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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.

The present paper reports the development of W-, Mo-, and V-free and Ni- and Cr-containing Co–Al–Ta-based superalloys. In particular, the presence of a metastable L12-γ′ phase is experimentally verified in Co–12Al–2Ta alloy. The results show that the γ′ phase stability is improved and the γ/γ′ composition range is broadened by rising the Ni content in alloys under study. Moreover, elemental partitioning proves that Cr was a γ-phase former, which addition reduces the γ/γ′ lattice misfit and the γ′ precipitate coarsening rate. Moreover, the developed Cr-containing alloys exhibit excellent γ′ phase stability even at high temperatures of 800–1100 °C. In particular, Co–30Ni–12Al–4Ta–12Cr (12Cr) alloy possesses a good combination of high solvus temperature (∼1152 °C), low density (∼8.38 g/cm3), low γ/γ′ lattice misfit (∼+0.33%), and low coarsening rate of γ′ precipitate (∼1.95 × 10−27 m/s at 900 °C). Besides, nominal and specific yield strength values of the developed 12Cr alloy at ambient and high temperatures are no worse than those of other available Cr-containing and W-free cobalt-based superalloys.

Since half a century ago, researchers have continuously focused on developing γʹ-strengthened Co-base superalloys to achieve an increased power and efficiency; these alloys can supposedly operate at higher temperatures than Ni-base superalloys. However, the yielded results have failed to meet the expectations. Herein, we successfully design novel W-free Co-V-Ta-base alloys by employing machine learning algorithm and CALPHAD methods, which exhibit low mass density (8.67–8.86 g/cm3), an extremely wide γ/γʹ region, a high γʹ solvus temperature (up to 1044 °C), and a high strength. The atom probe tomography results show that titanium is an extremely strong γʹ-former; therefore, it is expected to improve the thermodynamic stability of the γʹ phase. Furthermore, besides the very high tensile strength (18.7 GPa) of γʹ phase, indicated by first-principles calculations, the strength of Ti-incorporated alloy is higher than that of γʹ-strengthened Co-base superalloys; especially, the reported strength value is higher than that of the well-known Co-9Al-9 W alloy by approximately 322 MPa at 750 °C, which is comparable to that of a few commercial Ni-base superalloys. Therefore, the possibility of the Co-V-Ta-base system being a candidate for developing novel Co-base superalloys is strongly suggested in this study.

The γ/γ′ two-phase Co–Al–V-base superalloys are investigated in detail, including their phase equilibria, alloying effects, and alloy design. The experimental proof of the existence of a ternary compound with an L12-ordered γ′-Co3(Al, V) phase is provided in this study, and the γ/γ′ two-phase Co–5Al–14V (at.%) alloy is designed. The γ′-Co3(Al,V) phase is proved to be thermodynamically stable at 900 °C, and a wide γ/γ′ two-phase composition region in the Co–Al–V ternary phase diagram at 900 °C is identified. The performed investigation of Co–5Al–14V-2X (X: Ti, Cr, Nb, Mo, Ta, and W) and Co-xNi-8Al–12V (x = 10, 20, and 30) quaternary alloys revealed that Ti, Nb, Mo, Ta, W, and Ni tend to concentrate in the γ′ phase, whereas Cr tends to partition to the γ matrix. Besides, the γ/γ′ two-phase Co–30Ni–10Al–5V–4Ta–2Ti (30Ni4Ta2Ti) alloy is designed. The 30Ni4Ta2Ti alloy exhibits a very high γ′ solvus temperature (namely, 1242 ± 3 °C) combined with a low density (8.46 ± 0.08 g cm−3), which characteristics are comparable with those of the Mar-M-247 Ni-base superalloy. Moreover, the nominal and the specific yield strength values of the obtained 30Ni4Ta2Ti alloy within the temperature range from 600 to 900 °C are also close to those of the Mar-M-247 superalloy.

The influences of alloying elements Al and Ni to a Co-Ti-V master alloy on microstructures, phase stabilities and high-temperature mechanical properties have been investigated. A two-phase microstructure γ/γʹ with ultrahigh γʹ volume fraction was designed in the Co-Ti-V (master alloy), Co-Ti-V-Al (Al-modified) and Co-Ti-V-Ni (Ni-modified) alloys. Al shows a slight tendency to partition into γʹ, while Ni exhibits almost equal distribution between the γ and γʹ phases. Al is found to increase the volume fraction and solvus temperature of γʹ. The solvus temperatures of γʹ in the master alloy, Al-modified and Ni-modified alloys exceed that of Co-9Al-9W alloy (1000 °C) by 91, 112 and 82 °C, respectively. The flow stresses of the designed alloys exhibit an anomalous positive dependence on temperature rising from 600 to 750 °C. The strengths of the master alloy and Ni-modified alloys are not only higher than that of traditional Co-base superalloy MAR-M 302 at the temperature ranging from 700 to 1000 °C, but also comparable with that of the commercial Ni-base superalloy IN-939 between 850 and 1000 °C. In conclusion, the present Co-Ti-V-base alloys reinforced by γʹ are suggested as potential candidates for high-temperature utilizations.

The α(hcp)/β(bcc) phase equilibria of Ti-based multi-component alloys can be described by a Schaeffler-type diagram, where Al and Mo equivalents (Aleq and Moeq) are used. Aleq is thermodynamically defined by the ratio of partial molar free energy changes transfer of one mole of each α forming element and Al from a dilute solution of α to β phases, while Moeq is also deduced by similar thermodynamic quantities of β forming element and Mo. Aleq and Moeq for 40 alloying elements are estimated from the thermodynamic parameters assessed by Kaufman and Murray. It is shown that three types of Ti alloys, i.e., α and near α, α+β, and β alloys, can be exactly classified using Aleq and Moeq. The Ms and β transus temperatures can also be predicted by Aleq and Moeq. The proposed Aleq and Moeq are very useful for alloy design, heat treatment, and microstructural evolution of Ti-based alloys.

The microstructures and the phase equilibria of the equilibrated Co–V–Ta ternary alloys have been investigated. Moreover, four isothermal sections of the Co–V–Ta ternary system at 1300, 1200, 1100 and 900 °C are experimentally established. The corresponding results are summarized as follows: (1) the C14 phase with a large solubility of Co is observed both at 1300 and 1200 °C, while it forms a ternary single phase region at 1100 and 900 °C; (2) the C36 phase, containing a large solubility of V, is identified at 1300, 1200 and 1100 °C, while it exists as a ternary single phase region at 900 °C; (3) Co is in favor of stabilizing the C14 phase against low-temperature, while V plays an analogous influence on the C36 phase; (4) the solubility of Ta in σ-Co 2 V 3 phase decreases by a small amount as the temperature decreases from 1300 to 900 °C. In addition, the experimental information obtained in the present work is not only essential for the thermodynamic assessment of the Co–V–Ta ternary system, but also important for the development of the Co-base alloys.

Diffusion coefficients of the fcc Co–Al–W alloys were extracted from extensive diffusion couple experiments performed at 1173–1573 K, which were afterwards assessed to develop their diffusion mobility in the context of phenomenological treatment. We demonstrate that the mobility enables the prediction of diffusion picture of technologically important Co–Al–W alloys.

The authors have developed an Ir-containing Ni based superalloy tool, strengthened by γ′ precipitation, for friction stir welding (FSW) of steel and titanium alloys. The Ir-containing Ni based superalloy tool exhibited an acceptable performance during FSW of 304 stainless steel and Ti-6Al-4 V. In this study, feasibility of Ir-containing Ni based superalloy tool to friction stir spot welding (FSSW) of high strength steel was examined. FSSW was conducted on the lapped sheets of 1.2 mm-thick DP590 steel. The Ir-containing Ni base superalloy tool with 1.2 mm long probe successfully produced the spot welds on DP590 steel without macroscopic deformation. Even after 600 FSSW trials, the tool shape was hardly changed, suggesting that the Ir-containing Ni based superalloy tool is appropriate for FSSW of high strength steel.

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.

Thermodynamic assessment of Mn-RE (RE: Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu) binary systems has been carried out by means of the calculation of phase diagrams method on the basis of experimental data including phase equilibria and thermodynamic properties. The Gibbs free energies of liquid phase and solid solution phases in the Mn-RE systems were all described by the subregular solution model with the Redlich–Kister formulation, whereas those of intermetallic compounds were described by the sublattice model. Sets of thermodynamic functions with self-consistent parameters leading to satisfactory agreement between calculated results and experimental data were eventually obtained. A primary thermodynamic database for the phase diagrams of the Mn-RE (RE: Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu) binary systems was developed from these essential thermodynamic parameters. This database can be used not only to calculate the phase equilibria and thermodynamic properties of binary Mn-RE systems but also to extrapolate to higher-order systems, which can provide theoretical guidance for design and development of high-performance Mn-RE alloy materials.

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 between the γ (A1) and liquid phases and those between the γ, e (A3), σ (D8b) and α (A2) phases at temperatures between 750 and 1300 °C in the Co-Cr-Ni system were determined by differential scanning calorimetry and electron probe microanalysis. It was found that the γ solidus and liquidus temperatures decrease with increasing Cr or Ni content and that the difference between them increases with increasing Cr content. The phase equilibria at 800, 900, 1000, 1100, 1200 and 1300 °C were determined using two- or three-phase alloys, and the phase boundaries due to the magnetically induced phase separation in the γ and e phases were also observed at 850, 800 and 750 °C by the diffusion couple method.

Phase equilibria between αFe and γ(Fe,Ni) in the Fe–Ni binary system at low temperatures above 400 °C were determined experimentally, and thermodynamic descriptions to calculate the Gibbs energy of involved phases were revised with taking into account the interaction effect between the chemical and magnetic orderings. Heat-treatment for equilibration of gas-atomized powder of Fe–Ni alloys without deformation resulted in the formation of a microstructure consisting of directional γ precipitates in α' martensite matrix. Converge-milling processing, a kind of mechanical alloying technique, in advance of heat-treatment, was applied to introduce a large number of lattice defects into powder particles, which enhanced α + γ recrystallization to form an equiaxed dual-phase polycrystalline microstructure. Equilibrium compositions of the equiaxed grains of the α and γ phases were measured by an FE-EPMA, the spatial resolution of quantitative analysis of which is 0.5 μm in diameter with accelerating voltage of 6 kV. Equilibrium compositions of the γ phase coincided with the phase diagram assessed in accordance with experimental results in the literature. On the other hand, the solubility of Ni in the α phase exhibited considerable deviation from “retrograde solubility” determined according to previous data. Thermodynamic analysis with revised parameters suggests that the underestimated solubility of Ni in the αFe phase is caused by the additional Gibbs energy due to lattice defects in the α’ martensitic structure.

The effects of the addition of Nb and B on grain boundary precipitation, martensitic transformation and superelasticity were investigated in the Fe–Ni–Co–Al alloys. The addition of Nb increases the hardness and the martensitic transformation changes from non-thermoelastic to thermoelastic, while the addition of B is effective for suppressing the formation of brittle grain boundary precipitates. By the recrystallization texture developed by 98.5% cold-rolling and annealing, high ductility and superelasticity with 5% recoverable strain were realized in the Fe–28Ni–17Co–10.5Al–2.5Nb–0.05B polycrystalline alloy.

To obtain a large strain of Ni–Fe–Ga–Co ferromagnetic shape memory alloys, the effects of Mn on the magnetocrystalline anisotropy constant Ku, and the magnetic-field-induced strain (MFIS) under static stresses were investigated. The value of Ku was increased by the addition of Mn, and Ni49.5Fe14.5Mn4.0Ga26.0Co6.0 alloy was accompanied by a relatively large value of −1.5 × 105 J/m3 at room temperature. From the stress–strain curves of this alloy, the twinning stress is estimated to be 8–10 MPa. Consequently, the Ni49.5Fe14.5Mn4.0Ga26.0Co6.0 alloy provides a large MFIS of about 11.3% at room temperature under a static compressive stress of about 8 MPa.

The phase equilibria in the Cu-Fe-Zr ternary system was experimentally investigated by optical microscopy, electron probe micro-analyzer and x-ray diffraction on the equilibriated alloys. Three isothermal sections of the Cu-Fe-Zr ternary system at 1000, 1100 and 1200 °C were experimentally determined, and no ternary compound was found in this system. The further result in the present work shows that the Fe23Zr6 phase in the Cu-Fe-Zr ternary system is an equilibrium phase rather than oxygen-stabilized phase.

The effects of grain size on the stress–strain characteristics of Cu–Al–Mn-based pseudoelastic (PE) sheet specimens with various relative grain sizes d/t (d = grain size, t = sheet thickness) were investigated using cyclic tensile testing. The stress–strain characteristics such as the yield stress σy, work-hardening rate dσPE/de and stress hysteresis of pseudoelasticity Δσ decreased, and the obtained maximum PE strain e PE MAX increased with increasing d/t. The σy, dσPE/de, Δσ and e PE MAX plots as a function of d/t were divided into three regions. The critical points dividing the plots into the three regions were located at d/t ≈ 1 and d/t ≈ 2. These results can be explained from the standpoint of constraints between grains, depending on grain structure such as a fine equiaxed grain structure, a columnar-like grain structure and a fully columnar grain structure.

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.

The normal grain growth behaviors at 750, 800 and 900°C in block and sheet samples of Cu­Al­Mn shape memory alloy with the bcc single-phase structure were investigated. The grain growth exponents, n, evaluated in the two- and three-dimensional grain growths were found to be larger than those in most other metals and were located between 10 and 18. Furthermore, the two-dimensional growth in thin sheet samples was much slower than the three-dimensional growth in block samples due to the grooves formed along grain boundaries on the specimen surface, these grooves constituting a hindrance to the movement. [doi:10.2320/matertrans.M2013167]

In multiphase steels, control of the carbon contents in the respective phases is the most important factor in alloy design for achieving high strength and high ductility. However, it is unusually difficult to determine the carbon contents in multiphase structures with high accuracy by electron probe microanalysis (EPMA) due to the unavoidable effect of hydrocarbon contamination during measurements. We have investigated new methods for suppressing hydrocarbon contamination during field emission (FE) EPMA measurements as well as a conventional liquid nitrogen trap. Plasma cleaner inside the specimen chamber results in a improvement of carbon-content determination by point analysis, increasing precision tenfold from the previous 0.1 mass%C to 0.01 mass%C. Stage heating at about 100 °C dramatically suppresses contamination growth during continuous point measurement and mapping. By the combination of above two techniques, we successfully visualized the two-dimensional carbon distribution in a dual-phase steel. It was also noted that the carbon concentrations at the ferrite/martensite interfaces were not the same across all interfaces, and local variation was observed. The developed technique is expected to be a powerful tool for understanding the mechanisms of mechanical properties and microstructural evolution, thereby contributing to the design of new steel products with superior properties.

In multiphase steels, control of the carbon contents in the respective phases is the most important factor in alloy design for achieving high strength and high ductility. However, it is unusually difficult to determine the carbon contents in multiphase structures with high accuracy by electron probe microanalysis (EPMA) due to the unavoidable effect of hydrocarbon contamination during measurements. We have investigated new methods for suppressing hydrocarbon contamination during field emission (FE) EPMA measurements as well as a conventional liquid nitrogen trap. Plasma cleaner inside the specimen chamber results in a improvement of carbon-content determination by point analysis, increasing precision tenfold from the previous 0.1 mass%C to 0.01 mass%C. Stage heating at about 100 °C dramatically suppresses contamination growth during continuous point measurement and mapping. By the combination of above two techniques, we successfully visualized the two-dimensional carbon distribution in a dual-phase steel. It was also noted that the carbon concentrations at the ferrite/martensite interfaces were not the same across all interfaces, and local variation was observed. The developed technique is expected to be a powerful tool for understanding the mechanisms of mechanical properties and microstructural evolution, thereby contributing to the design of new steel products with superior properties.

Shape memory alloys are typical temperature-sensitive metallic functional materials due to superelasticity and shape recovery characteristics. The conventional shape memory effect involves the formation and deformation of thermally induced martensite and its reverse transformation. The shape recovery process usually takes place over a temperature range, showing relatively low temperature-sensitivity. Here we report novel Cu-Al-Fe-Mn shape memory alloys. Their stress-strain and shape recovery behaviors are clearly different from the conventional shape memory alloys. In this study, although the Cu-12.2Al-4.3Fe-6.6Mn and Cu-12.9Al-3.8Fe-5.6Mn alloys possess predominantly L21 parent before deformation, the 2H martensite stress-induced from L21 parent could be retained after unloading. Furthermore, their shape recovery response is extremely temperature-sensitive, in which a giant residual strain of about 9% recovers instantly and completely during heating. At the same time, the phenomenon of the jumping of the sample occurs. It is originated from the instantaneous completion of the reverse transformation of the stabilized 2H martensite. This novel Cu-Al-Fe-Mn shape memory alloys have great potentials as new temperature-sensitive functional materials.

The phase equilibria in the Mn-rich portion of Mn–Ga binary system were experimentally determined. The topological feature of the determined diagram was found to be similar to that reported by Wachtel and Nier [17] while the η phase with the D019 structure exists in a wider temperature and composition range and the τ phase has a wider solubility range. The complicated composition dependence on magnetization of the Mn-rich alloys reported by Masumoto et al. can successfully be explained with the determined phase diagram.

SUMMARY This paper presents the results on shaking table tests of half-scale brick walls performed to investigate the effectiveness of newly developed Cu–Al–Mn superelastic alloy (SEA) bars in retrofitting of historical masonry constructions. Problems associated with conventional steel reinforcing bars lie in degradation of stiffness and strength, or pinching phenomena, under cyclic loading, and presence of large residual cracks in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu–Al–Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Sets of unreinforced, steel reinforced, and SEA-reinforced specimens are subjected to scaled earthquake excitations in out-of-plane direction. Whereas steel-reinforced specimens showed large residual inclinations, SEA-reinforced specimens resulted in stable rocking response with slight residual inclinations. Corresponding nonlinear finite element (FE) models are developed to simulate the experimental observations. The FE models are further used to examine the sensitivity of the response with respect to the variations in experimental conditions. Both the experimental and numerical results demonstrate the superiority of Cu–Al–Mn SEA bars to conventional steel reinforcing bars in avoiding pinching phenomena. Copyright © 2012 John Wiley & Sons, Ltd.

National Natural Science Foundation of China [51031003, 51171159]; Ministry of Education of China [707037]; Ministry of Science and Technology of China [2009DFA52170, 2009AA03Z101]; Fundamental Research Funds for the Central Universities [201112G013]; CSC China

Phase equilibria of the solid phases including the magnetic and martensitic transformation temperatures in the Co­Mo system were investigated using two-phase alloys, the diffusion couple technique, differential scanning calorimetry, and vibrating sample magnetometry. Furthermore, ab initio calculations of D019-Co3Mo and several fcc-base ordered structures, including metastable compounds, were carried out to estimate the formation energy. Based on these results, a thermodynamic assessment using the CALPHAD method was performed. A foursublattice model was used for the fcc-base phase to describe the order­disorder phase transformation. For the ® phase, both a three and a foursublattice model were applied. The set of thermodynamic values describing the Gibbs energy of the Co­Mo system reproduces the experimental phase diagram well. The four-sublattice model for the ® phase reproduces the site fractions as well as the phase boundaries better than the threesublattice model. The calculated metastable fcc-base phase diagram considering chemical and magnetic ordering is also reasonable. This is important for estimating the phase stability of the L12 phase in Co-base £/£A superalloys. [doi:10.2320/matertrans.M2012149]

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.

TLPS (Transient Liquid Phase Sintering) process is a candidate method of heat-resistant bonding, which makes use of the reaction between low-melting temperature powder of Sn-Bi base alloys and reactive powder of Ag. During heat treatment above the melting temperature of a Sn-Bi base alloy, the molten Sn-Bi reacts rapidly with solid Ag particles, which results in the formation of heat-resistant intermetallic compound (IMC). In this study, the TLPS properties between Sn-17Bi-1Ag (at.%) powder with its liquidus temperature of 200?C and pure Ag powder were investigated. During differential scanning calorimetry (DSC) measurement, an exothermic reaction and an endothermic reaction occurred, which correspond to the formation of the e-Ag3Sn IMC phase and the melting of the Sn-17Bi-1Ag alloy, respectively. After the overall measurement, the obtained reactant consists of the Ag3Sn-IMC and Bi-rich phases, both of which start melting above 250?C, with a small amount of the residual Sn-Bi eutectic phase. These results suggest that the TLPS process can be applied for Pb-free heatresistant bonding.

The authors have developed a new friction-stir welding (FSW) tool that enables to weld high-softening-temperature materials (HSTMs), such as steels, titanium and zirconium alloys. The new tool is made of a Co-based heat-resistant alloy strengthened by precipitating intermetallics, Co3(Al,W), with a L12 structure at high temperatures. The Co-based alloy tool exhibits yield strengths higher than 500 MPa at 1000 deg C, so it might have a great potential as a tool material for FSW of HSTMs. In this study, the feasibility of using the Co-based alloy tool with various HSTMs was examined. Changes in the tool shape during FSW and the weld appearances produced with the Co-based alloy tool will be briefly shown.

This work first deals with the experimental investigation and thermodynamic calculation in the Al-Bi-Sn ternary system. The phase equilibria at 400 and 500 °C in the Al-Bi-Sn ternary system have been experimentally determined by electron probe microanalysis (EPMA) on the equilibrated alloys. Based on the experimental data determined in the present work, the phase equilibria in the Al-Bi-Sn ternary system have been thermodynamically assessed by using the CALPHAD (CALculation of PHAse Diagrams) method, and a consistent set of thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained. The additions of Sn can effectively reduce the stable liquid miscibility gap in the Al-Bi binary system and gradually decrease its critical temperature. And the additions of Bi can significantly stabilize the metastable liquid miscibility gap in the Al-Sn binary system. This is shown by an initial decrease in critical temperature with increasing Bi additions.

The spin-wave stiffness constant D and the Curie temperature TC for series of L21 phase in Co2CrGa, Co2MnGa, Co2Mn(Al1-xSix) , Co2Fe(Al1-xSix), and Co2Fe(Ga1-xSix) Heusler alloys were evaluated from the thermomagnetization measurements. For the Co2CrGa, Co2MnGa, and Co2Mn(Al1-xSix) alloys, there was a linear relation between D and TC . The tendency between D and TC was different from that for Co2Fe(Al1-xSix) and Co2Fe(Ga1-xSix) alloys, that is, TC was in the temperature region from 1040 to 1100 K indicating weak concentration dependence, whereas D was sensitive to the composition. For example, D changed from 2.28 meV ·nm2 for x=1 (Co2FeSi) to 5.24 meV ·nm2 for x=0 (Co2FeGa) in the case of Co2Fe(Ga1-xSix) alloys. It was suggested that magnetic stability against the temperature of the Co-based Heusler alloys containing Fe element was governed not only by the spin-wave excitation but also by the other kinds of excitation.

This paper investigates the applicability of newly developed Cu-Al-Mn shape memory alloy (SMA) bars to retrofitting of historical masonry constructions by performing quasi-static tests of half-scale brick walls subjected to cyclic out-of-plane flexure. Problems associated with conventional steel reinforcing bars lie in pinching, or degradation of stiffness and strength under cyclic loading, and in their inability to restrain residual deformations in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu-Al-Mn SMA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Three types of brick wall specimens, unreinforced, steel reinforced, and SMA reinforced specimens are prepared. The specimens are subjected to quasi-static cyclic loading up to rotation angle enough to cause yielding of reinforcing bars. Corresponding nonlinear finite element models are developed to simulate the experimental observations. It was found from the experimental and numerical results that both the steel reinforced and SMA reinforced specimens showed substantial increment in strength and ductility as compared to the unreinforced specimen. The steel reinforced specimen showed pinching and significant residual elongation in reinforcing bars while the SMA reinforced specimen did not. Both the experimental and numerical observations demonstrate the superiority of Cu-Al-Mn SMA bars to conventional steel reinforcing bars in retrofitting historical masonry constructions.

The effects of anti-phase domain (APD) boundaries on the magnetic properties of Ni2Mn(Ga0.5Al0.5) alloy were studied by magnetic measurements and transmission electron microscopic observations. The growth of APDs at 773 K followed the square root law for annealing time. While the saturation magnetization and the Curie temperature were hardly affected by the APD size, the magnetization curve in the specimen with smaller mean APD size became harder, caused by the pinning effect of the magnetic domain walls due to the APD boundaries.

National Natural Science Foundation of China [51031003]; Ministry of Education of China [707037]; Ministry of Science and Technology of China [2009DFA52170, 2009AA03Z101]; Fujian Provincial Department of Science Technology [2009I0024]; Xiamen City Departm

Magnetocrystalline anisotropy of the martensite phase was investigated in a single crystal of Fe44Mn28Ga28 shape memory alloy. It was found that the martensite phase of Fe44Mn28Ga28 alloy has a tetragonal distorted L21 structure, with a = 0.5368 nm and c = 0.7081 nm. An approximately single variant was obtained by thermomechanical treatment, and magnetization measurement revealed that the c-axis is the magnetic easy axis. The magnetocrystalline anisotropy constant Ku was determined to be 7.6 × 105 J m−3 at 300 K.

Recent progress in the development of thermodynamic and kinetic databases of micro-soldering alloys, which were constructed within the framework of the Thermo-Calc and DICTRA software, was presented. Especially, a thermodynamic tool, ADAMIS (alloy database for micro-solders) was developed by combining the thermodynamic databases of micro-solders with Pandat, a multi-component phase diagram calculation software program. ADAMIS contains 11 elements, namely, Ag, Al, Au, Bi, Cu, In, Ni, Sb, Sn, Zn and Pb, and can handle all combinations of these elements in the whole composition range. The obtained thermodynamic and kinetic databases can not only provide much valuable thermodynamic information such as phase equilibria and phase fraction, but also shows the kinetics and the evolution of microstructures when they are combined with some appropriate software programs and models, such as the phase field method and ADSTEFAN software. From the viewpoints of computational thermodynamics and kinetics, some technical examples were given to demonstrate the great utility of these databases for the applications in the development of micro-soldering materials. These databases are expected to be powerful tools for the development of micro-solders and Cu substrate materials, as well as for promoting the understanding of interfacial phenomena and microstructure evolution between solders and substrates in electronic packaging technology.

Phase transformations in the β (B2) phase of Co–21 and –23 at.% Al alloys were examined using transmission electron microscopy, energy dispersive X-ray spectroscopy and differential scanning calorimetry. The microstructures obtained from as-quenched specimens were found to be strongly affected by the quenching condition. While relatively thick sheet-specimens with a lower quenching rate showed bainitic plate precipitates with a fcc structure, a martensite-like structure was observed by optical microscopy in relatively thin specimens with a higher quenching rate. Regardless of the quenching condition, a spinodal-like microstructure composed of A2 and B2 phases was also detected and the A2 phase changed to a metastable hcp phase during further aging.

National Natural Science Foundation of China [51031003]; Ministry of Education of China [707037]; Ministry of Science and Technology of China [2009DFA52170, 2009AA03Z101]; Fujian Provincial Department of Science Technology [200910024]; Xiamen City Departm