Peritectic Transition Research Articles

Liquid state property and rapid peritectic solidification of refractory Mo-33.3 at.% Zr alloy under electrostatic levitation condition

The thermophysical properties and rapid solidification mechanism of liquid Mo-33.3 at.% Zr peritectic alloy were investigated by electrostatic levitation technique, which attained a maximum undercooling of 387 K (0.16 TL). At its liquidus temperature, the density, surface tension, viscosity and solute diffusion coefficient of this refractory alloy were determined as 8.14 g/cm3, 1.60 N/m, 11.32 mPa·s and 1.41 × 10−9 m2/s, respectively. The primary (Mo) dendrite growth started from multi-point nucleation, while its growth velocity agreed well with the prediction of LKT/BCT dendrite growth theory and reached an upper value of 43 mm/s. The subsequent peritectic transition was characterized by a power-law kinetics relation between the nominal growth velocity of peritectic Mo2Zr phase and peritectic undercooling, displaying a maximum velocity of 46 mm/s. The increase of liquid undercooling facilitated the completion of peritectic transition and refined the microstructure of residual primary (Mo) phase, thus enhancing the Vickers hardness of this alloy gradually up to 1190.9 HV at the maximum undercooling.

Benchmark of Techniques for the Characterization of the Mechanism of Phase Transformations in Steel of Near-Peritectic Composition

This study addresses challenges in elucidating the mechanism of phase transformations occurring in steel of near-peritectic composition. The importance of using and integrating, complementary experimental techniques is emphasized. While thermal analysis tools such as Differential Scanning Calorimetry (DSC) and Differential Thermal Analysis (DTA) are vital, they offer limited insight on events occurring during cooling. Employing standard thermal analysis (DSC) alongside high-temperature microscopy, incorporating simultaneous thermal analysis within a high-temperature microscope, and concentric solidification, two of steels of near-peritectic composition were investigated. Key findings include the correlation between heating rates and completion temperatures of phase transformation in the DSC heating experiments; absence of a peritectic transition inferred from DSC cooling curves supported by visual observation, and insights into restricted austenite phase nucleation attributed to diffusional constraint and limited nucleation sites. This investigation not only contributes to understanding phase transformation behaviour in peritectic steels, but more generally provides a framework for utilizing different techniques synergistically to address complexities in the interpretation of the mechanism of phase development.

Determination of the Eutectic to Peritectic Fold Transition in the Cu(Ni)–Fe–S System by Directional Crystallization of Melts

Determination of the Eutectic to Peritectic Fold Transition in the Cu(Ni)–Fe–S System by Directional Crystallization of Melts

Formation of delta-ferrite and its effect on impact toughness of GTAW weld metals in a 12 wt-% Cr steel

This research focused on the formation of the δ-phase and the corresponding effect on the impact toughness in a GTAW weld metal of a 12%Cr F/M steel. Two kinds of δ-phase were identified: one located at the prior austenitic grain boundaries (PAGBs) (called δPAGB) and the other was in the inter-dendritic region (called δinter). The δinter implied that the peritectic transition that occurred at the final stage of solidification in the DSC test, was suppressed in the welding process. A preheating treatment at 95°C decreased optimally the δ-phase fraction and thereby decrease the ductile-brittle transition temperature (DBTT). However, excessive preheating at higher temperatures enhanced the fraction of the δinter by promoting the micro-segregation and thus increased the DBTT.

Rapid crystal growth kinetics of tungsten dendrites under electrostatic levitation state

The rapid crystal growth kinetics of tungsten dendrites within extremely refractory W60Re40 liquid alloy was examined under electrostatic levitation state. Tungsten dendrite growth through two solidification modes was revealed through modulating the active nucleation and spontaneous nucleation within the liquid undercooling range between 145 and 470 K, leading to the displacement of normal peritectic transition by metastable isomorphous solidification. The tungsten dendrites kept the priority growth direction of 〈100〉 and their growth velocity versus undercooling showed a power law function. The liquid alloy would solidify through normal peritectic transition if assisted with active nucleation from bottom Mo electrode.

Simulation of the Peritectic Phase Transition in Fe-C Alloys.

In this work, a multi-phase cellular automaton (CA) model is extended for the quantitative simulation of peritectic phase transition. First, the effects of cooling rate/supersaturation and temperature on the peritectic transformation kinetics in Fe-C alloys are investigated by utilizing the present CA model. The CA simulations show that supersaturations in the parent phases (liquid and δ-ferrite) increase the L/γ interface growth velocity remarkably, but tinily for the δ/γ interface migration velocity. There exists a transition supersaturation for isothermal transformations, at which the growth rates of the two interfaces are equal. The transition supersaturation is found to increase with decreasing temperature. Microstructural evolution at different cooling rates during peritectic transformation is simulated using the experimental conditions. At low cooling rates, the δ/γ interface propagates at a higher velocity than the L/γ interface. At high cooling rates, however, the γ-phase grows more into the L-phase with a cellular morphology. Then, the proposed CA model is applied to simulate the microstructural evolution during peritectic reaction. It is observed that the γ-phase propagates along the L/δ interface and finally encircles the δ-phase. Meanwhile, the intervenient γ-phase grows in thickness through peritectic transformation. The CA simulations are compared reasonably well with the experimental data and analytical calculations.

Multiphase Field Modeling of Dendritic Solidification of Low-Carbon Steel with Peritectic Phase Transition

In the present study, an improved multiphase field model with taking into consideration the S/L interface anisotropy is proposed to simulate the dendritic growth with peritectic transition of low-carbon steel, and a new random heterogeneous nucleation method is proposed to treat the γ phase nucleation during the peritectic solidification process. The γ phase growth around the dendrite (the single dendrite and polycrystalline ferrite) and the subsequent peritectic transformation during the peritectic solidification are simulated. The results show that when the temperature reaches the γ phase nucleation temperature, γ nuclei suddenly nucleate at the δ/L interface, and laterally grow with the movement of L/γ/δ triple point around the δ/L interface of δ dendrite. After the δ dendrite is fully wrapped by the continuous intervening γ phase, the γ phase continues to grow with direct phase transformation from both δ phase and liquid phase. With the increase of melt undercooling, more δ phase and liquid phase are consumed to form γ phase, and the intervening γ phase between the δ dendrite and liquid phase becomes more and more thick, but the δ dendrite arm becomes more and more thin. During the dendritic solidification process, the solute would be rejected from dendrite trunk with the dendritic growth and enriched at the dendrite boundary, especially at the dendrite root. The solute enrichment at the dendrite root would inhibit the γ phase growth at the dendrite root and thus the thickness of intervening γ phase at the dendrite root is thinnest around the dendrite. Moreover, the solute concentration in γ phase is among the δ phase and liquid phase, because the carbon solubility in γ phase is higher than that in δ phase, but lower than that in liquid phase.

Phase-field investigation on the peritectic transition in Fe-C system

We adopt a thermodynamically consistent multi-phase, multi-component phase-field model to investigate the morphological evolution of peritectic transition in carbon steel though 2-D and 3-D simulations. By using phase-field method, we rationalize the peritectic solidification in both 2-D and 3-D simulations under different liquid supersaturations as well as on the δ particle with distinct microstructures. Through the comparison between 2-D and 3-D simulation results, we clarify the reason for the different growth rate of γ phase in two and three dimensions. In 3-D simulation, we observe the unequal growth rate of γ phase in radial and axis directions. In addition, a novel measurement method is proposed to determine the dynamic contact angle. We anticipate that the simulation results can be applied to interpret the isothermal peritectic transition with a liquid supersaturation in alloys.

Thermodynamic properties of Gd-Bi alloys determined by emf measurements in LiCl-KCl-GdCl3 electrolyte

Thermodynamic properties of binary Gd-Bi alloys (mole fraction, xGd = 0.02–0.35) were determined using electromotive force (emf) measurements in molten LiCl-KCl-GdCl3 electrolyte in complement with structural, microstructural, and thermal characterization. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) identified the phase constituents of Gd-Bi alloys (xGd = 0.02–0.35) as Bi matrix and GdBi compound. According to differential scanning calorimetry (DSC) measurements up to 1250 K, a eutectic transition [L = Bi + GdBi] was observed at 543 K but the reported peritectic transition [L + GdBi = GdBi2] was not detected, suggesting the absence of the GdBi2 compound. Based on structural, microstructural, and thermal characterization of Gd-Bi alloys (xGd = 0.02–0.35), the GdBi2 compound was not detected, and its thermodynamic stability is questionable. The emf of Gd-Bi alloy (xGd = 0.16) at 700–1048 K relative to Gd(s) was measured by electrodepositing pure Gd metal at 25 K increments. The emf values of Gd-Bi alloys were determined via coulometric titration of Gd into liquid Bi using a two-phase [L + GdBi] alloy as a reference electrode at 773–973 K. The solubility of Gd in liquid Bi was also estimated to be 0.50 mol% (773 K), 0.99 mol% (873 K), and 2.21 mol% (973 K) and the excess partial molar Gibbs energy (∆G̅Gdex) of liquid Gd-Bi alloys was as low as 65 kJ mol–1, indicating strong chemical interactions between Gd and Bi.

Phase-Field Investigation on the Peritectic Transition in Fe-C System

We adopt a thermodynamically consistent multi-phase, multi-component phase-field model to investigate the morphological evolution of peritectic transition in carbon steel though 2-D and 3-D simulations. By using phase-field method, we rationalize the peritectic solidification in both 2-D and 3-D simulations under different liquid supersaturations as well as on the δ particle with distinct microstructures. Through the comparison between 2-D and 3-D simulation results, we clarify the reason for the different growth rate of γ phase in two and three dimensions. In 3-D simulation, we observe the unequal growth rate of γ phase in radial and axis directions. In addition, a novel measurement method is proposed to determine the dynamic contact angle. We anticipate that the simulation results can be applied to interpret the isothermal peritectic transition with a liquid supersaturation in alloys.

New insights of the peritectic phase transition in steel through in-situ measurement of thermal response in a high-temperature confocal microscope

The topic of peritectic phase transition in steel has been widely studied using various in-situ experimental techniques including visual observation on a surface of a sample in a high temperature microscope and measurement of the thermal response from the bulk of the sample using differential thermal analysis (DTA) and differential scanning calorimetry (DSC). These two different techniques have inherent limitations leading to difficulties in interpretation of the results in the case of complex phase transformations such as the peritectic reaction, and there have been discrepancies among the interpretations from many previous studies of the peritectic transition in steel. A new technique was developed through a spatial combination of a DTA apparatus and a high-temperature laser-scanning confocal microscope to overcome these limitations. Solidification experiments with carbon steels of 0.061, 0.182 and 0.451 wt%C were conducted under conditions typical of conventional thermal analysis experiment, i.e. 90 mg of sample mass and 10 °C/min cooling rate, and the findings of earlier studies were revisited. We concluded that whether or not a peritectic reaction in a steel specimen of peritectic composition occurs, largely depends on the size of the sample used in the experiment. Deep undercooling for austenite nucleation can be experienced, in the absence of the occurrence of a peritectic reaction as a result of constrained nucleation of austenite, due to a limited number of nucleation sites in the small samples used.

Effect of hot pressing on the microstructure and thermoelectric properties of TGZM-grown YbFe-doped CoSb3 skutterudite

Skutterudites based on CoSb3 are considered potential candidates in thermoelectric applications in the field of mid-temperature power generation. The annealing process necessitates more than a week to complete the peritectic phase transition for traditional melting-quenching-annealing-sintering methods. Herein, a new strategy combining the temperature gradient zone melting process with hot pressing (TGZM-HP) was successfully employed to synthesize YbFe-doped p-type CoSb3 in a shorter time. The resulting samples show enhanced thermoelectric properties compared to TGZM-grown ones, especially in the case of 1 at.% YbFe-doped CoSb3. This compound exhibits a maximal Seebeck coefficient of 166.3 μVK−1 and a power factor of 1.8 mWm−1K−2 at 723 K, showing an increase in these values of 25% and 51%, respectively. Moreover, phonon scattering appears to be enhanced due to the significant reduction in the grain size of the TGZM-HP samples, resulting in a minimum thermal conductivity of 2.71 Wm−1K−1. A dimensionless figure of merit (ZT) of 0.48 was obtained for 1 at.% YbFe-doped CoSb3. This value is 1.6 times larger than that measured for TGZM-grown CoSb3. This work provides an alternative strategy to fabricate skutterudite materials and foster their development.

Experimental study and thermodynamic modeling of solid-liquid equilibrium of binary and ternary mixtures formed by C11H24, C12H26 and C14H30 for cryogenic thermal energy storage

Abstract In this study, experimental investigations of solid-liquid phase diagram of binary and ternary mixtures formed by the C11H24, C12H26 and C14H30 were carried out to employ the potential phase change materials (PCMs) for cryogenic applications using the differential scanning calorimetry (DSC). In addition, the thermodynamic equilibrium was modeled employing the ideal model, and the Wilson and NRTL model were applied to correlate the liquidus line. The results show that the C11-C12 system exhibits a peritectic transition and the composition of possibly peritectic point is 60wt% C12 with the temperature of 251.65 K. The compositions of the eutectic points appear at 10wt% C14 for C11-C14 system and 18wt% C14 for C12-C14 system with eutectic temperatures of 246.85 K and 260.45 K, respectively. The C11-C12-C14 ternary system presents two possibly eutectic points at compositions of 67wt% C11/5wt% C12 and 86wt% C11/10wt% C12 with eutectic temperatures of 246.45 K and 248.05 K, and has the slight supercooling (1.7 ˚C and 0.5 ˚C), indicating miscibility in liquid phase and immiscibility in solid phase. Moreover, the liquidus lines calculated by the theoretical models are in good agreement with the experimental results. The best predicted results of the ternary mixture and C11-C12 binary subsystem are obtained by the ideal model, with deviations of 0.75% and 0.58% respectively.

Multi-phase field simulation of multi-grain peritectic transition in multiple phase transformation

Taking Fe-C binary alloy as an example, based on the multi-phase field model, the nucleation and growth of δ phase, peritectic reaction, peritectic transformation, and the growth of subsequent austenite are simulated. Effects of the nucleation site of austenite on the peritectic reaction rate and the starting time of the peritectic transformation were studied. The simulation results show that the γ phase, as a shell, surrounds the δ phase and grows rapidly when the peritectic reaction occurs between the dendritic δ grains, and a layer of γ phase shell is formed around δ phase after the peritectic reaction. After the δ phase is surrounded by γ phase completely, the membrane shell separates the L phase from the δ phase, so that the phase transfers from peritectic reaction to peritectic transformation. During the peritectic transformation, since the solute diffusion coefficient of the liquid phase is much greater than that of the solid phase, the average growth rate of austenite in the liquid phase is visibly higher than that of the δ phase. The peritectic reaction rate is related to the curvature of the nucleation site of the γ phase on the δ phase grains. The peritectic reaction rate at the large curvatures is faster than that at small curvatures.

Peritectic phase transition of benzene and acetonitrile into a cocrystal relevant to Titan, Saturn's moon.

Benzene and acetonitrile are two of the most commonly used solvents found in almost every chemical laboratory. Titan is one other place in the solar system that has large amounts of these compounds. On Titan, organic molecules are produced in the atmosphere and carried to the surface where they can mineralize. Here, we report the phase diagram of mixtures of acetonitrile and benzene, and provide an account of the structure and composition of the phases. To mimic the environment on Titan more accurately, we tested the stability of the structure under liquid ethane. The results provide new insights into the structure and stability of potential extraterrestrial minerals. In light of Dragonfly, NASA's upcoming mission to Titan, revisiting the fundamental chemistry of the smallest molecules with modern methods and techniques can have significant contributions to this epochal mission and can open new research directions in chemistry.

Investigation of the Peritectic Phase Transition in a Commercial Peritectic Steel Under Different Cooling Rates Using In Situ Observation

In situ studies of two separate events of the peritectic phase transition during continuous casting, the peritectic reaction and the peritectic transformation, were performed using high-temperature confocal scanning laser microscopy (HTCSLM). The interface migration velocities during the peritectic transformation at different cooling rates were analyzed in situ by measuring the migration distance of the interface vs time. Moreover, the solute distributions near the moving liquid/solid interface during the peritectic reaction and the peritectic transformation were predicted using the commercial software package diffusion-controlled transformation. The results revealed that the images of HTCSLM clearly recorded these two separate events: the peritectic reaction (L + δ → γ) and the peritectic transformation (L → γ and δ → γ). In the initial stage of the peritectic reaction, the austenite (γ) phase was observed to nucleate at the liquid/δ-ferrite (L/δ) interface and then grow along the periphery of primary δ phases. Upon further cooling, these emerging γ phases gradually isolated the liquid and primary δ phases. Subsequently, the laterally growth of the γ phase was regarded as the peritectic transformation. The growth rate of the γ phase was governed by the liquid to γ and δ to γ phase transformations. As the cooling rate increased, the peritectic reaction was observed to occur at lower temperature. Higher cooling rates enhanced the migration rates of the L/γ and γ/δ interfaces during the peritectic transformation. Meanwhile, an interesting massive transformation of δ into γ phase was observed to occur at a cooling rate of 60 °C/min. All primary δ phases were quickly covered by wrinkled γ phases in a short time. Based on the assumption of the solute incomplete diffusion in the liquid phase, the predicted results revealed that the enrichment of carbon near the L/δ, L/γ, and γ/δ interfaces increased as the cooling rate increased. An increase in the cooling rate exacerbated the carbon segregation of the interface during continuous solidification, causing a nucleation suppression of the γ phase. In turn, the increasing carbon enrichment accelerated the interface migration with the diffusion of large amounts of solute across the interface, causing an increase in the driving force for the peritectic transformation.

Improved infrared thermography method for fast estimation of complex phase diagrams

Phase diagrams are a primordial tool in materials science, gathering key information for the materials synthesis and the understanding of their formation processes. Numerous experimental techniques exist to determine the phase diagram of a binary system but they are time-consuming. The previously developed IRT method (InfraRed Thermography) enabled the fast determination of preliminary phase diagrams of polyols binary systems in which only liquid-solid and eutectic transitions occur. This method thus allows accelerating their screening step which is crucial before each development of a new material. This work aims at improving the transitions detection and at adapting the IRT-method to more complex phase diagrams containing eutectic, peritectic and metatectic transitions. To do so, the phase diagram of the capric-palmitic fatty acids binary system is experimentally determined using the improved IRT-method. It is then compared with those obtained using standard Differential Scanning Calorimetry measurements (DSC) and an improved thermodynamic model. Eventually, the limiting factors and the parameters of influence such as the material droplet size, as well as the nature and roughness of the substrate are investigated and discussed.

Numerical and experimental study on peritectic transition in TiAl-Nb alloys

The solidification pathway and peritectic transition characteristic related to the solute concentration in TiAl-Nb system are calculated using the Thermo-Calc software. The results show that there are four typical solidification modes in the TiAl-Nb system, which are single β, hypo-peritectic, hyper-peritectic and single α solidification. The mole fraction of peritectic growth αp can be used to describe the undergoing extent of the peritectic tranformation (EPT) directly for the alloys with the peritectic transition, and βp/βmax can also be used to describe the EPT for the hypo-peritectic and Lp/(1 − βmax) for the hyper-peritectic. The mole fraction of αp shows a parabolic shape variation on a plot of solute Al at constant Nb content. The composition of the complete peritectic transformation (PT) is around 46.5 at.% Al for the TiAl binary alloy, and it gradually shifts to the direction of high Nb content with increase of solute Al. A temperature gap (△Tp) corresponding to the peritectic transition exists in Nb containing TiAl alloys and the △Tp shows a parabolic shape on a plot of solute Al at constant Nb content. The experimental results are generally in accordance with the theoretical rules.

Study of the Effect of Carbon on the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness

In the continuous casting process, the shrinkage of the peritectic phase transition during the initial solidification process has an important influence on the surface quality of peritectic steel. The initial solidification process of 0.10C%, 0.14C%, and 0.16C% peritectic steels was observed in situ by a high temperature laser confocal microscope, and the contraction degree during initial solidification was characterized by surface roughness. The results showed that under the cooling rate of 20 °C/s, the surface roughness value Ra(δ/γ) of 0.10C% peritectic steel was 32 μm, the Ra(δ/γ) value of 0.14C% peritectic steel was 25 μm, and the Ra(δ/γ) value of 0.16C% peritectic steel was 17 μm. With increasing carbon content, the contraction degree of the δ→γ transformation decreased, and the value of the surface roughness Ra(δ/γ) declined. Therefore, surface roughness can characterize the contraction degree of the δ→γ transformation in the initial solidification process of peritectic steel under the condition of a large cooling rate.

A phase-field study on the peritectic phase transition in Fe-C alloys

A quantitative multi-phase-field model, with an anti-trapping current and involving diffusion in the solid, is proposed to simulate the peritectic phase transition in Fe-C alloys. An interface field method with a newly defined step function is adopted to formulate the governing equation of the multi-phase-field variables. The proposed model is applied to simulate the γ-platelet tip growth during the peritectic reaction and the subsequent peritectic transformation (γ-platelet thickness growth) in large computational domains of the experimental length scale. It is found that the local liquid concentration at the triple junction point L/δ/γ is slightly higher than the liquid concentration in equilibrium with the δ-phase, but lower than the liquid concentration in equilibrium with the γ-phase. This leads to slight melting of the δ-phase in the vicinity of the triple junction, while the γ-platelet growth continues. Higher tip velocities at higher undercoolings produce a steeper carbon concentration gradient along the γ-platelet's thickness direction, and thus yield a higher thickness growth velocity. It is also found that the ratio of tip and thickness growth velocity of the γ-platelets increases at higher undercoolings, leading to decreasing tip radius and platelet thickness. Good agreement between the simulations and the experimental data reported in literature is achieved, demonstrating the quantitative prediction capabilities of the proposed model, and confirming the diffusion control for the peritectic phase transition close to equilibrium conditions.