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The high thermal conductivity, lightweight, and low cost of aluminum (Al) make it a promising substrate material for high power electronic and photonic packages and housings. It is particularly attractive for aerospace and space applications due to its lightweight. A main challenge for these applications is poor bondability. The native aluminum oxide (Al2O3) prevents aluminum from bonding by using popular die-attach materials such as solders. Zincating process is often needed to dissolve the Al2O3 layer and deposit a protection zinc layer which provides a basis for subsequent metallization or soldering process. However, the zincating and metallization processes could increase the processing cost and bring more reliability issues. In this research, a novel Ag foil bonding technique has been developed to bond Ag foils directly to Al substrates to produce Ag-cladded Al substrates. Two Ag-Al bonding processes are developed: solid-state and eutectic. Subsequently, Si chips are bonded to the Ag-cladded Al substrates using solid-state process at 300 °C without any additional die-attach material. For the Ag-Al bonding processes, no surface treatment is applied to Al substrates to remove the native Al2O3 layer. In the Ag-Al soli-state bonding process, Ag and Al atoms inter-diffused through the thin Al2O3 to react and form Ag2Al and Ag3Al compounds. In the Ag-Al eutectic bonding process, Ag2Al+(Al) eutectic structure forms at the Ag/Al interface without Ag3Al compound formation. The native Al2O3 layer, a potential fracture path, is broken into pieces during eutectic reaction and possibly dispersed into the eutectic structure. Shear test results of Si/Ag/Al joint samples far exceed the military criterion (MIL-STD-883H method 2019.8). The Si/Ag/Al structures break either along the Ag/Al interface or within the Si chip. With the advantages of high thermal conductivity, high reliability, lightweight, and process simplicity, the Ag-cladded Al structures should be highly valuable for applications in packages and housings where lightweight and high heat-conducting are necessary.

Aluminum-silicon alloys contain coarse, acicular Si plates that are detrimental to material properties. However, trace additions of Sr have been found to modify the eutectic Si to have a fine, fibrous structure, which improves elongation, strength, and thermal conductivity. In this study, in-situ neutron diffraction was conducted during the solidification of unmodified and Sr-modified binary Al-6 wt.% Si to obtain a novel view of the modification mechanism. Neutron diffraction intensity data was collected at temperatures ranging from 660 °C to 200 °C and was integrated to create fraction solid curves for the individual Al and Si phases in each alloy. Scanning electron microscopy revealed that the Sr-modified alloy microstructure contained many micro-sized Al-Si-Sr intermetallics scattered about the eutectic regions at the Al-Si interfaces, and a few Si flakes close to some β-(Al,Si,Fe) intermetallics, suggesting important interactions between both the Fe-bearing phases and Sr in the solidification of eutectic Si. Comparing the isolated phase evolution temperatures for each alloy revealed in-situ for the first time that Sr suppresses the nucleation temperatures of both the eutectic Al and eutectic Si phases by several degrees. Accordingly, the eutectic reaction was observed to evolve at a higher primary Al solid fraction with Sr modification.

Eutectic high-entropy alloys are potential replacements of structural alloys, due to their microstructure and properties. In this work, CoCrFeNiTax (x = 0.1, 0.2, 0.3, 0.395, 0.4 and 0.5, x value in molar ratio) eutectic high-entropy alloys were produced by arc melting technique. Two phases, FCC solid solution and Laves phase, are identified in the alloys. The alloys are transformed from hypoeutectic to hypereutectic solidification by increasing Ta content. CoCrFeNiTa0.395 eutectic high-entropy alloy exhibits an ultrahigh yield strength of 1.4 GPa, while CoCrFeNiTa0.3 hypoeutectic high-entropy alloy shows a compressive strength of 2.5 GPa and a considerable fracture strain of 44%. Such remarkable strengthening effects are shown to result from the ideal combination among the second-phase, solid solution, and boundary strengthening.

Dissimilar transient liquid phase joints were fabricated between Ni-based GTD-111 and Co-based FSX-414 superalloys using a 50 μm thick amorphous Ni Si B interlayer. The athermally solidified zone in the middle of joint contained the ternary eutectic of γ/Ni3B/Ni6Si2B and few amounts of Ni3Si. The amount of eutectic phase was decreased by increasing the bonding time. The complete isothermal solidification was obtained at the joining time of 100 min. The completion of isothermal solidification was controlled by several factors including the diffusion of Si and B from the bonding zone into the base metals, the diffusion of Ti, Al, Co and Cr from the base metals into the bonding zone and proportional re-distribution of them throughout the joint. The width of bonded zone (about 80 μm) was greater than the thickness of interlayer due to the coupled diffusion and dissolution phenomena. After the homogenization heat treatment, an increase of 34% in shear strength of the joint was observed due to the uniform distribution of strengthening precipitates across the bonding area.

A series of CoCrFeMnNiPdx (x = 0.2–2 at.%) eutectic high entropy alloys (EHEAs) were prepared and analyzed to show the alloying effect of Pd on the microstructure and phase constituents. It was found that the microstructure as the increase of x changes from the divorced eutectic to the coarse granular divorced eutectic around which are the fine lamellar dendrite eutectic and then to the seaweed dendrite eutectic. Hitherto, such seaweed eutectic dendrite was rarely reported in either high entropy alloys or conventional alloys. Specifically, a multimodal grain size distribution including several hundred microns for the eutectic-dendrite, several microns for the coarse granular eutectic, several hundred nanometers for the fine lamellar eutectics and the lath-shaped microstructures in the intermetallic phases, and even several nanometers for the nano-twins was observed. Since the CoCrFeNiMnPdx EHEAs obey all the design rules of HEAs with a single solid-solution phase but exhibits a two-phased microstructure, mere consideration of average physical properties of constituent elements was concluded to be not sufficient to the design of HEAs. The present work is not only enrichment of current EHEA systems but also of importance to the design of HEAs.

A series of Al-40Zn-5Si alloys with different additions of Eu were prepared by permanent mold casting. The nucleation phenomenon incorporating the modification of silicon phase was investigated by using the synchrotron radiation imaging technology, scanning electron microscopy, electron probe microanalysis and high resolution high-angle annular dark-field scanning transmission electron microscopy. It was found that the primary phase was α-Al dendrites and the pre-eutectic Si particles were precipitated continuously at the front of the solid/liquid interface in Al-40Zn-5Si alloys. The nodular pre-eutectic Si particles were observed when the Eu addition was 0.3%. Meanwhile, a flake-to-fibrous transition of eutectic Si was also observed. The needle-like eutectic Si crystals were seen to shoot out from the vicinity of primary α-Al dendrites into melt with high velocities leading the irregular eutectic interface in the unmodified Al-40Zn-5Si alloy. However, the eutectic grains with smooth interfaces nucleated mainly near primary or secondary α-Al branches in 0.3% Eu-modified Al-40Zn-5Si alloy. The eutectic grains began to nucleate on the nodular pre-eutectic Si particles when the α-Al surface reached so close to them. The formation of nodular pre-eutectic Si particles was attributed to the adsorption of Eu atoms along the growth direction of Si and at the intersection of Si twins. This is fully consistent with the well-known poisoning of twin plane re-entrant edge (TPRE) and the impurity induced twinning (IIT) modification mechanisms proposed for interpreting the modification of eutectic Si.

We report on a novel approach to design typical ultrafine lamellar eutectic structure in bimodal alloys fabricated by semi-solid sintering (SSS) of a eutectic mixture. In our work, ultrafine lamellar eutectic structure was implemented by controlling the phase composition of eutectic reaction, and consequently by regulating the structure of eutectic reaction-induced liquid phase through varying component number. Microstructure analysis indicate that although all SSSed alloys have the same three phase constitutions of bcc β-Ti, bcc Ti(Fe, Co), and fcc Ti 2 (Co, Fe), the morphology and distribution of the eutectic structure transforms from limited length and minor quantity, to partial fine alternating bcc β-Ti and bcc Ti(Fe, Co) lamellae, and further to typical complete ultrafine alternating continuous lamellae in the SSSed ternary Ti-Fe-Co, quaternary Ti-Fe-Co-Nb, and quinary Ti-Fe-Co-Nb-Al alloys. Interestingly, the SSSed Ti-Fe-Co-Nb-Al alloy presents a novel bimodal microstructure of coarse fcc Ti 2 (Co, Fe) surrounded by an ultrafine lamellar eutectic matrix containing ultrafine bcc β-Ti and bcc Ti(Fe, Co) lamellae. This bimodal microstructure exhibits ultra-high yield strength of 2050 MPa with plasticity in compression of 19.7%, which exceed published values of equivalent materials. Our results provide a novel pathway for fabricating new-structure metallic alloys for high-performance structural applications.

(Co 76 Sn 24 ) 100- x Nb x ( x = 0, 0.5, 0.8, 1.0) eutectic alloy melts were solidified at small undercooling for investigating the effect of Nb addition on microstructural development. With increasing Nb content, the solidification interface transits from eutectic seaweed ( x = 0) to eutectic dendrite ( x = 0.5) as a response to the change in the anisotropy of interfacial energy. Coupled eutectic growth can no longer be maintained within the main stems at x = 0.8 because the enrichment of Nb in the liquid ahead of the interface causes a significant difference in growth velocity between the α-Co and β-Co 3 Sn 2 phases and, as such, Co 3 Sn 2 doublons form. For x = 1.0, the difference in growth kinetics between the two eutectic phases is so large that divorced eutectic growth takes place on a large scale. Letting the undercooling prior to solidification increase, the eutectic interface morphology of (Co 76 Sn 24 ) 99.5 Nb 0.5 eutectic alloys returns from dendritic pattern back to factual seaweed pattern at more than 38 K undercooling and then transits to compact seaweed pattern at more than 181 K undercooling. The eutectic growth velocity slightly increases at low and intermediate undercooling but obviously decreases at large undercooling due with Nb addition.

Sn-34 wt%Bi, Sn-34 wt%Bi-2wt%Ag and Sn-34 wt%Bi-0.7 wt%Cu alloys have been directionally solidified (DS) under a broad range of solidification cooling rates. Microstructures have been characterized with emphasis on both eutectic growth and precipitation of Bi within the β-Sn dendritic matrix. The eutectic growth, for all alloys examined, is shown to be associated with the coexistence of coarse and fine lamellar structures with different length-scale of lamellar spacing (λ). Experimental growth relations of λ vs. the cooling rate have been proposed. The length-scale of the lamellae in the fine eutectic ranges from 0.8 to 2.5 μm while in the coarse eutectic from 1.8 to 4.0 μm. Taking as reference the Sn-Bi alloy, both the spacing between Bi precipitates (λp) and the fine eutectic spacing (λfine) increase with Cu and Ag additions, whereas λcoarse remains roughly unaltered. Both ternary Sn-Bi-Ag and Sn-Bi-Cu alloys are shown to have worse distributions of both lamellae in the fine eutectic and of precipitates within Sn-rich dendrites, which resulted in decrease in hardness.

This study is focused on the effect of boron addition, in the range of 0.011 wt% to 0.048 wt%, on the solidification behavior and microstructure of U720Li alloy. It has been found that boron increased the eutectic (γ + γ′) precipitation significantly, while reduces the formation of η phase and Zr-rich particles precipitated in front of the eutectic (γ + γ′) obviously. Boron greatly retards the γ matrix solidification which is verified by the fact that it markedly reduces the ’segregated area’ around the final liquid pool or eutectic (γ + γ′). Based on this phenomenon, boron is assumed to form a layer at the solid/liquid interface and inhibits the attachment of atoms to attach on or jumping off the solid front, and hence lowers the γ matrix solidification rate. Boron increases the eutectic (γ + γ′) precipitation mainly by retarding the γ matrix solidification, which resulting in deeper undercooling and more eutectic forming elements such as Ti left in the residual liquids. Subsequently, boron reduces the η-Ni 3 Ti and Zr-rich phase formation because the increasing eutectic (γ + γ′) precipitation favors the consumption of Ti and dissolving Zr in γ′ phase.

The influence of small amount of Ca addition on the microstructures and mechanical properties of three near-eutectic Mg-x Li (x = 6.8, 7.5, 8.4 wt. %) binary alloys under rapid solidification condition by using Copper-mould Suction Casting technique were investigated. The resultant microstructures were very distinct from those by conventional gravity casting technique in the morphology, grain size and the volume fraction of α-Mg phase. Mechanical properties of the Ca-modified Mg-x Li binary alloys were significantly enhanced. More interestingly, a eutectic growth mode transition from their regular divorced eutectic growth to the regular coupled eutectic structure was induced in Mg-8.4Li alloy via Ca addition. The eutectic transition mechanisms in three Mg-x Li alloys by Ca addition were discussed in terms of the freezing rate, Mg2Ca particle segregation, the relative volume fraction of α-Mg phase.

Directionally solidified Al 2 O 3 /Er 3 Al 5 O 12 (EAG) eutectic in situ composites are prepared by laser floating zone melting (LFZM) to investigate the solid–liquid interface characteristic and growth rate range under non-equilibrium solidification conditions. The solid–liquid ( S–L ) interface is in situ obtained by rapidly quenching, and its microstructure morphology and primary phase based on different eutectic compositions are analyzed. In stable growth zone, the composite presents typically “Chinese script” (CS) irregular eutectic structure consisting of interpenetrated Al 2 O 3 and EAG phases, but in quenched region the regular eutectic lamellae and CS structure are coexisted. Primary Al 2 O 3 phase in hypoeutectic composition is found both in S–L interface front and quenched region. Different from the stable growth zone, in quenched region as the solidification rate increases, the eutectic lamellae spacing does not show obvious decrease. The minimum eutectic lamellae spacing is refined to about 200 nm when the solidification rate is increased up to 100 μm/s. On the basis, according to the Jackson-Hunt (J-H) model, the maximum solidification rate in quenched region is calculated to be smaller than 1.26 × 10 3 μm/s, and the undercooling degree is 4.15 K.

Based on surveying the existing binary phase diagrams with eutectic points, a strategy of designing eutectic high entropy alloys (EHEAs) with desired high strength and ductility is proposed. Based on the computer-aided thermodynamic calculations, the pseudo eutectic binary alloy system of CoCrFeNiNbx (x = 0.1, 0.25, 0.5 and 0.8) was designed. The experimental results show that the eutectic alloys are composed of a ductile face centered cubic (FCC) phase and a hard Laves phase with fine laminar structures. The designed alloys show excellent integrated mechanical properties of ductility and strength. For the CoCrFeNiNb0.5 alloy, the compressive fracture strength and strain can reach above 2300 MPa and 23.6%, respectively.

A new mathematical model was developed to predict the average eutectic spacing under high pressure solidification. The model can be used in the binary alloy system which contains solid solution and intermetallic compound. Following this model, the change of eutectic spacing under high pressure can be predicted if the volumetric conditions of the phases are known. Application of the model to the binary Mg-20.3wt.%Al solidified under different pressure was conducted. It was found that the results predicted by this model show an excellent agreement with the eutectic spacing of Mg-20.3wt.%Al alloy solidified under high pressure. And during experiment, an ultimate pressure was found, the microstructure tends to grow as divorced eutectic when the solidified pressure is higher than this ultimate pressure, the formula is not applicable.

The Influence of the ternary alloying element Cu on eutectic nucleation in an Al-10 wt.%Si alloy in unmodified and Sr-modified conditions was studied. Cu additions had a relatively minor effect on the unmodified eutectic nucleation frequency. In Sr-modified Al–Si alloys where the nucleation frequency of the eutectic grains is very low compared to the unmodified alloys, the addition of Cu significantly increased the nucleation frequency. Further increases in the Cu concentration resulted in a continuous increase in the number of eutectic grains and an associated decrease in their size. It is proposed that constitutional supercooling plays an important role in promoting the nucleation of eutectic grains ahead of the solidifying interface especially in the case of Sr-modified Al–Si alloys.

A novel die-attachment method is demonstrated through quasi-transient liquid-phase bonding using Sn-plated Zn sheets. The bonding temperature can be decreased to 250 °C, which is ∼100 °C lower than that for typical Zn–Sn high-temperature solders. The bonded interface consists of primary α-Zn and Sn–Zn eutectic phases, and the microstructure can be controlled according to the diffusion velocities of metals. The high die-shear strength exceeding 30 MPa from the controlled microstructure is superior to typical Pb–5Sn solders strength around 20 MPa.

Containerless solidification of hypoeutectic Al–50%Ge and eutectic Al–51.6%Ge alloys has been carried out with an ultrasonic levitator. The undercooling of the two alloys achieves 112 K(0.16 T L ) and 95 K(0.14 T E ), respectively. In both of these alloys, (Al) phase always nucleates and grows primarily in Al–51.6%Ge eutectic alloy at small undercoolings. When the undercooling is larger than 80 K, competitive nucleation between (Al) and (Ge) phases occur and (Ge) solid solution can nucleate as primary phase. The (Al)+(Ge) eutectic composed of branched (Ge) phase and interspacing (Al) phase is much refined under ultrasonic levitation condition. Divorced eutectic of the two phases is obtained near the surface of acoustically levitated Al–50%Ge hypoeutectic alloy.

The phase formation behavior during solidification of Mo–Si–B ternary alloys in the Mo-rich compositional portion was experimentally examined with special attention to the Moss–T2 and Mo–Mo3Si–T2 eutectics. Primary phases observed in this study were in very good agreement with those shown in a liquidus projection thermodynamically calculated by Yang and Chang. A Mo–9.5Si–14.2B (at.%) alloy, which has a composition close to the Moss–T2 eutectic point, had two specific microstructural areas consisting of a superfine Moss–T2 eutectic and a fine Moss–Mo3Si–T2 three-phase eutectic. A Mo–19.1Si–6.5B alloy aimed to the Moss–Mo3Si–T2 eutectic point also had a fine Mo3Si–T2 eutectic and a Moss–Mo3Si–T2 eutectic. The compositions of the eutectic phases were determined by electron probe micro-analysis calibrated using a multipoint measurement method and details of the solidification pathways in the Mo-rich compositional portion are discussed based on the experimentally obtained results compared with the liquidus projection.

Nanoparticles often possess phase stabilities that differ from those of bulk materials, as a result of their large surface-to-volume ratio. Park and Lee suggested that the phase diagram of metallic nanoparticles can be calculated using the CALPHAD method through the introduction of the size effect. Based on Park and Lee’s model, the thermodynamic parameters for the Ag–Sn nanoparticle system (pure Ag and Sn, the intermetallic compound Ag3Sn, and liquid and solid solutions (fcc, hcp, and bct)) were optimized as a function of temperature, composition, and the size of the nanoparticle. The phase stability of the Ag3Sn nanoparticles was affected by the selection of the surface tension value for Ag3Sn; however, the eutectic temperature and composition are not affected by the phase stability of the Ag3Sn nanoparticles. When the size of the nanoparticles is decreased, the eutectic temperature decreases, and the eutectic composition approaches the Sn-rich corner. The present results exhibited a reasonable agreement with the reported experimental data.

Laser surface remelting experiments have been performed on a Ni–33 wt.%Sn hypereutectic alloy. The microstructure characteristic, grain orientation and microhardness were investigated. The lamellar eutectic spacing decreased with increasing the scanning velocity, and the lamellar eutectic spacing is reduced significantly after laser rapid solidification. The anomalous eutectic was obtained in the bottom of the molten pool when the sample was melted thoroughly with the low scanning velocity of 0.1 mm/s. It is found that the free nucleation and rapid growth of two eutectic phases should be a necessary condition for the formation of anomalous eutectic. The EBSD maps and pole figures indicated that the grain orientations of anomalous eutectic obtained by laser remelting are analogous to that obtained by high undercooling solidification. The microhardness of anomalous eutectic is lower than that of regular lamellar eutectic.

Non-equilibrium effects (e.g. strain energy) are stored upon highly undercooled solidification of Fe 40 Ni 40 B 20 eutectic alloy. Only for sufficiently high undercooling (e.g. >200 K), recrystallization, with the strain energy as the driving force, can occur upon annealing the as-solidified structure, thus forming a duplex structure consisting of as-recrystallized single-phase layer (outer) and as-solidified two-phase anomalous eutectic bulk (inner). As compared to the samples subjected to lower undercoolings, the mechanical properties of the samples with the duplex structure are improved substantially.

This paper addresses solidification and solid state precipitation phenomena during transient liquid phase (TLP) bonding of wrought IN718 nickel base superalloy using Ni–4.5Si–3.2B (wt.%) ternary filler alloy. The solidification sequence of the residual liquid in the joint centerline was found to be (1) formation of proeutectic γ, followed by (2) γ/Ni 3 B eutectic reaction, followed by (3) ternary eutectic of γ/Ni 3 B/Ni 6 Si 2 B. Extensive fine Ni 3 Si formed within the eutectic-γ via solid state precipitation during cooling. Extensive Cr–Mo–Nb rich boride precipitates were formed in the substrate region due to boron diffusion into the base metal during bonding process. The implications of the phase transformations on the mechanical properties, corrosion resistance and aging behavior of the joint, which are pertinent to the development of an optimum post bond heat treatment, are highlighted.

The microstructures of Si–Mn–P alloy manufactured by the technique of combining phosphorus transportation and alloy melting were investigated using electron probe micro-analyzer (EPMA). The phase compositions were determined by energy spectrum and the varieties of eutectic morphologies were discussed. It is found that there is no ternary compound but Si, MnP and MnSi 1.75− x could appear when the Si–Mn–P alloy's composition is proper. Microstructure is greatly refined by rapid solidification technique and the amount of eutectic phases change with faster cooling rates. Moreover, primary Si or MnP are surrounded firstly by the binary eutectic (Si + MnP) and then the ternary eutectic (Si + MnSi 1.75− x + MnP) which also exhibit binary structures due to divorced eutectic determined by the particularity of some Si–Mn–P alloys.

Modification of the eutectic silicon in hypoeutectic Al–Si alloys causes a structural transformation of the silicon phase from a needle-like to a fine fibrous morphology and is carried out extensively in industry to improve mechanical properties. It has been documented that the fibrous silicon phase in chemically modified alloys is heavily twinned. It has been proposed that this increased density of twinning results from the adsorption of impurity-elements at the solid–liquid interface perpetuating further growth according to a twin plane re-entrant edge (TPRE) model. In this paper, we discuss this mechanism of eutectic modification in light of experimental data obtained by synchrotron radiation and predictions based on theoretical calculations. This research utilizes a μ-XRF (X-ray fluorescence) technique at the SPring-8 synchrotron radiation facility X-ray source and reveals that different elements which theoretically satisfy the geometric requirements of the impurity-induced TPRE model do not have the same effect on the growth of silicon during solidification. Europium for instance is distributed relatively homogeneously in the silicon phase while ytterbium was not found in the silicon phase at all. This has important implications for the fundamental mechanisms of eutectic modification in hypoeutectic aluminium–silicon alloys.

DSC was used to investigate phase equilibrium in the AgBr–NdBr 3 system. This binary mixture was characterized as an eutectic system with solid solutions. The eutectic composition and temperature were found to be: x (AgBr) = 0.845 and T eut = 647 K, respectively. In addition, the AgNd 3 Br 10 compound was also evidenced; it decomposes in the solid state at 634 K. The electrical conductivity of AgBr–NdBr 3 liquid mixtures, together with that of pure components, was measured down to temperatures below solidification. Results obtained are discussed in terms of possible complex formation.

In the present work, the microstructure and the solidification process of an ingot metallurgy hypereutectic Al–Mg 2 Si alloy with extra Si were studied. Primary Mg 2 Si phase is surrounded by Al–Mg 2 Si binary eutectic and then by Al–Mg 2 Si–Si ternary eutectic structure. Primary Mg 2 Si phase at the centers shows dendritic or polyhedral morphologies. Al–Mg 2 Si binary eutectic cells with regular morphologies have flake-like Mg 2 Si surrounded by α-Al. Al–Mg 2 Si–Si ternary eutectic cells distribute among binary eutectic cells and make binary eutectic cells separated to be relatively independent “islands”.

On the basis of phase and microstructure selection in bulk undercooled Fe–B eutectic alloy melts, an extension of the eutectic zone and transformation from lamellar to anomalous eutectic are interpreted. In combination with a competition between metastable Fe 3 B and stable Fe 2 B above a critical undercooling, a selection map of eutectic zone as function of composition and temperature is given.

An ultra-fine eutectic structure has been obtained in the Ti 70.5 Fe 29.5 binary alloy by slow cooling from the melt through arc melting and cold crucible rod casting. The addition of 3.85 at.% Sn to the binary Ti–Fe alloy induces a change of the morphology of the eutectic and increases the volume fraction of the FeTi ( Pm 3 m ) phase. A significant improvement of the plastic deformability of the ternary alloy has been observed under uniaxial compressive loading resulting in 16% strain to failure compared to 3.4% for binary Ti 70.5 Fe 29.5 . The morphology of the eutectic colonies, their refinement and supersaturation of the β-Ti phase are crucial factors for improving the ductility of the ultra-fine eutectic alloys.

The high strength metastable Ti–Fe–Co alloys were produced by arc-melting in the shape of distorted semi-spherical ingots with the dimensions of about 25–30 mm in diameter and 7–10 mm in height. The structure of the hypereutectic Ti–Fe–Co alloys (at Fe/Co ratio ≥1) studied by X-ray diffractometry and scanning electron microscopy consisted of the primary dendrites of an ordered cP2 Ti(Fe, Co) compound and an eutectic consisting of the cP2 Ti(Fe, Co) compound and a disordered BCC cI2 β-Ti solid solution. The strongest Ti–Fe–Co alloys have a hypereutectic structure and exhibit a high strength exceeding 2000 MPa and a plastic deformation of about 15%. The quaternary Ti 67 Fe 14 Co 14 Sn 5 alloy exhibits a high strength of 1830 MPa and the largest plastic strain of 24%. The deformation behavior and the fractography of Ti–Fe–Co and Ti–Fe–Co–Sn alloys are studied in detail. The formation of a composite-like structure with hard carcass of the intermetallic phase in the relatively soft eutectic matrix enabled both high strength and ductility. The accommodation deformation can be explained by the intergranular sliding of the primary Ti(Fe, Co) dendrites in the softer eutectic matrix. Rough primary dendrites and eutectic rods of the cP2 intermetallic phase act as efficient barriers for shear strain and cracks propagation, while fine eutectic rods of submicron size are quite effortlessly cut by deformation bands and cracks. It is shown that the high strength and ductility values for Ti-based alloys can be achieved without using the injection mould casting or rapid solidification procedure.

A NiZrYAl eutectic point was located by means of DTA method, and near the eutectic point, an alloy Ni 56 Zr 16 Y 18.5 Al 9.5 was found to exhibit a better GFA than the previously reported similar alloy Ni 55 Zr 17 Y 17 Al 11 , which was confirmed by the results of DSC, XRD and SEM. Both the alloys exhibit a same melting temperature ( T m ), which indicates that they belong to the same quarternary eutectic system.

The dynamic evolution of the lamellar eutectic of binary alloys in directional solidifications was studied in detail using the Monte-Carlo technique. In our simulation, the solidification is executed by individual A and B atoms (Case I) and individual A atoms and AB dimers (Case II). We can find: (1) the off coupled eutectic pattern occurs easily in Case II by introducing the cluster deposition; (2) the fluctuation of branching degree ( D b ) of the lamella in Case II is larger than Case I; (3) the simulated tendency for the formation of the off-coupled and branched structures accords with the experimental results in the Al–Cu alloys and Al–Si alloy.

High temperature structural components demand materials that maintain satisfactory mechanical and chemical characteristics. These needs may be met by applying some eutectic alloys, including Ni-Ni3Si. This paper deals with the directional solidification of Ni-Ni3Si grown under several growth rates. The analysis of the eutectic microstructure was carried out using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The results obtained provided a precise analysis of the Ni3Si phase. It could be noticed that the solid/solid transformations by which Ni3Si phase goes through, deeply affects its morphology. In addition, quantitative information on the eutectic structure was obtained. It was confirmed that the growth rate variation deeply affects the final microstructure as it influences the efficiency of atomic diffusion along the solid/liquid interface.

Phase equilibria in the Ti-corner of the Ti–Zr–Si system were studied by the methods of metallography, differential thermal analysis, X-ray and microprobe analyses of as-cast samples. The results are given in the way of the melting diagram and of polythermal sections at 10 and 20 at.% Si. At 1300 °C invariant four-phase equilibrium of eutectic type L↔〈β-Ti〉(β)+〈Ti 5 Si 3 〉(Z)+〈(Ti,Zr) 2 Si〉 (S2) was shown to occur in the concentration interval studied. The location of the eutectic point E was determined to take place at ∼78Ti–11Zr–11Si. The ternary compound S2 formed from the melt by peritectic reaction L+Z→S2. Microhardness of the primary silicide grains and of eutectics microconstituents has shown that zirconium additions decrease the strength of the Z-phase and of the β+Z eutectic, while they do not change the strength of the S2-silicide and of the β+S2 eutectic. Based on the results of hot hardness measurements, below 550 °C the potential for attractive high-temperature structural properties is controlled by refinement of the microstructure, while above this temperature the α↔β transformation temperature of Ti limits the application.

In the Ni–Si system, the eutectic structure composed of Ni–Ni3Si presents inherent thermal stability, allowing composite materials to be obtained with well-aligned and finely dispersed microstructures. The work reported here consisted of an investigation into the microstructure and morphology of such a eutectic alloy from the standpoint of its growth conditions. A Ni–Si eutectic alloy was processed by applying the directional solidification method at low growth rates and the rapid solidification technique using a melt-spinning process. The results indicate that samples processed under conditions close to equilibrium show a regular and aligned microstructure, while rapid solidification leads to an anomalous microstructure and the formation of a metastable phase.

In the present work the fluxing technique was applied to the Sn–51 wt.% Se hypoeutectic alloy. The aim was to study the influence of the undercooling on the microstructure of this alloy, particularly concerning the formation of oriented microstructure and even some metastability occurrence. High undercooling (63 °C) was achieved for the primary SnSe phase leading to an oriented microstructure in the firstly solidified region. Although the undercooling for the eutectic was not so high (19 °C) morphological changes were observed. The rapid movement of the interface interfered with cooperative eutectic growth producing an irregular eutectic in the first region to solidify followed by a fine lamellar and directional eutectic. In order to detect some supersaturated solid solution in the SnSe phase a precise lattice parameter measurement was done from the accurate performed X-ray diffraction (XRD) on the firstly solidified region of the sample.

A prediction of the Ti-Dy phase diagram was given, according to which the system is of eutectic type with the eutectic coordinates ∼1270 °C and 82 at.% Dy. Experimental verification on the two key-alloys confirmed the type of system, as well as the eutectic coordinates. The last were established to be 1280 °C and 82 at.% Dy. The eutectic is fine with a grain size of about 0.2 μm. The hypo-eutectic alloy 95Ti-5Dy showed high plasticity at contraction that is on the level of pure titanium. The Ti-Dy system is proposed as a basis of composite materials of eutectic type.

A Cu–31% Sb eutectic alloy has been rapidly solidified during containerless processing in a drop tube. The microstructures are characterized by βCu3Sb grains plus a small amount of αCu solid solution formed at the grain boundaries, instead of cooperative growth into a eutectic like other binary eutectic alloys. With the decrease of droplet size, βCu3Sb grain is refined and equiaxed grain of αCu solid solution forms in droplets. Melt undercoolings up to 225 K (0.245TE) are estimated by a heat transfer model of droplet solidification. Both experimental and calculated results indicate that, as undercooling rises, the nucleation rate of βCu3Sb intermetallic compound increases. The growth velocities of eutectic structure and dendrites of βCu3Sb and αCu increase with rising undercooling. The growth of βCu3Sb phase is dominant when undercooling is lower than 53 K. When undercooling exceeds 53 K, the growth dominance of the βCu3Sb phase will be replaced by the αCu phase. In contrast, the growth of lamellar eutectic can never become dominant in undercooled melt. This is just the reason why a eutectic microstructure cannot be formed in Cu–31% Sb eutectic alloy during rapid solidification. Microstructural evolution of βCu3Sb grain dominates the microstructure of Cu–31% Sb eutectic alloy.

In the present work, the microstructures of the Al–10Ce–5Sr alloy solidified under conventional and rapid solidification conditions have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The microstructure of the Al–10Ce–5Sr alloy solidified under conventional conditions is composed of a primary intermetallic phase embedded in a matrix of α-Al dendrites with interdendritic eutectic. The primary intermetallic phase is Al 4 (Sr, Ce), with an occupation of about 25% Sr sites by Ce atoms. The eutectic may comprise distinct α-Al/Al 4 Sr and α-Al/α-Al 11 Ce 3 zones or comprise the single fully coupled α-Al/Al 4 Sr/α-Al 11 Ce 3 ternary eutectic. Furthermore, most of the Ce exists in the form of eutectic and most of the Sr exists in the primary intermetallic phase in the ingot-like Al–10Ce–5Sr alloy. In comparison, the microstructure of the melt-spun alloy is dominantly eutectic comprising distinct α-Al/Al 4 Sr and α-Al/α-Al 11 Ce 3 zones. Moreover, a certain orientation relationship exists in the α-Al/Al 4 Sr eutectic while no orientation relationship was found for the α-Al/α-Al 11 Ce 3 eutectic. Zones composed of cellular α-Al with intercellular α-Al 11 Ce 3 are also observed in the melt-spun alloy. The formation mechanisms of these microstructures are discussed.

An in-situ electron microscopic investigation of the formation of eutectic alloys in the systems amorphous Si/particle Ag and amorphous Si/particle Cu showed that the formation of eutectics is preceded by metal diffusion into amorphous silicon with the formation of metastable amorphous metal silicide. Decomposition of the formed metastable amorphous metal silicide results in the evolution of polycrystalline silicon. An oriented formation of liquid eutectic alloy is observed in the systems crystalline (100)Si/particle Ag and (100)Si/particle Cu. In these cases, at the metal–silicon eutectic/silicon crystal interface the formation of silicide phases and a dislocation structure are observed. Investigations allowed us to propose a scheme for the formation of eutectic alloys in the studied systems. The scheme involves the diffusion of metal atoms into the silicon crystal structure, leading to the formation of a metastable silicide or solid solution, the occurrence of strain at the interface and, as a consequence, the formation of defects of different types. The subsequent process is accompanied by synchronous dissolution of metal atoms into the liquid eutectics and by diffusion from the liquid eutectics to the solid crystalline silicon phase, giving rise to metastable silicide, so that an intermediate diffusion zone is always present at the interface between the liquid eutectics and crystalline silicon.

Thermodynamic models and eutectic growth theories have been used to investigate the effect of La on the Sn-rich halo formation in Sn60–Pb40 solder alloy. SEM observation showed that, by adding a small amount of the rare earth element La, the formation of the coarse Sn-rich halo surrounding the primary Pb-rich phase was depressed, and a homogeneous microstructure was obtained. Thermodynamic analysis showed that La has a higher affinity to Sn in the Sn–Pb system. This will lead to a variation of the Sn-rich phase contact angle at the three-phase junction of the solid/liquid interface during the eutectic solidification process. As a result, the eutectic can directly grow from the primary Pb-rich phase and the formation of the Sn-rich halo is depressed.

In this work, the directional solidification technique was employed in binary Fe–Pr and Fe–Nd eutectic alloys with compositions near to their respective eutectic points. Solidifying the Fe–Pr and Fe–Nd hypereutectic alloys in a vertical Bridgman crystal growth unit, we were able to obtain the two eutectic morphologies, one globular and other feathered, normally observed in as-cast samples, in a coarser form and sequentially displayed along the length of the samples. The transition temperatures nearby to the eutectic points were also determined using a Calvet type calorimeter. The phases comprising the globular and feathered morphologies were determined as being, respectively, Fe17R2 and Fe2R (R=Pr or Nd), for both systems. These experiments also showed very clearly the peritectic formation of the Fe2R phases from the Fe17R2 and the liquids. Thermomagnetic measurements gave the Curie temperature as being 44°C for the Fe2Pr phase and 252°C for the Fe2Nd phase.

The possibility of producing fiber-strengthened eutectic composites in situ in the quasibinary EuB6–MeB2 (Me–Zr, Hf, Sc) alloys is shown. By directional crystallization of the eutectic composition perfect real structures on the base of uniformly distributed MeB2 fibers in the EuB6 matrix may be formed.

The in situ electron microscopic investigations of the formation of eutectic alloys in the systems: amorphous Si/particle Au, amorphous Si/particle Al showed that the formation of eutectics is preceded by metal diffusion into amorphous silicon with the formation of metastable amorphous metal silicide. Supersaturation and decomposition of the metastable amorphous metal silicide leads to the evolution of polycrystal silicon. Morphological characteristics of the liquid eutectic formation in the systems crystalline (100)Si/particle Au and crystalline (100)Si/particle Al are similar to the well known morphological characteristics of the formation of etch pits in crystals. For the systems crystalline (100)Si/particle Au, an oriented formation of the liquid eutectic alloy is observed. The growth of the eutectic melt during the annealing of the system crystalline (100)Si/particle Al takes place isotropically. The crystallization of liquid eutectic alloy leads to topotaxial evolution of gold silicide islands at the interface: crystal eutectics–single crystal silicon.

It is shown that on cocrystallization of hexaboride (of f-transition metals) and diboride (of d-transition metals) phases in eutectic mixtures the crystallographic relation between rigid boron networks in both phases is kept constant and is defined by mutual joining of boron atom pairs in both structures, independently of the direction of crystallization.