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The aim of the present study is to identify the ternary eutectic Mo-Si-B composition to produce directionally solidified materials, which are expected to have excellent high-temperature properties due to the well-defined microstructure. Different alloy compositions in the respective primary solidification areas of the phases were chosen to investigate the microstructural evolution. The results were compared to thermodynamic calculations of the liquidus projection and isopleth phase diagrams using the software FactSageTM. By carrying out these experiments the eutectic point was found to have a nominal composition of Mo-17.5Si-8B (at.%). In the next step, the eutectic alloy was directionally solidified by a zone melting (ZM) process. The evolution of a typical eutectic microstructure due to the growth of lamella-like structures is shown by microstructural investigations. Furthermore, we present a eutectic phase field model for the eutectic Mo-Si-B alloy. The equilibrium interface geometries and interface mobility were calculated using an isotropic model. The results are shown to be in an adequate conformity with the experimental observations.

Sb is an effective additive to modify eutectic Si of Al-Si alloys and the modification mechanism has not yet been studied very clearly. In this paper, computer aided cooling curve thermal analysis and microstructure assessment were carried out to investigate the modification effects of Sb on Al7SiMg alloy. The results show that the Sb addition amount of 0.1~0.25% has improvement effect on eutectic Si morphology, which can be further confirmed from the thermal analysis results. The addition of Sb decreases the eutectic growth temperature by 5 °C to 7.8 °C, indicating an undercooling effect resulted from Sb modification. Compared to that of short rods, a better eutectic Si morphology of nearly granular particles can be obtained in a faster cooling rate. The length of silicon has been gradually shortened as holding time increased to 2.5 h from 0.5 h, which means a long period modification effect of Sb in Al-Si alloys. Owing to undercooling resulted from Sb addition in Al-Si alloys, the refinement structure of eutectic silicon can be achieved.

Rapid solidification of Co-Si alloys was investigated by using vacuum suction casting in this study. Different microstructures and intermediate phases were obtained. Eutectic εCo phase and eutectoid εCo + αCo2Si structures were obtained in the first eutectic Co76.9Si23.1 alloy. The microstructures of hypereutectic Co70Si30 alloys were composed of primary αCo2Si phase and interdendritic lamellar eutectoid εCo + αCo2Si. While for hypoeutectic Co63Si37 alloy at the second eutectic point, CoSi dendrites were the primary phase, and αCo2Si+CoSi eutectoid structures can be seen at the interdendritic region. Especially, a metastable CoSi2 phase was found in Co63Si37 alloy. This indicates that eutectoid decomposition βCo2Si→ CoSi+αCo2Si is restrained in eutectic Co60.3Si39.7 alloy. For rapid solidified Co55Si45 and Co52Si48 alloys, αCo2Si+CoSi eutectoid structures were not observed, while metastable CoSi2 were obtained. The higher hardness achieved in Co-Si alloys at the second eutectic point, for the reason of the higher volume fractions of compound phases.

Considering the safety of the charge filled in the chambers and the operational reliability, a low temperature eutectic alloy bonding was preferred for the final assembling process of MEMS-based solid propellant microthrusters (SPM) array with top-side igniters. The optimum conditions of the alloy coating are the pH value of the solution is 0.5, the base metal layer is composed of Ti (60nm)/Cu (500nm) deposited by magnetron sputtering. The bonding process was conducted in an oven with air and the bonding temperature is 70°C. To predict the performance of bonding layer, the temperature distributions of eutectic alloy layer were simulated by ANSYS software when the chamber is full of high temperature reactants. The simulation results demonstrated the bonding strength wouldn’t cut down since the heat transfer induced by the combustion of charge. The assembled MEMS-SPM array was tested under constant voltage, the results indicated that the eutectic solder bonding procedure meet the requirements of the MEMS-SPM assembling.

The surface of AZ31 magnesium substrate is coated by Zn-Al alloys using cast-penetrated cladding. The transverse section of alloy cladding is composed of cladding zone, diffusional zone, and bonding zone. The microstructure evolution, phase constitution, and chemical composition of the transition layer are studied. The experimental results exhibit cladding zone contained dendrite matrix and interdendritic eutectic structures. The plume eutectic structure and columnar eutectic structure are formed in diffusional zone and bonding zone, respectively. Zn and Al solid solutions gradually decrease and disappear owing to the diffusion of magnesium atom and the changes of magnesium element concentration. Mg7Zn3 phases are generated rapidly due to the interdiffusion of zinc and magnesium atoms rapidly in the diffusional zone and bonding zone. As Mg-Zn eutectic phases hinder the movement of Mg and Al atoms, the Mg-Al intermetallic compounds are eliminated completely. The microstructure is transformed into Mg solid solution and Mg7Zn3 eutectic structure to combine with AZ31 base metal.

The paper provides a new insight into the modification of eutectic Si in Al-Si based alloys. To date, impurity-induced twinning mechanism and twin plane re-entrant edge mechanism are the well-accepted theories. However, neither IIT nor TPRE can be used to interpret all modification observations. Therefore, a re-consideration of modification mechanisms is still required. In this contribution, recent advances on the understanding the modification of eutectic Si are reviewed. Two different cases are highlighted. In the case of Sr, Na and Eu addition, eutectic Si was modified from a faceted to a fibrous morphology, which involves the formation of multiple Si twinning. In the case of Yb and Ca addition, eutectic Si was refined to a smaller size, but still maintained a plate-like morphology. The possible modification mechanism was thus discussed in terms of (i) adsorption of atoms at twin re-entrant edge, and (ii) segregation across {111}Sigrowth planes. Furthermore, solute entrainment of modifying elements (M) was introduced to interpret the formation of Al2Si2M phase or M-rich clusters within Si crystals.

Eutectic alloys from the ternary system Al-Cu-Ag are excellent model alloys for the investigation of coupled eutectic growth, not only because most materials properties are well known but also because the system offers a rich variety of crystal structures and crystal orientation relationships (ORs) being associated to distinct minima of the solid-solid interface energy. This paper describes three research topics specifically related to bulk lamellar Al-Al2Cu eutectics, e.g. the maze-to-lamellar transition during early growth, the role of fault lines during lamellar spacing selection close to the pinch-off limit and the onset of eutectic cell formation above the constitutional supercooling limit. These topics are central to the microgravity experiments SETA presently being prepared for the MSL / SQF.

The sessile drop technique was used to evaluate the contact angle between liquid eutectic Fe-11wt%V-2.3wt%C alloy and VC substrate. This alloy solidifies through a eutectic reaction that starts at 1320°C and leads to the formation of the faceted/non-faceted austenite-VC eutectic. The effect of sulfur on the contact angle and on morphology of the austenite-VC eutectic in both non-directionally and unidirectionally solidified specimens was investigated. It was shown that sulfur increases the contact angle and modifies the eutectic morphology, thus indicating a relationship between eutectic morphology and liquid eutectic/faceted phase VC interfacial energy.

The liquidus temperature of molten salt NaCl-KCl-NaF-Na2WO4 system was measured by differential thermal analysis. The results show that in the molten salt system when 0.6 eutectic temperature is 542.1 °C and a phase transition temperature is 515.4 °C, eutectic composition become = 0.28, = 0.28, =0.14, = 0.3; when > 0.6, eutectic temperature and a phase transition temperature are respectively 597.7 °C and 495.8 °C, eutectic composition become = 0.12, = 0.12, = 0.06, = 0.7.

Effects of the technological parameters (superheat, cycle times and holding time) on undercooling and structure of Ag-28.1 wt.% Cu eutectic alloy were discussed by orthogonal experiment. It shows that the influence of the superheat on undercooling is biggest, followed by cycle times, and finally holding time. Then the optimum process parameters of getting different undercooling are given in this paper. In the Ag-28.1 wt.% Cu eutectic alloy melt, cellular growth of lamellar eutectics takes place because of the large difference in composition between the two eutectic phases and the very large thermal diffusion coefficient of the liquid, and when undercooling is equal to or higher than 76 K, lamellar eutectics grow in a dendritic form during rapid solidification.

A numerical model that describes solidification of primary aluminium grains and nucleation and growth of eutectic cells is used to analyse the solidification of an Al-12.5wt% Si alloy. Nucleation of eutectic cells is modelled using an Oldfield-type nucleation model where the number of nuclei in the melt is determined by the amount of active nuclei and the local undercooling from the surface to the centre of a plate casting. Eutectic grains are modelled as spheres growing between the dendrites. The growth velocity of the eutectic cells is a function of undercooling. Experimentally determined growth parameters from the literature that depend on the type of modification (unmodified, Na-modified or Sr-modified) are used to describe differences in growth of the alloys. Modelling results are compared with solidification experiments where an Al-12.5wt%Si alloy was cast in unmodified, Na modified and Sr modified forms. The model confirms experimental observations of how modification and alloy composition influence nucleation, growth and finally the size of eutectic cells in the alloys. Modelling results are used to explain how cooling conditions in the casting act together with the nuclei density in the liquid and the growth velocity of the eutectic cells to determine the size and distribution of eutectic cells in the solidified material.

The liquid structure of Ni2Sb98 eutectic alloy is studied with the method of X-ray diffraction and measurements of viscosity in this paper. Covalent bonding structures, which are characterized by the shoulder on the high- Q side of the first peak of structure factors, are observed over the full measuring temperature range. And the split of second peak of the pair correlation function suggests that the chemical short-range order structure exits in the melt. Correspondingly, variation of the viscosity obeys the Arrhenius law except the abrupt point near 1025K and the electrical resistivity changes abnormally at about 1020K. In addition, the coordination numbers prove that the A7-like structure is almost destroyed in liquid Ni2Sb98 alloy. This research is aim to provide new insight into the structure evolution of liquid alloys during the cooling process.

In the present study, superheating treatment has been applied on A357 reinforced with 0.5 wt.% (Composite 1) and 1.0 wt.% (Composite 2) continuous stainless steel composite. In Composite 1, the microstructure displayed poor bonding between matrix and reinforcement interface. Poor bonding associated with large voids also can be seen in Composite 1. The results also showed that coarser eutectic silicon (Si) particles were less intensified around the matrix-reinforcement interface. From energy dispersive spectrometry (EDS) elemental mapping, it was clearly shown that the distribution of eutectic Si particles were less concentrated at poor bonding regions associated with large voids. Meanwhile in Composite 2, the microstructure displayed good bonding combined with more concentrated finer eutectic Si particles around the matrix-reinforcement interface. From EDS elemental mapping, it was clearly showed more concentrated of eutectic Si particles were distributed at the good bonding area. The superheating treatment prior to casting has influenced the microstructure and tends to produce finer, rounded and preferred oriented α-Al dendritic structures.

Alumina/Al-Si alloy composites were manufactured by squeeze casting. The morphology of eutectic Si in the composite was observed on scanning electronic microscope, and the modified mechanism of the eutectic Si in the composite was approached. The alumina fiber in the composite could trigger twin during the growth of Al-Si eutectic and lead to modification of the eutectic Si near the fiber.

A stable form-phase change materials (PCM), based on capric-lauric acid eutectic served as the absorption material and the support of nano-silica material to prepare by sol-gel method. The best ratio capric-lauric acid eutectic combination is determined for 60 wt. %. Capillarity because of the influence of the hydrogen bonding, fatty acid and eutectic can be fixed in the three dimensional network structure of the construction of the silicon atom bonds and O still so solid sample melting point composite heating more fatty acid eutectic. Form and chemical properties of the composite phase change the transmission electron microscope, semi and Fourier transform infrared method.- Differential scanning calorimetric hot method is used for measuring phase transition temperature and phase change of latent heat composite, value 19.57 and 71.28 J/g , respectively. At the same time, service performance and other composite material thermal stability and thermal conductivity coefficient test using thermo gravimetric analysis and transient hotline method, respectively.

The well-aligned growth structures which derive from directional solidification of ceramic eutectics are of great interests due to their potential use in electronic devices and as structural materials at high temperatures. Because of the complexity of the component system and very high melting points, the solidification behavior on the oxide ceramic eutectic is still unclear up to date. In the presented paper, the Al2O3-Y2O3-ZrO2ternary eutectic ceramic is remelted by a DTA apparatus. The maximal heating temperature is 1950 °C. The melting and solidification behavior are investigated by the DTA analysis. The solidification microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The results show that solidus temperature and the liquidus temperature are 1738.4 °C and 1750.1 °C, respectively. The formation path of eutectic phase is discussed. The microstructure of as-solidified eutectic ceramic shows a divorced ternary eutectic structure consisting of Al2O3, YAG and ZrO2phases with a random distribution. Furthermore, the microstructural comparison with directionally solidified ternary eutectic ceramic is presented and discussed.

In this paper, the growth process of the interfaces of Mg-Al-Mg and Mg-Cu-Mg diffusion bonding layers which are prepared by the field-active diffusion bonding (FDB) process were investigated. The OM, SEM, EDS and XRD were applied to analyze the microstructure, phase components of the diffusion dissolution layer. The results show that the morphology and width of the diffusion dissolution layer were significantly affected by the electric field strength. At low temperature, the bonding layer was formed through solid state diffusion process, liquid phase existed between the two dissimilar metals at high temperature and eutectic layer was formed at the bonding interface. As for the Mg-Al couples, when the current density was 80Acm-2 the thickness of the transition layer was 120μm which was 12 times higher than current-free condition at 450°C for 50min.

The Al-Si eutectic alloy solidified under normal pressure was prepared by vacuum Ar-arc furnace. The alloy solidified under high pressure was prepared by hexahedral anvil equipment. The two heavily etched samples were observed by scanning electron microscope. The experiments show that the eutectic silicon phase solidified under high pressure presents curved and near parallel lamellar crystal, and there is definite spacing between the layers, which was very different from that of solidified under normal pressure. So the eutectic growth mode of Al-Si alloy solidified under high pressure was put forward, which indicate that the growth mode of Si have been changed gradually from facet to non-facet under high pressure.

Based on the interaction between nano-fiber and eutectic interphase, forth-phase mode is used to get the mechanical stress field of matrix in eutectic composite ceramics. The effective flexibility increment tensor of eutectic ceramic composite is obtained by the volumetric average strain. The remote stress boundary condition of the eutectic composite ceramis is accounted for getting the mechanical stress field in matrix. The results show the mechanical stress field of the matrix is associated with the stiffness and the volume fractions of each component in eutectic composite ceramic , the shape of interphase and nano-fiber. The stresses in matrix will decrease due to the strong constraining effects of the eutectic interphase. The eutectic interphase make the eutectic composite ceramics strengthen.

The microstructure of the aluminum-silicon (Al-Si) alloy solidified under high pressure was compared with that solidified under normal pressure. High-pressure solidification was performed at 4.0 and 5.0 GPa. The microstructures of the samples were observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The effects of pressure were analyzed by examining the microstructure of the alloy. The observed microstructures show an additional amount of primary a(Al) phase in the Al-13at%Si alloy solidified under high pressure; this indicates the existence of a eutectic point moving toward the silicon direction with increasing pressure. The eutectic cells of the Al-Si alloy solidified under high pressure are evident, and the eutectic silicon phases are presented as curved and near-parallel lamellar crystals, signifying that the growth mechanism of the eutectic silicon phase changed from faceted to non-faceted. The eutectic silicon lamellar phase and the primary b(Si) phase were refined by the applied pressure.

In order to investigate the effect of Ni on the high-temperature strength of Al-Si cast alloys, tensile properties of hypoeutectic and eutectic alloys were determined at 250 °C after long-term annealing at test temperature. LOM- and SEM-analysis revealed the existence of Al3Ni-phases in close contact to eutectic Si. It was shown that the strength can be increased by the addition of Ni, though just to a certain level, depending on the fraction of eutectic phase in the alloy. The alloys were considered as a coarse two-phase system where a hardening effect is caused by load transfer to the harder phase, which requires a certain connectivity/contiguity of the latter. The paper describes the extent of contiguity of the eutectic as well as the hard silicon and Al3Ni-phases within the eutectic, and discusses their contribution to an enhanced strength of Al-Si alloys at elevated temperatures.

During rheo-high pressure die casting (R-HPDC) of Al‑Zn-Mg-Cu alloys a coarse eutectic phase is formed. This eutectic phase is difficult to take into solution because of its size and it would require longer solution heat treatment times. The objective of this work was to determine the time for sufficient dissolution of the eutectic phase in this Al-Zn-Mg-Cu alloy. Solution heat treatment was carried out at 473°C for various time periods and the samples were quenched in water. The samples were then artificially aged at 120°C for 24 hrs. A component of the eutectic was observed to have dissolved and another component transformed to new intermetallic phases for all solution heat treatment times at 473°C.

The paper focuses on characterization of eutectic precipitations in three magnesium alloys (MSR-B, ZRE1 and WE43) containing rare earth elements. It was shown, that the structure of the tested alloys in a cast state consists of globular grains of the α-Mg solid solution and eutectic areas of different chemical composition and morphology. An untypical influence of the pouring temperature on the eutectic precipitations area fraction was observed. This phenomenon can be explained by impoverishment of the eutectic-forming elements in the areas of the slowest solidification. This results from the fact, that at the highest pouring temperature a considerable amount of eutectic forms in places solidified as the first.

In this work an analytical solution is used to explain the mechanism of dissolved sulfur influence on the transition from graphite to cementite eutectic in cast iron. It is found that this transition can be related to (1) the nucleation potential of graphite (characterized by nucleation coefficients, Ns and b (2) the growth rate coefficient of graphite eutectic cell,  (3) the temperature range, Tsc = Ts - Tc (where Ts and Tc is the equilibrium temperature of the graphite eutectic and the formation temperature of the cementite eutectic respectively) and (4) the liquid volume fraction, fl after solidification of the pre-eutectic austenite. It has been shown that the main impact of dissolved sulfur on the transition from graphite to cementite eutectic consists in reducing the growth rate of graphite eutectic cell. Analytical equations were presented to describe the absolute chilling tendency, CT, and the chill, w of cast iron. Finally, it has been shown that as dissolved sulfur content in cast iron increases, the eutectic cell count, N, the maximum degree of undercooling at the onset of graphite eutectic solidification, ∆Tm, and the chilling tendency index, CT and chill, w increase as well.

The solidification of the austenite-spheroidal graphite (SG) eutectic is one of the most complex and therefore most difficult liquid-to-solid transformations to describe through computational modeling. This is because the iron-carbon equilibrium phase diagram is an asymmetric diagram that predicts that at relatively low solidification velocities it is possible to produce primary austenite in a casting of eutectic composition. In addition, the two phases of the eutectic solidify as a divorced eutectic, with only the austenite being in contact with the eutectic liquid. The paper proposes a computational model for the eutectic solidification of SG iron with visualization of the microstructure evolution using a cellular automaton technique. The model is an extension of the earlier Zhu-Stefanescu model for primary phase solidification and includes the growth of primary SG in the liquid, of primary austenite and of the austenite-graphite eutectic controlled by carbon diffusion through the solid austenite shell. The model outputs realistic images of the microstructure evolution from the beginning to the end of eutectic solidification of SG cast iron.

Piezoelectric sensor can produce voltage when deflected (function as an energy harvester) while piezoelectric actuator can deflect when a voltage is applied. Different device applications have different requirements on the thickness and in-plane geometry of the Lead Zirconate Titanate(PZT) piezoelectric layers and thus have their own processing difficulties. In this paper, PZT-Au-Si cantilever is fabricated by eutectic bonding and dicing process.The properties of lapped PZT ceramics and silicon cantilever is also evaluated. The PZT-Au-Si cantilever applications for both piezoelectric actuators and energy harvesters have been confirmed.

As an energy conversion material, piezoelectric ceramic lead zirconate titanate (PZT) has been used in a wide range of areas. And a PZT wafer bonding with a silicon wafer technology is a promising method to fabricate micro-sensors and micro-actuators using well-established silicon machining techniques. In order to obtain the excellent piezoelectricity and suitable thickness from the bulk PZT, a method is presented. It is to bond a bulk PZT onto a silicon wafer via an intermediate layer. In this paper, two bonding methods are presented. One is to bond a bulk PZT with a silicon wafer by anodic bonding technique using a thin glass film as the intermediate layer. The other is to bond a bulk PZT with a silicon wafer by eutectic bonding using a thin gold film as the intermediate layer. The glass film is 2µm in thickness, deposited by sputtered method. Anodic bonding conditions are: 0.8MPa in pressure, 500 oC in temperature, 250V in voltage and different bonding time. The bonding strength test shows that the maximum bond strength is 13.93 MPa when the bonding time was 60 min. It is void-free structure in the interface of the PZT-Glass-Si structure. The gold film is 1.6µm in thickness, deposited by evaporation method. The eutectic bonding conditions are: 0.8MPa in pressure, 500 oC in temperature, and different bonding time. The bond strength of the PZT-Au-Si structure was tested and the maximum value was 13.19 MPa when the bonding time was 60 min.

Semi-continuously direct chill (DC in short) casting was carried out to modify the size and morphology of eutectic Si particles in eutectic Al-Si alloy. Successively, the size, morphology, distribution characters of eutectic Si particles and the hot plasticity ability of the alloy during heating and hot-rolling were investigated by the observation of optical microstructure characterization and the rolling of wedge bar. The results show that the eutectics in the eutectic Al-Si alloy can be remarkably fined by semi-continuously DC cast. The eutectic Si phase particles will coarsen and spheroidize after holding at 480°C for 2h, which enables eutectic Al-Si alloy to possess excellent hot plasticity free of cracked edge with compression ratio of rolling up to 85% by single pass. Though little difference on the size of spheroidized Si particles during hot rolling can be observed, uniform distribution of the Si particles can be obtained by hot rolling with compression ratio of 85%.

Dissimilar metal combinations are often necessary when manufacturing a component in order to meet particular functional and engineering requirements or protect against environmental degradation. Stainless steels are used in a diverse range of applications due to their excellent corrosion resistance, formability and strength. The 316L stainless steel also shows good crashworthiness due to its high strain rate sensitivity which makes it suitable for the transportation industry. The joining together of the 316L steel and AZ31 magnesium alloy cannot be achieved using conventional fusion welding methods and therefore, diffusion bonding using interlayers was used to overcome the differences in their physical properties. The results show that Cu and Ni interlayers form a eutectic with the magnesium which enhances wettability and bond formation through isothermal solidification. The effect of hold time on the microstructural developments across the joint region was studied at a bonding temperature of 530oC and 510oC for the Cu and Ni interlayers respectively using a bonding pressure of 0.2 MPa. This preliminary investigation shows that by increasing the bonding time from 5 to 60 minutes results in a Cu-Mg and Ni-Mg eutectic phase structure forming along the bond interface. By holding the joint at the bonding temperature for 15 minutes initiates isothermal solidification of the joint and this was confirmed by DSC analysis. However, the movement of the solid/liquid interface on solidification pushes intermetallic phases into the center of the bond during the solidification stage. The intermetallics increase the hardness value of the bond interface and lower final bond strengths.

For determining of the micro-structural changes taking place in a near eutectic Al-Si-Cu aluminium cast alloy during heating and cooling process the UMSA device (Universal Metallurgical Simulator and Analyzer) was used. In this work the dependence between the regulated cooling speed and structure on the basis of the thermo-analysis was carried out. The thermal analysis was performed at a cooling rate in a range of 0,2 °C to 1,25 °C. The changes were examined and evaluated qualitatively by optical and electron scanning microscopy methods and the EDS microanalysis. During the investigation the formation of aluminium reach (α-Al) dendrites was revealed and also the occurrence of the α+β eutectic, the ternary eutectic α+Al2Cu+β, as well a iron and manganese containing phase was confirmed. The performed investigation are discussed for the reason of an possible improvement of thermal and structural properties of the alloy. The achieved results can be used for liquid metal processing in science and industry – for example foundry for developing and obtaining of a required alloy microstructure and properties influenced by a proper production conditions.

Ultrasonic vibration has been applied to various molten metal processes owing to the functions of (a) improvement in wettability, (b) liquid adhesion at a vibrating end surface and (c) sono-solidification such as grain refinement. The present study is focused on the sono-solidification with acoustic cavitaion in hypereutectic Al-18mass%Si alloy. There appears an equilibrium microstructure composed of primary silicon and coupled eutectic -Al/Si phases in Al-18mass%Si alloy, however, non-equilibrium -Al grains develop along with the equilibrium phases through the sono-solidification. During the sono-solidification of Al-18mass%Si alloy, non-equilibrium -Al grains are recognized in the molten metal close to the ultrasonic radiator just before reaching the eutectic temperature of 577 oC in addition to the refined primary silicon particles. The appearance of -Al grains is understood through acoustic cavitation: ultrasound in molten Al-Si alloys exhibits two outstanding behaviors of cavitation bubbling and acoustic streaming. Firstly the de-coupled eutectic reaction, which is recognized in the solidified eutectic Al-Si alloy with severe stirring, causes divorced -Al grains by the acoustic streaming with cavitation. Secondly it is expected that high pressure of over 1 GPa generated by the collapse of cavitaion babbles leads to not only an increase in the eutectic temperature, but also higher silicon content at the eutectic point in Al-Si alloy. Consequently, non-equilibrium -Al grains are nucleated at collapsed cavitaion bubble sites, and they are characterized by higher silicon content compared with that of primary -Al grains in hypoeutectic Al-7masst%Si alloy.

The study is performed to implement the Gold-Gold thermocompression bonding for the wafer-level packaging of MEMS chips. Numerous experimental attempts have been carried out to select the metal film adhesive to avoid the Au-Si melt together and optimize bonding processes to intensify the Au-Au eutectic bonding. Finally the results display that the eutectic bonding of the gold-gold are arrived as electrical as well as mechanical interconnection of the MEMS structure and as seal as well as bonding intension.

ZrB2-SiC composites were prepared by arc melting using ZrB2 and -SiC powders as raw materials and their oxidation behavior were investigated. The eutectic composition of the ZrB2-SiC system was ZrB2-58.5mol%SiC and the melting point temperature was about 2570 K. At 1673 K mass gain was observed in the oxidation of ZrB2-SiC eutectic composition and the mass gain rate increased with decreasing Ptot. The oxide scale consisted of an amorphous SiO2 layer, a ZrO2-SiO2 eutectic-like layer and a Si-deficient layer.

A study of the effect of strontium on some solidification parameters, such as eutectic nucleation temperature, eutectic growth temperature, eutectic undercooling temperature and eutectic undercooling time, has been carried out using thermal analysis for a composite reinforced with 15 vol. % SiCP and, for comparison, for an A356 aluminum alloy. The composite is prepared by the melt stirring technique with a SiC particle size of 38 μm. Thermal analysis results show that the presence of SiCP in the unmodified A356 aluminum alloy increases the eutectic growth temperature (TE) and the eutectic nucleation temperature (TNucl); on the contrary, SiCP decreases the eutectic undercooling temperature (θ) and the eutectic undercooling time (tE). These phenomena suggest that SiC particles give favorable conditions for the growth of eutectic silicon. On the other hand, the modification with strontium of the composite material, although showing basically the same effect on the eutectic parameters as the one described for the A356 aluminum alloy, brings about certain differences due to the presence of the SiC particles. Microstructural analysis shows that the eutectic structures in the composite are coarser than those of the matrix alloy and they do not have the classic fibrous eutectic shape obtained in the matrix alloy. For the matrix alloy, when the Sr concentration increases beyond the quantity required to obtain a well-modified structure, the eutectic structure suffers a gradual coarsening or a reversion from fine fibrous silicon to coarser silicon; subsequently, when the Sr concentration is higher than 0.068%, Al2Si2Sr particles are produced. In the composite material there is also a gradual coarsening of the eutectic structure, although the appearance of Al2Si2Sr particles is just seen when the Sr concentration reaches 0.106%.

Nb-NiTi and Nb-CoTi eutectic alloys were directionally solidified in an optical floating zone furnace. Rod-type eutectic structures with Nb rods aligned parallel to the growth direction are obtained for Nb-41Ni-40Ti grown at relatively slow growth rates below 1.0mm/h, while lamellar-type eutectic structures are obtained for Nb-35Co-34Ti grown at the same condition. The hydrogen permeability for the Nb-41Ni-40Ti DS alloy with Nb rods perpendicular to the membrane surface is 2.60×10-8mol H2 m-1 Pa-1/2 at 673K, which is about 2.5 times higher than that of as-cast sample. No hydrogen embrittlement is observed between 573 and 673K, indicating that the Nb-NiTi rod-type eutectic structure effectively suppresses the hydrogen embrittlement of Nb during hydrogen permeation.

Silver free Ti-43at.%Cu (Ti-Cu) eutectic alloy have been developed for the brazing of Be and Cu99.32Cr0.6Zr0.08 (CuCrZr). The structural and microstructural properties of the as obtained alloys were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS). The analysis have revealed that the Cu-Ti eutectic alloy have a fine and homogeneous eutectic structure with the phase composition corresponding to the Ti-Cu phase diagram. These observations are consistent with the thermal properties of the alloys determined by DTA-TG analysis. The role of Mn on the eutectic structure, as well on the wetability properties was also studied. The effect of Mn is to produce a less coarse eutectic structure and to decrease the wetability angle. The mechanical testing of CuCrZr/Ti-Cu/CuCrZr junctions have demonstrated that these alloys are suitable for the brazing of Be and CuCrZr. The shear strength of the CuCrZr/TiCuMn/ CuCrZr increases with Mn concentration reaching the value of about 280 MPa for 2at% Mn.

As Recently, wafer level packaging (WLP) received lots of attention in system because it shows the potential to reduce packaging cost, while the yield of devices after dicing and packaging can be increased. In this study, we newly proposed WLP for light emitted diodes (LED) using MEMS technology. Our silicon package structure is composed of base and reflector cup. The role of base is that settle LED chip at desired position and supply electrical interconnection for LED operation. Reflector cup was formed by an-isotropic wet etching. Package platform could be fabricated by eutectic bonding between base and reflector cup using AuSn. We carried out process using six sigma methodology. We first decided 2 factors and 3 levels by design of experiment (DOE). One factor is the kind of metal model. The other is the shape of pattern. It was used that three-kind metal models are Au (cup), AuSn (cup), and AuSn (base). The bonding strength is measured using a die shear strength tester. It carried out in the repetition experiment by a unit of 3 times. As a result of this test, the AuSn(base) metal model and the No.3 pattern were applied by the optimal condition. We set the value of the low limit at shear strength 950g/mm2 for applying sigma level. This value is a generally used for eutectic bonding packages. The experiment results have 3.13 sigma level (95% yield). In this paper, We show the final LED package which is finished up to LED attach, wire bonding, encapsulation, etc. This wafer level bonding process demonstrates its promising potential at the wafer level packaging in LED packaging.

The surface oxidation behavior was investigated over a range of solid state bonding condition of the Ti-6Al-4V ELI alloy. Since the oxides at the bonding interface may prevent the materials from complete bonding, it is important to understand the oxidation behavior at solid state bonding condition. The activation energy of oxidation of Ti-6Al-4V ELI is estimated to be 318 KJ/mol in an environment of solid state bonding process. For Ti-6Al-4V ELI alloy, strucutral integrity of bonding interface without oxides have been obtained at 850°C applying pressure of 3MPa for 1 hour. Solid state diffusion bonding of Ti-15V-3Cr-3Sn-3Al alloy was also obtained under a pressure of 6MPa for 3 hours at 925°C.

Our experiments highlight that gold-silicon eutectics are fairly influenced by the thickness of Au layer and the wastage of Si, i.e. the wasting thickness of the silicon die. In the experiments, a bonding intensity testing method, called Press-arm model, is used to verify the Au-Si eutectics bonding strength. Through the intensity value of the bonding interface, we analyze the eutectics condition of the bonding interface at different temperatures and discuss the optimum procession of the wafer capsulation.

By the development of high power LED for solid states lighting, the requirement for driving current has increased critically, thereby increasing power dissipation. Heat flux corresponds to power dissipation is mainly generated in p-n junction of LED, so the effective removal of heat is the key factor for long lifetime of LED chip. In this study, we newly proposed the silicon package for high power LED using MEMS technology and estimated its heat dissipation characteristic. Our silicon package structure is composed of base and reflector cup. The role of base is that settle LED chip at desired position and supply electrical interconnection for LED operation, and finally transfer the heat from junction region to outside. For improved heat transfer, we introduced the heat conductive metal plated trench structure at the opposite side of LED attached side. The depth and the diameter of trench were 150 and 100um, respectively. Copper with high thermal conductivity than silicon was filled in trench by electroplating and the thickness of copper was about 100um. Reflector cup was formed by anisotropic wet etching and then, silicon package platform could be fabricated by eutectic bonding between base and reflector cup. The thermal resistance of silicon package was about 6 to 7K/W from junction to case, and also, thermal resistance reduction of 0.64K/W was done by metal plated trench. This result could be comparable to that of other high power LED package. Our silicon package platform is easy to be expanded into array and wafer level package. So, it is suitable for future high efficiency and low cost package.

In this paper, a low temperature hermetic wafer level packaging scheme for the RFMEMS devices is presented. For hermetic sealing, Au-Sn multilayer metallization with a square loop of 70 %m in width is performed. The size of the MEMS package is 1mm × 1mm × 700 %m. The shear strength and hermeticity of the package satisfy the requirements of MIL-STD-883F. The total insertion loss for the packaging is 0.075 dB at 2 GHz.

Coupled, regular eutectic growth of α(Al) and Al2Cu from ternary Al-Cu-Ag liquid alloys is investigated with focus on the formation and the characteristics of eutectic cells in unidirectionally solidified, polycrystalline, bulk samples. The topologic anisotropy of the lamellar eutectic leads to destabilization along the lamellae with elongated cells being intermediate to stable cells, irrespective of the crystallographic orientation of the phases. The formation of stable cellular patterns with elongated or regular cell structure is explained with reference to the crystal orientation of the phases α(Al) and Al2Cu, measured by electron backscatter diffraction (EBSD).

Within the frame of the ESA research program SETA, “Solidification along a Eutectic Path in Ternary Alloys”, experiments have been performed focussing on several distinct subtopics. One of these subtopics is to study coupled growth along the univariant eutectic reaction: L → α + β. In this paper, the influence of the growth velocity v on the morphology of the solid/liquid interface is evaluated in a ternary Al-Cu-Si alloy with a composition close to the univariant eutectic groove L → α(Al) + θ-Αl2Cu. Different structural regions can be identified in terms of the stability of the solid-liquid interface (morphological stability) and the stability of the coupling (competitive growth) during unidirectional solidification as function of the solidification parameters. It is found that two-phase planar growth with a lamellar arrangement can be obtained at a sufficiently low growth rate v. The measured interlamellar spacing follows the Jackson and Hunt relationship λ2v = constant. At a higher growth velocity first a destabilisation of the solid/liquid interface is observed and finally competitive growth is observed revealing primary θ-Al2Cu growing ahead of the eutectic interface. It is assumed that the cellular break-up is a two-step process related to the crystallography of the system. Fitting the different morphologies into one microstructure map, an extension of the coupled zone concept as has been proposed for binary alloys is necessary.

In this study, a diffusion bonding of aluminium alloy A6061 was preformed using an Ag-28Cu filler metal in order to conduct eutectic brazing. Melting mechanism was surveyed. Interface behaviors of the brazed joints were observed after brazing and T6 solution treatment. Also, tensile property of the brazed joints was examined. During diffusion bonding of Al6061 alloys with Ag-28Cu filler metal, eutectic melts were formed by eutectic reaction between Al6061 and Ag-28Cu filler metal. It was found that the reaction layer consist of two phases formed at the interface between AA6061 and Ag-28Cu filler metal. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. Tensile strength was 300 MPa after ageing treatment at 175°C.

Ni3Al has been considerable research area due to its high temperature behavior increasing strength with increasing temperature. A series of directional solidification studies showed that the eutectic occurred between g’/b and the metastable eutectic of g/b forms under slightly different conditions, however, it is not well established whether the eutectic is composed of g/g‘, g’/b, or g/b . In order to understand solidification behavior of the eutectic structure, directional solidification experiments have been carried out with solidification rate near the Ni3Al composition in this study. The effects of the solidification rate and composition on formation of the equilibrium and metastable eutectics have been discussed. The (g’+g) coupled phase was also shown to form with the eutectic at the solid/liquid interface.

Sn-Ag-Cu alloys are considered one of the most favorable lead-free solder systems. In slowly-cooled eutectic Sn-Ag-Cu alloys, sometimes large primary Ag3Sn or Cu6Sn5 intermetallic compounds (IMCs) form. These IMCs may affect the mechanical properties of solders. However, explanations for the formation of these IMCs are still not clear. This study deals with interrupted tests in order to clarify the nucleation of IMCs in the liquid phase. In this study, Sn-4.41Ag-0.63Cu and Sn-3.30Ag-1.47Cu alloys were prepared. According to the thermodynamic calculation, Pandat, the equilibrium solidification paths are described as follows: Sn-4.41Ag-0.63Cu :L → primary Ag3Sn → binary eutectic (Ag3Sn +Sn) → ternary eutectic; Sn-3.30Ag-1.47Cu :L → primary Cu6Sn5 → binary eutectic (Cu6Sn5 + Sn)→ ternary eutectic. The actual solidification process was different from the estimation from the equilibrium phase diagram. In the case of Sn-4.41Ag-0.63Cu, only Ag3Sn grew as a primary phase in the liquid, while in the case of Sn-3.30Ag-1.47Cu, not only primary Cu6Sn5 but also pseudo-primary Ag3Sn grew in the liquid. Ag3Sn may nucleate easily in the liquid phase, but Cu6Sn5 would not nucleate in the liquid.