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The phase equilibria of Sn-In-X (X=Ag, Bi, Sb, Zn), the most basic information necessary for the development of Pb-free micro-soldering alloys, were studied using the CALPHAD method. Thermodynamic analyses for describing the Gibbs energies of the constituent phases were made by optimizing the obtained data on the experimental phase diagrams, and such data in the literature, including data on thermochemical properties. The present results combined with the thermodynamic database which was recently developed by our group [I. Ohnuma et al., J. Electron. Mater. 28, 1164 (1999)] provide various information on phase equilibria such as liquidus and solidus surfaces, isothermal and vertical section diagrams, mole fractions of the phase constitutions, etc., and thermodynamic properties such as activity, heat of mixing, surface energy, viscosity, etc., in multi-component soldering alloy systems including the elements of Pb, Bi, Sn, Sb, Cu, Ag, Zn, and In. Typical examples for the phase diagrams and thermodynamic properties of Sn-In-X ternary systems are shown. The application of the database to the alloy design for Pb-free solders is also presented.

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.

Phase equilibria between the α(A3), α2 (D019), β(A2 or B2) and the γ(L10) phases in the Ti–Al base ternary systems were investigated over the temperature range 1000–1300°C. The tie lines and the phase boundaries were determined by electron probe microanalysis using multiphase alloys. It was established that almost all the elements except Zr tended to partition into the β phase rather than into the α, α2 or the γ phase, while Zr mostly partitioned into the γ phase. At 1000°C, in the equilibrium state between the α2 and the γ phases, V, Cr, Mo, Ta and W partitioned to the α2 phase rather than to the γ phase, whereas Mn, Fe, Co, Ni, Cu and Zr tended to concentrate into the γ phase. The partition coefficients for the alloying elements were only slightly dependent on their concentration. Based on these data, the relative stabilizing effects of alloying elements on the α, α2, β and γ phases are discussed.

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.

A thermodynamic assessment of the binary systems Ni-Pb, Cu-Pb and the ternary system Cu-Ni-Pb was carried out by the CALPHAD method. The Gibbs free energies of both the liquid and solid solution phases were described by subregular solution models. A set of parameters describing the Gibbs energies of the different phases in this ternary system was optimized using experimental phase diagram and thermodynamic information. Good agreement between the calculated phase diagrams and experimental data was obtained in the binary Ni-Pb, Cu-Pb and ternary Cu-Ni-Pb systems.

Ti–5.5Al–1Fe alloys consisting of the h.c.p.-α phase and the b.c.c.-β phase were investigated for microstructural changes during superplastic deformation at temperatures from 1050 to 1200 K. Observed changes occurred in two steps: (1) agglomeration of the β phase to grain boundaries perpendicular to the tensile axis and (2) subsequent increase of the β volume fraction. The β volume fraction after failure was found to increase with increasing deformation temperature. The first step was considered to be induced by the gradient of traction force acting upon grain boundaries. The second step was considered to be induced by stress concentration at grain boundaries of the α phase where the β phase was depleted by agglomeration to the perpendicular boundaries. The phase equilibrium under stressed condition was calculated by increasing the Gibbs energy of the α phase by 500 J/mol relative to that of the β phase. An excellent quantitative agreement was found between calculated results and experimental results of the β volume fraction and the Fe composition in each phase. The present work indicates that the phase transformation accompanied by diffusion can be induced by application of stress of the order of 100 MPa. This new type of stress-induced phase transformation can decrease the β transus temperature by more than 100 K.

Phase equilibria in the Fe-rich side of the Fe-Mn-S ternary system were analyzed on the basis of the thermodynamic analysis of the Fe-FeS, Fe-Mn, Mn-MnS and Fe-FeS-MnS-Mn systems. The Gibbs energy of individual phases was approximated by the sublattice model, assuming S to be interstitial atoms. Most of the experimental information was well reproduced by the present set of thermodynamic descriptions. The present analysis is useful for understanding sulfide formation during solidification, precipitation ip solids, and the cause of the so-called hot shortness in mild steels.

The effect of Co addition on the order-disorder transition temperature, Ms temperature, ductility, hardness and the shape memory properties of ductile Cu-Al-Mn shape memory (SM) alloys was investigated by differential scanning calorimetry (DSC), cold-rolling, and tensile test techniques. It was found that the addition of Co to the Cu-Al-Mn alloys stabilized the B2 phase and decreased the Ms temperature. In the Cu 71 Al 17 Mn 10 Co 2 alloy, the B2 to L2 1 ordering transformation was suppressed by quenching from 900°C and the retained B2 parent phase transformed to the 6M martensite. In several other alloys of this system, the presence of the CoAl (B2 type) precipitate phase was observed. Even though the CoAl precipitate caused a decrease in the cold-workability and the degree of elongation, it nonetheless improved the SM and pseudoelastic (PE) properties of the alloy by solid solution or/and precipitation hardening.

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.

Phase equilibria in the Fe-Cr-S system were analyzed on the basis of the thermodynamic evaluation of the Fe-FeS, Fe-Cr, Cr-CrS and Fe-FeS-CrS-Cr systems. The Gibbs energy of individual phase was approximated by the two sub-lattice model for describing the thermodynamic properties. Most of the experimental information was well described by the present set of thermodynamic parameters. In particular, the calculated liquidus surface in the Fe-rich portion and the solubilities of S in the fcc and the bcc phases were shown to be in excellent agreement with experimental results. Discrepancies observed in some experimental phase diagrams were explained on the basis of the calculated results.

Order-disorder, martensitic and magnetic transformations in the Ni 2 AlMn alloys have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The critical temperatures corresponding to the above transformations have been determined. It is shown that, on aging at low temperature, the parent phase structure changes from that of B2 to L2 1 by an ordering reaction causing the Ms temperature to decrease. The Curie temperature which has the highest value of about T c = 92°C at the Ni 2 AlMn composition decreases steeply on deviating from the stoichiometric composition. Two kinds of new martensite phases have also been detected in the as-aged Ni-21Al-25Mn and Ni-22Al-25Mn alloys.

The effect of alloying elements on the Ms temperature, ductility and the shape memory properties of Cu–Al–Mn ductile shape memory (SM) alloys was investigated by differential scanning calorimetry, cold-rolling and tensile test techniques. It was found that the addition of Au, Si and Zn to the Cu73–Al17–Mn10 alloy stabilized the martensite (6M) phase increasing the Ms temperature, while the addition of Ag, Co, Cr, Fe, Ni, Sn and Ti decreased the stability of the martensite phase, decreasing the Ms temperature. The SM properties were improved by the addition of Co, Ni, Cr and Ti.

Five polycrystalline Ni–Al–Fe alloys with 14–26 (at.)% Al and 16–26% Fe were made and heat-treated to have β and γ dual phases with from 87% to less than 1% of β phase and to exhibit M s temperatures at about 300 K. Depending on the β phase fraction and prestraining temperature, the alloys showed pseudoelastic strain recovery ratio from 1–2 up to 35% and shape memory strain recovery ratio from over 10–90% after prestraining by up to 1%. In the alloy with 87% β phase, the latter ratio reached 100% against 0.8% prestrain after a few cycles of shape memory training. Observed results were analyzed based on a model that assumed a simple linear mixture of the properties of the β and γ phases. The results of the analysis suggest that the γ phase after the training in certain conditions is almost elastic and thus acts as a bias spring.

A thermodynamic database for the calculation of phase diagrams in micro-soldering alloy systems, which include the elements Pb, Bi, Sn, Sb, Cu, Ag, and Zn has been developed using the CALPHAD method. The various thermodynamic parameters for describing the Gibbs energies of the different constituent phases have been evaluated by optimizing experimental data on phase boundary compositions and thermochemical properties such as activity, heat of mixing and enthalpy of formation. The resulting database provides the means whereby the liquidus and solidus surfaces, isothermal and vertical section diagrams, phase percentages and the mole fraction of the phase constitutions etc., in multi-component soldering alloys can be readily calculated. Related information such as the surface tension and viscosity of the liquid phase can also be predicted, thus rendering the database as a valuable tool for developing leadbearing and lead-free solders.

Temperature dependence of the self-diffusivities in B2-type intermetallic compounds has been investigated. The self-diffusivities plotted against the inverse of temperature normalized by the solidus temperatures, T f , show that the activation energy, Q, is related to T f by Q = (19 ± 8)RT f B2 J/mol, and the pre-exponential factor, D 0 , is in a certain range, D 0 = 10 -2 ∼ 10 -6 m 2 s -1 . How-ever, the results of CuZn, which have the order-disorder transformation below solidus temperature, are out of range of a large number of data. The hypothetical T 0 temperature between the ordered and liquid phases, T 0 B2 , is evaluated from thermodynamic consideration, which reveals that the temperature dependence of the self-diffusivity of CuZn replotted against T 0 B2 /T shows a tendency similar to that of other B2-type intermetallic compounds. The relationship between the activation energy of self-diffusion and the enthalpy of fusion of the ordered phase is also discussed.

The effects of additions of C, Si, Ti, and Al on the morphology of (Mn,Cr)S inclusions in Fe-15Cr-1Mn-0.3S (mass%) and Fe-15Cr-0.5Mn-0.3S base alloys have been investigated using optical and scanning electron microscopy. Three types of (Mn,Cr)S inclusions morphology have been observed (1) globular-shaped sulfide, (2) rodlike (Mn,Cr)S, and (3) angular (Mn,Cr)S, depending on the Mn content and the presence of additional elements. The formation mechanisms of (Mn,Cr)S inclusions are discussed on the basis of phase diagram information. It is shown that (a) the globular (Mn,Cr)S inclusions observed in 1% Mn alloys are formed through the metastable monotectic reaction, (b) the rodlike (Mn,Cr)S observed on the addition of Ti and Al are the products of a stable eutectic reaction that proceeds by nucleation of (Mn,Cr)S crystals by the high-melting-point particles such as TiN and Al2O3, (c) the globular (Mn,Cr)S morphology observed in 0.5% Mn base alloys is the result of a stable monotectic reaction that proceeds through the formation of the low-melting globular (Mn,Cr)S inclusions, and (d) the addition of C and Si promote the stable eutectic reaction by lowering the melting point of Fe-rich solid solution.

A thermodynamic calculation of the Al-Mn binary system that takes into account recent experimental results and includes five intermetallic compounds and all the solid-solution phases is presented. The Gibbs energy of the body-centered cubic (bcc) phase has been described on the basis of the two-sublattice model that includes the second-order A2/B2 ordering reaction as well. A consistent set of optimized thermodynamic parameters has been arrived at for describing the Gibbs energy of each phase in this system leading to a better fit between calculation and experiments.

The pressure derivative of the reverse martensitic transformation temperature d T R /d p of Ni 50 Mn 36 Sn 14 has been obtained from the results of temperature dependence of initial permeability under various pressures. The value of d T R /d p is found to be +2.4 K/kbar. The pressure change of the Curie temperature is also studied.

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).

Phase equilibria and ordering reactions in the bcc aluminides of the Co-Cr-Al systems over a temperature range of 1000-1350 C have been investigated mainly by the diffusion couple method. The compositions of the γ (Al: fcc-Co). β (B2: CoAl), α (A2: bcc-Cr) and a (sigma phase: D8 b ) phases in equilibrium, and the critical boundaries of the A2/B2 continuous ordering transition in the bcc phase region have been determined. It is shown that both continuous and discontinuous A2 to B2 phase ordering transitions and elliptically shaped A2+B2 miscibility gap islands with wide composition ranges exist in these systems in isothermal sections. The phase equilibria involving the γ, β, α and σ phases are presented and stability of the ordered bcc aluminides is discussed.

The morphology of TiS in steels formed during solidification and the modification of this morphology by the addition of alloying elements of Mn, Zr, Cr and C were investigated by means of optical and scanning electron microscopy. It is shown that the morphologies can be classified into three types: (i) globular (ii) rod-like and (iii) plate-like sulfides. The morphology of TiS in the Fe-0.5%Ti-0.3%S base alloy is the rod-like sulfide while additions of Mn and Zr change the morphology from rod-like to globular. The tendency of enrichment of alloying elements in the sulfide is in the order Zr>(Ti)>Mn>Cr, which is similar to that in MnS. The formation of different TiS morphologies is discussed based on phase diagram information.

The phase equilibria and ordering reactions in the composition region up to 50 at.% Al have been investigated in the Ni–Mn–Al and Co–Mn–Al systems at temperatures in the interval 850–1200°C mainly by the diffusion couple method. The compositions of the γ (A1: fcc-Ni, -Co, γ-Mn), γ′ (L12: Ni3Al), β (B2: NiAl, CoAl, NiMn), β-Mn (A13: β-Mn type), δ-Mn (A2: bcc-Mn) and e (A3: hcp-(Mn, Al)) phases in equilibrium and the critical boundaries of the A2/B2 continuous ordering transition in the bcc phase region have been determined. It is shown that in the Mn-rich portion of the ternary systems both continuous and discontinuous A2 to B2 ordering transitions exist. The A2+B2 two-phase region in the isothermal sections has a lenticular shape and exists over a wide temperature range. The phase equilibria between the γ, γ′, β, β-Mn, δ-Mn and e phases are presented and the stability of the ordered bcc aluminides is discussed.

The outline of the CALPHAD method, which has been developed to alleviate the difficulty in obtaining phase diagrams by experiments alone, is presented. This method enables calculation of stable and metastable phase equilibria, as well as thermodynamic properties such as activity, enthalpy, driving force, and so on. Some examples of the calculated phase diagrams, obtained by applying the CALPHAD method are reviewed, in connection with the design of their microstructures.

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.

Ordering and phase separation in {alpha}-Fe alloys of the Fe-Al-Ti system have been investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and electron-probe microanalysis (EPMA). The results indicate that the partial replacement of Fe with Ti in the Fe-rich Fe-Al binary alloys results in drastically stabilizing the B2 (FeAl) and D0{sub 3} (Fe{sub 3}Al) phases and increasing the A2-B2-D0{sub 3} successive order-disorder transition temperatures. It is confirmed that there are two kinds of phase separations of the BCC phase, (A2 + D0{sub 3}) and (B2 + D0{sub 3}) in the composition range below 25 at.% Al. The width of the two-phase region drastically increases with decreasing Al composition. The two-phase regions close at ternary tricritical points. Calculations of BCC phase equilibria have been performed with the cluster variation method (CVM) using the irregular tetrahedron approximation. First and second nearest pair interactions as well as tetrahedron interactions are taken into account. Starting from binary and ternary phase equilibria the numerical values of these interactions have been determined and an excellent agreement between calculation and experiments was obtained.

Results pertaining to the phase equilibria between the phases α (A1), β (A2, B2 or L21(D03)) and γ (γ-bronze type), and the two-stage order–disorder transition and decomposition reaction A2–B2–L21 in the ternary system Cu–Al–Mn are reported. Ternary isothermal section diagrams at 800, 700, 600 and 550°C have been constructed using Energy Dispersion X-ray Spectrometry (EDX) analysis results, and it is found that the β single-phase region in the Cu–Al system is very significantly widened on increasing the Mn content. The critical temperatures (Tc) of the A2–B2–L21 order–disorder transitions, determined by Differential Scanning Carolimetory (DSC) analysis are found to be strongly dependent on the Al content rather than on the Mn content. It is confirmed by DSC measurements and TEM-EDX analysis that a miscibility gap island between Cu3Al and Cu2AlMn phases exists in the L21 phase region. The second order ordering reaction between D03 and L21 structures has also been detected by X-ray diffraction. The stability of the bcc β phase is discussed in terms of atomic and magnetic ordering.

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 phase equilibria in the Cu–Al binary system over the temperature range 500∼1000°C and the composition range 15∼60 at.% Al have been determined using diffusion couple technique, differential scanning calorimetry (DSC) and high temperature X-ray diffraction (XRD) methods. While the results from this study pertaining to the phase equilibria α/β and ϵ1(ϵ2)/liquid are in agreement with those reported in previous works, significant differences have been found between the earlier results and the present work in the composition range 25∼40 at.% Al. They are: (a) In the composition range 32∼38 at.% Al only a second order reaction, γ1 (D83)→γ0 (D82), is seen to occur and not a two-phase equilibrium γ0/γ1 reaction as reported before (b) The β0 phase is absent at high temperature near 1000°C and compositions near 30 at.% Al. (c) The equilibrium eutectoid γ0→β+γ1 and peritectoid γ0+ϵ1→γ1 reactions do not occur in this system.

The giant magnetoresistance of Cu–Mn–Al melt-spun ribbons with compositions along the Cu3Al–Cu2MnAl tie line, was investigated. X-ray diffraction and TEM observations revealed that the as-spun ribbons have either an L21 or a D03 type structure. The Cu–15Mn–25Al ribbon exhibited the highest MR ratio of 1.1% (measured at room temperature) among the as-spun ribbons. Two phase decomposition into the Cu3Al and Cu2MnAl phases, occurs after heat treatment within the miscibility gap, and the coherent two phase microstructure grows with increasing heat treatment temperature. This results in an increase in the magnetization and the MR ratio of the ribbons. The Cu–10Mn–25Al ribbon showed the highest MR ratio of 3.9% (measured at room temperature), after a heat treatment at 423 K for 6 h. From the phase diagram, the volume fraction of Cu2MnAl phase in this ribbon is 35.7%, which corresponds to the optimum volume fraction of ferromagnetic phase reported in other granular type GMR materials. The high MR ratio region is narrow and closely related to the two phase decomposition area of Cu–Mn–Al.

Effect of titanium addition on the size and dispersion of MnS inclusions in Fe-0.1 C-1 Mn-0.025(mass%) base alloys has been investigated by microscopy. Titanium addition brings about a marked decrease in the size of MnS inclusions which are otherwise large and globular in Ti-free specimens. The formation mechanism of MnS inclusions is discussed on the basis of phase diagram information and thermodynamics of particle engulfment during solidification. It is shown that the reduction in size of the MnS particles consequent on Ti addition is directly the result of successive nucleation events involving (Ti,Mn)O and MnS at the solid/liquid interface of iron.

The effect of alloying elements on the solubility of Cu in solid Fe has been investigated by using solid-liquid diffusion couples. An addition of Co, Ni, and Al results in an increase of the solubility of Cu, while that of V, Cr, Mn, Si, and Sn decreases the solubility. Thermodynamic calculation of the solid/liquid phase equilibria in the Fe-Cu-X ternary system has been also performed, where a set of thermodynamic parameters of solid and liquid phases has been evaluated. Furthermore, the equation that describes the change of the solubility of Cu in solid Fe with an addition of alloying elements has been derived by thermodynamic analysis of these experimental values.

La partition des elements (V, Nb, Ta, Cr, Mo, W, Hf, Zr, Mn, Fe, Co, Cu, Al, Si) entre les phases γ(L1 2 :Ni 3 Al), η(DO 24 :Ni 3 Ti), β 1 (B2:NiAl), β 2 (B2:NiTi) and H(L2 1 :Ni 2 AlTi) dans les systemes a base de Ni-Al-Ti a ete etudiee, a 1100°C, principalement par la methode de diffusion couplee. Il est confirme que: 1) dans le cas des equilibres entre les phases H et β 1 et H et β 2 , les elements ayant un grand volume atomique tels que Ta, Nb et Hf preferent migrer vers la partie riche en Ti de la phase H, 2) dans le cas des equilibres entre les phases H, γ et η les elements c.c. tels que Zr, V and Cr prefere se concentrer dans la phase H plutot que dans les phases γ ou η et 3) dans le cas des equilibres entre les phases γ et η, les elements presentant un grand volume atomique tels que Ta, Zr, W, Hf, Nb et Mo preferent migrer vers la phase η plutot que vers la phase γ. Ceci suggere que le facteur de taille et la stabilite du reseau des elements ont un effet significatif sur la stabilite relative de ces phases intermetalliques. Ces donnees sur la partition des elements allies au systeme de base Ni-Al-Ti sont la preuve de leur utilite lors de la conception des super-alliages a base de nickel.

Zener-Smith proposed the original relation R = 4r 3f v in 1948, where R and r are the mean radii of the matrix grains and dispersed particles, and f v is the volume fraction of dispersed particles. They derived the relation under the assumption that the configuration of the grain boundary was independent of particle distribution. In the present work a modified relation R=4r/3f 2/3 v has been obtained by assuming that (1) the grain boundary is roughened by particle pinning, and (2) the amplitude of the roughness is λ/2, where λ is the inter-particle distance. Experimental data on the radii of austenite grains and the dispersed cementite particles in high C high Mn steels are shown to agree well with the modified relation.

Phase separation behavior of Co-Mo thin films and magnetic anisotropy energy of Co-Mo and Co-Mo-Cr thin films deposited on Cr(112)//MgO(110) single crystal substrates have been studied by using an analytic transmission electron microscope and a vibrating sample magnetometer. The results show that the phase separation does happen in the Co-Mo thin films, resulting in Mo-rich phase surrounding Co-rich magnetic grains, similar as that in the Co-Cr system. However, the Mo-rich phase still shows the ferromagnetic characteristic at room temperature due to its not so high Mo content. The first order anisotropy constants of the Co-Mo thin films are about double that of the Co-Cr thin films in the composition range of 4.0-14.0 at.%Mo (or Cr). With the addition of Cr into the Co-8.7 at.%Mo thin film, the magnetic anisotropy constants show no obvious deterioration, but it results in the increase of anisotropy field.

Structural and optical anisotropies have been investigated in some chalcogenide glasses exposed to illumination of linearly polarized light. X-ray diffraction patterns of illuminated As2S3 manifest a structural modification at ∼1 Å-1. Photoinduced birefringence in As2S3 becomes maximal at some temperature, which is higher for illumination with a lower photon energy. The photoinduced birefringence becomes greater in the order of As2Se3, As2S3, and Se, which is the same with the order of the natural birefringence in the corresponding crystals. These observations suggest that the photoinduced anisotropy arises from orientation of quasicrystalline clusters. The model is compared with photoinduced anisotropies observed in other materials.

The characteristics of the B2(β) to L10(β′) martensitic transformation in NiAl base alloys containing a small amount of third elements have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It is found that in addition to the normal Ll0 (3R) martensite, the 7R martensite is also present in the ternary alloys containing Ti, Mo, Ag, Ta, or Zr. While the addition of third elements X (X: Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta, W, and Si) to the binary Ni64Al36 alloy stabilizes the parentβ phase, thereby lowering the Ms temperature, addition of third elements such as Co, Cu, or Ag destabilizes theβ phase, increasing the Ms temperature. The occurrence of the 7R martensite structure is attributed to solid solution hardening arising from the difference in atomic size between Ni and Al and the third elements added. The variation in Ms temperature with third element additions is primarily ascribed to the difference in lattice stabilities of the bcc and fcc phases of the alloying elements.

Ductile shape memory (SM) alloys of the Cu-AI-Mn system have been developed by controlling the degree of order in the β phase. Additions of Mn to the binary Cu-Al alloy stabilize the β phase and widen the single-phase region to lower temperature and lower Al contents. It is shown that Cu-Al-Mn alloys with low Al contents have either the disordered A2 structure or the ordered L21 structure with a lower degree of order and that they exhibit excellent ductility. The disordered A2 phase martensitically transforms to the disordered Al phase with a high density of twins. The martensite phase formed from the ordered L21 phase has the 18R structure. The SM effect accompanies both the A2 → Al and L21 → 18R martensitic transformations. These alloys exhibit 15 pct strain to failure, 60 to 90 pct rolling reduction without cracking, and 80 to 90 pct recovery from bend test in the martensitic condition. Experimental results on the microstructure, crystal structure, mechanical properties, and shape memory behavior in the ductile Cu-AI-Mn alloys are presented and discussed.

A simple thermodynamic calculation to assess the effect of grain size on grain boundary segregation has been performed. It is shown that in binary alloys when the bulk solute content is small, segregation increases with increasing grain size. In ternary alloys, however, intergranular segregation depends both on the magnitude of segregation free energy and the bulk concentrations of the solute. It is pointed out that grain size could play an important role in the segregation phenomena, not only in metallic but also in ceramic systems.

The phase equilibria in the binary MnAl system have been investigated over the temperature range 800 to 1200 °C and the composition range 50 to 80 at.% Mn using a combination of diffusion couple techniques, optical metallography. X-ray diffraction, and differential scanning calorimetry. The results show that: (i) the e/δ − Mn phase boundary is located at approximately 72 at.% Mn, (ii) the e phase region is wider and extends to higher Mn content than that reported before, and (iii) the eutectoid reaction (δ-Mn → e + β-Mn) occurs at approximately 1040 °C, i.e. at a temperature higher than that previously reported (970 °C). While the results from this study on the e/γ and e/β-Mn phase equilibria are in satisfactory agreement with the data of previous workers, the results on the e/δ-Mn phase equilibrium differ from those reported previously. It is explained that this discrepancy may be due to the presence of the previously undetected transformation from the e to the β-Mn phase on quenching, which occurs only in the e phase alloys with Mn content over 58 at.%.

Results of investigations on the microstructural features of β(B2) + γ′ (L12) two-phase NiAlFe alloys fabricated through various thermomechanical processes are reported. It is found that three types of β + γ′ structures: blocky, lamellar and widmanstatten structures, are formed when alloys quenched from high temperatures are reannealed at 800 °C. The formation of the blocky structure is brought about by the following successive reactions, the β → β′(L10) martensitic transformation, the β′ → Ni5Al3 (Pt5Ga3 type) ordering reaction and the Ni5Al3 → β + γ′ transition similar to a discontinuous transition occurring during heating up to 800 °C. On the other hand, the lamellar structure results from the Ni5Al3 → γ′ transition and a heterogeneous precipitation of the β phase on the boundaries between the γ′ variants after the formation of the Ni5Al3 from the β′ phase. It is also observed that the mechanical properties are affected by the type of microstructures present. These results suggest that the NiAlFe dual-phase alloys are amenable to microstructural control through thermomechanical treatments to realise optimum mechanical properties as in the case of Fe base alloys. Key words: Nickel aluminides, microstructural control, martensitic transformation, order-disorder transition, lamellar structure

Temperature dependence of the magnetic microstructure in a ferromagnetic shape memory alloy Ni51Fe22Ga27 has been studied by electron holography, by which the distribution of magnetic flux is clearly imaged. Although the magnetic flux is quite even in the parent phase near room temperature, it undergoes considerable modulation when the temperature approaches Ms (martensitic transformation start temperature). The magnetization distribution in the martensite appears to be inherited from that in the parent phase. The observations shed further light on the precursor phenomenon of martensitic transformations.

The phase stability and magnetic properties of the half-metal-type Co2Cr1−xFexAl alloy system were investigated. It was found that the occurrence of two-phase separation is unavoidable in a concentration range of less than x=0.4, leading to deviation of the saturation magnetic moments from the generalized Slater–Pauling line. The L21-type phase becomes stable in a concentration range of more than x=0.7, where no half-metallic behaviors are present. Consequently, it is concluded that the most favorable concentration for applications to spintronic devices is located around x=0.4 in Co2Cr1−xFexAl alloys having the B2-type phase.