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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.

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 .

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.

Phase equilibria in the Ir–W, Ir–Al and Ir–W–Al systems at temperatures between 1100 °C and 1600 °C were experimentally investigated using diffusion couples and two- or three-phase alloys, and the mechanical properties of γ′ (L12) strengthened Ir–W–Al alloys were examined by hardness and compression tests at room and elevated temperatures. The phase boundaries between the γ(A1)/e′(D019), e′/e(A3) and e/e″(B19) in the Ir–W system at 1400 °C–1600 °C and those between the γ/β(B2) and β/Al2.7Ir in the Ir–Al system at 1100 °C–1400 °C were determined. The phase diagrams in the Ir-rich corner of the Ir–W–Al ternary system at 1300 °C and 1400 °C were also determined. The existence of the γ′ phase of the Ir3(W,Al) ternary compound was confirmed, and this system was found to consist of the γ, γ′, e, e′ and β phases in the Ir-rich portion. It was also found from hardness and compression tests up to 1200 °C that Ir–Al–W alloys having the γ + γ′ structure with a small lattice misfit show high hardness and strength at room and high temperatures.

New experimental measurements of the phase diagram and the mixing enthalpy of liquid phase along with the previous experimental data were used in a reassessment of the Ni–Ga system. A set of self-consistent thermodynamic parameters of the Ni–Ga system is obtained using the calculation of phase diagram (CALPHAD) technique, and the available phase diagram and thermodynamic data are reproduced well within experimental error limits. Some noticeable improvements are obtained in the present work compared with the previous assessment: (1) the calculated Ga-rich liquidus is more reasonable; (2) Ni3Ga7 is adopted as the most Ga-rich compound rather than NiGa4; (3) the Ni5Ga3 phase is treated as the nonstoichiometric compound with consideration of its narrow homogeneity range; (4) the phase transformation between B81.5_Ni3Ga2 and Ni13Ga9 is considered instead of treating them as Ni3Ga2 phase simply; (5) the latest experimental data of mixing enthalpy for the liquid phase are adopted. The present study can be used as a basis for the development of a thermodynamic database of the Ni-based semiconductor alloy systems.

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.

Phase equilibria in the Fe–Si binary system were investigated experimentally and thermodynamic assessment was carried out. The αFe (A2) + α"Fe3Si (D03) two-phase microstructures at 600°C and 650°C were obtained, whose grain sizes were sufficiently coarsened to be analyzed by FE-EPMA with a spatial resolution below 0.5 μm under the condition of 6 kV accelerating voltage. α'FeSi (B2) + α"Fe3Si (D03) two-phase equilibria above 700°C were detected for the first time and equilibrium compositions were determined by the diffusion couple method. The horn-shaped two-phase miscibility gap extends from the low temperature αFe + α"Fe3Si equilibrium along the B2/D03 second-order transition boundary and closes below 1000°C. Four-sublattice split compound energy formalism was applied to calculate the Gibbs energy of the bcc phases, A2(αFe), B2(α'FeSi) and D03(α"Fe3Si), and the thermodynamic parameters in the Fe–Si binary system were evaluated. Equilibrium relations in the binary system were well reproduced, especially the effect of the B2 and D03 ordering on the liquidus and solidus curves and the miscibility gap between bcc phases. Optimized thermodynamic parameters as well as the experimental results are expected to be helpful for developing higher multi-component systems for practical steels.

Mechanical properties of Fe-20Mn-(10-14)Al-(0-1.8)C (mass%) quaternary and Fe-20Mn-(10-14)Al-(0.75-1.8)C-5Cr (mass%) quinary alloys were investigated by hardness, cold-workability and tensile tests at room temperature. The γ(fcc) alloys in both quaternary and quinary systems with a low density of less than 7.0 g/cm 3 showed an excellent ductility and their hardness and tensile strength increased with increasing Al and C contents. The γ+α(bcc) duplex alloys also exhibited a high tensile strength by controlling the α volume fraction. TEM observation confirmed that high hardness and tensile strength of the alloys with high Al and C contents are caused by the precipitation of nano-size κ-carbide with perovskite structure during cooling from the annealing temperature. Fe-20Mn-11Al-1.8C-5Cr alloy with a density of 6.51 g/cm 3 showed a high specific strength of more than 180 MPa · cm 3 /g with a good tensile elongation of 40 %. The present Fe-20Mn-Al-C(-5Cr) alloys showed a higher specific strength than conventional steels.

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.

The National Natural Science Foundation of China [50425101, 50571084]; The Ministry of Science and Technology of China [2004CCA04200]; The Ministry of Education of China [20050384003, 105100, 707037]; Grant-Aid Core Research for Evolution Science and Tech

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.

The Zn-Al(-Cu) eutectic alloys (melting point 381°C) are candidates for use as Pb-free high-temperature solders as a substitute for Pb-based solders, which are suitable for severe working environments such as the engine room of hybrid vehicles equipped with an inverter system as well as a heat engine. In this study, the interfacial reaction between Zn-Al(-Cu) alloys and the Ni substrate during soldering, aging, and thermal cycling was investigated. Semiconductor chips and Ni substrates were soldered with Zn-Al(-Cu) alloys at various temperatures under a nitrogen atmosphere. The soldered assemblies were then heat-treated at 200°C and 300°C to examine the microstructural evolution at the soldered interface. The effect of severe thermal cycles between −40°C and 250°C in air on the microstructure and fracture behavior at the solder joint was investigated. Even after a 1000-cycle test, the thickness of the Al3Ni2 layer formed at the interface between the Zn-Al-based solder and the Ni substrate, which is responsible for the damage of the soldered assemblies, was quite small.

The recrystallization and grain growth characteristics of pre-deformed Fe–1.9vol%Bi alloy specimens in the two-phase region of αFe and liquid Bi were investigated by microstructural observation. Precipitate-free zones (PFZs) were mainly formed in the vicinity outside of the curved grain boundaries. Furthermore, large Bi particles were also observed on the grain boundaries of the matrix along the PFZs. These results suggest that the intragranular liquid Bi particles were trapped and dragged by grain boundaries. The grain growth of the matrix phase was extremely retarded by the effect of this dragging.

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.

Chemical reactions between Cu substrates and Zn-Al high-temperature solder alloys, Zn-4Al and Zn-4Al-1Cu (mass%), at temperatures ranging from 420°C to 530°C were experimentally investigated by a scanning electron microscope using backscattered electrons (SEM-BSE) and an electron probe microanalyzer (EPMA). Intermediate phases (IMPs), β(A2) or β′(B2), γ(D82), and e(A3) phases formed and grew during the soldering and aging treatments. The consumption rate of the IMP for Cu substrates is described by the square root of t in both the alloys, while the additional Cu in the molten Zn-Al alloy slightly suppresses the consumption of Cu substrates. The growth of IMPs during soldering treatment is controlled by the volume diffusion of constituent elements, and its activation energy increases in the order of Q e

Maximum bubble pressure, dilatometric, and meniscographic methods were used in the investigations of the surface tensions, densities, wetting times, wetting forces, contact angles, and solder-flux interfacial tensions of liquid Sn-Ag-Cu-Bi alloys with various additions of Sb. Density and surface tension measurements were conducted in the temperature range 230 to 900 °C. Surface tensions at 250 °C were measured in air and under a protective atmosphere of Ar-H2 and were combined with data from meniscographic studies done under air or with a protective flux. Meniscographic data with a nonwetted Teflon substrate provided data on solder-flux interfacial tensions, and meniscographic data with a Cu substrate allowed determinations of wetting times, wetting forces, and calculations of contact angles. Additions of Sb to quaternary Sn-Ag-Cu-Bi alloys improve wettability, move the parameters closer to those of traditional solders, and affirm, as found in previous studies of Bi additions to the Sn-Ag-Cu near-eutectic compositions, that interfacial tensions and contact angles are the two parameters most important as a metric of wettability. However, in contrast to results found in studies of quaternary Sn-Ag-Cu-Bi alloys, the changes in quinary Sn-Ag-Cu-Bi-Sb alloys of interfacial tensions and contact angles do not correlate with decreasing wetting time and increasing wetting force.

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.

Bismuth and its alloys are candidates for Pb-free high-temperature solders that can be substituted for conventional Pb-rich Pb−Sn solders (melting point (mp) = 573 – 583 K). However, inferior properties such as brittleness and weak bonding strength should be improved for practical use. To that end, BiCu−X (X=Sb, Sn, and Zn) Pb-free high-temperature solders are proposed. Miscibility gaps in liquid BiCu−X alloys were surveyed using the thermodynamic database ADAMIS (alloy database for micro-solders), and compositions of the BiCu−X solders were designed on the basis of calculation. In-situ composite solders that consist of a Bi-base matrix with fine intermetallic compound (IMC) particles were produced by gas-atomizing and melt-spinning methods. The interfacial reaction between in-situ composite solders and Cu or Ni substrates was investigated. The IMCs at the interface formed a thin, uniform layer, which is an appropriate morphology for a reliable solder joint.

The carbide dispersion carburizing process was applied to Fe-based high-speed steels, which contained multiple carbide-forming elements, Mo and V. Fine carbides precipitated during the carburization and the dispersed particles in the Fe–Mo–V–C alloys heat-treated at 1 200°C were identified as VC, (Mo, V)2C, and (Fe ,Mo)6C, which behave as effective inhibitors against the grain growth of austenite and as reinforcers resulting in increased hardness of the martensitic matrix. The maximum Vickers hardness of the Fe–10Mo–5V–2.05C alloy quenched from 1 200°C and tempered at 600°C achieved values of 1 100 and 1 000, respectively. Thermodynamic calculation of the Fe–Mo–V–C quaternary system proved to be useful for optimizing the composition of carbide forming elements, the carburizing conditions, and the microstructure of carburized and solution-treated alloys.

Microstructure and grain growth characteristics of pre-deformed Al-Bi alloys annealed at 773 K were investigated mainly by scanning electron microscopic (SEM) observation. In addition to very fine liquid-Bi particles in the grains, large Bi particles were observed on the grain boundaries, and non-precipitation zones are mainly formed in the vicinity outside of the curved grain boundaries. This result suggests that the Bi particles on the grain boundaries were dragged by the grain boundaries. The grain growth is significantly retarded by the effect of this dragging, the origin of which can be explained by the decrease of the interfacial energy of the intragranular Bi particles. Quantitative analysis showed that the diffusion of Al atoms in the liquid Bi particles on the grain boundaries is the rate-determining process of this dragging.

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.

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.

Thermodynamic assessments have been made for the Cu-Sb and Sb-Zn binary systems by means of the CALPHAD technique. The Gibbs energies of the liquid, bcc, and fcc phases are described by a substitution solution model and a Redlich-Kister formalism. All of the compounds were treated as stoichiometric compounds. Moreover, the liquidus temperatures of the Zn-rich portion in the Sb-Zn system were measured to check the unusual shape reported by previous work. It was confirmed that the liquidus line is not peculiar but smooth. A consistent set of the thermodynamic parameters was optimized to obtain a better fit between calculated results and experimental data including phase diagram and thermodynamic quantities.

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.

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.

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.

The solubility product of TiN in an austenitic steel was experimentally determined using a diffusion couple technique. Diffusion couples consisting of Ti–N steels with various compositions were annealed at temperatures between 1 473 and 1623 K, taking special care to exclude the oxygen contamination during the annealing. The solubility limit of TiN was determined from the break points of iso-activity lines for nitrogen. A thermodynamic analysis was also carried out to arrive at solubility products by considering the wide range of temperature dependence of the TiN formation energy. Solubility products in austenite (γ), ferrite (α or δ) and liquid phases were determined as log(mass%Ti)(mass%N)γ=4.35–14 890/T, log(mass%Ti)(mass%N)α(δ)= 4.65–16310/T and log(mass%Ti)(mass%N)liq=4.46–13500/T respectively.

The microstructure of powders that are applicable for electronic materials were studied for some systems in which there is a liquid miscibility gap. The characteristic morphologies of an egg-like core type and a uniform second-phase dispersion are shown in relation to the phase diagram, where thermodynamic calculations are a powerful tool for alloy design and the prediction of microstructure. Typical examples of microstructural evolution and properties of Pb-free solders and Ag-based micropowders with high electrical conductivity produced by a gas-atomizing method are presented.