Bi Alloy Research Articles

Effects of Different Mold Temperature on Dendrite Morphology of Sn-Bi Alloy in Directional Solidification

The directional solidification process of Sn–10 wt% Bi alloy with low melting point was observed by synchrotron X-ray imaging technology. The mold temperature was controlled, and the dynamic images of a series of alloy solidification behavior were obtained. The results show that columnar crystal grows in dendrite morphology. It is also found that dendrite morphology changes at different mold temperature. With the decrease of the mold temperature, the dendrite morphology begins to change from irregular to regular, and finally, the primary dendrites and the secondary dendrites are perpendicular to each other.

Surfactant-induced chemical ordering of GaAsN:Bi

We have examined the influence of an incorporating surfactant on chemical ordering in GaAsN:Bi alloys. Epitaxy with a (2 × 1) reconstruction leads to the formation of GaAsN alloys, while the introduction of a Bi flux induces long-range chemical ordering of the {111} planes of GaAsN:Bi. We propose a mechanism in which Bi enhances the alignment of dimer rows along the [110] direction, facilitating N incorporation beneath surface dimers and Bi incorporation between dimer rows to form alternating N-rich and Bi-rich {111} planes. These findings suggest a route to tailoring the local atomic environment of N and Bi atoms in a wide range of emerging dilute nitride-bismide alloys.

Microstructural array and solute content affecting electrochemical behavior of Sn Ag and Sn Bi alloys compared with a traditional Sn Pb alloy

Abstract The aim of this investigation is focused on the electrochemical impedance behavior of Sn-2 wt.% Ag (SA), Sn-10 wt.% Bi (SB) and Sn-22 wt.% Pb (SP) casting alloys in a stagnant and naturally aerated 0.15 M NaCl solution at environmental temperature. Both uncoated and coated samples are casting centrifuged and similar microstructural arrays are produced. Coated substrates and joints utilize Sn-based alloys in microelectronic applications. Gold-coated samples are commonly used in jewelry industry. The roles of the solute contents on the microstructural parameters, eutectic fractions and cathode-to-anode area ratios of each proposed alloy are discussed. Electrochemical impedance spectroscopy (EIS) analysis using equivalent circuit is discussed. It is found that indistinctively of the examined uncoated or coated samples, the corrosion resistance sequence favors the SB alloy, followed by SA and SP alloys.

Effect of Cold Rolling and Annealing Temperature on the Characteristics of Cu-28Zn-1.1Bi Alloy Produced by Gravity Casting

The microstructures, mechanical properties, deformation mechanism, and recrystallization behavior of Cu-Zn-Bi alloys for cartridge case application have been investigated in this research. Cu-28Zn-1.1Bi wt. % alloys were produced by gravity casting and subjected to a homogenization – cold rolling – annealing sequences with variations on reduction level and annealing temperature. Samples characterizations were done through optical emission spectroscopy, optical microscopy, SEM-EDS imaging, and X-ray mapping modes, while hardness measurements were performed using micro Vickers method. The presence of Bi was found to increase cartridge brass hardness through a dispersoid strengthening mechanism in which dislocation movements are rendered by Bi particles. Higher deformation levels resulted in higher microhardness of the alloy. Recrystallization took place at grain boundaries and areas surrounding Bi dispersoid at 400 °C, while further heating resulted in grain growth phenomenon. Bismuth addition accelerated the recrystallization process in cartridge brass by a particles stimulated nucleation (PSN) mechanism.

Optimal design of a bio-inspired self-healing metal matrix composite reinforced with NiTi shape memory alloy strips

Utilizing smart materials such as shape memory alloys as reinforcement in metal matrix composites is a novel method to bio-mimic self-healing. This study aims to investigate the influence of design factors of a self-healing metal matrix composite by employing the Taguchi method for designing of the experimental procedure. Three design factors, each in three levels, were studied simultaneously according to L-9 standard Taguchi orthogonal array to determine the optimal level of each factor in mechanical properties enhancement with a reduced number of experiments. Composite specimens were fabricated from Sn-13 wt.% Bi alloy as matrix and nickel–titanium shape memory alloy strips as reinforcement with gravity casting process. Matrix alloy was melted and casted in a preheated metallic mold in which SMA strips were installed in various quantities (one, two, or three strips) and different pre-strains (0%, 2%, or 6%). After fabrication of the specimens, a tensile test was conducted until fracture to specify mechanical properties. Then, specimens were placed in a furnace in three different temperatures (170°C, 180°C, and 190°C) to activate the shape memory effect of strips and achieve crack closure and healing. Specimens were tensile tested again after healing to calculate the amount of healed properties and healing efficiency. Results show that using three strips with 6% of pre-strain and applying 190°C healing temperature can maximize the ultimate tensile strength efficiency. Also, the existence of one strip, 0% pre-strain, and 190°C healing temperature creates the best circumstances for healing ductility.

A Study on the Effect of Ultrasonic Treatment on the Microstructure of Sn-30 wt.% Bi Alloy.

The effect of ultrasonic treatment on the microstructure of Sn-30 wt.% Bi alloy was studied at different temperatures. Results showed that the ultrasonic treatment could effectively refine the microstructure of Sn-30 wt.% Bi alloy at a temperature range between the liquidus and solidus. Application of the ultrasound could fragment the primary Sn dendrites during solidification due to a mixed effect of ultrasonic cavitation and acoustic streaming. The divorced eutectic formed when the ultrasonic treatment was applied for the whole duration of the solidification. The eutectic phase grew and surrounded the primary Sn dendrite, and pure Bi phase grew in between the Sn dendritic fragments. The mechanism of the fragmentation of dendrites and the divorced eutectic structure by ultrasonic treatment was discussed.

Study of Microstructure and Mechanical Properties of Commercially Pure Sn and Sn-4%Bi Alloys Fabricated by Permanent Mold Gravity Casting and Forging

The influences of 4 wt% bismuth addition and room temperature strain on microstructure and mechanical properties in tin alloys were investigated in this study. Commercially pure tin and Sn-4%Bi alloys were fabricated by permanent mold gravity casting. The samples were then subjected to forging process at room temperature. As-cast microstructures were compared with 0.25 and 0.5 strained samples. Differential Scanning Calorimetry (DSC) was used to confirm the effect of bismuth on undercooling. The recrystallization and grain growth processes were confirmed by grain size distribution and misorientation study using Electron Backscattered Diffraction (EBSD). Furthermore, position and morphology of the bismuth precipitates were investigated by using Field Emission Scanning Electron Microscope (FESEM). X-ray Photoelectron Spectroscopy (XPS) revealed that tin oxide was the main species found on the surface of these alloys. There was no evidence of bismuth oxide on the surface. Furthermore, the Hall-Petch hardness approximation analysis revealed that there were other influences, which increased the hardness beyond the grain refinement effect.

Evolution of the microstructure and solute distribution of Sn-10wt% Bi alloys during electromagnetic field-assisted directional solidification

The effects of forced flows at different velocities on microstructure and solute distribution during the directional solidification of Sn-10 wt% Bi alloys under a simultaneous imposition of a transverse static magnetic field (TSMF) and an external direct current (DC) have been investigated experimentally and numerically. The experimental results show that the solid-liquid interface will gradually become sloping with the increase of the forced flow velocity when the thermoelectric magnetic convection (TEMC) dominates the forced flow at solidification front. However, the interface will gradually become planar as the flow velocity further increases when the electromagnetic convection (EMC) dominates the forced flow. Moreover, when the flow velocity gradually increases, the primary dendrite spacing decreases from 384 to 105 μm accordingly. The simulation results show that the solute distribution at the two sides of the sample can be significantly changed by the forced flow at solidification front. The rejected solute will be unidirectionally transported to one side of the sample along the TEMC (a low-velocity forced flow), thereby causing the formation of a sloping interface. However, the rejected solute will be returned back along the EMC (a higher-velocity force flow), which results in a planar interface. Furthermore, the solute content at the two sides of the sample under the forced flows at different velocities was measured. The results are in good agreement with the simulation results, which shows that the solute content difference between the two sides of the sample reaches the maximum when a 0.5 T TSMF is applied, while the solute content difference decreases to zero with a simultaneous application of a 0.5 T TSMF and a 1.6 × 105 A/m2 external DC.

Study of microstructure and thermal properties of the low-melting Bi–In eutectic alloys

This study reports the results of microstructure and thermal analysis of low-melting Bi–In alloys with potential for commercial application in the field of phase change materials. Three eutectic alloys Bi–47.44In, Bi–66.33In, Bi–77.92In (all in at.%) were prepared and investigated by means of scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS) and differential scanning calorimetry (DSC). Microstructure of the prepared eutectic alloys was analysed using SEM–EDS, and identification of co-existing phases was done. Melting temperatures and latent heats of eutectic melting were measured using DSC technique. Experimentally obtained results were compared with the results of thermodynamic calculation according to CALPHAD (calculation of phase diagram) method, and good mutual agreement was noticed.

Microstructure and mechanical properties of indium–bismuth alloys for low melting-temperature solder

Application of a low-temperature soldering process is preferred in developing wearable and flexible electronic devices because of the temperature sensitivity of unconventional polymer-based substrates or other low-heat budget materials. In this context, indium-based alloy has advantages such as low melting point, wettability, and thermal-fatigue resistance. In particular, indium has good ductility for elastic deformation without fatigue. These solders were developed for low-temperature applications with the alloying element: 30 mass% Bi, 33.7 mass% Bi, 40 mass% Bi and 50 mass% Bi. The alloys were designed to have an onset temperature between 72.7 and 91.3 °C. In the present study, the effect of alloy composition on the microstructure, melting properties, and mechanical properties of In–Bi alloys were investigated. The analysis on the measured characteristics was conducted to optimize the design of the In–Bi alloy.

Impact of permanent magnet stirring on dendrite growth and elastic properties of Sn–Bi alloys revealed by pulse echo overlap method

Studying and understanding the dendritic growth process is a challenging topic related to liquid-solid phase transition, as it helps to predict the final microstructure controlling the solder properties. In a specific case of the design of Sn-Bi and Sn-Bi-Cu alloys, the solidification microstructures and corresponding electrical and elastic properties were studied with and without permanent magnetic stirring (PMS), as their influence on the growth morphology of dendrites is not yet fully assessed to date. We use pulse echo overlap (PEO) method for measuring the polycrystalline bulk modulus K, Young's modulus E, shear modulus G, Poisson ratio υ and hardness H. The PMS-driven flow caused a disruption of the columnar β-Sn dendrites and columnar-to-equiaxed transition (CET). Such behavior is believed to evolve from dendrite fragmentation, arises through complex hyper-branched morphologies at the origin of Lorentz force and Seebeck effect that acting on the melt. Both the hardness and elastic modulus are increased as the Poisson's ratio decreased. Moreover, the Pugh ratio clarified the ductility behavior of the alloy samples, while Poisson's ratio and electrical resistivity display slight decrease in the ionic contribution with applying PMS and/or Cu content. These results open new ways to predict the final microstructure controlling the dendritic growth in metallic alloys.

Designing of some platinum or palladium-based nanoalloys as effective electrocatalysts for methanol oxidation reaction

Nano alloys contain noble metal nanostructures exhibit a wide theoretical and experimental interest in the field of fuel cells. Hard endeavors have been enhanced to improve the catalytic performance and minimize the usage of precious metals by alloying them with non-precious ones. Formation of bimetallic and trimetallic noble metal alloys with well-designed structures provide the opportunity to reach this goal. In this study, we first discuss the synthesis of noble metal alloy nanostructured thin films such as PtCu, PdCu, PtCu/reduced-graphene oxide (RGO), PdCu/RGO, PtCo, PtCo/RGO, PtPdCu and PtPdCu/RGO via a simple reduction of organometallic precursors including [PtCl2 (cod)] and [PdCl2(cod)], (cod = cis, cis-1,5-cyclooctadiene), in the presence of [Cu(acac)2] and [Co(acac)3] (acac = acetylacetonate) at oil/water interface and room temperature, including nanoparticles and nanosheets. Then the effects of the well-defined nanostructures on the improved electrochemical properties are outlined. Finally, we conclude that these non-precious bi and trimetallic alloy nanostructured thin films have better electrocatalytic performance than Pt monometallic thin films and other Pt nanostructures due to the geometric, electronic and stabilizer effect.

Effect of Bi Additions on the Creep Behaviour of SAC Solder Alloys

Microstructural evolution resulting from long-term thermal exposure and creep behaviour of cast Sn-0.6Ag-0.7Cu-xBi solder alloys for electronic packaging applications are investigated. Deformation mechanisms are determined via creep tests conducted at a temperature range of 25–150°C using 7.5–12.5 MPa stress and in-depth scanning electron microscopy analysis. In all compositions, dislocation based processes are responsible for creep deformation. The creep strengthening of the 1.5–2.5 wt.% Bi alloys is from Cu6Sn5/Ag3Sn intermetallic phases. The higher coarsening rate of the Cu6Sn5 phase compared to Ag3Sn leads to loss of creep resistance. The low creep resistance of Sn-0.6Ag-0.7Cu-5Bi solder alloy is attributed to the presence of the Bi phase with polygonal morphology causing earlier failure in creep.

Achieving dispersed fine soft Bi particles and grain refinement in a hypermonotectic Al–Bi alloy by severe plastic deformation and annealing

The present work revealed that equal-channel angular pressing (ECAP) deformation combined with appropriate annealing could represent as an efficient route to modify immiscible as-cast microstructure of a monotectic Al–8Bi alloy by a complete redistribution of immiscible Bi particles and grain refinement of alloy matrix. Especially, we found that the mean size of Bi particles in the 4-pass ECAPed Al–8Bi sample decreases after annealing at 200 °C for 8 h, due to inverse coarsening driven by the reduction of elastic energy and interfacial energy induced by morphology change and spatial distribution of Bi particles.

Microstructural Development of an AlNiBi Alloy and Influence of the Transient Horizontal Solidification Parameters on Microhardness

The combination of the structural and tribological properties presented by AlNiBi alloys has motivated us to establish, as the main objective of this study, the investigation of the microstructural evolution and its influence on the microhardness (HV) of Al-3wt pct Ni-1wt pct Bi alloy horizontally solidified via a water-cooled directional solidification device. Temperature mapping by thermocouples inserted in the metal has been performed for experimental determination of the solidification thermal parameters, such as the growth rate and cooling rate (VL and TR, respectively). The microstructure has been characterized by optical and scanning electron microscopy and by microanalysis of the composition via dispersive energy spectroscopy (EDS composition). The macrostructure of the as-solidified ingot is characterized by columnar grains, and the final microstructure consists of an Al-rich primary phase (α-Al) and a eutectic mixture composed of two phases: α-Al + Al3Ni intermetallic (β) with Bi particles anchored on the β phase. The Bi droplet scale is affected by the thermal parameters. The primary phase (α-Al) is characterized by a reverse cellular-to-dendritic microstructural transition. Cellular and dendritic microstructures have been quantified by the cell, primary dendrite arm, secondary dendrite arm, and tertiary dendrite arm spacings (λC, λ1, λ2, and λ3, respectively). The relationships of λC, λ1, λ2, and λ3 with VL and TR have been established via power-type mathematical expressions. The HV dependence on λC, λ1, λ2, and λ3 has been analyzed in both cellular and dendritic microstructural zones. It has been observed that the HV values do not vary in the dendritic zone; however, Hall–Petch’s mathematical equations characterize the HV variation with these thermal and microstructural parameters in the cellular zone.

An Electromagnetic Compounding Technique for Counteracting the Thermoelectric Magnetic Effect During Directional Solidification Under a Transverse Static Magnetic Field

An external direct current (DC) was introduced to counteract the thermoelectric magnetic effect during the directional solidification of Sn-10 wt pct Bi alloy under a 0.5 T transverse static magnetic field. The results show that the single-side Bi segregation induced by the thermoelectric magnetic effect gradually becomes weakened, disappeared, and then reversed with the increasing current density of the external DC. Therefore, a new method for counteracting the thermoelectric magnetic effect during materials processing under the magnetic field was proposed. In order to verify this method, the absolute thermoelectric power of Sn-10 wt pct Bi alloy and the internal thermoelectric current under the experimental conditions were measured and calculated, respectively. A 2D numerical simulation was established to simulate the evolution of the solid–liquid interface morphology, flow field, and composition segregation with the increasing current density of the external DC during directional solidification under a transverse static magnetic field. The present study not only facilitates the understanding of the effects of the forced flows on the directionally solidified microstructures and composition segregation, but also provides a new way for eliminating segregation and obtaining the higher-quality solidification structure by using the electromagnetic compounding technique.

Microstructure and phase composition of hypoeutectic Te–Bi alloy as evaporation source for photoelectric cathode

A hypoeutectic 60Te–40Bi alloy in mass percent was designed as a tellurium atom evaporation source instead of pure tellurium for an ultraviolet detection photocathode. The alloy was prepared by slow solidification at about 10−2 K·s−1. The microstructure, crystal structure, chemical composition, and crystallographic orientation of each phase in the as-prepared alloy were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The experimental results suggest that the as-prepared 60Te–40Bi alloy consists of primary Bi2Te3 and eutectic Bi2Te3/Te phases. The primary Bi2Te3 phase has the characteristics of faceted growth. The eutectic Bi2Te3 phase is encased by the eutectic Te phase in the eutectic structure. The purity of the eutectic Te phase reaches 100wt% owing to the slow solidification. In the eutectic phases, the crystallographic orientation relationship between Bi2Te3 and Te is confirmed as $${[0001]_{B{i_2}T{e_3}}}//{[1\bar 21\bar 3]_{Te}}$$ and the direction of Te phase parallel to $${[11\bar 20]_{B{i_2}T{e_3}}}$$ is deviated by 18° from Te $$N{(2\bar 1\bar 11)_{Te}}$$ .

The effect of Lanthanide doping on the structural, elastic, thermodynamic and electronic properties of YBi: An ab-initio study

The main investigation goal of this work is to give report on the effect of Lanthanide doping in YBi. The present results were done by means of DFT calculations. The analysis of structural calculations reveals that, the lattice parameters of LaxY1-xBi varies linearly with the investigated concentration x, which indicates that the Vegard's law is valid for this calculation showever, for the effect on bulk modulus the results show the existing of a large deviation from a linear concentration dependence (LCD). The elastic constants Cij and their related macroscopic moduli was predicted. The influence of La-doped on thermodynamic stability was explored on the basis of regular solution model. Furthermore, the temperature effect on: heat capacity at constant volume (CV), thermal expansion (α) and Debye temperature (θD) have been investigated by the quasi-harmonic Debye model. To calculate the electronic structure of the investigated compounds we have used the Tran and Blaha-modified Becke–Johnson (TB–mBJ) method. The electronic structures reveal that the compounds with the concentration 0, 0.25 and 0.5 have semi metallic characters. Furthermore, the results reveal a gapless semiconducting behavior for La0.75Y0.25Bi alloy.

Electrochemical Reduction of Carbon Dioxide at Alloy Systems: Cu-In and Cu-Bi

The ability to maintain high efficiencies while simultaneously tuning the selectivity of the electrochemical reduction of CO2 (ERC) using low cost electrodes has proven to be one of the greatest obstacles to the widespread commercialization of this technology. In this study, we prepare dendritic copper-indium and copper-bismuth alloys of various compositions and investigate their catalytic activity and selectivity towards the reduction of CO2. The Cu-In electrocatalysts are increasingly dendritic with higher In fraction and, depending on composition, consist of mixed phases of Cu, In and Cu-In intermetallic phases. ERC at these electrodes produces formate at high efficiencies (up to 62% with a 80 at% alloy, -1 V)) while also tuning the CO/H2 ratio to achieve an ideal syngas composition with a 40 at% In alloy, -1 V. The observed product distribution as a function of alloy composition and applied potential is rationalized in terms of the relative adsorption strengths of CO and COOH intermediates at Cu and In sites, and their distinct variation with applied potential may be induced by the differences in electronic structure. We also studied dendritic Cu, Bi, and Cu-Bi alloys with various compositions. The dendritic structures exhibit a high density of defect sites such as grain boundaries and twins, with these defects being increased at alloy dendrites. While the pure metals exhibited high H2 production and relatively high formate formation, the alloys exhibit a lower overall current density and a much higher selectivity towards formate, up to about 90%. Most importantly we show in this work that a combination of a d metal (Cu) with a p-block metal (In, Bi) with intimate contact between the two components is capable to tune the relative adsorption strength of the intermediates, thus steering the product distribution towards formate. The relatively purity of this product would be of interest for the direct feed of a direct formate fuel cell. Differences between In and Bi will be discussed in terms of the affinity for oxygen. This study highlights the opportunities of using alloys to enhance control over the product distribution and suggests that suitable alloys could be promising catalysts for the inexpensive and efficient production of fuels.

Effects of Bi on band gap bowing in InP1-xBix alloys

The effects of Bi in InP1-xBix ternary semiconductor alloys are studied based on first-principles. The mBJLDA potential is used to obtain accurate band structures. The band gap is modified mainly by the large Bi atom-induced strain at high concentration. The incorporation of Bi mainly perturbs the valence bands due to the interaction of Bi impurity states with heavy/light hole bands and spin-orbit split off bands. Several different Bi complexes including [100] chain, [111] chain, clustered and SQS in a 128-atom supercell are considered. For random Bi distribution at high concentration, the resulting band structures can be understood together as a work of all Bi complexes arrangements. Measuring band gap narrowing mechanism dependent on configurations as a function of Bi composition can potentially help to distinguish the types of Bi arrangement distributions in samples as well as to promote the applications in mid-infrared regime.