Pb-based Alloys Research Articles

Fabrication, microstructural modifications, elastic properties and radiation attenuation performance of ZnO nano-sized particles-reinforced Pb-based alloys for radiation shielding applications

We intended to obtain new appropriate materials suitable for radiation protection applications. Therefore, the choice of appropriate materials in industrial and medical applications has become one of the major research topics. An attempt has been made to conceive the possibility of using different compositions Sn-40Pb, Sn-39.5Pb-ZnO, Zn-40Pb and Zn-39.5Pb-ZnO were prepared and synthesized by the melt-spun process. This work aims to investigate the effects of rapid solidification processing and loading 0.5 wt.% ZnO NPs into the Sn- and Zn-based binary systems and the stability of the structure, mechanical and shielding properties. The structure revealed that the plain and composite alloys contain the crystalline β-Sn (body-centred tetragonal), α-Pb (cubic) Fm-3 m for the Sn-Pb system in addition to α-Pb(fcc), Zn (Hexagonal) P63/mmc and revealed ZnO (Zincite) P63mc for the Zn-Pb system. Doping ZnO nano-sized cause refines the eutectic structure as revealed in microstructural morphology. The experimentally measured density values for the plain and composite alloys have been used in evaluating the linear attenuation coefficient, which is further used to calculate mass, attenuation coefficient, mean free path, half value layer and tenth value layer. Furthermore, the variation of a mean free path, HVL and TVL with incident photon energy for the binary and composite alloys has been investigated. It was found that nano-ZnO-doped Sn-Pb and Zn-Pb enhance the amount of radiation absorbed in the material inside and as a result of which affected the radiation attenuation properties of the material. It was concluded and recommended that the composite alloys containing ZnO NPs can be used effectively as a shielding material for gamma rays with a comparable attenuation percentage compared with plain alloys.

Nuclear shielding properties of Ni-, Fe-, Pb-, and W-based alloys

This paper presents an extensive evaluation for the nuclear shielding features of Ni-, Fe-, Pb-, and W-based alloys using FLUKA simulations and XCOM nuclear database. The simulations procedures were applied based on the concept of the narrow beam experiment for gamma energies between 0.284 MeV and 1.275 MeV. The findings of the simulations were consistent with the XCOM nuclear database, and this reflects the capability of FLUKA as an accurate technique for developing new alloys for shielding applications in nuclear sites. Here, the maximum radiation protection efficiency is found at 0.284 MeV with values of 64.5692%, 59.0452%, 98.3307% and 99.3249% for Ni-based, Fe-based, Pb-based and W-based alloy, respectively. On the other hand, the neutron cross sections of the present alloys are very close to each other and there is not significant variation of such cross sections with the chemical compositions of the studied alloys.

A study on the degassing mechanism of Pb-based alloy under ultrasonic treatment

In recent years, the ultrasonic technique is being developed at a pretty faster speed, whose assisting tactic has been applied in the electronic packaging field. What we need is to determine the mechanisms of ultrasonic treatments on electronic packaging fillers. In this paper, Pb-based alloy is typically chosen as the filler metal, in this paper, it is found that the flowability of which can be improved under ultrasonic vibration. Also, ultrasonic degassing efficiency is greatly promoted, with the best parameter for degassing that ultrasonic power and duration time of 1000W and 60s, a molten alloy’s treating temperature of 340°C. The assistance of ultrasonic is deeply explained from the thermodynamic aspect. Understanding of the atomic level interactions of liquid Pb atoms and vacuum is crucial, so we make an ultrasonic-assisted molecular dynamic simulation of melting Pb to room temperature to 330°C in 10ps, and the diffusion behavior of Pb atom under periodic vibration is revealed.

Drop Calorimetric Measurement of In-Zn system for Lead-Free solder applications

Circuit boards installed inside vehicles in the automotive industry are subjected to significant thermal stress due to temperatures above 150 °C. It can be reduced by using In-Zn solder alloys instead of hazardous Pb-based solder alloys, representing Pb-free solder alloys' development. The formation of an alloy is determined by its phase diagram, which is then measured to determine its thermodynamic properties. Using a drop calorimeter, the mixing heat effect (mixing enthalpy) as partial enthalpies and integral enthalpies of mixing in the liquid phase of In-Zn systems were investigated at 800 K and 900 K. The plots of mixing enthalpies are plotted versus zinc composition. When the Redlich–Kister polynomial is fitted, it is compared to our experimental data to identify the binary interaction parameters. This will help to predict the thermodynamic properties of multicomponent systems by using values of interaction parameters of the binary system (In-Zn). For all compositions at 800 K and 900 K, the model value was found to be close to the experimental values. The integral enthalpy of mixing of In-Zn system at 800 K and 900 K is endothermic in nature all through the composition and its most value in the range of XZn ∼ 0.48–0.52. It is also visible that the enthalpy of mixing is symmetrical with the composition of Zn.

Phase segregating and complex forming Pb-based (=X-Pb) liquid alloys

ABSTRACT We have used a theoretical model based on the assumption of compound formation in binary alloys to study the thermodynamic, microscopic and surface properties of Bi-Pb and In-Pb liquid alloys. A review of the phase diagrams for these alloys shows that one of the stable complexes for Bi-Pb liquid alloy is BiPb3; also that In-Pb is a stable phase in liquid In-Pb alloys. Using the same interaction parameters that are fitted for free energy of mixing, we have been able to compute the bulk and thermodynamic properties of the alloys. From our observations, we are able to show that the Bi-Pb liquid alloy exhibits compound formation over the whole concentration range and the In-Pb alloys undergo phase separation. With regard to surface properties Pb segregates more to the surface in In-Pb alloys than in Bi-Pb alloys. The viscosity isotherms have positive deviation from ideality for both Bi-Pb and In-Pb alloys.

Calculation of vapor-liquid equilibria of binary lead-based alloys in vacuum distillation using simplified molecular interaction volume model

In this work, the molecular interaction volume model (MIVM) was reasonably simplified. The values of the first coordination numbers (Zi and Zj) were set as 10, and the molar volume of the component i in the liquid state (Vmi) was replaced by its molar volume in the solid state (Vi). The activities of the components of Pb-based alloys (PbSn, PbSb, PbAg, PbCu, PbBi, and PbCd) were predicted by using the simplified MIVM (SMIVM). The prediction deviations of SMIVM were overall smaller than those of MIVM, indicating that the simplification of the MIVM is reasonable and the SMIVM is reliable for predicting the activities of the components of Pb-based alloys. The biggest advantage of the SMIVM lies in its simplicity in calculation and higher prediction accuracy than MIVM. Vapor-liquid equilibria (VLE) phase diagrams for the PbSn, PbSb, PbCu, PbAg, and PbBi alloy systems in vacuum distillation were calculated based on the SMIVM and VLE theory. The experimental VLE data deviated from the calculated results to a certain extent. This study summarizes the shortcomings of current research on the VLE of alloy systems for future research and development.

Microstructure and mechanical properties of Sn–Cu alloys for detonating and explosive cords

ABSTRACTTo develop alloys as the substitute of Pb-based alloys for cladding materials in detonating and explosive cords, the materials requirement was analysed and Sn–Cu based alloys were selected as potential candidates. Four alloys including Sn–0.3 wt-%Cu, Sn–0.5 wt-%Cu, Sn–0.7 wt-%Cu, and Sn–1.0 wt-%Cu were prepared by casting and rolling. Microstructures of as-cast Sn–Cu alloys comprised Sn solutions with Cu6Sn5 intermetallic in the matrix. The as-rolled hypoeutectic Sn–Cu alloys (0.3–0.5 wt-%Cu) offered the yield strength from 26.1 to 31.9 MPa, UTS from 30.1 to 34 MPa and elongation from 86.4 to 87.5%, which were found to be appropriate for detonating and explosive cords. Particularly, the Sn–Cu alloys exhibited strain softening behaviour under tensile stress, which will benefit cladding manufacture and subsequent processing after assembly with high-energy explosive materials.

Hot embossing of Au- and Pb-based alloys for x-ray grating fabrication

Grating-based X-ray phase-contrast interferometry has a high application impact in materials science and medicine for imaging of weakly absorbing (low Z) materials and soft tissues. For absorbing gratings, casting of highly X-ray absorbing metals, such as Au and Pb alloys, has proven to be a viable way to generate large area periodic high aspect ratio microstructures. In this paper, the authors review the grating fabrication strategy with a special focus on a novel approach of casting low temperature melting alloys (Au-Sn and Pb-based alloys) into Si grating templates using hot embossing. This process, similar to nanoimprint lithography, requires particular adjusting efforts of process parameters as a function of the metal alloy and the grating feature size. The transition between the solid and liquid state depends on the alloy phase diagram, the applied pressure can damage the high aspect ratio Si lamellas, and the microstructure of the solid metal can affect the grating structure. The authors demonstrate that metal casting by hot embossing can be used to fabricate gratings on a large area (up to 70 × 70 mm2) with an aspect ratio of up to 50:1 and a pitch in the range of 1–20 μm.

In situ XRD investigation of the evolution of surface layers on Pb-alloy anodes

The electrochemical behaviour of a number of Pb-based anode alloys, under simulated electrowinning conditions, in a 1.6 M H2SO4 electrolyte at 45 °C was studied. Namely, the evolution of PbO2 and PbSO4 surface layers was investigated by quantitative in situ synchrotron X-ray diffraction (S-XRD) and subsequent Rietveld-based quantitative phase analysis (QPA). In the context of seeking new anode alloys, this research shows that the industry standard Pb-0.08Ca-1.52Sn (wt%) anode, when exposed to a galvanostatic current and intermittent power interruptions, exhibited poor electrochemical performance relative to select custom Pb-based binary alloys; Pb–0.73Mg, Pb–5.05Ag, Pb–0.07Rh, and Pb–1.4Zn (wt%). The in situ S-XRD measurements and subsequent QPA indicated that this was linked to a lower proportion of β-PbO2, relative to PbSO4, on the Pb-0.08Ca-1.52Sn alloy at all stages of the electrochemical cycling. The best performing alloy, in terms of minimisation of overpotential during normal electrowinning operation and minimising the deleterious effects of repeated power interruptions – both of which are significant factors in energy consumption – was determined to be Pb–0.07Rh.

Correlation between microstructure and hardness of a Bi-1.5wt%Ag lead-free solder alloy

In the present study a hypoeutectic Bi-1.5wt%Ag alloy was directionally solidified under transient heat flow conditions and the microstructure was analysed. Bi-Ag alloys are considered as potential alternatives to replace Pb-based alloys as solder materials for metallic connections under high temperatures. However, a lack of understanding regarding the effects of solidification thermal parameters (growth rate - VL, the cooling rate - Ṫ) on microstructural aspects is reported in literature. Another challenge is to improve properties and reliability. The results of the present study include the determination of the tip growth rate and the cooling rate by cooling curves recorded by thermocouples positioned along the casting length, metallography, X-ray fluorescence (XRF) and Vickers hardness. The entire directionally solidified Bi-1.5Ag microstructure was arranged by faceted Bi-rich dendrites surrounded by a eutectic mixture (Bi+Ag). The primary and secondary dendrite arm spacing (λ1 and λ2), the interphase spacing (λ) and the diameter of Ag-rich particles were also measured along the casting length; and experimental growth laws. Relating these microstructural features to the experimental thermal parameters are proposed.

Prediction of vapor–liquid equilibria for the Pb-X (X=Ag, Cu and Sn) systems in vacuum distillation using ab initio methods and Wilson equation

In this work, interaction energies between pairs of atoms for the Ag–Pb, Cu–Pb and Sn–Pb systems have been calculated using ab initio methods. These energies are then used as the interaction energy parameters in the Wilson equation. Phase diagram of vapor–liquid equilibria (VLE) for the Pb-based alloy systems in vacuum distillation are obtained based on the calculated parameters. The results indicate that this approach can lead to accurate VLE predictions for alloy systems in vacuum distillation based only on properties of pure components and the structure of the clusters. The comparisons show the computational results are in good agreement with the experimental data.

Analysis of the natural activities of radionuclides, heavy metals, and other poisonous elements in lead-free Sn–6.5Zn solders with different alloying elements

Problem statementSn–Zn solders are candidate alternatives to Sn–Pb-based solder alloys. With the increasing requirement for lead-free solders, the reliability of successor solders in microelectronics assemblies is in high demand. The elimination of radionuclides, heavy metals, and other poisonous elements in lead-free Sn–6.5Zn solders in the microelectronics industry is a worldwide goal. As a result, it is useful to identify the natural concentrations of radioactive nuclides, heavy metals and other poisonous trace elements (both macro- and micro-element contents), such as Au-196, Th-227, Ag-110M, Fe-59, Zn-65, Rb-89, Rh-106M, Bi-207, Cs-137, Eu-154, Sb-126, Eu-152, Co-56, Co-58, Co-60 and K-40. If this lead-free solder contains high concentrations of natural radioactive nuclides, then workers handling it might be exposed to significant levels of radiation. Therefore, it is important to determine the levels of radioactive nuclides in this solder to protect workers; these levels provide background for the safety rules and precautions that should be applied for those working in this field. ApproachThe levels of natural radionuclides (238U, 232Th, and 40K) and their daughter products contained in Sn–6.5Zn solders have been estimated via gamma-ray spectrometry using a 100% Hyper-Pure Germanium (HPGe) detector. ResultsThe mean activities due to radionuclides, heavy metals, and other poisonous elements were measured, and the results are summarised in tables. ConclusionThe results of this assessment obtained by gamma-ray spectroscopic analysis indicated the presence of high levels of natural radioactivity, heavy metals and other poisonous elements. This result implies that a comprehensive study should be conducted to protect workers from high doses of hazardous substances.

Development of new multicomponent Sn–Ag–Cu–Bi lead-free solders for low-cost commercial electronic assembly

Eutectic Sn–Ag–Cu (SAC) solder is one of the candidate alternatives to Sn–Pb-based solder alloys. The coupling effect of both minor alloying Bi addition and reducing the amount of Ag phase have been proposed as an important approach to optimize existing and to develop new SAC solders. Characteristics of new Sn–Ag–Cu–Bi solders were analyzed and compared with those of as-solidified Sn–1.5Ag–0.7Cu (SAC157) alloy. The results of differential scanning calorimetry (DSC) indicate significant reduction of both undercooling, eutectic temperature, solidus and liquidus temperatures with the addition of Bi into SAC(157) solder, although the pasty range remains the same or slightly increased. Moreover, SAC(157) solders containing Bi were found to have a higher creep resistance (126.1 times) than SAC(157) solder at the same stress level and testing temperature. The higher creep resistance was contributed by the solid solution and precipitations strengthen effects of Bi. The precipitation of these Bi atoms or particles can significantly refine the microstructure, blocks the movement of dislocations and increases the creep resistance of Bi-containing solders. The creep life time of plain SAC(157) alloy was extremely enlarged 23.7 times with the addition of 3wt.% Bi. Constitutive Garofalo model of creep for both SAC(157) and Sn–Ag–Cu–Bi solders was assembled based on the experimental data.

Mechanical performance and microstructure array of as-cast lead–silver and lead–bismuth alloys

The aim of this study is to establish correlations between mechanical properties of Pb–Ag and Pb–Bi alloys and parametric features of their as-cast microstructures, as well as to develop a comparative analysis with the corresponding properties of Pb–Sn alloys considering applications of these alloys in the manufacture of Pb-acid battery components. A wide range of microstructures are obtained using an upward water-cooled directional solidification system. Ultimate (UTS) and yield tensile strengths (YS) and elongation are experimentally determined as a function of cellular and dendritic spacings, and Hall-Petch type experimental equations are proposed relating UTS to these microstructure parameters. Despite the higher specific strengths of Pb–Ag alloys, as compared with those of Pb–Bi and Pb–Sn alloys, their corresponding relative costs are the highest of all Pb-based alloys examined. It is found that the Pb–Bi and Pb–Sn alloys examined have similar specific strengths and relative costs.

The use of a directional solidification technique to investigate the interrelationship of thermal parameters, microstructure and microhardness of Bi–Ag solder alloys

Bi–Ag alloys have been stressed as possible alternatives to replace Pb-based solder alloys. Although acceptable melting temperatures and suitable mechanical properties may characterize such alloys, as referenced in literature, there is a lack of comprehension regarding their microstructures (morphologies and sizes of the phases) considering a composition range from 1.5 to 4.0wt.%Ag. In order to better comprehend such aspects and their correlations with solidification thermal parameters (growth rate, v and cooling rate, Ṫ), directional solidification experiments were carried out under transient heat flow conditions. The effects of Ag content on both cooling rate and growth rate during solidification are examined. Microstructure parameters such as eutectic/dendritic spacing, interphase spacing and diameter of the Ag-rich phase were determined by optical microscopy and scanning electron microscopy. The competition between eutectic cells and dendrites in the range from 1.5 to 4.0wt.%Ag is explained by the coupled zone concept. Microhardness was determined for different microstructures and alloy Ag contents with a view to permitting correlations with microstructure parameters to be established. Hardness is shown to be directly affected by both solute macrosegregation and morphologies of the phases forming the Bi–Ag alloys, with higher hardness being associated with the cellular morphology of the Bi-2.5 and 4.0wt.%Ag alloys.

Characteristics of Pb-based alloy prepared by powder rolling method as an insoluble anode for zinc electrowinning

In this study, a PbAg alloy anode was prepared by a “powder rolling method”, and its possible use as an alternative insoluble anode for an electrowinning application was investigated. The Pb-0.71wt.% Ag cast-rolled alloy, which is currently an insoluble anode for zinc electrowinning, caused remarkable creep deformation under the stress of 15.0MPa in a 150gL−1 H2SO4 solution at 303K, and fractured at about 100ks. The Norton plot data allowed the determination that the creep of the Pb-0.71wt.% Ag cast-rolled alloy proceeded by a “dislocation mechanism”. On the other hand, a Pb-0.71wt.% Ag powder-rolled alloy did not deform at all even at a current density of 10mAcm−2, which confirmed the fact that the Pb-0.71wt.% Ag powder-rolled alloy was an outstanding creep-resistant material in a highly concentrated H2SO4 solution. For galvanostatic electrolysis, it was shown that the oxygen evolution overpotential and the energy efficiency of the Pb-0.71wt.% Ag powder-rolled alloy were nearly equal to those of the present Pb-0.71wt.% Ag cast-rolled alloy. Moreover, the amount of Pb impurities in the deposited Zn on the Al cathode was a low value, i.e., only 57% of the Pb-0.71wt.% Ag cast-rolled alloy. Therefore, the Pb-0.71wt.% Ag powder-rolled alloy may be considered an alternative Pb-based insoluble anode with both an excellent durability and a good energy efficiency for electrolysis.

Physical mesomechanics of grain boundary sliding in a deformable polycrystal

The temperature-rate dependences of strain resistance and the mechanisms of grain boundary sliding in Pb polycrystals and Pb-based alloys under active tension were investigated. The activation energy of plastic deformation and grain boundary sliding was determined. The structural mechanisms of grain boundary sliding were studied in a wide temperature range. The conclusion was made that self-consistency of grain boundary sliding and intragranular plastic flow has its origin in rotational deformation modes, with the grain boundary sliding being a primary process. Theoretical analysis of rotational deformation modes involved in grain boundary sliding was performed. It is shown that the dependence of deforming stress on the polycrystal grain size is impossible to describe by one universal Hall-Petch equation.

Finite element analysis of the effect of silver content for Sn–Ag–Cu alloy compositions on thermal cycling reliability of solder die attach

Thermal performance of a chip-scale packaged power device can be improved by attaching a heat spreader to the backside of the heat generating silicon die via solder thermal interface materials [STIMs]/solder die-attach. Driven by government legislation, electronics industry has advanced to lead (Pb)-free solders due to environmental and health concerns emanating from the use of Pb-based solders. Though solder compositions in the form of Sn–Ag–Cu (SAC) ternary system have been widely accepted and preferred by the electronic industry as replacements for the traditional Pb-based solder alloys, debate continues over the optimal silver content in the Sn–Ag–Cu (SAC) solder alloys. Apparently, the effect of silver (Ag) content on thermo-mechanical reliability of SAC alloy compositions as small area solder joints (flip chip solder bump or ball grid array (BGA)) has been extensively studied but not enough information exist on the effect of Ag percentage in SAC solder alloys when employed as large area solder joint (die-attach application). In this study, non-linear finite element method (FEM) is used for a comparative analysis of the effect of Ag content on the thermal fatigue performance of Sn–3Ag–0.5Cu (SAC305) and Sn–4Ag–0.5Cu (SAC405) when used in die-attach applications under three different thermal cyclic loading cases. The results show that Von-Mises stresses and strain energy in each of the two different SAC solder joints were strong function of the thermal cycle profiles, increasing in the order −55–80°C<−55–125°C<−65–150°C. In addition, this study suggests that the range of stress was relatively greater for the SAC alloy with higher Ag content (SAC405) while the lower Ag content SAC solder (SAC305) experiences a comparatively larger accumulated plastic work under the same thermal cycling condition. Further failure analysis via visual inspection reveals that for all cases of thermal cyclic loading employed in this study, maximum values of strain energy were all located in the corner regions (critical regions) of the solder joints at the side next to the silicon die independent of the Ag content of the solder joints. This paper also highlights the concerns as regards the implementation of conventional thermal fatigue models for accurate life time prediction of large area solder joint.

Polarization Behavior of Lead-Silver Anodes in Zinc Electrowinning Electrolytes

Lead anodes performance is important in zinc electrowinning (EW) as it greatly influences the final product quality and operating costs. Pb-based alloys are used in EW because they are cheap, conductive, and relatively stable at high potentials and low pH. In this study, polarization behavior and the oxygen evolution reaction (OER) on a Pb-Ag alloy were examined as a function of H2SO4, Mn2+, Cl−, Zn2+ concentrations and solution temperature. The slope of the oxygen evolution region and the OER potential were determined using potentiodynamic experiments. Corrosion products were studied using potentiostatic experiments along with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). The relationship between surface morphology of the electrode and operating potential was studied.

Application of molecular interaction volume model in vacuum distillation of Pb-based alloys

A method is presented for calculating the separation coefficients of Pb–Au and Pb–Sn alloys in vacuum distillation based on molecular interaction volume model (MIVM). A significant advantage of the model lies in its ability to predict the thermodynamic properties of liquid alloys using only binary infinite activity coefficients. The calculated results of Pb–Ag, Pb–Au, Pb–Sb, Pb–Sn and Sb–Sn show good agreement with experimental data in literature. It shows that the prediction effect of the proposed method is of better stability and reliability because the MIVM has a good physical basis.