition of Fe promotes the demixing tendency of the Cu–Co–Fe ternary system during solidification. With the application of a magnetic field, the (Fe, Co)-rich phases transform from a globular shape to an elongated form along the direction of the magnetic field during solidification, which is due to the existence of the counteracting behavior of the interparticle magnetic dipole-dipole force at the critical droplet size. Under a high magnetic field, the obtained samples had a more dispersed minority phase, higher microhardness and better conductivity. However, the saturation magnetization of the samples with large undercooling decreases with increasing magnetic field due to the suppression of the phase separation behavior under a high magnetic field. This study proposes a novel technology for preparing immiscible alloys with excellent properties by applying a superimposed magnetic field during solidification.

The microstructure and properties of a Cu50Co50 immiscible alloy prepared by directional solidification were investigated experimentally via heat treatment assisted by a magnetic field of 10 T. The alloys were subjected to a heat treatment assisted high magnetic field in the solid state at 1070 degrees C and semi-solid state at 1300 degrees C for 6 h respectively. The results showed that in the solid state, with an applied high magnetic field, the fragmentation and refinement of the Co-rich dendrite phase can be ascribed to the reduction in the coarsening coefficient. In the semi-solid state, the refinement of dendrites was due to the melting of the dendrite outer shell. However, the fragmentation of dendrites and the deviation of the growth direction could be ascribed to the coupling effect of Lorentz, TEMF and TEMC, which changed the flow of the melt and affected solute migration. In both cases, the hardness of the Cu-rich matrix can be improved by imposing a high magnetic field. The variation in magnetic properties mainly relied on the decrease in the diamagnetic phase contribution and the change in alloy orientation under a high magnetic field. The current research initiates a novel method to tailor the microstructure and fabricate immiscible alloys with excellent properties via high magnetic field assisted heat treatment.

The effect of a high magnetic field (HMF) on phase transition and microstructure formation in Fe-Ga alloys with a Ga concentration of about 25 at.% has been investigated using experimental research and ab initio modeling. We found that the HMF of 25 T significantly accelerates the D0(3) to L1(2) transformation in the hyperstoichiometric Fe-27 %Ga alloy upon isothermal annealing at 475 degrees C. At the same time, the field has little effect on the transformation in the hypostoichiometric Fe-24 %Ga alloy. We have found that HMF does affect the kinetics of the transformation rather than the energy of the phases. We have shown that the effect of HMF is mainly associated with the ferromagnetic ordering of magnetic moments, which leads to lattice instability of the D0(3) phase and enhancement of the D0(3) -> L1(2) transition due to the initiation of the barrierless mechanism. (C) 2022 Elsevier B.V. All rights reserved.

The structure and crystallographic texture formation processes in two Fe–Ga magnetostrictive alloys during annealing of deformed samples under high magnetic field (HMF) 20 T have been studied. It was shown that the effect of the magnetic field on the structure transformation during annealing depends on the features of the recrystallization in alloys. In the case of recrystallization in a single-phase binary Fe-Ga alloy, the application of HMF along the rolling direction promotes the formation of <100> grains along this direction. This leads to a twofold increase in the magnetostriction of the polycrystalline sample. In the same alloy, but with the presence of particles of the second phase, HMF does not affect the texture. The reasons for this phenomenon were discussed. In addition, it was found that in both alloys, the application of HMF during annealing retards the processes of structure evolution.

The effect of a high magnetic field (HMF) on phase transition and microstructure formation in Fe-Ga alloys with a Ga concentration of about 25 at.% has been investigated using experimental research and ab initio modeling. We found that the HMF of 25 T significantly accelerates the D0(3) to L1(2) transformation in the hyperstoichiometric Fe-27 %Ga alloy upon isothermal annealing at 475 degrees C. At the same time, the field has little effect on the transformation in the hypostoichiometric Fe-24 %Ga alloy. We have found that HMF does affect the kinetics of the transformation rather than the energy of the phases. We have shown that the effect of HMF is mainly associated with the ferromagnetic ordering of magnetic moments, which leads to lattice instability of the D0(3) phase and enhancement of the D0(3) -> L1(2) transition due to the initiation of the barrierless mechanism. (C) 2022 Elsevier B.V. All rights reserved.

The structure and crystallographic texture formation processes in two Fe-Ga magnetostrictive alloys during annealing of deformed samples under high magnetic field (HMF) 20 T have been studied. It was shown that the effect of the magnetic field on the structure transformation during annealing depends on the features of the recrystallization in alloys. In the case of recrystallization in a single-phase binary FeGa alloy, the application of HMF along the rolling direction promotes the formation of <100> grains along this direction. This leads to a twofold increase in the magnetostriction of the polycrystalline sample. In the same alloy, but with the presence of particles of the second phase HMF does not affect the texture. The reasons for this phenomenon were discussed. In addition, it was found that in both Fe-Ga alloys, the application of HMF during annealing retards the processes of structure evolution.

The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement. A crossover was observed on the 1/M-T curve during the overheating process, indicating that a liquid-liquid structure transition (LLST) took place in the melt. Based on this information, the effects of LLST on the solidification behavior, microstructure and tribology property were investigated experimentally. The sample solidified with the LLST exhibits significantly different solidification behaviors, i.e., the nucleation undercooling and the recalescence extent are conspicuously enlarged, and the solidification time is shortened. As a result, the microstructure is effectively refined and homogenized, and the hardness and wear resistance are significantly enhanced. The present work might be helpful for not only theoretically understanding the influence of LLST on the solidification behavior but also providing an alternative approach to tailor the microstructure and properties.

Eliminating phase segregation under high temperature at high growth rate remains a long term challenge. Methods such as adding third element, inoculations and nanoparticle bring materials pollution and difficulties for compatibility. This work provides a path to realize a diffusional growth through extremely reducing the size of the segregated phase by highly superheating the system and suppressing their collision and coagulation via magnetohydrodynamic effect in Zn-6 wt%Bi immiscible system. The application of super high static magnetic field (SHSMF) compounded with superheating technique resulted in a homogeneous distribution of phase concentrated to about 3-4 & micro;m when increased the magnetic flux density (MFD) from 0 T to 24 T and the superheating temperature from 600 degrees C to 900 degrees C. The undercooling of monotectic reaction was improved about 5-6 times from 0.4 degrees C to 2.1 degrees C when increased the super heating temperature from 600 degrees C to 900 degrees C with and without SHSMF. Bi-rich droplets grow as a near pure diffusion way when the particle size distribution follows the near LSW theory at 24 T. SHSMF has not only suppressed the mass transport of Bi atom but also decreased the size of Bi-rich clusters and even suppressed the precipitation of Bi-rich phases. The practicality has been proved by the same immiscible system with a critical composition. This novel method overcomes the microstructure refinement limit only through adding the extraneous and contaminated elements and realizes a contactless green way for growth control of phase. It has practical significance and is opening for expanding its scope of applications. (c) 2021 Elsevier B.V. All rights reserved.

While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors, the research conducted with an ultra-high magnetic field greater than 20 T is still preliminary. In the current study, the structure evolution of Co-B alloys are experimentally studied with undercooling. The effects of a 25 T magnetic field on the solidification behavior and the subsequent solid-state phase transformation behavior have been investigated. The 25 T magnetic field is confirmed to have little effect on the homogeneous nucleation, but have some influence on the heterogeneous nucleation of Co3B and Co23B6 phases by modifying the wetting angle θ. The decomposition of Co23B6 phase in the subsequent cooling process can be effectively suppressed by applying the 25 T magnetic field. The present work might be helpful for not only theoretically understanding the influence of ultra-high magnetic field on the phase transformation behaviors but a potential technology of field-manipulation of magnetic materials.

High magnetic field assisted heat treatment process was used to regulate the microstructure and properties of AlCoCrCuFeNi high-entropy alloy. Results show that applying magnetic field can refine the FeCoCr-rich phase and suppress the large regional segregation of Cu-rich phase. The strength of the alloy increases greatly from 1482 MPa to 1795 MPa and the elongation also increases from 23% to 27%. The saturation magnetization is depressed after the magnetic field is applied. These variations are attributed to the decrease of Cu-rich phase segregation, grain refinement, and also the slightly decreased volume fraction of BCC phase upon applying high magnetic field.

Immiscible alloy is a kind of functional metal material with broad application prospects in industry and electronic fields, which has aroused extensive attention in recent decades. In the solidification process of metallic material processing, various attractive phenomena can be realized by applying a high magnetic field (HMF), including the nucleation and growth of alloys and microstructure evolution, etc. The selectivity provided by Lorentz force, thermoelectric magnetic force, and magnetic force or a combination of magnetic field effects can effectively control the solidification process of the melt. Recent advances in the understanding of the development of immiscible alloys in the solidification microstructure induced by HMF are reviewed. In this review, the immiscible alloy systems are introduced and inspected, with the main focus on the relationship between the migration behavior of the phase and evolution of the solidification microstructure under HMF. Special attention is paid to the mechanism of microstructure evolution caused by the magnetic field and its influence on performance. The ability of HMF to overcome microstructural heterogeneity in the solidification process provides freedom to design and modify new functional immiscible materials with desired physical properties. This review aims to offer an overview of the latest progress in HMF processing of immiscible alloys.