Eutectic Sn Research Articles

Microstructure evolution at the interface between Cu and eutectic Sn–Bi alloy with the addition of Ag or Ni

The study investigated the growth kinetics and rate-controlling processes of intermetallic layers formed at the interface between Cu and eutectic Sn–Bi alloys with Ag or Ni addition at solid-state temperatures. Isothermal sections of the equilibrium phase diagram were calculated to understand phase stability at the interface. The thicknesses of the intermetallic layers were plotted against annealing time, and a power function equation with an exponent slightly smaller than 0.25 described their relationship, indicating boundary diffusion with grain growth as the predominant control mechanism. The relationship between the exponent and annealing temperature suggested that the grain growth in the intermetallic layer followed an approximate parabolic law. The eutectic microstructure in Sn–57Bi–1Ag and Sn–57Bi–1Ni alloys changed with annealing, with differences in the Bi region width. However, the contact surface area between the Bi region and Cu6Sn5 compound was similar in both alloys. Activation enthalpies for the rate-controlling process of intermetallic layer growth were evaluated, providing insights into the energy barrier for atomic diffusion or transport across the interface.

Growth behavior of intermetallic layers at the interface between Cu and eutectic Sn–Bi by grain boundary diffusion with the grain growth at solid-state temperatures

The growth kinetics and rate-controlling processes of intermetallic layers formed in Cu/(Sn-58 wt% Bi) diffusion couples were investigated. Isothermal annealing of diffusion couples was conducted in the temperature range of 363–393 K for various times up to 384 h. In the diffusion couple, an intermetallic layer composed of Cu6Sn5 with irregular scallop shapes and Cu3Sn with relatively uniform thickness forms at the Cu/(Sn–Bi) interface. Isothermal sections of the equilibrium phase diagram in the ternary Bi–Cu–Sn system were calculated at the isothermal annealing temperatures and the peak temperature of the reflow process by a CALPHAD (calculation of phase diagrams) method. The diffusion path passes through the three-phase tie-triangle, including Cu6Sn5 and Cu3Sn. The obtained thicknesses were plotted against the annealing time, and a power function equation was found to describe their relationship. The values of the exponent in the power function were close to 0.25, indicating that the layer growth was predominantly controlled by boundary diffusion with the grain growth. Furthermore, the exponent values were relatively insensitive to the annealing temperature. The relationship between the exponent and the annealing temperature was analyzed, and it was concluded that the grain growth in the intermetallic layer followed a parabolic law. The growth and morphology evolution of the intermetallic compound and Sn–Bi eutectic microstructure at the interface were depicted, shedding light on the widening of the eutectic microstructure. Additionally, the activation enthalpy for the rate-controlling process of intermetallic layer growth at solid-state temperatures was evaluated using a least-squares method, providing insights into the energy barrier for the diffusion or transport of atoms across the interface. This study contributes to a better understanding of intermetallic layer formation and growth in Cu/(eutectic Sn–Bi) diffusion couples, offering valuable information for developing reliable solder joints and high-temperature solders.

Microstructural, thermal and mechanical properties of Co added Sn–0.7Cu lead-free solder alloy

This study investigated the effects of cobalt microalloying addition on the microstructural features, thermal characteristics and mechanical behavior of eutectic Sn–0.7wt%Cu lead-free solder alloys. The results show that minor cobalt addition of ~ 0.05 wt% causes significant grain refinement of β-Sn, facilitates the formation of fine fibers (Cu,Co)6Sn5 phases and preventing the formation of η′-Cu6Sn5 phases, whereas a large amount of Co (~ 0.5 wt%) additions accumulated in the (Cu,Co)6Sn5 IMCs and clearly changed into coarse fibers. The precipitation strengthening mechanisms of fine fibers (Cu,Co)6Sn5 in the β-Sn matrix increased the ultimate tensile strength (UTS) and Young’s modulus (Y) of the alloy from 30.5 MPa and 15 GPa to 44.6 MPa and 22.3 GPa, respectively, but the ductility decreased from 60 to 45.7%. The coarse fibers (Cu,Co)6Sn5 in eutectic alloys is of interest from not only increased UTS and Y to 38.7 MPa and 16.3 GPa but also maintaining the ductility at the same level, allowing for unique microstructure design. Furthermore, 0.05wt% of Co significantly reduce the onset, eutectic temperatures and undercooling, although pasty rang has been slightly raised, which may enhance the thermal characteristics. This presumably has important implications for the reliability of solders as well as their performance in electronic service.

Microstructure and morphology of the soldering interface of Sn–2.0Ag–1.5Zn low Ag content lead-free solder ball and different substrates

Eutectic Sn–Ag–Cu lead-free solder has limited applications due to cost and reliability issues. Sn–Ag–Zn solder has the advantages of low melting point, good mechanical properties and reliable welding interface. However, the research system of low silver content Sn–Ag–Zn solder is incomplete. In this paper, Sn–2.0Ag–1.5Zn low silver content alloy solder is soldered to different substrates. The interfacial reaction after soldering and the microstructure and reliability under different aging treatment conditions are studied. Sn–2.0Ag–1.5Zn solder is made into solder balls by direct melting method. The solder balls are placed in a solder strength tester to be heated and welded to the substrate, and then the solder joints are placed in a heating furnace for aging treatment. The results show that the solder is soldered to the bare Cu substrate, and a dense double-layer Intermetallic Compound (IMC) structure of Cu5Zn8 and Ag3Sn is formed at the interface after aging treatment. The double-layer structure blocks each other, limiting the development of copper-tin IMCs. The solder is soldered with the Cu substrate electroplated with Ni barrier layer, and the soldering interface forms a thin layer of Ni3Sn4 metal compound. After aging for 1000 h, the thickness of Ni3Sn4 is about 1 μm, the thickness of Ni barrier layer is kept at 2–3 μm, and the barrier effect of Ni barrier layer is stable. Sn–2.0Ag–1.5Zn solder has excellent loss performance in long aging treatment. It has good heat-resistance aging treatment, good quality of solder connection, high interface reliability and less environmental pollution. The low silver content in Sn–2.0Ag–1.5Zn solder results in a significant cost reduction. Coarse IMC Ag3Sn is not easily formed. The optimized ratio of Ag and Zn in Sn–2.0Ag–1.5Zn solder improves the strength and toughness of the solder joint. The performance has been improved, and it is a very promising alloy solder.

Microalloying effects of Sb and Ag on the microstructural evolution of eutectic Sn–Bi alloys

Microalloying effects of Sb and Ag on the microstructural evolution of eutectic Sn–Bi alloys

Experimental investigation of melt infiltration and solidification in a pre-heated particle bed

Fluid infiltration, solidification, and remelting in a particle bed are complex phenomena that can occur in the lower head of a reactor pressure vessel (an in-vessel phenomenon) or in the reactor cavity below the vessel (an ex-vessel phenomenon) during a severe accident in a nuclear power plant. When the non-homogeneous corium, consisting of metal and oxide components, reheats, the lower-melting metals will melt first and move downward to the bottom of the reactor pressure vessel. This will change the global debris bed configuration and its physical and chemical properties, and thereby actively influence the accident progression, specifically the mode and timing of possible vessel failure and the melt characteristics upon release. Similar ex-vessel debris can form on the cavity floor below the vessel, which can threaten containment integrity if stable cooling is not established. In this paper, we present an experimental program employing recently constructed MRSPOD (multicomponent remelting, relocation, and solidification in porous debris) facility that mainly investigates melt infiltration, solidification, remelting, and relocation in a particulate debris bed. The facility uses a 12 × 130 cm2 (OD × Length) quartz tube in a cylindrical furnace and allows a debris bed to be configured, heated, and/or pressurized prior to fluid infiltration through the bed. The MRSPOD experiments were instrumented with thermocouples (TCs), fiber Bragg grating (FBG) sensors, laser sensor, video, and infrared cameras, which are essential in describing the overall melt infiltration and solidification behavior. Here, a eutectic Sn–Bi melt with superheat temperature between 50 and 70 °C is poured into a preheated particle bed consisting of 1.5-mm spherical particles made of either copper (Cu), Sn-coated Cu, stainless steel (SS), Sn-coated SS, and/or glass beads to study the effect of thermal properties and wettability on the melt infiltration. Moreover, melt infiltration into a single-layer, multi-layer, and two-columnar particle beds is performed. Measurements from TCs, FBGs, and observations from video cameras have revealed a non-linear kinetics of melt infiltration. Moreover, the extracted ingots after the experiments have shown the complex infiltration process under similar test conditions.

Reliability of laser soldering using low melting temperature eutectic Sn Bi solder and electroless Ni-electroless Pd-immersion Au-finished Cu pad

The demand for flexible wearable devices/substrates with miniaturization and improved integration in microelectronic devices has intensified the research interest in low-temperature laser soldering processes as an alternative to conventional reflow soldering processes owing to their advantages, such as local heating, non-contact heating, and short bonding time. In this study, we compared and evaluated the reliability of laser soldered and conventional reflow soldered joints using representative low melting temperature eutectic Sn Bi solder and thin electroless Ni-electroless Pd-immersion Au (ENEPIG)-finished Cu pads. Laser soldering was performed using various laser powers (130, 150, and 170 W) and times (2 and 4 s). Furthermore, an aging test was performed at 110 °C for 2000 h to evaluate the long-term reliability of the soldered joints. The mechanical properties, including the top and cross-sectional views and fracture surfaces, of the soldered joints were analyzed by conducting shear tests after aging. During laser soldering, various intermetallic compounds (IMCs) were formed at the joints depending on the applied energy. The metallization layer and Cu reacted with Sn in the solder after different aging durations, and additional IMCs were formed and grown. After aging for 2000 h, the shear strength decreased, and the interfacial IMC thickness increased. As the aging time increased, the fracture mode changed from an initial ductile fracture to brittle fracture (between the solder and IMCs and/or between IMCs and the Cu pad). The reflow soldered joints exhibited stable shear strength, resulting in ductile fracture until aging for 500 h. However, the shear strength decreased sharply after aging for 1000 and 2000 h, and Bi-segregation was observed after aging for 1000 h, resulting in inferior long-term reliability. After laser soldering at 150 and 170 W for 4 s, the strength of the samples decreased sharply after aging for 1000 and 250 h, respectively, and Bi-segregation was observed after aging for 2000 h. The shear strength of the sample laser soldered at 170 W for 2 s gradually decreased with increasing aging time and maintained a stable shear strength until aging for 2000 h. Therefore, laser soldering at 170 W for 2 s was considered as the optimal condition for long-term reliability. • Soldering properties of laser soldered Sn-58Bi/Au/Pd/Ni-finished Cu joints evaluated. • Laser soldering results were compared with conventional reflow soldered joints. • Various IMCs were formed depending on laser power and irradiation time. • Laser conditions with low applied energy displayed superior long-term reliability. • Selection of the optimal laser conditions is crucial to ensure reliable solder joints.

Effects of tin particles addition on structural and mechanical properties of eutectic Sn–58Bi solder joint

Effects of tin particles addition on structural and mechanical properties of eutectic Sn–58Bi solder joint

Development of holmium doped eutectic Sn-Ag lead-free solder for electronic packaging

PurposeThis study aims to summarize the effects of minor addition of Ho REE on the structure, mechanical strength and thermal stability of binary Sn- Ag solder alloys for high-performance applications.Design/methodology/approachThis study investigates the effect of a small amount of holmium addition on the microstructure, thermal stability, mechanical behaviour and wettability of environmentally friendly eutectic melt-spun process Sn – Ag solder alloys. Dynamic resonance technique, X-ray diffraction (XRD) and scanning electron microscopy were carried to study stiffness, identification of the phases and the morphology features of the solder. Structure and microstructure analysis indicated that presence of rhombohedral ß-Sn phase in addition to orthorhombic IMC Ag3Sn phase dispersed in Sn-matrix. Also, the results showed that Ho rare earth addition at a small trace amount into Sn-Ag system reduces and improves the particle size of both rhombohedral ß-Sn and orthorhombic IMC Ag3Sn based on the adsorption effect of the active RE element. The adsorption of Ho at grain boundaries resulted in Ag3Sn more uniform needle-like which is distributed in the ß-Sn matrix. The fine and uniform microstructure leads to improvement of mechanical strength. The microstructure refinement is due to the high surface free energy of IMC Ag3Sn grains, and it prevents the dislocation slipping. This maybe enhance the micro-hardness and micro-creep hence delays the breaking point of the solder. Ho (RE) trace addition could enhance the melting temperature and contact angle up to 215°C and 31°, Respectively, compared with plain solder. All results showed that Ho trace addition element has an effective method to enhance new solder joints.FindingsEffect of rare earth element Ho particles on the microstructure and mechanical behavior of eutectic Sn-3.5Ag solder alloy was studied. Some important conclusions are summarized in the following: microstructure investigations revealed that the addition of Ho particles to eutectic Sn-3.5Ag inhibited in reducing and refines the crystallite size as well as the Ag3Sn IMC which reinforced the strength of plain solder alloy. The mechanical properties values such as Young’s modulus, Vickers microhardness of Sn-3.5Ag solder alloy can be significantly improved by adding a trace amount of Ho particles compared with plain solder due to the existence of finer and higher volume fraction of Ag3SnIMC. These variations can be understood by considering the plastic deformation. The strengthening mechanism of the Sn-3.5Ag-Ho solder alloy could be explained in terms of Ho harden particles and finer IMC, which are distributed within eutectic regions because they act as pinning centres which inhibited the mobility of dislocation that concentrated around the grain boundaries. The results show that the best creep resistance is obtained when the addition of Ho 0.5 is compared to plain solder. The addition of Ho on Sn-3.5Ag lead-free solder alloy decreases the melting temperature to few degrees.Originality/valueDevelopment of holmium-doped eutectic Sn-Ag lead-free solder for electronic packaging.

Effect of Zn addition on alloy by 0.3, 0.6 and 0.9 wt.% on thermal properties, electrical conductivity and microstructure of eutectic Sn-3.5Ag alloy

In this work, the effects of 0.3, 0.6 and 0.9 wt.% Zn additives on the characteristic of Sn3.5Ag eutectic solder alloy, have been diluted to produce four micro alloys. Effects of 0.3 to 0.9 wt% Zn- additions on phase transformation and electrical resistivity of Sn-3.5Ag eutectic solder alloy have been investigated using Differential Scanning Calorimetry (DSC) and Keithley Source Meter (SMU), respectively. The addition of Zn reduced the melting point of the eutectic Sn–3.5Ag alloy and the pasty range (Tend - Tonset) for the Sn-3.5Ag-0.3Zn, Sn-3.5Ag-0.6Zn and Sn-3.5Ag-0.9Zn solder alloys are 8.34, 8.31 and 7.12 °C respectively, decreased from four micro alloys 8.34 °C to 7.12 °C. These results show that the Zn addition is beneficial to decrease the heat of fusion of the Sn-3.5Ag solder alloy This improvement is an indication for property enhancing the mechanical properties. It is showing that the solder alloy needs the lowest energy for melting and it is a useful for saving energy also the resistivity increases continuously with Zn content.

Effect of Sb and Zn Addition on the Microstructures and Tensile Properties of Sn-Bi-Based Alloys.

The tensile behavior of Sn–Bi–Cu and Sn–Bi–Ni alloys has been widely investigated. Reportedly, the addition of small amounts of a third element can refine the microstructures of the eutectic Sn-58mass% Bi solder and improve its ductility. However, the superplasticity mechanism of Sn-based alloys has not been clearly established. Therefore, in this study, the effects of Sb and Zn addition on the microstructures and tensile properties of Sn–Bi-based alloys were investigated. The alloys were subjected to tensile tests under various strain rates and temperatures. We found that Zn- and Sb-added Sn–Bi-based alloys demonstrated superplastic deformation at high temperatures and low strain rates. Sb addition significantly affected the elongation of the Sn–Bi–Sb alloys because the metal dissolves in both the primary Sn phase and the eutectic Sn–Bi matrix. The segregation of Zn and formation of needle-like Zn particles at the eutectic Sn–Bi phase boundary affected the superplastic deformation of the alloys. The deformation of the Sn–40Bi-based alloys at high temperatures and low strain rates led to dynamic recovery, dynamic recrystallization, and/or grain boundary slip because of the accumulation of voids.

Influence of Sb additions on surface tension and density of Sn–Sb, Sn–Ag–Sb and Sn–Ag–Cu–Sb alloys: Experiment vs. modeling

Abstract Surface tension and density measurements by maximum bubble pressure and dilatometric techniques were carried out in an extensive range of temperature on liquid alloys close to the ternary eutectic Sn3.3Ag0.76Cu with different Sb content. It has been found that the addition of Sb to Sn, Sn–Sb, to binary eutectic Sn–Ag and to Sn3.3Ag0.76Cu decreases the surface tension and density. The values of the surface tension calculated by the Butler model and by the method based on the binary alloys surface tension data with the ternary and quaternary correction factors were compared with the experimental results. The best agreement between the measured and the calculated values was observed for the model comprising the binary data with the correction factors.

Mixed Assembly of Lead-free Solder Joint: A Short Review

The transition from lead (Pb) to Pb-free solder has arisen the need for the development of the reliability of mixed assemblies solder joint research. Mixed assemblies are defined as solder joints that joint together with different compositions or solder forms for example Ball Grid Array (BGA) and solder paste. During the transition period of solder materials, mixed assemblies are still used in electronic packaging. In addition, Pb-free manufacturing has been forced to release some of the product categories since legislation banning the use of lead solder in electronic assemblies. This phenomenon causes health and environmental concern of the Pb solder used in electronic assembly. Hence, some electronic assemblies will continue to use traditional eutectic Sn–Pb solder paste while others will use Pb-free solder paste. This situation indicates that the use of mixed assemblies in electronics manufacturing is still inevitable. This paper presents a projection of the reliability of mixed assembly’s Pb-free solder joint.

Graphene as a diffusion barrier at the interface of Liquid–State low-melting Sn–58Bi alloy and copper foil

Graphene is widely used as a barrier at the solid–solid and gas–solid state interface. However, the use of graphene as a barrier at the liquid–solid interface has been rarely reported, particularly in the case of a liquid-state metal and a solid-state metal interface. Herein, a graphene layer is synthesized on a Cu foil, and single-layer and bilayer graphene is detected via Raman spectroscopy. The interfacial intermetallic compound between eutectic Sn–58Bi alloy with a melting temperature of 138 °C and Cu with a melting temperature of 1085 °C can be significantly suppressed by graphene using different reflow temperatures (180 °C and 300 °C) and reflow times (144–625 s). Cu diffusion through graphene is visible in the Sn–Cu intermetallic compound (IMC) formations in the SB58 solder and at the interface after the reflow processes. We found that the activation energy of Cu diffusion through graphene into the liquid-state graphene is ∼ 32.6 kJ/(mol∙k), which is higher than that attained without graphene. Therefore, the findings of this study show that graphene is a promising diffusion barrier for the liquid–solid interface.

Influence of bismuth (Bi) addition on the structure and properties of annealed Sn-9Zn eutectic binary solder alloy

ABSTRACT The Sn-9Zn eutectic alloy has been considered as a potential replacement for toxic lead-based solders for its lower melting point (198 °C) and improved mechanical properties compared to traditional lead-based solder alloys. This paper investigates the influence of bismuth (Bi) addition as a surface-active element on the structural, thermal, mechanical, and electrical properties of eutectic Sn–9Zn alloy. Different amounts of Bi were added (x = 0.5, 1, 2, 3, wt %) to study the characteristics of Sn-9Zn-xBi ternary alloys followed by annealing at 150 °C for 60 minutes. Microstructures and phase constituents of developed alloys were examined and compared using optical microscopy and XRD respectively. The melting point and coefficient of linear thermal expansion were determined by differential thermal analysis and thermo-mechanical analysis. Tensile Properties (ultimate tensile strength, elongation, %), microhardness (HV), and electrical conductivity (% IACS) were measured. The results indicated that the addition of Bi decreased the melting point by about 10 °C, the heat of fusion, coefficient of thermal expansion, electrical conductivity than Sn-9Zn eutectic alloy. Bi addition enhanced the ultimate tensile strength and hardness by about 65% by 50% respectively. SnBi inter-metallic compound (IMC) precipitates were formed and extracted from the β-Sn matrix with a non-uniform microstructure.

Enhancement of electrochemical and thermal bonding reliability by forming a Cu3Sn intermetallic compound using Cu and Sn–58Bi

Cu–Cu bonding was successfully achieved through the transient liquid phase sintering (TLPS) bonding method using Cu and an eutectic Sn–Bi alloy. The bonding process was performed for total bonding process time of 2 h under a pressureless condition in air. The bonding temperature was 220 °C considering that the Cu6Sn5 intermetallic compound (IMC) and Bi react at 195.9 °C to transform into Cu3Sn and a liquid. The shear strength of Cu-70(Sn–58Bi) was approximately 22.06 MPa with the formation of the Cu3Sn. The residual eutectic Sn–Bi structure remained at Cu-90(Sn–58Bi), and the voids were largely observed at Cu-50(Sn–58Bi). In case of Cu-70(Sn–58Bi) and Cu-50(Sn–58Bi), the remelting temperature increased to 270 °C by the IMC reaction between Cu and Sn. On the other hand, the remelting temperature of Cu-90(Sn–58Bi) joint remained at 139 °C due to residual eutectic Sn–Bi structure. The salt spray test was conducted at 35 °C under the 5% NaCl condition for 24, 48, and 96 h to evaluate the bonding reliability under the salt spray condition. The corrosion behavior was evaluated using the electrochemical impedance spectroscopy measuring method. In addition, the thermal bonding reliability was investigated through a high-temperature storage test at 200 °C for 100, 500, and 1000 h. Analysis results of the experiment showed that the electrochemical and thermal bonding reliabilities were improved with the Cu3Sn formation owing to its high resistance properties under the salt spray and high-temperature conditions.

Sn – Zn – Ga alloys for leadfree soldering obtained by rapid quenching

The paper presents the results of a study of the structural-phase state of the foil of eutectic near eutectic Sn – Zn alloys doped by Ga obtained by rapid melt quenching at a melt cooling rate of 105 K/s. Using the methods of X-ray diffraction analysis, scanning electron microscopy, and X-ray spectrometry, it was established that the foil solidifies with the formation of tin-based supersaturated solid solution and its microstructure is formed as a result of the decomposition of the solid solution by discontinuous mechanism at room temperature. The homogeneity of the composition and distribution of gallium and zinc inclusions over the volume of the foil was established. Using the electron backscatter diffraction technique, it was shown that the foils have a microcrystalline structure due to the deep supercooling of the melt, which leads to a high crystal nucleation rate. The grain size decreases depending on the distance to the mold. The increase in grain size is associated with a change in the solidification conditions over the thickness of the foil: deterioration of heat removal and a decrease in supercooling. There is no pronounced grain texture in the foils.

Chromium improvements on the mechanical performance of a rapidly solidified eutectic Sn–Ag alloy

The eutectic Sn–Ag alloy considered a good replacement to the conventional solders. This study aims to enhance the mechanical performance of the eutectic Sn–Ag alloy in terms of both elasticity and plasticity through investigating the effects of chromium (Cr) content with x = 1, 3, and 5 wt.% on the mechanical and thermal properties of melt-spun Sn–3.5%Ag alloy. Ternary melt-spun Sn–Ag–Cr alloys investigated using x-ray diffractions (XRD), Scanning electron microscope (SEM), Instron machine, Vickers hardness tester, and Differential scanning calorimetry (DSC). The results revealed that the Cr content modifies the microstructure by refining the microstructure of the matrix of Sn solder; suppressing coarse intermetallic compound (IMC) formation; and changing the morphology of the IMC in Sn solder. The high concentration of multi-oriental Ag3Sn that formed with 3 wt.% of Cr, in addition to the compatibility among β-Sn (Tetragonal), Ag3Sn (004) (orthorhombic), and Cr (200) (bcc), enhance the elasticity of melt-spun Sn93.5–Ag3.5–Cr3 solder alloy by 330% (87.98 GPa) and obstructed the fracture process. The tensile test for that melt-spun alloy (3 wt.% of Cr) showed obvious improvements in ultimate tensile strength (UST) by 19% (23.42 MPa), and in toughness by 15.31% (911.15 J m−3) compared to that of the eutectic melt-spun Sn–Ag alloy. Its hardness (Vickers hardness) value has improved by 22.37% (171.50 GPa) compared with that of the eutectic melt-spun Sn–Ag alloy. Slight improvements in thermal performance for that alloy have appeared through thermal conductivity by 8% (49.971 w m−1 k−1) and thermal diffusivity by 85.4% (2.758 × 10–7 m2 s–1) compared to that of the eutectic melt-spun Sn–Ag alloy. All of the above-mentioned improvements are related to the microstructural changes with 3 wt.% of Cr to the eutectic Sn–Ag alloy. The high elasticity, high plasticity, low ∆T, and relatively low melting temperature (Tm) that have been taking place with 3 wt.% of Cr are suggested to increase the mechanical reliability of this alloy to become more desirable in soldering applications and electronic assembly.

Improvement of microstructure and tensile properties of Sn–Bi–Ag alloy by heterogeneous nucleation of β-Sn on Ag3Sn

Different weight fractions (0, 0.5, 1.0, 2.0, and 3.0 wt%) of sliver (Ag) were used to dope Sn–Bi eutectic alloys in this study. The microstructure and tensile and thermal properties of Sn–Bi eutectic alloys doped with Ag were investigated. The results indicate that the addition of Ag increases the solidification temperature and reduces the fusing latent heat of alloy, but it has no significant effect on the melting point of the alloy. According to the electron backscattered diffraction (EBSD) analysis and calculation of the disregistry between ε-Ag3Sn and β-Sn, ε-Ag3Sn can be used as the heterogeneous nucleation substrate of β-Sn, thus refining lamellar eutectic spacing. The orientation relationship between the ε-Ag3Sn phase and the β-Sn phase was as follows: [ 0 2‾1 ]Ag3Sn//[ 0 1 2 ]β-Sn, (0 1 2)Ag3Sn//(‾1 2‾1) β-Sn, and [‾1 2 0 ]Ag3Sn//[ 0 1 2 ]β-Sn, (2 1‾1)Ag3Sn//(‾1 2‾1)β-Sn. The tensile strength of the eutectic Sn–Bi alloy with addition of 1.0 wt% Ag reached 72 MPa, which was 20% higher than that of the original alloy. The analysis showed that Ag doping increase the tensile strength of the eutectic Sn–Bi alloy, because of fine grain strengthening and second phase strengthening mechanism

The structure of rapidly solidified foil of the eutectic Sn – 8.8 wt. % Zn alloy

Microstructure of rapidly solidified eutectic alloy foil Sn – 8.8 wt. % Zn was studied. The alloy foil consists of solid solutions of zinc and tin. Dark equiaxed dispersed precipitates of zinc solid solution are uniformly interspersed in the matrix of tin solid solution. The parameters of the microstructure were determined. The average chord of a random secant at the sections of precipitates of a solid solution of zinc is 0.33 mm, and the specific interface surface is 0.81 mm–1. The precipitations of the tin solid solution have a microcrystalline structure. Specific surface of high angle boundaries less than 1 mm–1. The texture of the precipitates of solid solutions of tin and zinc in the foil was studied, and the pole densities of the diffraction lines of these phases are presented. The tin solid solution has the texture (100), and the zinc solid solution has the (0001) texture, which is explained by the predominant growth of grains, in which the crystalline planes of (100) tin and (0001) zinc are most closely packed and perpendicular to the heat flux. Eutectic alloy Sn – 8.8 wt. % Zn is in an unstable state. Annealing the foil causes the dissolution of small and coarsening of large particles of zinc solid solution, as well as the decomposition of a supersaturated tin solid solution. These processes cause an enlargement of the microstructure: an increase in the average particle size (dZn) of a solid solution of zinc and its volume fraction (VZn), a decrease in the specific surface (S ) of interphase boundaries.