Sn-Bi Alloys Research Articles

Preparation of Microencapsulated Low‐Melting‐Point Sn–Bi Alloy for Latent Heat Storage

Low‐melting‐point SnBi alloy is a good phase change material (PCM) with high thermal conductivity and good stability for heat storage over 100 °C, which can be used for waste heat recovery and solar thermal storage. To solve the critical leakage problem and increase the heat transfer area of PCM, the fabrication of microcapsules of SnBi that are encapsulated by the stable SnO2 oxide shell is reported. The microcapsules are prepared by a two‐step method, in which the SnBi alloy microspheres are first treated by hot water or vapor and second heat treated under an oxygen atmosphere. The SnBi@SnO2 microcapsules are well sealed, and can endure a melting–solidification thermal cycle over 100 cycles with good stability. The microcapsules have a melting point of around 139 °C and an enthalpy of around 43 J g−1, similar to the theoretical values of SnBi. The simple preparation method and good thermal properties of the microcapsules ensures their application in heat storage and thermal management.

Highly anisotropic metallized wood obtained by filling basswood channels with low-melting-point Sn-Bi alloy

Basswood and Sn-Bi alloy have several complementary properties—the former has a low density, no electromagnetic shielding, poor thermal and electrical conductivity, and low impact toughness, while the latter has exactly the opposite properties. Combining the natural porous structure of basswood with a low-melting Sn-Bi alloy can produce a composite with the merits of both materials. In this study, basswood was pretreated with 5 % ammonia water, and then the Sn-Bi alloy was filled into the cell lumens and vessels without lignin at 138 ℃ and 3000 Pa. After metallization, the density of the basswood increased from 0.5 g·cm−3 to 3.0 g·cm−3, reaching six times its initial value, which also doubled the impact toughness. The total electromagnetic interference shielding effectiveness of the metallized basswood obtained using different filling methods ranged from 45 dB to 70 dB. Heat-transfer simulations and circuit experiments were carried out to investigate the thermal and electrical conductivity of this composite, and the results demonstrated its anisotropic conductivity. These properties showed that the metallized basswood could be used as a functional or structural material in different fields.

Effect of nano-phased bismuth–tin alloy surface coating on tribo-mechanical properties of basalt fiber reinforced composites

A novel method for coating basalt fiber with a eutectic bismuth–tin (Bi–Sn) mixture was developed. Bi-Sn nanoparticles were synthesized using a sol-gel process and deposited on basalt fiber by chemical vapor deposition, with the aim of evaluating the tribo-mechanical properties of the final epoxy-composite material. X-ray diffraction showed that the synthesized Bi–Sn alloy was highly polycrystalline with equal distribution of tetragonal and orthorhombic Bi–Sn polymorph phases with crystallite sizes between 17 and 55 nm. High-resolution electron microscopy revealed that the sample possesses highly fused, flake-stacked planar layers, with 50 nm-thick flakes of variable length. Elemental analysis determined that the alloy contains 57% Bi (at.wt%), and Raman spectroscopy confirmed the characteristic Bi–Sn fingerprint peaks of 148, 201, and 397 cm−1. Thermal analysis of the composites showed good thermal stability with only 4% mass loss at 700 °C. Furthermore, an increase in the Bi–Sn loading enhanced the tribo-tensile properties. It was found that at a Bi-Sn gravimetric loading of 0.2 g the composite yielded the highest ultimate tensile strength of 303 MPa compared to the reference (154 MPa), even as the Young's moduli showed a decrease in elasticity by up to 24.99%. Moreover, the tribology results showed a good friction coefficient (0.5), with a negligible wear rate (4.53 × 10−8 mm3/Nm) and relatively low wear volume (0.118 mm3). Thus, the proposed method resulted in alloy composites with improved tribo-mechanical properties, and has potential applicability in the development of lead-free solders.

Microstructural analysis and thermal conductivity of the Ag–Bi–Sn alloys

Structural and thermal properties of five Ag–Bi–Sn ternary alloys with tin content ranging from 12.8 to 75.1 mass% and nearly equal mass contents of silver and bismuth were investigated in this study. Microstructures and melting properties of as-solidified alloy samples were examined using scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS), X-ray diffraction (XRD) analysis, and differential thermal analysis (DTA) in combination with the CALPHAD (CALculation of PHase Diagram) method. The observed microconstituents were Ag3Sn, (Sn) and, (Bi) phases as well as ternary (Sn)+(Bi)+Ag3Sn eutectic. The measured temperature of the ternary eutectic reaction was 138.0°C.The flash method was used for thermal diffusivity measurements in the temperature range from 25 to 100°C. Based on the measured values of thermal diffusivity, thermal conductivity of the solid Ag–Bi–Sn alloys was obtained. Thermal conductivity of the studied Ag–Bi–Sn ternary alloys considerably increases with increasing tin concentration and slightly decreases with increasing temperature.

Dynamic recrystallization behavior and strengthening mechanism of quasi-precipitate-free dilute Mg–Bi–Sn alloy

In this study, a dilute Mg–0.5Bi–0.5Sn alloy system was designed and subjected to extrusion at a low temperature of 250 °C. The dynamic recrystallization behavior and strengthening mechanism of the extruded alloy were discussed in detail. At the initial stage of the extrusion process, the dynamic recrystallized grains were formed through twinning-induced dynamic recrystallization (TDRX), continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). In the middle stage of extrusion, the emergence of CDRX and DDRX were synergistic. In the later stage of extrusion, DDRX and CDRX were exclusive and DDRX was the dominant mode. For the dilute extruded Mg–0.5Bi–0.5Sn alloy, the ultimate tensile strength, tensile yield strength and elongation were 282 MPa, 212.4 MPa and 36.3%, respectively, reaching an excellent high strength-ductility balance. The enhanced strength has been an outcome resulting from grain boundary strengthening and texture strengthening, along with dislocation strengthening. Ductility enhancement is closely related to the easily activation of <c+a> slips, which can be ascribed to the relatively high Schmid factor.

Microstructure and Mechanical Properties of Sn58Bi Components Prepared by Laser Beam Powder Bed Fusion

As a low melting point alloy, Sn58Bi alloy plays a unique role in many fields. However, the brittleness of Sn58Bi alloy is a limitation that has to be addressed for wider applications. According to previous studies, third element addition is favorable for improved ductility, which is attributable to structure refinement. Therefore, laser beam powder bed fusion technology was adopted to prepare Sn58Bi alloy components. Additionally, the as-printed specimens presented more refined structures compared to the as-cast specimen, so they showed better plasticity. The Sn58Bi alloy showed excellent formability when specimens were prepared by LBPBF between 40–80 W. The density of specimens nearly remained stable above laser power higher than 40 W, and CT scanning could not detect internal defects, so the Sn58Bi alloy specimen was likely to be well fabricated at high laser power. Within the laser power range of 40–80 W, with the variation of laser power or scanning velocity, the laser energy density changed accordingly, and the mechanical strength of specimens was improved with the increase of laser power density. This strength change was probably related to the microstructure evolution and internal residual stress in the printing process.

Self-healing action of Bi in high-performance Sb–Bi–Sn positive electrodes for liquid metal batteries

Li||Sb–Bi–Sn liquid metal batteries (LMBs) have comprehensive advantages of a high energy density, excellent rate capability, low material costs, and high cycle performance. However, the corrosion of the positive electrode to the current collector at high temperatures cannot be neglected over the long term. Here, we investigate the corrosion behavior of SS304 in two types of Sb–Bi–Sn alloys under static and cell cycling conditions. Interestingly, we find that the cell performance of Li||Sb–Bi–Sn LMBs are not affected by corrosion between the positive electrode and stainless-steel current collector. The corrosion products and their participation in the cell reaction process are determined using ex situ analyses and electrochemical measurements. Bi not only inhibits the dissolution of SS304 in Sb–Bi–Sn alloy but also spontaneously promotes the decomposition of Fe–Sb and Fe–Cr–Sb corrosion products during lithiation, releasing the active component Sb, and Sb–Bi–Sn alloy is recovered. Encouragingly, even in the event of corrosion, the cell capacity, efficiency, and cycle stability remain almost unaffected due to this self-healing action of Bi. This study represents a new direction toward inhibiting the corrosion of positive electrode and stabilizing cell performance for practical application and commercialization by alloying.

Effects of various second phase ratios and contents on microstructure and mechanical properties of eutectic Sn58Bi alloy

A distinctive low melting point heterostructure alloy (LMH) Sn-Bi-Cu-Zn-Ag-Sb was prepared by introducing different ratios and contents of second phase into the eutectic Sn58Bi alloy (SBE). Rapid solidification results in a dispersion of Cu5Zn8, Ag3Sn, and SbSn precipitated phases in Sn53Bi3Cu3Zn2Ag2Sb (LMH32). Besides, the nano-sized η'-Cu6Sn5 and Ag3Sn phases were also observed in the alloy matrix. During solidification, the Cu5Zn8 and Ag3Sn phases are used as the heterogeneous nucleation matrix of the Sn and Bi phases, which significantly refines the eutectic structure and leads to fine-grained strengthening. And the formation of Sn(Sb) solid solution phase leads to solid solution strengthening. The significant mechanical incompatibility between the matrix and the second phases of the LMHs produces a higher back stress hardening effect. The coupling effect of multiple strengthening mechanisms causes the ultimate tensile strength (UTS) of LMH32 reaches 102 MPa, higher 88.9% than that of SBE, and the elongation reaches 12.8%, but the melting point does not change significantly.

The corrosion behavior of Sn-58Bi alloy in DL-malic acid solutions with various concentrations

The corrosion behavior of Sn-58Bi alloy in DL-malic acid solutions with different concentrations has been explored via electrochemistry and physical methods. Results indicate films formed on the surface of Sn-58Bi alloy are p-type semiconductors, consisting of SnO2 and nonstoichiometric SnOx (1 < x < 2). With the increasing of DL-malic acid concentration, the corrosion resistance increases first then decreases, and the maximum appears at 7 wt%, where the thickest film and the minimum proportion of SnOx emerge. The SnOx with massive electron holes as charge carriers makes the film less protective. Both the thickness of the film and the proportion of SnOx are responsible for the corrosion behavior of Sn-58Bi alloy in DL-malic solutions.

Effect of Low Bi Content on Reliability of Sn-Bi Alloy Joints Before and After Thermal Aging

Sn-58Bi, an eutectic alloy, has been explored for use as a low-temperature lead-free solder alloy. However, the properties of Sn-Bi alloys as well as those of their joints need to be improved significantly so that these alloys can be applicable for practical use. In particular, two drawbacks need to be addressed: the intrinsic brittleness of Bi and the microstructure coarsening of these alloys during aging. In this study, Sn-Bi-Zn (SBZ) and SBZ-In (SBZI) alloys with low Bi contents were examined to elucidate the effects of the addition of Zn and In to the Sn-45Bi alloy on the interface and shear strengths of Cu/Cu joints before and after aging. In the case of the SBZ/Cu and SBZI/Cu joints, Bi coarsening was not observed either near or at the interfaces of the Cu/Cu joints. The shear strengths of the SBZ and SBZI joints remained unchanged after aging for 1008 h, suggesting that the SBZI alloy demonstrated the highest long-term reliability among all the joints examined.

Impact of precipitated phases on the microstructure and mechanical properties of eutectic Sn58Bi alloy

A new type of low-melting-point heterogeneous alloy (LMH), based on Sn58Bi alloy (SBE), was prepared using Cu, Zn, Ag, and Sb microalloying and rapid solidification. The addition of Cu and Zn elements in equal mass ratios resulted in the Cu5Zn8 phase being dispersed in the Sn55Bi3Cu3Zn (LMH3) alloy. Subsequently, the additional Cu reacted with Sn to form a nano-sized η′-Cu6Sn5 phase at the interface of the Sn-Bi eutectic phase. Sn53Bi3Cu3Zn2Ag2Sb (LMH32) was prepared by adding appropriate amounts of Ag and Sb based on LMH3, leading to the precipitation of Ag3Sn and SbSn phases in the SBE matrix. The different precipitated phases in turn produced different types of fiber textures that existed in the matrix phase of SBE, LMH3, and LMH32. In addition, compared to LMH3, the presence of Ag3Sn and SbSn phases in LMH32 caused the formation of Bi twins identified via electron backscattered diffraction. The twin planes (101̅1) and (11̅02) had corresponding rotation axes and rotation angles of 93.8°[7̅431] and 90.2°[5̅415̅], respectively. Nanoindentation results indicated that LMH32 exhibited higher creep resistance than Sn55Bi3Cu3Zn (LMH3) and SBE. The precipitated phase significantly refines the grain size and eutectic lath structure of the matrix phase (Sn and Bi). During the deformation process, the fine lath structure and the interfacial η′-Cu6Sn5 nanophase can hinder the slippage of the eutectic interface. Moreover, the presence of the precipitated phase forms a large strain gradient in the alloy matrix, which produces a significant back-stress hardening effect and induces substantial dislocation nucleation. The formation of more dislocations made the creep mechanism of LMHs depend on dislocation climbing.

Understanding the Effect of Reflow Profile on the Metallurgical Properties of Tin–Bismuth Solders

Sn–Bi alloys are desirable candidates for soldering components on printed circuit boards (PCBs) because of their low melting point and reduced cost. While certain tin–bismuth solders are well characterized many new alloys in this family have been developed which need proper characterization. The following study looks at the behavior of four different Sn–Bi alloys—traditional 42Sn58Bi and 42Sn57Bi1Ag and two new tin–bismuth alloys—in solder paste during the reflow soldering process. Each alloy was processed using different reflow profiles that had varying times above liquidus (TALs) and peak temperatures. The PCBs were then analyzed to see how the processing variables influenced wetting, voiding, microstructure, intermetallic layer composition, and thickness. After analysis, the PCBs were then subjected to thermal cycling experiments to see how reflow profile impacted microstructure evolution. The results demonstrated that reflow profile affects properties such as metal wetting and voiding. It does not however, greatly impact key metallurgical properties such as intermetallic layer thickness.

Mechanical properties and constitutive model of Sn-58Bi alloy

Sn-58Bi alloy is a strain-rate-sensitive material. To study the mechanical properties of Sn-58Bi alloy, an MTS universal testing machine and split-Hopkinson pressure bar were used to conduct quasi-static and dynamic testing on Sn-58Bi alloy, obtaining the stress-strain curve of Sn-58Bi alloy at the strain rate of 0.001–6316 s−1. By comparing the tensile and compressive stress–strain curves of Sn-58Bi alloy under quasi-static conditions, it is found that Sn-58Bi alloy is brittle, with its tensile yield strength lower than its compressive yield strength. By comparing the compressive stress–strain curves of Sn-58Bi alloy at different strain rates, it is found that the yield strength of Sn-58Bi alloy increases with increasing strain rate, and a strain-hardening phenomenon is manifested at high strain rate. By revising the Johnson–Cook constitutive model, the constitutive model of Sn-58Bi alloy at different strain rates was established, with the calculated results of the model in good agreement with the experimental results.

Dynamic Recrystallization Behavior and Strengthening Mechanism of Quasi-Precipitate-Free Dilute Mg‒Bi‒Sn Alloy

Dynamic Recrystallization Behavior and Strengthening Mechanism of Quasi-Precipitate-Free Dilute Mg‒Bi‒Sn Alloy

Highly Anisotropic Metallized Wood Obtained by Filling Basswood Channels with Low-Melting-Point Sn-Bi Alloy

Highly Anisotropic Metallized Wood Obtained by Filling Basswood Channels with Low-Melting-Point Sn-Bi Alloy

Microstructural Evolution and Mechanical Properties of Sn‐58Bi Solder Alloys with Different Cooling

Herein, influences of air‐cooling, water‐cooling, and liquid nitrogen‐cooling (LN‐cooling) on microstructures and mechanical properties of Sn–58Bi alloy are studied. It is observed that nearly complete eutectic structures are obtained in air‐cooled Sn–58Bi alloy. Fine grains and many low‐angle grain boundaries (LAGBs) are obtained in water‐cooled Sn–58Bi alloy. The LN‐cooling method causes Bi atoms to form large, regular rectangular shapes, and there are many high‐angle grain boundaries (HAGBs) distributed inside the specimen. Impact tests are performed at room temperature. When the impact rate is 0.98 m s−1, the fracture energy of the water‐cooled Sn–58Bi alloy peaks to 71.5 mJ. The fracture of the LN‐cooled impact specimen has a large cleavage step due to the interaction of cleavage cracks and the HAGBs. These experimental results lay the relevant theoretical foundation for the practical application of Sn–58Bi solder alloys.

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.

Simulation and experimental characterization of microporosity during solidification in Sn-Bi alloys

The formation of microporosity during solidification of Sn-Bi alloys is investigated through experiments and simulations. Samples of varying composition with 20, 30, 47 and 58 wt% Bi are solidified in a copper mould and the pore fraction is measured through scanning electron microscopy. Finite element models are derived from X-ray micro computed tomography data and a material model is implemented to capture the effect of liquid pressure and volumetric swelling. The experimental assessment of solidification porosity shows a strong dependency on alloy composition. The round morphology of porosity found in the Sn-20 wt% Bi alloy indicates its formation in the terminal stage of solidification. Microporosity formation is computed by means of Finite Element simulations and the results correlate with experimental findings. The analysis confirms volumetric shrinkage in the liquid state of confined eutectic domains as the mechanism for pore formation and determines the composition dependency of Sn-Bi alloys.

Kinetics and thermodynamics of compound growth due to reactive diffusion between solid Cu and binary Bi-Sn alloys

The growth behavior of compounds for the reactive diffusion between solid Cu and molten binary Bi-Sn alloys was experimentally examined using semi-infinite diffusion couples prepared by an isothermal bonding technique. Isothermal annealing of (Biy-Sn1-y)/Cu diffusion couples with Bi mol fraction of y = 0.27–0.46 was conducted in the temperature range of 453–603 K (180–330 °C) for various times up to 345.6 ks (96 h). In the diffusion couple with y = 0.44, an intermetallic layer composed of Cu6Sn5 with irregular scallop shapes and Cu3Sn with relatively uniform thickness forms at the (Bi-Sn)/Cu interface at 453–523 K (180–250 °C). In contrast, at 563–603 K (290–330 °C), the intermetallic layer consists of only Cu3Sn. Isothermal sections of the equilibrium phase diagram in the ternary Bi-Cu--Sn system were calculated at 453–603 K (180–330 °C) by a CALPHAD (calculation of phase diagrams) method. For the diffusion couple with y = 0.44, the diffusion path passes through the three-phase tie-triangles containing Cu6Sn5 and/or Cu3Sn in the isothermal section at 523 K (250 °C), but through only that containing Cu3Sn in the isothermal section at 603 K (330 °C). As a result, for y = 0.44, the intermetallic layer is composed of Cu6Sn5 and Cu3Sn at 453–523 K (180–250 °C), whereas it consists of only Cu3Sn at 563–603 K (290–330 °C). The mean thickness of the intermetallic layer is proportional to a power function of the annealing time, and the exponent of the power function is mostly smaller than 0.5. Such smaller values of the exponent mean that the layer growth is controlled by boundary diffusion across the intermetallic layer. Adopting the common value of 0.30 as the exponent of the power function for the Cu3Sn layer at 563–603 K (290–330 °C), we obtain a value of 17.9 kJ/mol for the activation enthalpy of the proportionality coefficient of the power function.

Doping Process of 2D Materials Based on the Selective Migration of Dopants to the Interface of Liquid Metals

The introduction of trace impurities within the doping processes of semiconductors is still a technological challenge for the electronics industries. By taking advantage of the selective enrichment of liquid metal interfaces, and harvesting the doped metal oxide semiconductor layers, the complexity of the process can be mitigated and a high degree of control over the outcomes can be achieved. Here, a mechanism of natural filtering for the preparation of doped 2D semiconducting sheets based on the different migration tendencies of metallic elements in the bulk competing for enriching the interfaces is proposed. As a model, liquid metal alloys with different weight ratios of Sn and Bi in the bulk are employed for harvesting Bi2 O3 -doped SnO nanosheets. In this model, Sn shows a much stronger tendency than Bi to occupy surface sites of the Bi-Sn alloys, even at the very high concentrations of Bi in the bulk. This provides the opportunity for creating SnO 2D sheets with tightly controlled Bi2 O3 dopants. By way of example, it is demonstrated how such nanosheets could be made selective to both reducing and oxidizing environmental gases. The process demonstrated here offers significant opportunities for future synthesis and fabrication processes in the electronics industries.