Microstructure and Thermal Analysis of As-Cast Ag-Bi-Ni alloys

Materials Characterization, 2014

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 4.0 wt.%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 4.0 wt.%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 4.0 wt.%Ag alloys.

Calphad, 2008

The activities of Sn of liquid Ag-Bi-Sn alloys for three cross-sections with the constant molar ratios of Ag:Bi = 2:1, 1:1, and 1:2 are measured at 627 and 727 • C by an electromotive force (emf) method with a liquid electrolyte. The previous thermodynamic descriptions of the Ag-Bi-Sn ternary system are modified by considering the literature data and our own experimental results. The thermodynamic interaction parameters of the Bi-Sn binary and the Ag-Bi-Sn ternary liquid phase are optimized using the emf and calorimetric data from the present work. Based on the self-consistent optimized thermodynamic parameters the phase diagram and thermodynamic properties of the Ag-Bi-Sn ternary system are calculated and compared with the experimental data. The agreement between the calculated results and the experimental data has been significantly improved.

Journal of Alloys and Compounds, 2016

Microstructure and phase transitions of the selected alloys of the ternary BieGaeIn system were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and differential thermal analysis (DTA). Experimentally obtained results were compared with the results of thermodynamic extrapolation of the BieGaeIn ternary phase diagram. Experimentally detected coexisting phases in the investigated ternary alloys were in agreement with corresponding predicted phase structures at room temperature. Phase transition temperatures of selected ternary alloys with compositions along three vertical sections Bi 0.5 In 0.5 eGa, Bi 0.5 Ga 0.5 eIn and In 0.5 Ga 0.5 eBi were measured using DTA and several invariant reactions were identified. Hardness of selected alloys was determined using Vickers microhardness test and Brinell hardness test. Calculated liquidus projection and invariant equilibria of the BieGaeIn ternary system were presented.

Revista De Metalurgia, 2015

Structural, mechanical and electrical properties of selected alloys in ternary Ag-Bi-Zn system are presented in this paper. Chosen alloys were investigated using X-Ray Diffraction (XRD), light optical microscopy, Scanning Electron Microscopy combined with Energy Dispersive Spectrometry (SEM-EDS), as well as by electrical conductivity and Brinell hardness measurements. Isolines of electrical conductivity and hardness for the entire Ag-Bi-Zn system were calculated using regression models.

International Journal of Thermophysics, 2019

In this study, the phase diagram of the ternary Ag-Bi-Ge system was thermodynamically assessed and experimentally investigated, which to our knowledge has not been previously done. Differential thermal analysis (DTA), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray powder diffraction (XRD) were applied in order to experimentally assess three vertical sections and two isothermal sections at 200 °C and 400 °C of the Ag-Bi-Ge system. Results of the SEM-EDS and XRD analysis revealed existence of (Ge), (Ag) and (Bi) solid solution phases and absence of any ternary phases. Crystal structures of the identified phases and their corresponding lattice parameters were determined by XRD technique. Phase transition temperatures, including liquidus, solidus and temperature of an invariant reaction, were determined by means of DTA. Thermodynamic calculation of the Ag-Bi-Ge ternary phase diagram was carried out on the basis of optimized thermodynamic parameters for the constitutive binary systems acquired from the literature. Calculated liquidus projection of the Ag-Bi-Ge system and the determined invariant reactions are presented in the study as well. A close mutual agreement between the experimental results and the calculated phase equilibria was obtained.

Journal of Mining and Metallurgy, Section B: Metallurgy, 2017

Phase diagram of the Bi-Cu-Ga ternary system has been investigated experimentally with 27 alloys and analytically by using a Calphad method. Thirteen annealed alloys at 200?C were investigated by using scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), and X-ray powder diffraction (XRD) methods. Temperatures of phase transformation were determined with 14 alloys which are lying along three vertical sections Bi-Cu0.5Ga0.5, Cu-Bi0.5Ga0.5 and Ga-Bi0.5Cu0.5 by using differential thermal analysis (DTA). Based on the experimental result and by using Calphad method, ternary phase diagrams were constructed with a new description of liquidus phase. Calculated phase diagram and experimentally obtained results are in good agreement. Liquidus projection and invariant reaction were calculated by using new thermodynamic parameters for liquidus phase.

Journal of Alloys and Compounds, 1998

The equilibrium phase diagram of Ag-Bi-Sn ternary system was studied by X-ray powder diffraction analysis, differential scanning calorimetry and differential thermal analysis. Three isopletic sections were studied: 10 at.% Bi, 40 at.% Ag and 70 at.% Bi. Three transitory invariant reactions were characterized: two ternary transitory peritectics and one ternary eutectic. Moreover, from all equilibrium temperatures we were able to propose a description of ternary liquidus surface in the whole composition range.

Journal of Alloys and Compounds, 2013

This work investigates the effects of the Vickers micro-hardness of Ag powders on the alloying process undergone by Ag 90 Bi 10 powder mixtures submitted to ball milling. The transformation kinetics has been studied by quantitative X-ray diffraction. The experimental findings indicate that Bi gradually dissolves into Ag, finally forming a crystalline solid solution in which thermodynamic solubility limits are largely exceeded. It is shown that the rate of Bi dissolution, and the solubility degree, decrease as the Vickers micro-hardness of Ag powders increases.

Journal of the Serbian Chemical Society, 2006

The results of the calculation of the thermodynamic properties for liquid Ga-Sb-Tl alloys at the temperature 1073 K are presented in this paper. Initially, the most appropriate thermodynamic model for the investigated system was selected. Based on a comparison of the values calculated by different geometric models (Kohler, Muggianu, Toop, Hillert, Chou) with the existing experimental based data, asymmetric models of calculation were determined to give the best results. The asymmetric nature of the investigated ternary system was additionally confirmed by the Chou similarity coefficient concept. For these reasons, further complete thermodynamic calculations were performed according to the Hillert model in five sections of the ternary Ga-Sb-Tl system from each corner with the mole ratio of other two components being 9:1; 7:3; 5:5; 3:7 and 1:9. The obtained results include integral excess Gibbs energy dependences on composition for all the investigated sections. The calculated activity values at 1073 K for all components are given in the form of isoactivity diagrams. Comparison between the calculated and experimentally obtained gallium activities shows good agreement.

Replace of Pb-Sn with Pb-free solders (LFS) is one of the most important issues in the electronic industry. Eutectic and near-eutectic Sn-Ag-Cu (SAC) alloys are recommended as lead-free replacement in welding processes of electronic devices. Close to the eutectic ternary composition, the solidification occurs with three distinctive phases: Sn-rich dendritic primary phase, and the intermetallic phases Ag 3 Sn and Cu 6 Sn 5 , showing a limited solubility into the Sn-rich phase. Given the key role of the solidification process in the microstructure development of the alloy, samples of Sn-Ag-Cu with a composition close to the ternary eutectic were directionally grown to analyze the mechanisms involved in the solidification process of these alloys. The typical microstructure agrees withe above description, but shows two different mechanisms, depending on the interface advance velocity, resulting in different distribution of the intermetallic phases.