Calculated Phase Diagram Research Articles

Phase stability in cast and additively manufactured Al-rich Al-Cu-Ce alloys

Additively manufactured (AM) eutectic Al alloy systems have been studied extensively for advantageous thermal stability and mechanical properties due to their refined microstructures. Al-Cu-Ce alloys are one subset of these AM eutectic alloys. Here we studied phase stability in AM Al-Cu-Ce alloys and compared it to that of conventionally cast ones. A new phase, Al8Cu3Ce, was identified in the microstructures of both AM and cast Al-Cu-Ce alloys. This Al8Cu3Ce phase was not previously included on experimental or thermodynamically calculated phase diagrams of the Al-Cu-Ce system. Therefore, we performed additional thermodynamic modeling of the system. These models were experimentally validated with cast and subsequently heat-treated Al-Cu-Ce alloys. We found that despite the refined microstructure of the AM alloys, the phases formed were consistent with the cast alloys, suggesting that AM processing did not significantly alter the formation and stability of phases from that in the conventional alloys. This work has resolved inconsistent previous descriptions of the Al-Cu-Ce ternary phase diagram in the Al-rich region and resulted in the addition of the Al8Cu3Ce as an equilibrium phase above 500 ℃.

Phase equilibria in the FeO–Fe2O3–SiO2 system: Experimental measurement and thermodynamic modeling

Knowledge about the phase equilibria of the FeO–Fe2O3–SiO2 system is very important for the resource utilization of waste slag. To solve the controversy over the calculated isothermal section at 1723 K in the literature, key experiments were carried out using equilibrium/quenching, X-ray diffraction (XRD) and electron probe microanalysis (EPMA). According to the present experiments, the existence of the three-phase region liquid + spinel (Fe3O4) + tridymite (SiO2) at 1723 K was confirmed. The ionic two-sublattice model (Fe+2, Si+4)P(O−2, Va, SiO4−4, SiO2, FeO1.5)Q was used to describe the liquid phase. The FeO–Fe2O3–SiO2 system was then critically evaluated by means of the CALPHAD (CALculation of PHAse Diagram) method in view of phase diagram and thermodynamic data. A new and improved self-consistent set of thermodynamic parameters for the FeO–Fe2O3–SiO2 system is obtained, and the calculated results show good agreement with the experimental data. The present thermodynamic modeling is of interest for the comprehensive recycling of solid waste resources.

Reclamation of Red Mud for the TiO2 Production by Ilmenite Smelting at Lower Temperature

ABSTRACT Red mud produced from the Bayer process was used for the high temperature metallurgical processing of ilmenite. The major components of the red mud were Fe2O3, Al2O3, Na2O, and TiO2, which play important roles in the flux material. The process temperature of ilmenite slag was lowered from 1794 K (1521°C) to 1687 K (1414°C), as a preliminary study by a high-temperature microscope. Thermochemical calculations using FactSageTM 7.0 confirmed the effect of red mud on the lowered melting temperature of ilmenite slag. The discrepancy between the observed results of the microscope and the calculated phase diagram was due to the slag viscosity, which was significantly affected by Al2O3 in red mud. The reduction of ilmenite at lower temperatures by the addition of red mud was investigated at 1723 K (1450°C). Ilmenite, pseudobrookite, and associated clay minerals were the major phases in the reduced ilmenites which was confirmed by X-ray diffraction (×RD) analysis. Microscopic images obtained by scanning electron microscopy (SEM) showed variations in the pseudobrookite phases according to the amount of fluxed red mud. The benefits of red mud utilization are discussed with regard to the lower energy consumption and recovery of resources.

A CALPHAD-based model on the viscosities: A case study on Zr–Fe–Cu liquid alloys

Viscosity is an important thermodynamic property for alloy design, especially for refractory alloy. CALculation of PHAse Diagram (CALPHAD)-based viscosity calculations are highly desirable since they can accurately predict the viscosity in the alloy with different compositions. However, the current viscosity calculation model lacks the ability to fit the situations where the viscosity varies largely with temperature. Here, we propose a new equation to describe the excess viscosity using an exponential equation. The physical meaning of each parameter is explained. Moreover, the proposed model is not only compatible with the previous model but also suitable for all the situations. We further calculate the viscosity using different models in the Zr–Fe–Cu system which is important in the fields of nuclear fuel and magnetic refrigerants. The proposed model gives a better description than the other two models with fewer optimizing parameters, verifying the advantages of the current model. Based on the established viscosity database of Zr–Fe–Cu, we further predict its metallic glass-forming ability. The theoretical analyses together with the viscosity calculation examples suggest that the proposed model can provide accurate viscosity calculations in liquid alloys as a function of temperature and composition. Therefore, the proposed model is suitable for the design of refractory alloys.

Kinetically Induced Fine Secondary α-Ti Phase Formation in a Novel As-Cast Titanium Alloy

The formation of fine secondary hexagonal close packed (HCP) α-Ti precipitates provides major strengthening in a new Ti-6Al-5Fe-0.05B-0.05C (mass fractions in pct) cast alloy. The phase transformation mechanisms from the body-centered cubic (BCC) β-Ti matrix to fine α phase in this new α-β titanium alloy were investigated experimentally and computationally using CALculation of PHAse Diagram (CALPHAD)-based thermodynamic and kinetic models. The discrete distribution of α precipitates was observed in the as-cast alloy with evidence of strong Fe partitioning. Two main size groups of α precipitates and the Fe partitioning were characterized using scanning electron microscopy, scanning transmission electron microscopy, and synchrotron-based small-angle X-ray scattering techniques. A hypothesis of Fe-partitioning driven α precipitate nucleation and growth was validated by precipitation simulation using TC-PRISMA with customized thermodynamic and kinetic descriptions. These results suggested a new titanium alloy design route involving high-mobility elements (enhancing fine secondary α precipitates) and demonstrated the capability of CALPHAD-based modeling in titanium alloy design.

Hot cracking during the fabrication of Inconel 625/stainless steel 308 L functionally graded material by dual-wire arc additive manufacturing

In the present work, dual-wire arc additive manufacturing was used to fabricate the functionally graded material (FGM) with a smooth composition transition from 100 wt% Inconel 625 (IN625) to 100 wt% stainless steel 308 L, whose composition transition was along the torch-travelling direction. With such a composition transition, position with the weakest mechanical properties could be clearly and easily located in the composition gradient path, allowing the issue to be fully exposed. During the fabrication, cracks were found near the position with IN625 of 20 wt%. By analyzing the fracture morphology and crack location, they were judged as liquation cracks, which belong to hot cracks. The segregation and aggregation of carbides at the grain boundary formed the low-melting-temperature eutectic phase, which is liquefied into the liquid film by the heating of subsequent layers and is then pulled apart by residual stress. According to the experimental results and the calculations of phase diagrams, the cracks always appeared near the position with IN625 of 20 wt%, where the FGM has the highest crack sensitivity. Therefore, it was determined as the weakest position of the FGM and its weakening mechanism could be clarified easier owing to the composition transition, which provides a high possibility to get better mechanical properties if a more targeted optimization method is applied. Process parameter optimization reduces the heat input per unit height to thin dendrites and to alleviate cracking, but there is still a cracking tendency in the weak composition range. The composition gradient path optimization, by removal of the corresponding composition range, can solve the cracking issue more thoroughly, and the tensile strength and elongation increased by 39.5 % and 221.7 %, respectively, which greatly improved the mechanical properties of the FGM.

Assessment of the Mg–Al–Sb system supported by experiments and extrapolation to the Mg–Al–Sn–Sb quaternary system

The phase equilibria and transformation temperatures of the Mg–Al–Sb ternary system were investigated via thermodynamic modeling coupled with key experiments. The isothermal section of the Mg-rich corner at 400 °C and two vertical sections in the Mg–Al–Sb ternary system were constructed by the metallographic analysis and thermal analysis. No ternary compound was found in the Mg-rich corner. The thermodynamic modeling of Al–Sb and Mg–Al–Sb systems was carried out using the CALculation of PHAse Diagram (CALPHAD) approach. The associated solution model was used to describe the short-range ordering for the liquid phase. The calculated phase diagram and thermodynamic property of the Al–Sb system are consistent with most of the experimental data. A set of reliable and self-consistent thermodynamic parameters were obtained combining with Mg–Sb and Mg–Al systems as well as the updated Al–Sb system in the present work. The solidification paths in Sb-containing Mg alloys were analyzed using the present thermodynamic description of Mg–Al–Sn–Sb quaternary system extrapolated from that of the constituent sub-ternary systems.

Revealing the effects of Nb micro-alloying on microstructure and mechanical properties of FeCrAl thin films: Experimental and computational investigations

FeCrAl-based materials have attracted ever-increasing attentions due to their excellent resistances against high-temperature oxidation and stress-corrosion cracking, while enhancement of their mechanical properties can expand their potential applications. In this work, the micro-alloying method by adding Nb was applied to enhance the mechanical property of FeCrAl. The FeCrAl thin films with different Nb contents (Fe-16Cr-5Al, Fe-14Cr-5Al-1Nb, Fe-12Cr-5Al-2Nb, Fe-13Cr-3Al-7Nb, in wt%) were synthesized using magnetron co-sputter deposition. Benefiting from the refined grain size, the as-deposited Fe-13Cr-3Al-7Nb thin film exhibited the highest hardness (3.3 GPa), followed by Fe-14Cr-5Al-1Nb (1.5 GPa) and Fe-12Cr-5Al-2Nb (1.2 GPa), whereas the hardness of Nb-free film was the lowest (0.8 GPa). The fracture resistance (which is related to the ratio of hardness and elastic modulus) also enhances with the addition of Nb. After annealing (873 K for 6 h), the hardness of the Fe-13Cr-3Al-7Nb thin film further increased to ~6.7 GPa, in contrast to the as-annealed Nb-free thin film with no obvious hardness change. The CALPHAD (CALculation of PHAse Diagram) results indicate that with adding Nb the original single BCC (body centered cubic) phase tended to decompose into the Fe-rich and Cr-rich BCC domains, which is consistent with the transmission electron microscopic (TEM) observations. The observed strengthening of the annealed Nb-containing samples is therefore attributed to the phase separation. The first-principles calculations also support this notion. Thus, the current work has delineated the effect of Nb addition on both deposited and annealed FeCrAl-based thin films, which shows the usefulness of combined experimental and computational methods in interpreting microstructure and mechanical property evolutions of engineering materials.

Effect of Si and P Content on the Si Phase and Solidification Behavior of Al-40Zn-xSi Alloys Using Synchrotron Radiation Real-Time Imaging

In this paper, the effect of Si (1, 3, 5, 6 wt.%) and P (5, 10, 15, 20, 30 ppm) content on the Si phase and solidification behavior of Al-40Zn-xSi alloys are investigated via phase diagram calculation, scanning electron microscopy (SEM) and synchrotron radiation real-time imaging. It is found that Si content has a great influence on the microstructures of Al-40Zn-xSi alloys, and two distinct primary phases were separated by a critical composition at 5.49 wt.% Si in the calculated phase diagram. The microstructure contained not only needle-like eutectic Si, but also blocky primary Si particles in “hypoeutectic” commercial-purity Al-40Zn-5Si alloys. However, the synchrotron radiation real-time imaging experiment showed that the primary phase was α-Al in commercial-purity Al-40Zn-5Si alloys. The effect of P on the Si phase of the high-purity Al-40Zn-5Si alloy was also studied, showing that the number and size of the blocky primary Si particles in the high-purity “hypoeutectic” Al-40Zn-5Si alloys were mainly related to the P impurity content. A small minority of primary Si particles were found during the whole solidification process of the high-purity Al-40Zn-5Si alloy without P impurities, while a large number of primary Si particles were precipitated continuously at the front of α-Al dendrites in the high-purity Al-40Zn-5Si alloy with the addition of 20ppm P, which may have been caused by the fact that AlP particles can act as the heterogeneous nucleation sites of primary Si particles by a small undercooling in P-impurity-containing alloys.

Phase diagram of the TIP4P/Ice water model by enhanced sampling simulations.

We studied the phase diagram for the TIP4P/Ice water model using enhanced sampling molecular dynamics simulations. Our approach is based on the calculation of ice-liquid free energy differences from biased coexistence simulations that reversibly sample the melting and growth of layers of ice. We computed a total of 19 melting points for five different ice polymorphs, which are in excellent agreement with the melting lines obtained from the integration of the Clausius-Clapeyron equation. For proton-ordered and fully proton-disordered ice phases, the results are in very good agreement with previous calculations based on thermodynamic integration. For the partially proton-disordered ice III, we find a large increase in stability that is in line with previous observations using direct coexistence simulations for the TIP4P/2005 model. This issue highlights the robustness of the approach employed here for ice polymorphs with diverse degrees of proton disorder. Our approach is general and can be applied to the calculation of other complex phase diagrams.

Phase diagram, thermodynamic studies, and ab-initio calculations of the Ge-Li system

The limiting enthalpy of solution of liquid germanium in the liquid tin ΔsolH¯Ge(l)∞ was measured at 927 K and equals 3.24 ± 0.34 kJ/mol at. The standard enthalpy of formation of intermetallic phases from the Ge-Li system were calculated at 747 K with the use of the solution calorimetric method. These alloys and intermetallic phases were prepared from pure, metallic germanium and lithium, which were melted in a glove-box filled with high purity argon with a very low concentration of impurities. The X-ray diffraction measurements were conducted to verify the structure of the prepared alloys. The electromotive force studies were performed at three temperatures: 634 K, 807 K, and 841 K by the titration technique. Based on obtained results and other thermodynamic quantities available in the literature the thermodynamic properties of phases were optimized, and the Ge-Li phase diagram was determined.

CALPHAD-guided optimization of the microstructure of Sn–Sb–Cu bearing alloys

The increasing Cu content of Sn–11Sb-xCu (wt.%, x = 0, 2, 4, 6) bearing alloys promotes the growth of ordered Sn3Sb2, and Sn3Sb2 with the maximum mean diameter (161.3–177.3 μm) is observed in Sn–11Sb–6Cu alloy. Gravity-driven aggregation of Sn3Sb2 occurs in the top region of Sn–11Sb ingot. The inhomogeneous distribution of Sn3Sb2 driven by density difference between Sn3Sb2 and matrix is suppressed with Cu addition due to the formation of Cu6Sn5 with a density of 8.06 g/cm3, and homogeneous microstructure is obtained in Sn–11Sb-xCu alloys (x = 2, 4, 6). Sn3Sb2 changes from regular cube morphology to irregular morphology with Cu content reaching 6 wt%. The relatively high Cu content in liquid leads to the nucleation of Cu6Sn5 around the liquid/Sn3Sb2 interface. Cu6Sn5 inside Sn3Sb2 can thus effectively affect the growth direction of Sn3Sb2, and finally lead to the formation of Sn3Sb2 with irregular morphology. The influence of Cu on microstructure evolution of Sn–Sb–Cu bearing alloys is revealed with the guidance of phase diagram calculation (CALPHAD), which can contribute to the further optimization of Sn–Sb–Cu and other bearing alloy.

High strength, high conductivity and good softening resistance Cu-Fe-Ti alloy

Cu alloys with high strength, high electrical conductivity (EC) and good softening resistance (SR) are urgently needed in many fields. A Cu-1.06 wt% Fe-0.44 wt% Ti alloy was designed concerning the calculation of phase diagrams. It was expected that the Fe2Ti phases could precipitate to obtain high performance. The designed alloy was prepared and it obtained the most excellent properties of 211 HV hardness, 542 MPa tensile strength, 9.8% uniform elongation, 79% IACS EC and 575 °C softening temperature after solid solution, cold rolling (90% reduction of thickness) and aging at 450 °C for 24 h. The Fe2Ti phases indeed precipitated in the Cu matrix, which proved the alloy design idea. The precipitation kinetics, interaction between recrystallization and precipitation, and the effects of precipitation on strength, EC and SR were discussed. It was concluded that the precipitation driving force of the Fe2Ti phase itself in Cu was weak, and the cold rolling could significantly promote the precipitation. The precipitation of Fe2Ti slowed down the recrystallization to a certain extent. The high strength and high EC were mainly due to the precipitation strengthening and purification effects of the Fe2Ti precipitation on the Cu matrix. Besides, the good SR was mainly due to the low diffusion rate of Fe in Cu and the weak precipitation driving force of Fe2Ti.

Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings

Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase formation, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were investigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 °C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 °C exhibited a single NaCl-type multicomponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 °C, or exposed to UHV annealing at 1000 °C, however, revealed the decomposition of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in applications at elevated temperatures.

Precipitation in lean Mg–Zn–Ca alloys

While lean Mg–Zn–Ca alloys are promising materials for temporary implants, questions remain on the impact of Zn and Ca on the microstructure. In this context, the precipitation of Zn and Ca in Mg-1.5Zn-0.25Ca (in wt.%), initially extruded at 330°C, towards Mg–Ca binary precipitates or Ca–Mg–Zn ternary precipitates was probed in a multiscale correlative approach using atom probe tomography (APT) and analytical transmission electron microscopy (TEM). Particular focus was set on the ternary precipitate phase whose structure is debated. In the as-extruded material, the binary precipitates are made of hexagonal C14 Mg2Ca containing up to about 3 at.% of Zn. The ternary ones are based on the hexagonal Ca2Mg5Zn5 prototype structure with a composition close to Ca3Mg11Zn4, as deduced from atomically resolved EDS mapping and scanning TEM imaging, supported by simulations. The precipitation sequence was scrutinized upon linear heating from room temperature to 375°C, starting from the solutionized material. Three exothermic differential scanning calorimetry (DSC) peaks were observed, at respectively 125, 250 and 320°C. Samples were taken after the peak decays, at respectively 205, 260 and 375°C for structural analysis. At 205°C, APT analysis revealed Ca-rich, Zn-rich and Zn‒Ca-rich clusters of about 3 nm in size and with a number density of 5.7 × 1023 m−3. At 260°C, APT and TEM showed mono-layered Zn‒Ca-rich Guinier‒Preston (GP) zones of about 8 nm in size and with a number density of 1.3 × 1023 m−3. At 375°C, larger and highly coherent elongated precipitates were found, with a size of about 50 nm. They occur as binary Mg–Ca precipitates or ternary Ca2Mg6Zn3 precipitates, as deduced from scanning TEM-based energy dispersive X-ray spectroscopy (EDS) and nanodiffraction in TEM. Here, the binary precipitates outnumber the ternary ones, while in the as-extruded material the ternary precipitates outnumber the binary ones, which corresponds well to the calculated phase diagram. We correlated the microstructure to hardness probed by Vickers testing. The largest hardening relates to the end of the 125°C DSC peak and thus to GP zones, which outperform the hardening induced by the nanometer-sized clusters and the larger intermetallic particles. The complexity of the precipitation sequence in lean Mg–Zn–Ca alloys is discussed.

Thermodynamic Analysis and Experimental Study on the Oxidation of PbX (X = S, Se) Nanostructured Layers.

Heat treatment in an oxygen-containing medium is a necessary procedure in the technology of forming photodetectors and emitters based on lead chalcogenides. Lead chalcogenide layers (PbS, PbSe) were prepared via a chemical bath deposition method. Surface oxidation of lead chalcogenide layers was analyzed using X-ray diffraction and Raman spectroscopy methods, and thermodynamic analysis of the oxidation of PbSe and PbS layers was also performed. The calculated phase diagrams from 20 °C to 500 °C showed good agreement with the experimental results. According to the thermodynamic analysis, the oxidation products depend on the initial composition of the layers and temperature of the annealing. In some cases, the formation of a separate metallic phase Pb is possible along with the formation of lead oxide PbO and other oxides. The performed thermodynamic analysis makes it possible to substantiate the two-stage annealing temperature regimes which ensure an increase in the speed of photodetectors.

Formation of hypoeutectic structure and strengthening mechanism of Co4Cr1.5Fe1.5Ni5 high entropy alloy alloyed by Al

To reveal the phase formation mechanism and the strengthening mechanism, the AlxCo4Cr1.5Fe1.5Ni5 alloys (x = 1.0, 1.2, 1.4, 1.6, 1.8, 2.0) were prepared by arc melting. Phase formation and prediction, tensile properties, strengthening mechanism and deformation mechanism were researched in detail. Results show that the microstructure of AlxCo4Cr1.5Fe1.5Ni5 alloys changes from single FCC phases (x ≤ 1.4)) to FCC and BCC phases (x＞1.4), which was in good agreement with the calculated phase diagram (CALPHAD) prediction. The lower mixing enthalpy of Ni-Al leads to the segregation of Al element at the inter-dendritic region, which promotes the formation of BCC and FCC lamellar structure in hypoeutectic Al2Co4Cr1.5Fe1.5Ni5 alloy. The ultimate tensile strength of Al2Co4Cr1.5Fe1.5Ni5 alloy is 835 MPa, meanwhile the fracture strain is 31.8 %. The tensile strength of Al2Co4Cr1.5Fe1.5Ni5 alloy is attributed to the interface strengthening and the solid solution strengthening. The massive cross slip of dislocations in primary FCC phases and the dense dislocations blocked by the FCC-BCC interface increase the tensile strength. The interface barrier strength of the BCC-FCC interface in Al2Co4Cr1.5Fe1.5Ni5 alloy was estimated to be 3.9 GPa, which shows the higher barrier strength than conventional BCC-FCC interfaces. Coupled effects of the primary FCC and the lamellar structure of FCC and BCC phases will maintain good mechanical properties.

High-temperature wear mechanisms of TiNbWN films: Role of nanocrystalline oxides formation

Refractory high/medium entropy nitrides (HENs/MENs) exhibit comprehensive application prospects as protective films on mechanical parts, particularly those subjected to sliding contacts at elevated temperatures. In this study, a new MEN system TiNbWN, forming a single fcc solution, is designed and its wear performance at temperatures ranging from 25 to 750 °C is explored. The wear mechanisms can be rationalized by examining the subsurface microstructural evolutions using the transmission electron microscopy as well as calculating the phase diagrams and interfacial adhesion behavior employing calculation of phase diagram (CALPHAD) and density functional theory (DFT). To be specific, increased wear losses occur in a temperature range of 25–600 °C, being predominantly caused by the thermally-induced hardness degradation; whereas at the ultimate temperature (750 °C), the wear loss is refrained due to the formation of nanocrystalline oxides (WnO3n−2, TiO2, and γTiOx), as synergistically revealed by microscopy and CALPHAD, which not only enhance the mechanical properties of the pristine nitride film, but also act as solid lubricants, reducing the interfacial adhesion. Thus, our work delineates the role of the in situ formed nanocrystalline oxides in the wear mechanism transition of TiNbWN thin films, which could shed light on the high-temperature wear behavior of refractory HEN/MEN films.

Experimental investigation and thermodynamic assessment of the Ag–Cr–Y and Ag–Cu–Y ternary systems

The phase equilibria of the Ag–Cr–Y system were investigated by a combination of key experiments and thermodynamic modeling. Eleven ternary alloys were prepared to determine the isothermal sections of the Ag–Cr–Y system at 500, 600 and 800 °C, by means of X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS). No ternary compound was found in the Ag–Cr–Y system. Based on the experimental phase equilibria data, thermodynamic assessment of the Ag–Cr–Y and Ag–Cu–Y systems was performed by the CALPHAD (CALculation of PHAse Diagrams) method. Two ternary compounds τ1 and τ2 in the Ag–Cu–Y system with the compositions of Ag3Cu12Y5 and (AgxCu2-x)Y (x: 22.9–43.1 at.%) were described by two sublattice model (Ag, Cu)4Y1 and (Ag, Cu)2Y1, respectively. A set of self-consistent thermodynamic parameters of the two systems were obtained. Most of the reliable experimental data can be well reproduced by the present thermodynamic modeling.

Microscopic Phase-Field Simulation of γ′ Precipitation in Ni-Based Binary Alloys Coupled with CALPHAD Method

In the present work, the first (1st) and second (2nd) nearest-neighbor interaction energies are calculated by coupling the microscopic phase-field kinetic model with the calculation of phase diagrams (CALPHAD) method. The morphological evolution of the γ′ precipitate and the variation of its atomic ordering parameter for Ni–X (X = Al, Fe, Mn, Pt, or Si) alloys during aging are studied. The simulation results predict different occupation preferences for solute and solvent atoms in the γ′ phase, i.e., solute atoms are inclined to occupy the corner sites and solvent atoms tend to occupy the face sites. In order to understand the precipitation process of the γ′ phase systematically, the ordering and clustering behaviors of solute atoms are analyzed.