Miscibility Gap Research Articles

Residual stress versus microstructural effects on the strength and toughness of phase‐separated PbO–B2O3–Al2O3 glasses

AbstractA few authors have reasonably proposed that liquid–liquid phase‐separated (LLPS) glasses could show improved fracture strength, Sf, and toughness, KIc, as the second phase could provide a barrier to crack propagation via deflection, bowing, trapping, or bridging. Due to the associated tensile or compressive residual stresses, the second phase could also act as a toughening or a weakening mechanism. In this work, we investigated five glasses of the PbO–B2O3–Al2O3 system spanning across the miscibility gap: Four of them undergo LLPS—three are binodal (two B2O3‐rich and one PbO‐rich) and one is spinodal—and one does not show LLPS (composition outside the miscibility gap). Their compositions were designed in such a way that the amorphous particles are under compressive residual stresses in some and under tensile residual stresses in others. The following mechanical properties were determined: the Vickers hardness, ball on three balls (B3B) strength, and toughness, KIc‐SEVNB (single‐edge V‐notch beam [SEVNB]). The microstructures and compositions were analyzed using scanning electron microscopy with energy‐dispersive X‐ray spectrometry. The spinodal glass showed, by far, the best mechanical properties. Its KIc‐SEVNB = 1.6 ± 0.1 MPa m1/2, which embodies an increase of almost 50% over the B2O3‐rich binodal composition, and 90% considering the PbO‐rich binodal composition. Moreover, its fracture strength, Sf = 166 ± 7 MPa, is one of the highest ones ever reported for an LLPS glass. Fracture analyses evidenced that the spinodal composition exhibited the lowest net stress at the fracture point. Moreover, calculations indicate that the internal residual stress level is the lowest in the spinodal glass. The overall results indicate that the microstructural effect of the spinodal glass is the most significant factor for its superior mechanical properties. This work corroborates the idea that LLPS provides a feasible and stimulating solution to improve the mechanical properties of glasses.

Exponential Temperature-Dependent Parameters for Thermodynamic and Structural Properties of Al-Ti Melt

Thermodynamic and structural properties of Al-Ti melt have been estimated in the framework of Redlich-Kister (R-K) polynomial using linear temperature-dependent (T-dependent) interaction parameters above melting temperatures. These calculations show the existence of the artificial inverted miscibility gaps (artifacts) at temperatures 2000 K, 2500 K, and 2700 K. Therefore, interaction parameters are assumed to vary exponentially with temperature and have been optimised for excess free energy of mixing. The artifacts do not appear in the calculation of these properties of the concerned alloy when these optimized parameters are used. BIBECHANA 19 (2022) 75-82

Experimental constraints on miscibility gap between apatite and britholite and REE partitioning in an alkaline melt

Abstract Apatite containing 14 wt% TREO (total rare earth oxide) and coexisting with calciobritholite with 37.2 wt% TREO has been synthesized at 800 °C and 10 kbar from a felsic melt with the addition of NaCl. The analysis of the experimental products with regression analysis of time-resolved (RATR) laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data allowed to estimate the composition of the coexisting phases. The results suggest that equilibrium has been established during the run and both apatite and calciobritholite contained REE in [Si4+REE3+] to [Ca2+P5+] solid solution, whereas the coupled substitution [Na1+REE3+] to [2Ca2+] was insignificant despite crystallization from an alkaline, Na-rich melt. The coexistence of the apatite and calciobritholite and available experimental data allowed the miscibility gap to be constrained between apatite and calciobritholite, and suggest complete miscibility between apatite and britholite above 950 °C. The melt that produced coexisting apatite and calciobritholite was characterized by a significant Cl content of (0.51 wt%) and elevated REE (526 ± 19 ppm Ce) and low-P content (112 ± 49 ppm). The change of the accessory mineral association from monazite to apatite and calciobritholite with the addition of NaCl illustrates the importance of halogens for mineral associations. The partition coefficients of britholite are similar to those of apatite and are distinguished mainly by a higher preference for REE and Th. Henry’s law was not acting for the total REE content in the melt because of the buffered system; however the partition coefficients could still be used for the prediction of the relative REE patterns for melts that generated high-REE apatite and/or calciobritholite. These results have implications for the interpretation of the phosphate associations in alkaline volcanic and plutonic rocks.

Damping Properties of Selective Laser-Melted Medium Manganese Mn-xCu Alloy.

In this work, selective laser melting (SLM) technology was applied to directly realize the in situ synthesis of medium manganese Mn-xCu (x = 30-40 wt.%) alloys based on the blended elemental powders. The effects of heat treatment on the microstructural evolution and damping properties of the SLMed Mn-xCu alloys were investigated. The metastable miscibility gap was studied by thermodynamic modeling and microhardness measurement. The results showed that γ-(Mn, Cu) phase with dendritic arm spacing (DAS) of 0.9-1.2 μm was the main constituent phase in the as-SLMed alloys, which was one to two orders of magnitude finer than those of the as-cast samples. Aging at 400-480°C for the Mn-30%Cu or 430°C for Mn-40%Cu alloys can induce spinodal decomposition, martensitic transformation, and α-phase precipitation, whose direct evidence was provided for the first time by transmission electron microscopy and 3D atom probe tomography in the work. The miscibility gap obtained from thermodynamics calculation was basically consistent with the microhardness results for the SLMed Mn-xCu alloys. Solution and aging (SA) treatment can improve the microstructure, tensile and damping properties of the SLMed Mn-xCu alloys more obviously than aging treatment. A 2.3-2.8 and 4.3-4.5 times increase was produced in damping capacity in the aged SLMed and SLMed+SAed Mn-xCu samples, respectively.

Atom Probe Study of the Miscibility Gap in CuNi Thin Films and Microstructure Development.

The unclear miscibility of CuNi alloys was investigated with atom probe tomography (APT). Multilayered thin film samples were prepared by ion beam sputtering (IBS) and focused ion beam (FIB) shaping. Long-term isothermal annealing treatments in a UHV furnace were conducted at temperatures of 573, 623, and 673 K to investigate the mixing process. The effective interdiffusion coefficient of the nanocrystalline microstructure (including defect diffusion) was determined to be Deff = 1.86 × 10−10 m2/s × exp(−164 kJ/mol/RT) by fitting periodic composition profiles through a Fourier series. In nonequilibrium states, microstructural defects like grain boundaries and precipitates were observed. While at the two higher temperatures total mixing is observed, a clear experimental evidence is found for a miscibility gap at 573 K with the boundary concentrations of 26 and 66 at%. These two compositions are used in a subregular solution model to reconstruct the phase miscibility gap. So, the critical temperature TC of the miscibility gap is found to be 608 K at a concentration of 45 at% Ni.

Probing the Miscibility Gap of the Pt–Pd Binary System by Atom Probe Tomography

Abstract To solve the uncertainty of the platinum (Pt)–palladium (Pd) phase diagram, especially the existence of a suggested miscibility gap, atom probe tomography (APT) was used to determine the time evolution of the composition after heat treatment. Due to the extraordinarily slow diffusion in the temperature range of the controversial phase separation, the investigated volume was limited to nano-sized multiple layers deposited by ion beam sputtering (IBS). The evaporated volume was reconstructed from the obtained datasets and the respective diffusion coefficients were determined using the Fourier series solution of the diffusion equation. Beginning with pure Pt and Pd layers annealed at 673, 773, 873, and 973 K, the mixing appears to be purely diffusion controlled in the chosen annealing times, but the state of complete mixing was still not observed. Therefore, extended isothermal annealing sequences at 673 and 773 K with pre-alloyed layers have been carried out. They clearly suggest complete mixing even at the lowest investigated temperatures.

Salt-induced diffusiophoresis of a nonionic micelle: Roles of salting out and proximity to surfactant cloud point

• Salt-induced diffusiophoresis is the migration of a colloidal particle in water caused by a salt concentration gradient. • Tyloxapol micelle was identified as model particle with surface properties governed by polyethylene glycol (PEG) chains. • Na 2 SO 4 was chosen because it is a common salt and a strong salting-out agent according to Hofmeister series. • Gradient of Na 2 SO 4 drives micelle diffusiophoresis from high to low salt concentration due to PEG preferential hydration. • Near surfactant cloud point, diffusiophoresis becomes dominant mechanism responsible for micelle transport. Salt-induced diffusiophoresis is the migration of colloidal particles in water caused by salt concentration gradients. A widespread example of colloidal particles is represented by those with interfacial properties governed by polyethylene glycol (PEG) functionalities. Since salting-out salts strongly affect PEG-water interactions, their gradients are expected to generate diffusiophoresis of PEG-based particles. In this work, diffusiophoresis of nonionic micelles of tyloxapol, a polyoxyethylene surfactant, was characterized in the presence of Na 2 SO 4 . Specifically, multicomponent-diffusion coefficients were measured at 25 °C for the ternary tyloxapol-Na 2 SO 4 -water system using Rayleigh interferometry. These transport data, together with measurements of cloud points and dynamic-light-scattering diffusion coefficients, were used to determine the effect of salt concentration on micelle mobility, salt-induced micelle diffusiophoresis and salt osmotic diffusion induced by micelle gradients. It was found that gradients of Na 2 SO 4 induce micelle diffusiophoresis from high to low salt concentration. Moreover, diffusiophoresis becomes the dominant mechanism responsible for micelle transport near surfactant cloud point due to increase in both micelle size and osmotic compressibility with salt concentration. A hydration model was employed to theoretically describe salt salting-out effect on micelle diffusiophoresis and salt osmotic diffusion. This work is the first report showing salt-induced diffusiophoresis of a neutral PEG-based colloidal particle and characterizing its magnitude near miscibility gaps.

Spontaneously formed multiscale nano-domains in monophasic region of ternary solution

HypothesisTernary mixtures, containing one hydrotrope and two immiscible fluids, both being soluble in the hydrotrope at any proportion, exhibit unexpected solubilization power and unusual mesoscopic properties, which are a subject of long-standing controversies for decades. ExperimentsThis work investigates the entire monophasic region of ternary trans-anethol/ethanol/water system, where multiscale nanostructurings with correlation lengths exceeding dimensions of individual molecules are identified by dynamic light scattering. The physical properties of the ternary mixture are characterized, with revealing the compositional dependence of refractive index and dynamic viscosity. FindingsIn surfactant-free microemulsion (SFME) regime, the single phase consists of two distinct nanoscopic domains in equilibrium, one trans-anethol-rich aggregate at the molecular scale (∼1 nm) and one mesoscopic droplet at the mesoscale (∼100 nm). However, only a tiny fraction of the hydrophobic component trans-anethol (<∼0.025%) are initially incorporated in mesoscale structures, and the vast majority are molecularly dissolved or in the form of aggregates. The concentration of mesoscopic droplets increases sharply when shifting toward the miscibility gap, but their size exhibits a weak compositional dependence. The nanoscopic domains exhibit long-term physical stability, and the Ostwald ripening is still the primary mechanism governing such mesoscopic droplet aging, but with a rather low ripening rate.

The thermophysical properties of Bi-Ga alloys

In this work, an experimental study was conducted to show the effect of Ga addition to Bi-Ga alloys on density, surface tension, and viscosity. The thermophysical properties of the Bi-Ga system in the liquid state were determined using the discharge crucible method in the temperature range of 573–823 K. The experimental results were compared with the literature data and showed a good correlation on changes for studied properties with Ga addition. The isothermal section at 573 K of the investigated properties shows very good agreement with literature data, and with data obtained from models. Segregation in the liquid has a huge effect on the changes in studied properties. A very big reduction of surface tension value with the addition of Bi content was observed. Moreover, increasing viscosity is connected with the miscibility gap region in the Bi-Ga system.

Butler‐based thermodynamic modeling of interfacial energies for in‐vessel corium systems

The modeling of transient phase segregation phenomena in corium multicomponent thermodynamic systems is complicated especially in the liquid miscibility gap which can lead to phase separation (stratification of the liquid phases for corium) and is of tremendous importance. The modeling of the associated phase separation transients in corium stratification is limited by a deficiency in the interfacial energy data, which are difficult to measure experimentally for these high-temperature systems. The limitations of summarizing the interfacial energies as constant coefficients were observed in a recent work on simulation of the stratification kinetics of a corium pool and the necessity to improve the estimation of interfacial energies [1,2]. This work tests the efficacy of a thermodynamic approach to evaluate the interfacial tensions, initially proposed for metallic systems by Kaptay [3]. This method is based on the Butler equation and makes use of existing thermodynamic databases for multicomponent systems constructed by the CALPHAD method. In practice, the application of this method to corium systems was performed using the open-source code openIEC [4]. To do so, this code was modified to enable required features, both functionally and methodically. In particular, the OpenCalphad Gibbs energy minimizer has been interfaced in this framework and benchmarked against previous results. Then, interfacial energies were calculated for two relevant corium systems (U-O and U-O-Zr-Fe) using two different existing databases (TAF-ID and NUCLEA). The first results obtained were analyzed in terms of general trends and compared to existing theoretical aspects. Large differences were observed depending on the thermodynamic database that was used.

A comprehensive investigation of carbon micro-alloying on microstructure evolution and properties of metastable immiscible Cu-Fe alloy

In the present study, the effect of C micro-alloying on microstructure evolution and properties of metastable immiscible Cu-20Fe alloy was comprehensively investigated. Experimental results indicate that the microstructure of Cu-Fe alloy is extremely sensitive to the C content. It was found that obvious liquid-liquid phase separation (LLPS) behavior is observed in Cu-20Fe alloy after C micro-alloying, and the tendency of LLPS is enhanced with increasing C content. The calculation of ΔScc(0) suggests that C atoms preferentially pair with free Fe atoms to form new Fe (C) atomic clusters, thus resulting in the enhancement of bonding of the like-atom pairs. In addition, the quasi-binary phase diagram calculation further reveals the existence of a stable miscibility gap for C-containing alloys, and the temperature interval of miscibility gap is significantly enlarged with increasing C content. Meanwhile, the interface energy between two liquids formed by LLPS also slightly increases as C content increasing. These above reasons should be responsible for the microstructure evolution of Cu-20Fe-xC alloys. In addition, the C micro-alloying deteriorates the soft magnetic properties of Cu-Fe alloys to a certain extent, whereas improves its corresponding wear-resistance.

Phase equilibria and liquidus projection determination of the Hf–Si–V ternary system

The phase equilibria including the isothermal sections at 1100 and 1300 °C as well as the liquidus surface projection of the Hf–Si–V ternary system were experimentally determined. The microstructures, crystal structures and phase constitutions of the annealed and the as-cast alloys in whole composition range were investigated by means of scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction and electron probe microanalysis, respectively. The isothermal sections of the Hf–Si–V system at 1100 and 1300 °C were accordingly constructed. Fifteen three-phase regions were confirmed, the ternary compound HfVSi was identified, and the solubilities of the third element in the binary compounds were determined. In the meanwhile, based on the XRD data obtained in the present work and by means of the JADE software package, the lattice parameters of each compound are calculated. Furthermore, the solidification paths of the Hf–Si–V as-cast alloys were analyzed to verify the primarily solidified phases from the liquid phase. Fifteen primary solidification regions were finally confirmed in the liquidus surface projection. Particularly, transmission electron microscopy results revealed that the binary stoichiometric compound V6Si5 extended into the Hf–Si–V ternary system, forming the line compound (V,Hf)6Si5. With the decrease of temperature, the line compound (V,Hf)6Si5 can decompose into two phases, one of which V(Hf)6Si5 has the composition near V6Si5, another near Hf2V4Si5, but with the same structure type. The Hf2V4Si5 phase is proposed to form due to the miscibility gap of the line compound (V,Hf)6Si5. The present experimental results are useful for the thermodynamic assessment of the Hf–Si–V ternary system, and the database development for the Nb/Mo–Si–V–Hf containing multi-component superalloy materials.

Efficient, Selective Sodium and Lithium Removal by Faradaic Deionization Using Symmetric Sodium Titanium Vanadium Phosphate Intercalation Electrodes.

NASICON (sodium superionic conductor) materials are promising host compounds for the reversible capture of Na+ ions, finding prior application in batteries as solid-state electrolytes and cathodes/anodes. Given their affinity for Na+ ions, these materials can be used in Faradaic deionization (FDI) for the selective removal of sodium over other competing ions. Here, we investigate the selective removal of sodium over other alkali and alkaline-earth metal cations from aqueous electrolytes when using a NASICON-based mixed Ti-V phase as an intercalation electrode, namely, sodium titanium vanadium phosphate (NTVP). Galvanostatic cycling experiments in three-electrode cells with electrolytes containing Na+, K+, Mg2+, Ca2+, and Li+ reveal that only Na+ and Li+ can intercalate into the NTVP crystal structure, while other cations show capacitive response, leading to a material-intrinsic selectivity factor of 56 for Na+ over K+, Mg2+, and Ca2+. Furthermore, electrochemical titration experiments together with modeling show that an intercalation mechanism with a limited miscibility gap for Na+ in NTVP mitigates the state-of-charge gradients to which phase-separating intercalation electrodes are prone when operated under electrolyte flow. NTVP electrodes are then incorporated into an FDI cell with automated fluid recirculation to demonstrate up to 94% removal of sodium in streams with competing alkali/alkaline-earth cations with 10-fold higher concentration, showing process selectivity factors of 3-6 for Na+ over cations other than Li+. Decreasing the current density can improve selectivity up to 25% and reduce energy consumption by as much as ∼50%, depending on the competing ion. The results also indicate the utility of NTVP for selective lithium recovery.

Manipulation of the spinodal decomposition behavior in a multicomponent system

Spinodal decomposition has been widely studied in binary or ternary material systems but rarely in multicomponent systems. Here we propose a strategy to manipulate the spinodal decomposition behavior in a typical Ti-Zr-C-N-Ni cermet system based on the Gibbs free energy and its second derivative of Fcc-(Ti, Zr)(C, N) phase. The impact of constituents and temperature on miscibility gap and spinodal decomposition was visualized. Interestingly, Ni impeded the spinodal decomposition of this system, while N had a complex effect. Furthermore, a subtle increase in Ni content (by 0.5 at.%) counteracted the effect of 20 at.% N addition at 1500 °C. The calculated results are further supported by the microstructure analysis of (Ti, Zr)(C, N)-Ni samples. The adopted strategy presented herein enables the optimization of cermet constituents and heat-treated temperature to manipulate the spinodal decomposition behavior for designing high-performance multicomponent materials.

Pushing the Boundaries of Multicomponent Alloy Nanostructures: Hybrid Approach of Liquid Phase Separation and Selective Leaching Processes.

ConspectusAlloying, or mixing of multiple metallic elements, is the classical way of novel materials development since the Bronze age. Increased numbers of principal elements expand the compositional space for alloy design vastly, leading to nearly endless possibilities of unexpected and unique materials properties. In contrast to bulk alloying processes represented by casting of molten metal mixtures, the fabrication of multicomponent alloy (MCA) nanostructures such as nanoparticles and nanofoams with more than three elements is often challenging, and a few methodologies for directly synthesizing alloy nanostructures up to denary systems have been suggested recently. However, forming alloy nanoparticles inside another metal matrix, instead of inside aqueous media in wet-chemical synthesis, is a fairly well understood strategy in terms of physical metallurgy. Extracting those alloy nanophases from the matrix could provide an alternative way to fabricate novel MCA nanostructures.In this Account, we describe a hybrid approach of metallurgical bottom-up and chemical top-down processes for fabricating MCA nanostructures including nanoparticles and nanofoams. The former utilizes a liquid-state phase separation process that resembles "oil and water" but occurs at the nanoscale due to thermodynamic mixing relations among alloying elements and a rapid quenching process. Thermodynamic prediction of the immiscible boundary in a temperature-composition space (miscibility gap) plays a key role in designing precursor alloys for MCA nanostructures. Selective leaching, the chemical top-down process for extracting the alloy nanostructures from the precursors, uses the chemical reactivity difference between the embedded nanostructures and the matrix phase against a certain chemical solution. We discuss here that the precise control of alloy composition and cooling rate based on thermodynamic assessments enables researchers to prepare phase-separating precursor alloys for fabricating both nanoparticles and nanofoams with a broad size range from a few nanometers to a few hundred nanometers. Depending on the alloy systems, the atomic structure of alloy nanostructures could be controlled from fully amorphous to nanocrystalline and even to quasicrystalline structure. We demonstrate how the different sizes of alloy nanostructures fabricated by a single hybrid procedure can be effectively exploited for investigating size-dependent physical properties. The future and potential research directions for this hybrid approach are also briefly discussed. This unique approach for fabricating nanosized alloys provides an extended methodology to discover novel metallic nanomaterials with promising properties in diverse compositional spaces of MCA systems.

Automated Quantum Dots Purification via Solid Phase Extraction.

The separation of colloidal nanocrystals from their original synthesis medium is an essential process step towards their application, however, the costs on a preparative scale are still a constraint. A new combination of approaches for the purification of hydrophobic Quantum Dots is presented, resulting in an efficient scalable process in regard to time and solvent consumption, using common laboratory equipment and low-cost materials. The procedure is based on a combination of solvent-induced adhesion and solid phase extraction. The platform allows the transition from manual handling towards automation, yielding an overall purification performance similar to one conventional batch precipitation/centrifugation step, which was investigated by thermogravimetry and gas chromatography. The distinct miscibility gaps between surfactants used as nanoparticle capping agents, original and extraction medium are clarified by their phase diagrams, which confirmed the outcome of the flow chemistry process. Furthermore, the solubility behavior of the Quantum Dots is put into context with the Hansen solubility parameters framework to reasonably decide upon appropriate solvent types.

Liquid–liquid equilibria in mixtures of formaldehyde, water, methanol, and isoprenol

Isoprenol (3-methyl-3-buten-1-ol) is an important intermediate in the chemical industry. It has to be separated from mixtures containing formaldehyde, water, and methanol in the production process. As water and isoprenol are only partially miscible in the liquid phase, these mixtures exhibit a liquid–liquid miscibility gap. Knowledge of this miscibility gap is essential for understanding the isoprenol process; however, only few experimental data and no models are presently available in the literature. Therefore, in the present work, liquid–liquid equilibria in the systems (water + isoprenol), (formaldehyde + water + isoprenol), and (water + methanol + isoprenol) were measured at 278, 293, and 313 K. The new experimental data were used to develop a model of the liquid–liquid equilibrium in mixtures of formaldehyde, water, methanol, and isoprenol, which can now be used in simulation studies of the isoprenol process.

Phase diagrams and critical temperatures for coherent and incoherent mixtures of InAs1−xSbx alloys using first-principles calculations

Phase diagram calculations are performed for incoherent and coherent mixtures of an InAs1−xSbx (InAsSb) ternary alloy, which is an important material for the applications to infrared detector technology. Our calculations are based on the cluster expansion approach and Monte Carlo simulations combined with first-principles total energy calculations in the framework of density functional theory with Perdew–Burke–Ernzerhof (PBE) and Heyd–Scuseria–Ernzerhof (HSE) exchange-correlation functionals. Because of a lattice mismatch (∼7%) between InAs and InSb, coherency strain plays an important role for the phase stability of the InAsSb alloys. The alloys without the coherency strain (incoherent mixtures) show a miscibility gap with the critical temperature at ∼700 K with 42% (45%) Sb concentration in PBE (HSE), which is in good agreement with the experimentally determined equilibrium miscibility gap temperature. The alloys with the coherency strain (coherent mixtures) show several ground states whose structures are short period superlattices along the [201] direction. The critical temperature is ∼200 K with 50% Sb concentration in both PBE and HSE, which is reduced by ∼500 K compared to that of incoherent mixtures. This reduction of the critical temperature is consistent with the experimental observation where the homogeneous InAsSb alloy continues to grow inside the empirical miscibility gap.

Fluid-Induced Inhomogeneous Cr-spinel in Dunite and Wehrlite from the Duke Island Complex, Southeastern Alaska

Cr-spinel [(Mg, Fe2+)(Cr, Al, Fe3+)2O4)] is a common mineral in the ultramafic core of the Duke Island complex in southeastern Alaska, US. Cr-spinel grains with an unmixed texture have been observed in dunite and wehrlite of the complex. Inhomogeneous Cr-spinel with a ratio of Cr/(Al + Cr + Fe3+) &lt;0.37 is prominent in dunite. The inhomogeneous Cr-spinel consists of two completely different compositions: Al-rich Cr-spinel, and Fe3+-rich Cr-spinel with a wide range of Cr content (from 11.8 wt.% to 28.6 wt.% Cr2O3). The unmixed texture is complex, and three subtypes of inhomogeneous Cr-spinel are recognized: TypeB1 Cr-spinel showing complete separation, crystallographically oriented type B2 Cr-spinel, and irregular Al-rich Cr-spinel rimmed type B3 Cr-spinel. The unmixed texture was achieved by an unmixing process at around 600 °C due to the miscibility gap of spinel between Al-rich and Fe3+-rich phases. The unmixed patterns of inhomogeneous Cr-spinel are controlled by the initial chemical composition, grain size of the initial spinel, and the cooling process. We propose that the initial composition of inhomogeneous Cr-spinel was formed by the interaction of high-temperature fluid and olivine; Cr-spinel that experienced unmixing may be a useful proxy to unveil the activity of high-temperature fluid in the formation of Alaskan-type complexes.

Precipitation behavior of coherent nano-ordered particles in Fe-Mn-Al-Ni shape memory alloys with different Ni contents

In Fe-Mn-Al-based shape memory alloys, the essential strategy for obtaining good superelasticity is precipitating coherent B2 nano-particles by adding Ni element. In the present paper, we investigated the effect of Ni contents on the precipitation behavior of nano-ordered particles in Fe-Mn-Al-Ni alloys subjected to solution treatment followed by water quenching and air cooling, respectively. D03 nano-particles were precipitated in water-quenched and air-cooled specimens with the Ni content of 2.1 at.%. However, coherent B2 nano-particles were precipitated in the water-quenched and air-cooled specimens with the Ni contents of 4.0–10.8 at.%. In addition, their average diameters increased linearly with increasing Ni contents, and were 3.4–14.5 nm for the water-quenched specimens and 9.5–32.3 nm for the air-cooled specimens. The precipitation of B2 nano-particles cannot be suppressed even by water quenching owing to the formation of a miscibility gap after adding Ni element in Fe-Mn-Al-Ni alloys.