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Phase transformations and phase stability in the Fe-Cr-Co-20Mn (at.%) alloy system were investigated using optical microscopy, transmission electron microscopy, x-ray diffraction, and vibrating sample magnetometry. Thermal-induced martensitic transformation from the BCC α parent phase to the HCP e martensite phase was observed in the samples with near 36Fe-24Cr-20Co-20Mn compositions. Bainitic transformation from the α phase occurred with aging. Although the α parent phase coexisted with the e martensite phase in the as-quenched specimen and transformation did not proceed with sub-zero treatment, the e martensite was completely induced by cold rolling. Furthermore, the FCC γ phase was obtained by heavy deformation. These results indicate that multiple martensitic transformations from α to e and e to γ occurred. The γ → e martensitic transformation was also observed for 48Fe-16Cr-16Co-20Mn. The phase stabilities of the α, e, and γ phases were similar. The calculated T0 lines successfully predicted the α → e martensitic transformation when the e phase was more stable in the database. Thermodynamic analysis revealed that magnetic ordering in the α phase affected the phase stability, resulting in the novel e loop in addition to the conventional γ loop.

To efficiently construct phase diagrams of alloy systems, a machine learning-based method advanced by thermodynamics on phase equilibria is proposed. With the use of uncertainty sampling in active learning, the next point to be synthesized or measured can be recommended to efficiently draw the phase diagram. For appropriate recommendations, two ingenuities are introduced in the machine learning method: training data preparation when the multiphase coexisting region is detected and search space reduction based on the Gibbs’ phase rule. We demonstrate the construction of ternary phase diagrams using our machine learning method by incorporating these ingenuities. The complicated phase diagram of alloy systems could be effectively plotted even when knowing only the information of single-component systems in the initial step. The recommendation made by our machine learning method can help reduce the number of experiments required to construct a phase diagram to approximately 1/8 compared with random sampling.

A critical determination of a phase diagram of the Zn-Fe binary system was carried out by EPMA analysis for skillfully prepared and equilibrated two-phase alloys for solid phases and by EDS areal analysis for the Fe solubility in the heterogeneously solidified liquid phase instead of the conventional diffusion couple method. It was newly confirmed that equilibrium compositions of intermetallic compounds tend to shift toward the Fe side compared to the previous phase diagram on the whole and that the solubility ranges of the Γ-Fe3Zn10 and Γ1-Fe11Zn40 phases are much narrower than those in the literature. The critical composition of the second-order order-disorder transition between δ1k-FeZn7 and δ1p-FeZn10 at high temperature was estimated by Vickers hardness measurement. Furthermore, the phase separation, i.e., the first-order transition, between the δ1k and δ1p phases in the low temperature region was directly found out and its equilibrium compositions were confirmed by EPMA analysis for the two-phase microstructures. The width of the δ1k + δ1p two-phase region at 500 °C is only 0.5 at.% and the δ1p decomposes into the δ1k and ζ-FeZn13 phases via a eutectoid reaction at a temperature between 455 °C and 445 °C. While being mostly coincident with those in the previous literature at temperatures between 1000 °C and 600 °C, the solubility of Fe in the liquid (L) Zn phase is about twenty times larger than the assessed value in the literature at temperatures below 500 °C. A eutectic reaction, L → ζ + (ηZn), was confirmed to occur by precise EPMA analysis and DSC measurement.

In the present study, the formation and growth behaviors of intermetallic compound (IMC) layers in the interfacial reaction of solid Fe and molten Zn during hot dipping at 450 °C were investigated. In the early stage of the interfacial reaction, Γ-Fe4Zn9, δ1k-FeZn7, and ζ-FeZn13 phases were formed, among which the growth of the ζ layer was dominant. Columns of the δ1p-Fe13Zn126 phase were formed on the δ1k/ζ interface at approximately 90 s, and the four IMC layers grew simultaneously until 600 s. Subsequently, a layer of the Γ1-Fe21.2Zn80.8 phase was formed along the Γ/δ1k interface and started growing, after which all the equilibrium IMC phases of Γ/Γ1/δ1k/δ1p/ζ grew competitively. The total thickness of the five IMC layers, dtotal, increased proportionally with the square root of the reaction time, t, i.e., dtotal = d0 t 0.5, which suggested that the growth of the entire IMC layers was controlled by the volume diffusion. However, the values of the time exponent, n, for the individual IMC layers differed depending on their microstructures and chemical concentrations, under equilibrium or nonequilibrium conditions. The formation of the multilayered columnar ζ phase can be attributed to the heterogeneous supersaturation of Fe in the liquid Zn near the columnar ζ / liquid Zn interface during the early stage of the interfacial reaction. The interdiffusion fluxes, J ϕ , of Fe and Zn in the ϕ phase ( ϕ = Γ, δ1k, and ζ) were estimated from the measured concentration profiles of each phase. This suggested that J ϕ caused the growth of each phase as well as the supersaturation of Fe near the interfacial boundaries, thereby resulting in considerable deviations from the equilibrium concentrations. In the later stage of the interfacial reaction, the interfacial concentrations gradually approached the equilibrium concentrations with decreasing J ϕ .

A thermal fluctuation-based nucleation model for use in a phase-field model is proposed. In the model, a normally distributed random temperature fluctuation is imposed on a calculation system, and if a given grid temperature is lower than the average, the undercooling is converted to an increase in the crystallized/precipitated phase fraction. The conversion coefficient is derived as a function of a phase-field critical value for nucleation. The idea of a threshold of nucleation for the phase field, i.e., a critical value, is introduced first in the present study. The model is applied to homogeneous nucleation during solidification in a supercooled pure metal, and a reasonable nucleation probability curve is successfully obtained from the numerical calculations. An application to the homogeneous nucleation of an Al-Cu alloy is also demonstrated.

Phase equilibria in multi-phase Zn–Fe–Al alloys were experimentally measured using a field-emission electron probe micro-analyzer for alloy samples, and a precise iso-thermal phase diagram at 450 °C in the entire composition range of the Zn–Fe–Al ternary system, except for the Fe-rich corner, was determined. The ternary solubility ranges of the Γ-Fe4Zn9, Γ1-Fe21.2Zn80.8, δ1k-FeZn7, and ζ-FeZn13 on the Fe–Zn side and of the ζ-FeAl2, η-Fe2Al5, and θ-Fe4Al13 on the Fe–Al side were consistent with the latest corresponding binary data, whereas no δ1p-Fe13Zn126 phase was detected. The single-phase region of the Γ2-Fe8Zn87Al4 ternary intermetallic compound phase is significantly narrower than that reported in the previous studies. The solubility of Fe in the liquid phase increased consistently and continuously from the value in the Zn–Fe binary system (0.6 at.%) up to 1.2 at.% at 31 at.% Al with increasing Al content. In the Al-rich portion of the phase diagram at 450 °C, the Fe(Al, Zn)6 intermetallic compound phase was newly discovered, and confirmed to be an isomorph extended from the FeAl6 phase which is metastable in the Fe–Al binary system.

Al-rich portion of the Al–Fe binary phase diagram was determined by conventional heat-treatment for equilibration, the diffusion couple method and thermal analysis. Equilibrium compositions are mostly coincident with the generally accepted phase diagram in the literature up to 1000 °C, except the solubility range of θ-Fe 4 Al 13 phase. The solubility ranges of the η-Fe 2 Al 5 and the θ-Fe 4 Al 13 phases were confirmed to increase and incline to the Fe-rich side with increasing temperature. Phase boundaries and the eutectoid composition of the e-Fe 5 Al 8 phase were determined from the diffusion couple method and heating curves of DSC measurement, which were slightly shifted to a higher Fe concentration. Transformation temperatures of liquidus, solidus and invariant reactions determined from heating curves of DSC measurement were mostly lower than those in the phase diagram evaluated by Kattner and Burton. An invariant reaction related to the formation of the θ-Fe 4 Al 13 phase was confirmed as the peritectic reaction of Liquid + η-Fe 2 Al 5 = θ-Fe 4 Al 13 in this study taking equilibrium compositions of the η-Fe 2 Al 5 + θ-Fe 4 Al 13 phases and solidus temperatures of the θ-Fe 4 Al 13 phase into consideration.

Experimental investigation and thermodynamic evaluation of the Co–Ta binary phase diagram was carried out. Equilibrium compositions obtained in two-phase alloys and diffusion couples were measured by electron probe microanalyzer (EPMA). A very narrow λ3(C36) + λ2(C15) two-phase region is confirmed to be present around 26.5 at.% Ta at temperatures between 950 °C and 1448 °C. Equilibrium relationships above 1500 °C among the liquid, Laves (λ1(C14), λ2 and λ3, whose stoichiometry is described by Co2Ta), μ(D8b) and CoTa2(C16) phases were investigated by microstructural examination in as-cast Co-(24–60 at.%)Ta alloys. The solvus temperature of the γ′ Co3Ta (L12) phase precipitated in the 5.8 at.%Ta γ(Co) and the peritectoid temperature of the Co7Ta2 phase in an 8.5 at.%Ta alloy were determined to be 1013 °C and 1033 °C, respectively, by differential scanning calorimeter (DSC). Fine precipitates of the γ′ phase precipitated in the γ (A1) matrix were observed by transmission electron microscope (TEM). Analyzing the present experimental results synthetically, the γ′ Co3Ta phase was identified to be a metastable phase, of which the γ/γ′ transition temperature of the stoichiometric Co3Ta alloy was estimated to be 2000 °C. Thermodynamic assessment of the Co–Ta binary system was carried out based on the present results as well as on experimental data in the literature. Calculated results of not only stable but also metastable equilibria were found to be in good agreement with the revised phase diagram. The evaluated stability of the metastable γ′ Co3Ta coincides with the enthalpy of formation (ΔH(γ'Co3Ta) = −23.44 kJ/mol) calculated by the ab initio method.

The phase equilibria among γ (A1), γ′ (L12), χ (D019), β (B2) and μ (D85) phases and the γ′ solvus and γ solidus temperatures were investigated in the Co–Al–W-based quaternary systems with alloying elements of Ti, V, Nb, Ta, Cr, Mo, Mn, Fe, Ni, Si, Zr, Hf, Ru and Ir by electron probe microanalysis (EPMA) using multiphase alloys and by differential scanning calorimetry (DSC). It was found that Ta, Nb, Ti, V, Mo and W are partitioned to the γ′ or χ phase rather than to the γ phase, while Cr, Mn and Fe tend to be distributed to the γ phase. The correlation between the partition coefficient of alloying elements between γ/γ′, γ/χ and γ/β phases and ab initio formation energy of Co3X (L12), Co3X (D019) and CoX (B2) was respectively obtained. It was also found that the γ′ solvus temperature increases by the addition of the γ′ former elements such as Ta, Nb and Ti, which decreases the γ solidus temperature.

A materials design tool for developing Pb-free soldering alloys in electronic package was developed based on comprehensive experimental data of phase equilibria and thermodynamic properties data accumulated with the CALPHAD (calculation of phase diagrams) method and contains 10 elements, namely, Ag, Au, Bi, Cu, In, Ni, Sb, Sn, Zn and Pb. It can handle the calculation of phase diagrams in all combinations of these elements and all composition ranges. In addition, based on this tool, the liquidus, solidus, phase fractions and constitutions, equilibrium and non-equilibrium solidification behavior, surface tension and viscosity of liquid, diffusion reactions and microstructural evolution, etc. can be predicted. Typical examples of the calculation and application of this tool are presented. The design tool is expected to be a powerful tool for the development of Pb-free solders, as well as for promoting the understanding of the interfacial phenomena between Cu substrate and Pb-free solders in electronic packaging technology.

The phase equilibria at 200 °C, 250 °C, 300 °C, and 400 °C and the phase transformation of the Sn-Au-Bi system were investigated by using the electron probe micro-analyzer (EPMA) and differential scanning calorimeter (DSC), respectively. It is found that there is a new ternary intermetallic compound with a possible AuSn structure (called the ϕ phase in the present work), which has a limited solubility of Au in the Au-rich portion, and the ϕ phase decomposes peritectically at about 313 °C. Based on the experimental data reported in the previous papers and new experimental data determined by the present work, thermodynamic assessments of the Sn-Au-Bi system were carried out by the calculation of phase diagrams (CALPHAD) method. The thermodynamic parameters for describing the Gibbs free energy of each phase were optimized, and reasonable agreement between the calculated results and experimental data was obtained in the Sn-Au-Bi ternary system.

Phase equilibria and stabilities of intermetallic phases appearing in the Co-rich portion of the Co-W-Ga ternary alloys were investigated and isothermal section diagrams at 1200, 1100, 1000, and 900 °C were determined. A fine cuboidal phase with an L12 structure was observed at 900 and 800 °C, where the composition of the new ternary compound obtained by aging at 900 °C for the Co-7.4W-12.0Ga alloy was Co-11.2W-11.4Ga (at.%). It was confirmed that this compound is metastable at 900 °C but is more stable at 800 °C. These results mean that the thermodynamic stability of the metastable Co3W L12 phase, especially in the low temperature region, increases by the addition of Ga.

Phase equilibria between the α (A2), α' (B2) and γ (A1 ) phases in the Fe-Rh binary system were investigated using electron probe micro-analysis (EPMA) and differential scanning calorimetry (DSC) techniques. The A2/B2 order-disorder transformation temperature was also examined by a transmission electron microscope (TEM) observations and high-temperature X-ray diffraction (HTXRD). It was confirmed that while the transition temperature from the α (A2) phase to the γ (A1 ) phase decreases with increasing Rh content up to about 20 at% Rh, the b.c.c. region is stabilized by further Rh addition in the composition range between about 20 and 50 at% Rh, and then again the stability of b.c.c. phase decreases in the composition region over 50 at% Rh. It was also shown by TEM observation and HTXRD examination that the compositions of the phase boundary of the A2/B2 ordering at 500°C and 600°C were determined to be 16.5 and 19.1 at% Rh, respectively. On the basis of those experimental results, a thermodynamic analysis was carried out. The results of the thermodynamic calculation suggest that the anomalous behavior of the stability of the b.c.c. phase is caused by the A2/B2 ordering.

Phase equilibria between the y and y' phases at 900°C in the Co-(10-70)Ni-Al-W system were determined by electron probe microanalysis (EPMA) and X-ray diffractometry (XRD). It was found that the "/ phase with L1 2 structure continuously exists from the Co side to the Ni side in Co-Ni-Al-W system and that it widens to the low W region with increasing Ni content. The partition of Al into the y' phase increased with Ni content, while the W changed from a y' former to a y former by increase of Ni content. Differential scanning calorimetry (DSC) measurements also revealed that the y' solvus temperature increases with Ni content, while the solidus temperature is hardly affected by such content. The lattice parameter of the y and y' phases and the mismatch decreased with increasing Ni content, which caused the morphologic change of the γ' precipitates from cubes to spheres.

Abundant experimental diffusion data in two Co-base binary systems, that is, Co-Ni and Co-Fe, have been assessed to develop the atomic mobility for the face-centered cubic (fcc) phase of the two binaries. The general agreement is obtained by comprehensive comparisons made between the calculated and experimental diffusion coefficients. The developed mobility database, in conjunction with the CALPHAD-type thermodynamic description, has been successfully used to simulate such typical experimental interdiffusion phenomena as the concentration profiles, the microstructural stability of the Kirkendall plane, and the lattice plane displacement.

The phase equilibria, A2/B2 and B2/L21 order–disorder transitions and ferromagnetic/paramagnetic transition on the Co–Fe side of the Co–Fe–Ga system were examined by electron probe microanalysis (EPMA), differential scanning calorimetric (DSC) measurement and vibrating sample magnetometer (VSM). The equilibrium compositions of interrelations mainly among γ (A1: disordered fcc-Co), α (A2: disordered bcc-Fe), β (B2: ordered bcc-CoGa or FeGa) and β′ (L21 or D03: ordered bcc-Co2FeGa or Fe3Ga) phases were determined using diffusion couples and two-phase bulk specimens. It was confirmed that a bcc single-phase region composed of α, β and β′ at 700–1000° C exists in a wide composition range and that the ferromagnetic region appearing on the Co–Fe side extends to the center of the Gibbs triangle with decreasing temperature. On the other hand, the β′ phase appears along the Fe3Ga–Co3Ga section and the maximal critical temperature of the B2/L21 order–disorder transformation was determined to be 825 °C at a stoichiometric composition expressed as Co2FeGa. The obtained phase diagram was examined in comparison with that of the Co–Fe–Al system.

In the present paper, the surface tensions and interfacial energies for pure metals and alloys for different structures were predicted by combining with the evaluated thermodynamic parameters in the framework of the CALPHAD (Calculation of Phase Diagrams) method. It is shown that the calculated results are in good agreement with the existing experimental data. On the basis of the predicted values of surface tension and interfacial energy, the phase stability and phase diagram with nano-size particles can be calculated by considering the Gibbs-Thomson equation. The calculated results for pure Fe indicate that the fcc phase is more stable with the decreasing of size of particles, which is in agreement with the experimental data reported, and the phase diagram with nano-size particle can be calculated.

The phase equilibria of the In-Ag-Bi and In-Ag-Sb systems were determined by differential scanning calorimetry (DSC) and electron probe microanalysis (EPMA). Thermodynamic calculations of these systems were also carried out by taking the experimental results into account. The Gibbs energies of the liquid and solid solution phases are described on the basis of the sub-regular solution model, and that of the intermetallic compounds are based on the two-sublattice model. A consistent set of thermodynamic parameters was optimized for describing the Gibbs energy of each phase, which leads to a good fit between calculated and experimental results. In addition, the surface tension and viscosity of liquid phase were calculated on the basis of the thermodynamic parameters obtained in the present assessment.

Phase equilibria on the Fe-Cu side in the Fe-Cu-X (X: Co, Cr, Si, V) system were experimentally determined over the temperature range of 1073–1273 K. Based on the present results and previous works, the thermodynamic assessments of the phase equilibria in the Fe-Cu-X system were evaluated using the Calculation of Phase Diagram (CALPHAD) method. The Gibbs energies (G) of the bcc, fcc, and liquid phases are described by the subregular solution model, and a set of thermodynamic parameters enable us to calculate various isothermal and vertical sections and the miscibility gaps of the solid and liquid phases.

A thermodynamic description of the Bi–In–Sb ternary system of lead-free solder alloys using the CALPHAD (Calculation of Phase Diagram) method is presented. Phase equilibria information such as vertical sections, liquidus projection and thermochemical quantities were calculated and compared with the experimental data. The calculated and experimental data are in excellent agreement in most cases.

α (A2)/γ (A1) phase equilibria of the Fe–Co system between 400 and 800°C were determined by means of lattice parameter measurement using thin film specimens. Bulk specimens were also analyzed to compare the extent of attainment to the equilibrium. The thin film technique was found to be greatly advantageous for obtaining the phase equilibria at lower temperatures where solid-state reactions are too slow to reach the equilibrium state in the conventional methods using bulk specimens. It was confirmed that the α+γ two-phase region extends below the temperature at which the α (A2)/α′ (B2) transus meets the α/α+γ boundary. Thermodynamic analysis was also conducted by taking the magnetic and chemical ordering contributions of the B2 structure into account, findings of which confirmed the extension of the α+γ two-phase region below the α/α′ ordering temperature.

The evolution of sulfide morphology in the Fe-(0.3-18)mass%Cr-(0.05-0.3)mass%S alloys during solidifi-cation and heat treatment was investigated by means of optical microscopy, scanning electron microscopy, analytical electron microscopy and X-ray diffraction. In situ observation of the formation of the fine particle sulfide was also conducted at elevated temperatures by confocal scanning laser microscopy. The morphology of sulfide in the Fe-Cr-S ternary alloys was found to change from a cell wall type to a globular type with increasing Cr content. Accompanying the phase transformation of the matrix from the δ phase to the γ phase, two types of transgranular fine particle sulfide were formed. One is a fine spherical sulfide formed from the FeS-rich liquid phase through the remelting reaction of δ→γ+Liq. in less than 5 mass% Cr alloys, and the other is a fine rod-like sulfide formed through the eutectoid reaction of δ→γ+sulfide in 5 to 13 mass% Cr alloys. The formation mechanism of various types of sulfide morphology was examined based on phase diagram information.

Phase stability of the BCC phases with A2, B2 and D03 structures and phase equilibria among these phases in the Fe-rich portion of the Fe–Al binary system were examined using diffusion couples, transmission electron microscopy (TEM), energy dispersion spectroscopy (EDS) and Vickers hardness (VH) measurement. TEM observations of the diffusion couples annealed at the temperatures between 300 and 700 °C were performed to identify the crystal structure of the ordered phases and to measure the average size of the B2 and D03 ordered domains. Phase boundaries between A2 and B2 or D03 phases were then evaluated by comparison between the concentration profile and the profiles of the ordered phase domain size or Vickers hardness. It was clarified that the present results in the high temperature range over 450 °C are in agreement with the previous data, while the A2+D03 two-phase field extends beyond the A2/D03 phase boundary in the currently available phase diagram into a lower Al range at temperatures below 450 °C. The A2→B2, B2→D03 and para→ferro continuous ordering temperatures were also measured by differential scanning calorimetry (DSC).

A thermodynamic description of the In–Sn–Zn ternary system, which is of technical importance to optimize lead-free solder alloys, is presented using the CALPHAD method. Phase equilibria, such as isothermal and vertical sections, liquidus projection and mole fractions of the phase constitution, and thermochemical quantities were calculated and compared with the experimental data. They are in excellent agreement in most cases.

The stability region of the B2 phase at 1000°C in the Ti-rich part of the Ti–Al–Cr and Ti–Al–Fe ternary systems are investigated by energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) using two-phase alloys and diffusion couples. It is established that the critical boundaries of the A2/B2 continuous ordering transition are functions of both the Al and Fe or Cr contents, and the phase equilibria between the α2 and the β and between the β and FeTi (B2) phases are strongly affected by the A2/B2 order–disorder transition. By extrapolating these ternary data to the Ti–Al binary and using the Bragg–Williams–Gorsky approximation a metastable A2/B2 ordering boundary is postulated to exist at 1000°C in the vicinity of 23.5 at%Al in the Ti–Al binary system.

New experimental results on the phase equilibria between the β -Ti (A2), α -Ti (A3), α 2 -Ti 3 Al (D0 19 ) and the γ -TiAl (L1 0 ) phases in the Ti–Al system using specimens with low levels of oxygen are presented. The results obtained on the α / γ and the α 2 / γ equilibria are in good agreement with the previous experimental and calculated phase boundaries, while the ones obtained on the α / β equilibrium deviate significantly from the previously proposed phase diagram. It is confirmed that the β phase field extends to higher aluminum contents and that the width of the α + β two-phase region is very narrow, less than 1 at.% Al. The presence of the A2/B2 order–disorder transition in the β phase is also confirmed by a combination of differential scanning calorimetric (DSC) analysis and extrapolation of ordering phase boundaries from the Ti–Al–X (X=Cr, Fe) ternary systems. A thermodynamic analysis has been carried out taking into account the ordering configurations in the β -Ti (A2)/ β 2 -TiAl (B2), f.c.c.-Al (A1)/ γ -TiAl (L1 0 ) and α -Ti (A3)/ α 2 -Ti 3 Al (D0 19 ) equilibria. It is proposed that the anomalous α / β equilibrium is due to the A2/B2 ordering reaction.

Phase equilibria in the Cu-Fe portion of the Cu-Fe-Mo and the Cu-Fe-Nb systems, in the temperature ranges 1073 to 1573 K and 1373 to 1573 K, respectively, were determined by metallography and scanning electron microscopy-energy dispersive x-ray methods. Based on the present experimental data combined with the previous assessments of the component binary systems, thermodynamic calculations of phase equilibria were carried out adopting the subregular solution model to describe the Gibbs energies of the liquid, bcc, and fcc phases. The evaluated thermodynamic parameters lead to a better fit between calculations and experimental data in both the Cu-Fe-Mo and Cu-Fe-Nb systems.

Grain growth in dual-phase structures has been studied by computer simulation techniques using a two-dimensional lattice model. Grain coarsening in each phase follows the cube power law. This is the result of mutual retardation of grain growth and is affected by the mutual wettability of both phases which in itself is a function of the interfacial energy ratios ραα/ραβ and ρββ/ραβ between the two phases. The Lagrange multipliers, under the incidental condition R α+R β = constant has been applied to the interfacial energy minimization problem and a relation between the mean grain radii and volume (or area) fractions of α and β phases, , has been obtained. It is shown that computer simulation results and experimental data on the radii of austenite and ferrite grains in dual-phase low-alloy steel and duplex stainless steel agree well with the proposed relation.

Microstructural investigation of the Co–11.0Ge–5.7W (at.%) ternary alloy was conducted. Fine cuboidal precipitates were observed in this alloy annealed at 1173 K and the crystal structure of the precipitate phase was identified as an L12 structure with a composition of Co–12.6Ge–8.2W (at.%). The solvus temperature of this phase was about 1180 K. Since a stable L12 phase has not been reported in the Co–W and Co–Ge binary systems, this ternary compound is a new L12 phase designated as γ′-Co3(Ge, W).

Investigations relating to the phase equilibria involving the α, γ, σ and liquid phases and the ordering reactions in the bcc aluminides of the Fe–Ni–Si system in the temperature interval 800∼1200°C have been carried out by energy dispersion X-ray spectroscopic (EDS) analysis and transmission electron microscopy (TEM). The equilibrium compositions of the γ (A1: fcc-Fe), α (A2: bcc-Fe), σ (σ phase) and liquid phases and the critical boundaries of the continuous ordering transition in the α phase region have been determined. It is observed that the critical temperatures of the continuous ordering transitions α(A2)/α′(B2) and α′/α″(D03) are mainly functions only of Si content, and not of Ni. It is also found that the tie-line configurations and the partition behavior of the constituents at the α/γ phase equilibrium are strongly affected by the order–disorder transitions in the α phase. Results pertaining to these phase equilibria and the stability of the ordered bcc aluminides are presented and discussed.

Investigations relating to the phase equilibria involving the α, γ, σ and liquid phases and the ordering reactions in the bcc aluminides of the Fe–Ni–Si system in the temperature interval 800∼1200°C have been carried out by energy dispersion X-ray spectroscopic (EDS) analysis and transmission electron microscopy (TEM). The equilibrium compositions of the γ (A1: fcc-Fe), α (A2: bcc-Fe), σ (σ phase) and liquid phases and the critical boundaries of the continuous ordering transition in the α phase region have been determined. It is observed that the critical temperatures of the continuous ordering transitions α(A2)/α′(B2) and α′/α″(D03) are mainly functions only of Si content, and not of Ni. It is also found that the tie-line configurations and the partition behavior of the constituents at the α/γ phase equilibrium are strongly affected by the order–disorder transitions in the α phase. Results pertaining to these phase equilibria and the stability of the ordered bcc aluminides are presented and discussed.

Under the guidance of the calculation of phase diagrams method, the self-organized Cu alloy/stainless steel composite powders with a core/shell microstructure were developed based on the gas atomization process, and the formation evolution of self-organized core/shell structure composite powders was modeled by the phase field method. This paper gives a more detailed explanation for the formation of self-organized core/shell structure composite powders from the viewpoints of thermodynamics and kinetics. Such core/shell structure composite powders have good combination of high strength and corrosion resistance (Fe-rich phase) and high electric and thermal conductivities (Cu-rich phase) with many potential advanced applications in electronic devices.