Navegando por Autor "Garcia, Amauri"

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An alternative thermal approach to evaluate the wettability of solder alloys
(Elsevier, 2016-08-25) Santos, Washington Luis Reis; Silva, Bismarck Luiz; Bertelli, Felipe; Spinelli, José Eduardo; Cheung, Noé; Garcia, Amauri
The aim of the work is to propose an alternative method to qualitatively evaluate the wettability of different alloys of a particular alloy system. The technique is based on a thermal approach supported by experimental/theoretical methodologies involving a directional solidification procedure and numerical simulations based on the solution of the inverse heat conduction problem (IHCP). The wettability strongly affects the heat ability to flow across the alloy/substrate interface during solidification, which is construed as a heat transfer coefficient (hg). Particularly, for the alloys used in soldering processes, the wettability plays an important role in the integrity of solder junctions, being a fundamental parameter for selecting the most appropriate solder composition. The experiments were carried out with high temperature Zn-Sn solder alloys (10, 20, 30 and 40 wt%Sn) in a solidification device in which heat is extracted only through a water-cooled steel bottom. Experimental thermal profiles collected during solidification are used as input data to solve the IHCP and determine expressions hg vs. time for each alloy examined, permitting a tendency of wettability to be established. In order to validate the wetting behavior indicated by the hg values, alloy/substrate contact angles (θ) were measured on a steel substrate using a goniometer. It is shown that both hg and θ indicate improvements in wettability with the decrease in the alloy Sn content
Assessing microstructure and mechanical behavior changes in a Sn-Sb solder alloy induced by cooling rate
(Elsevier, 2019-11-15) Schon, Aline Ferreira; Reyes, Rodrigo Valenzuela; Spinelli, José Eduardo; Garcia, Amauri; Silva, Bismarck Luiz
In the present investigation a directional solidification experiment was performed in order to examine distinct microstructures related to different slices of the solidified Sn-2 wt.%Sb alloy casting. Such alloy is an alternative of interest with the target of replacing lead-containing solder alloys (containing 85 to 97 wt% of Pb) given that lead (Pb) is considered an important environmental complaint and has devastating effects on the human body. The imposed conditions in the present experiment may lead to solutal and thermal stability of the melt throughout solid growth towards the liquid. It was found that Sn-rich cells may prevail for cooling rates higher than 1.0 K/s whereas only Sn-rich dendrites appear for specimens solidified at rates lower than 0.3 K/s. The growth of dendrites is delayed when compared to previous results in the literature. In the presence of convective flow originated either thermally or solutally, β-Sn dendrites were reported to grow for samples solidified at rates as high as 1.5 K/s (i.e., 5 times higher). It appears that convection currents induce instabilities to happen at the solidification front and the growth of dendrites is benefited over such conditions. Tensile tests were also performed for Sn-Sb samples having distinct cellular and dendritic dimensions. It was found that unstable plastic flow happened during all tensile tests. The formation of bands along a specimen gauge was recognized as being a manifestation of the Portevin – Le Chatelier (PLC) effect. A homogeneous deformation stage preceded the start of serrations of stresses in the samples of the investigated alloy. The amplitudes of the serrations were found to be lower in the samples having cells as compared to those associated with dendritic microstructures
A comparative analysis of microstructural features, tensile properties and wettability of hypoperitectic and peritectic Sn-Sb solder alloys
(Elsevier, 2018-02) Dias, Marcelino; Costa, Thiago Antônio; Silva, Bismarck Luiz; Spinelli, José Eduardo; Cheunga, Noé; Garcia, Amauri
Sn-Sb alloys are among the current alternatives for the development of alloys for high-temperature lead-free solders. The Sn-Sb alloys having 5.5 wt.% Sb or less are known to have good mechanical properties, and despite the quite low liquidus temperature have been considered adequate in the development of solder joints. The increase in the Sb content up to the limit of solubility in Sn at about 10 wt.% is supposed to be detrimental to the mechanical properties due to the extensive formation of an intermetallic compound. Investigations on the interrelation of microstructure of this alloy and the corresponding mechanical properties are fundamental to an appropriate evaluation of its application in solder joints. The present investigation analyses the relationship between microstructural features of the peritectic Sn-10 wt.% Sb alloy, solidified under a wide range of cooling rates, and the resulting mechanical properties. A cellular β-Sn matrix, typified by cellular spacings that decrease with the increase in the solidification cooling rate, and Sn3Sb2 particles are shown to characterize the alloy microstructure. The ultimate tensile strength is higher as compared with the corresponding values of the hypoperitectic Sn-5.5 wt.% Sb solder alloy, however the elongation is shown to decrease. A comparison with Bi-Ag alloys, considered good high temperature solders alternatives, has shown that the tensile properties of the Sn-10 wt.% Sb alloy, including elongation, are significantly higher. Wettability tests have been carried out and the experimental results, according to reports from the literature, are associated with good wettability
Complex eutectic growth and Bi precipitation in ternary Sn-Bi-Cu and Sn-Bi-Ag alloys
(Elsevier, 2017-01-15) Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo
Sn-34 wt%Bi, Sn-34 wt%Bi-2wt%Ag and Sn-34 wt%Bi-0.7 wt%Cu alloys have been directionally solidified (DS) under a broad range of solidification cooling rates. Microstructures have been characterized with emphasis on both eutectic growth and precipitation of Bi within the β-Sn dendritic matrix. The eutectic growth, for all alloys examined, is shown to be associated with the coexistence of coarse and fine lamellar structures with different length-scale of lamellar spacing (λ). Experimental growth relations of λ vs. the cooling rate have been proposed. The length-scale of the lamellae in the fine eutectic ranges from 0.8 to 2.5 μm while in the coarse eutectic from 1.8 to 4.0 μm. Taking as reference the Sn-Bi alloy, both the spacing between Bi precipitates (λp) and the fine eutectic spacing (λfine) increase with Cu and Ag additions, whereas λcoarse remains roughly unaltered. Both ternary Sn-Bi-Ag and Sn-Bi-Cu alloys are shown to have worse distributions of both lamellae in the fine eutectic and of precipitates within Sn-rich dendrites, which resulted in decrease in hardness
Cooling thermal parameters and microstructure features of directionally solidified ternary Sn–Bi–(Cu,Ag) solder alloys
(Elsevier, 2016-04) Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo
Low temperature soldering technology encompasses Sn–Bi based alloys as reference materials for joints since such alloys may be molten at temperatures less than 180 °C. Despite the relatively high strength of these alloys, segregation problems and low ductility are recognized as potential disadvantages. Thus, for low-temperature applications, Bi–Sn eutectic or near-eutectic compositions with or without additions of alloying elements are considered interesting possibilities. In this context, additions of third elements such as Cu and Ag may be an alternative in order to reach sounder solder joints. The length scale of the phases and their proportions are known to be the most important factors affecting the final wear, mechanical and corrosions properties of ternary Sn–Bi–(Cu,Ag) alloys. In spite of this promising outlook, studies emphasizing interrelations of microstructure features and solidification thermal parameters regarding these multicomponent alloys are rare in the literature. In the present investigation Sn–Bi–(Cu,Ag) alloys were directionally solidified (DS) under transient heat flow conditions. A complete characterization is performed including experimental cooling thermal parameters, segregation (XRF), optical and scanning electron microscopies, X-ray diffraction (XRD) and length scale of the microstructural phases. Experimental growth laws relating dendritic spacings to solidification thermal parameters have been proposed with emphasis on the effects of Ag and Cu. The theoretical predictions of the Rappaz-Boettinger model are shown to be slightly above the experimental scatter of secondary dendritic arm spacings for both ternary Sn–Bi–Cu and Sn–Bi–Ag alloys examined
Cu and Ag additions affecting the solidification microstructure and tensile properties of Sn-Bi lead-free solder alloys
(Elsevier, 2017-09-29) Silva, Bismarck Luiz; Xavier, Marcella Gautê Cavalcante; Garcia, Amauri; Spinelli, José Eduardo
Over the past few years Sn-based solders containing third and fourth elements have become of great interest to try and improve the consistency of solders during application. In most reported cases this involved the addition of either Ni in Sn-Cu or Ag in Sn-Bi solder alloys. Still there is a lack of research showing how the combination of third element additions and varying cooling rates affect the mechanical properties of Sn-Bi-X solder alloys. As such the present investigation examines the effects of minor additions of Ag and Cu on a Sn-34 wt%Bi solder alloys produced by directional solidification. Directional solidification was used as the transient regime attained during directional solidification in a water-cooled mold may allow for similar cooling rates to those found in industrial reflow soldering operations. Microstructural analysis on the Sn-Bi-X alloys was conducted using eutectic spacing (λE), Bi precipitates spacing (λp) and the secondary dendritic spacing (λ2) measurements. These measurements represented the complex eutectic growth, the solid-state precipitation of Bi within the β-Sn phase and the length-scale of the Sn-rich dendritic array respectively. In conjunction with these measurements the evolution of tensile strength and ductility as a function of λ2 was examined. Considering the Sn-34 wt%Bi, Sn-34 wt%Bi-0.1 wt%Cu, Sn-34 wt%Bi-0.7 wt%Cu and Sn-33 wt%Bi-2 wt%Ag alloys, it was found that the modified alloys containing 0.7 wt%Cu and 2.0 wt%Ag showed lower tensile properties and lower ductility. In contrast, the addition of 0.1 wt%Cu increased the ductility for λ2 < 14 µm while preserving the tensile strength, representing the best alternative of all alloys examined
Dendritic and eutectic growth of Sn–0.5 wt.%Cu solders with low alloying Al levels
(SAGE Publications, 2018-06-22) Lima, Thiago Soares; Silva, Bismarck Luiz; Garcia, Amauri; Cheung, Noé; Spinelli, José Eduardo
The dependences of microstructures on the solidification thermal parameters of Sn–0.5 wt.%Cu, Sn–0.5 wt.%Cu–0.05 wt.%Al, and Sn–0.5 wt.%Cu–0.1 wt.%Al alloys are examined. Ranges of sizes and morphologies of microstructural phases have been quantitatively assessed due to the broad spectra of cooling rates and thermal gradients associated with the experiments. Various types of growth relations are proposed to represent the microstructural progresses. Al addition does not change either the matrix primary dendritic spacing or the spacing between Cu6Sn5 particles. However, it is shown that the secondary dendrite arm spacing, λ2, is greatly affected, increasing with the increase in the Al content. Both globular-type and fibrous-type morphologies typify the Cu6Sn5 intermetallics located in interdendritic zones
Dendritic growth, solidification thermal parameters, and Mg content affecting the tensile properties of Al-Mg-1.5 Wt Pct Fe alloys
(Springer, 2017-02-08) Gomes, Leonardo Fernandes; Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo
Al-Mg-Fe alloys are appointed as favorable ones with respect to the costs and all the required properties for successful vessel service. However, the experimental inter-relations of solidification thermal parameters, microstructure, and mechanical strength are still undetermined. In the present research work, the dependences of tensile properties on the length scale of the dendritic morphology of ternary Al-1.2 wt pct Mg-1.5 wt pct Fe and Al-7 wt pct Mg-1.5 wt pct Fe alloys are examined. Transient heat flow conditions during solidification have been achieved by the use of a directional solidification system, thus permitting a comprehensive characterization of the dendritic microstructures to be performed. Thermo-Calc computations, X-ray diffraction, and scanning electron microscopy analyses are carried out to give support to the extensive microstructural evaluation performed with both ternary Al-Mg-Fe alloys. Experimental growth relations of primary, λ 1, and secondary, λ 2, dendrite arm spacings with cooling rate (T˙L) and of tensile properties with λ 2 are proposed. For both alloys examined, Hall–Petch type formulas show that the tensile strength increases with the decrease in λ 2. The soundest strength–ductility balance is exhibited by the Al-7 wt pct Mg-1.5 wt pct Fe alloy specimen with refined microstructure. This is shown to be due to a more homogeneous distribution of intermetallic particles in connection with solid solution strengthening propitiated by Mg. Functional experimental inter-relations of tensile properties with growth (V L) and cooling rates (T˙L) for both ternary Al-Mg-Fe alloys have also been derived
Directional solidification of a Sn-0.2Ni solder alloy in water-cooled copper and steel molds: related effects on the matrix micromorphology, nature of intermetallics and tensile properties
(Elsevier, 2017-11-05) Xavier, Marcella Gautê Cavalcante; Cruz, Clarissa Barros da; Kakitani, Rafael; Silva, Bismarck Luiz; Garcia, Amauri; Cheung, Noé; Spinelli, José Eduardo
The present investigation is focused on, firstly, performing transient directional solidification experiments with a Sn-0.2 wt.% Ni solder alloy using two different substrates as mold sheets separating the alloy casting from the cooling fluid: copper and low carbon steel. Secondly, the examination of the obtained microstructures is carried out highlighting not only the micromorphology aspects of the formed β-Sn phase but also the nature and the shape of the intermetallic compounds (IMCs) developed. The purpose of this research work is to verify the influences that different substrate materials may have on the alloy solidification kinetics, resultant microstructures and tensile properties of the Sn-0.2 wt.%Ni solder. The microstructure characteristics may be correlated with thermal solidification parameters such as the eutectic cooling rate and eutectic growth rate along with a qualitative evaluation of Fe and Cu dissolutions into the alloy. The results display that the dissolution of Cu into the Sn-Ni alloy provided the prevalent growth of the (Cu,Ni)6Sn5 fiber-like eutectic phase along the length of the casting. Other than, the Cu-containing Sn-Ni alloy allowed the growth of high-velocity β-Sn cells only for very high cooling rates, associated with positions closer to the bottom of the alloy casting. Farther positions are characterized by a complex growth of β-Sn dendrites. On the other hand, for the alloy solidified against the steel mold, a predominance of the non-equilibrium NiSn4 eutectic phase with plate-like shape has been identified by SEM/EDS and XRD. In this case, the predominant growth of β-Sn cells associated with the presence of the plates of the NiSn4 IMC allowed lower tensile strength and higher ductility to be attained
Effects of solidification thermal parameters on microstructure and mechanical properties of Sn-Bi solder alloys
(Springer, 2017-01-10) Silva, Bismarck Luiz; Silva, Vítor Covre Evangelista da; Garcia, Amauri; Spinelli, José Eduardo
Samples extracted along the length of directionally solidified (DS) castings of three Sn-xBi alloys (x = 34 wt.%Bi, 52 wt.%Bi and 58 wt.%Bi) were first evaluated metallographically and then subjected to scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses. The characteristic length scale of both eutectic and dendritic phases forming the microstructure were determined and correlated with solidification thermal parameters (growth rate V, and cooling rate Ṫ). Tensile and Vickers hardness tests were performed to allow strength and ductility to be discussed as a function of both microstructure features and alloy solute content. The tertiary dendrite arm spacings along the length of the DS Sn-52 wt.%Bi alloy casting are shown to be lower than those obtained for the Sn-34 wt.%Bi alloy casting. The results of mechanical tests show that, with the decrease in the alloy Bi content, both tensile strength and hardness are improved. This is shown to be mainly attributed to the higher density of Bi precipitates decorating the Sn-rich dendrites, which are finer than the equivalent phase developed for the Sn-52 wt.%Bi alloy. However, the ductility is shown to be significantly improved for specimens associated with regions of more refined microstructure of the Sn-52 wt.%Bi alloy DS casting. A microstructure combining much branched dendrites, fine Bi particles within the β-Sn dendritic matrix and an important proportion of very fine eutectic formed by alternate Bi-rich and Sn-rich phase, seems to be conducive to this higher ductility. In this case, the fracture surface is shown to be more finely broken with presence of dimples for this particular condition, i.e., characteristic of a ductile fracture mode
High cooling rate, regular and plate like cells in Sn–Ni solder alloys
(Wiley, 2018-03-13) Xavier, Marcella G. C.; Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo
Broad ranges of cooling rates (urn:x-wiley:14381656:media:adem201701179:adem201701179-math-0001) 0.8–30.5 and 0.4–5.0 K s−1 are attained during directional solidification of eutectic Sn–0.2 wt% Ni and hypereutectic Sn–0.5 wt% Ni alloys, respectively. A reverse high cooling rate cell‐to‐dendrite transition occurs for the eutectic composition and a transition from high cooling rate cells to plate like cells for the hypereutectic alloy. High cooling rate β‐Sn cells are associated with cooling rates >5.5 and >2.7 K s−1 for eutectic and hypereutectic compositions, respectively. A processing diagram, relating the ‘urn:x-wiley:14381656:media:adem201701179:adem201701179-math-0002–Ni content’ space with the microstructural morphology, is proposed. A combination of plate like cells and plate NiSn4 eutectic phase results in higher ductility
Interplay of wettability, interfacial reaction and interfacial thermal conductance in Sn-0.7Cu solder alloy/substrate couples
(Springer, 2020) Lima, Thiago Soares; Cruz, Clarissa Barros da; Silva, Bismarck Luiz; Brito, Crystopher; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
Directional solidification experiments coupled with mathematical modelling, drop shape analyses and evaluation of the reaction layers were performed for three different types of joints produced with the Sn-0.7 wt.%Cu solder alloy. The association of such findings allowed understanding the mechanisms affecting the heat transfer efficiency between this alloy and substrates of interest. Nickel (Ni) and copper (Cu) were tested since they are considered work piece materials of importance in electronic soldering. Moreover, low carbon steel was tested as a matter of comparison. For each tested case, wetting angles, integrity and nature of the interfaces and transient heat transfer coefficients, ‘h’, were determined. Even though the copper has a thermal conductivity greater than nickel, it is demonstrated that the occurrence of voids at the copper interface during alloy soldering may decrease the heat transfer efficiency, i.e., ‘h’. Oppositely, a more stable and less defective reaction layer was formed for the alloy/nickel couple. This is due to the suppression of the undesirable thermal contraction since the hexagonal Cu6Sn5 intermetallics is stable at temperatures below 186°C in the presence of nickel
Microstructure characterization and tensile properties of directionally solidified Sn-52 wt% Bi-1wt% Sb and Sn-52wt% Bi-2wt% Sb alloys
(Elsevier, 2020-08) Paixão, Jeverton Laureano; Gomes, Leonardo Fernandes; Reyes, Rodrigo Valenzuela; Garcia, Amauri; Spinelli, José Eduardo; Silva, Bismarck Luiz
Sn-Bi-based Thermal Interface Materials (TIM) are adequate alloys to promote heat dissipation in power electronics. However, despite the necessary thermal connection, mechanical support for different components and substrates are of prime importance in microelectronic devices. In this framework, the effects of Antimony (Sb) additions on the microstructure and tensile properties of the Sn-52 wt% Bi alloy are investigated. Various Sn-Bi(-Sb) samples solidified at different cooling rates and two levels of Sb-containing alloys allow a comprehensive examination of length scales of either dendritic or eutectic microstructures. A number of experimental techniques are used here to permit a sound analyses of the ternary Sn-Bi(-Sb) alloys: transient directional solidification, optical microscopy (OM), triangle and intercept quantification methods, scanning electron microscopy (SEM), x-ray fluorescence (XRF), x-ray diffraction (XRD), tensile tests and fractography. The addition of Sb enhances the nucleation of primary dendritic trunks, which resulted in a decrease in the primary dendritic arm spacing (λ1) by about 5 times for the Sn-52 wt% Bi-2 wt% Sb alloy as compared to the results for the binary Sn-Bi alloy. The relationships found for tensile properties as a function of the secondary dendritic arm spacing (λ2) demonstrate that Sb additions increase the alloy strength while preserving the ductility. This is due to very thin SnSb intermetallic particles formed in the Sn-rich dendritic matrix. The influence of λ2 variation on both the yield and ultimate strengths is roughly insignificant while the ductility varies strongly between 14.4% and 52% for samples solidified from 0.05 °C/s to 5.0 °C/s respectively. When 2.0 wt% Sb is added, there is a maintenance in the levels of ductility as those found for the binary Sn-Bi alloy. This occurs especially for very refined dendritic and eutectic microstructures samples, which also exhibit a ductile fracture mode
Solder/substrate interfacial thermal conductance and wetting angles of Bi–Ag solder alloys
(Springer, 2015-10-31) Silva, Bismarck Luiz; Bertelli, Felipe; Canté, Manuel Venceslau; Spinelli, José Eduardo; Cheung, Noé; Garcia, Amauri
Bi–Ag lead-free alloys are considered interesting alternatives to Pb-based traditional solders due to compatible melting point and strength. During soldering, the ability of a liquid alloy to flow or spread over the substrate is crucial for the formation of a metallic bond driven by the physicochemical properties of the liquid solder/solid substrate system. In addition, the wettability is intimately associated with the solder/substrate thermal conductance represented by a heat transfer coefficient, hi. In this work, three Bi–Ag alloys (hypoeutectic—1.5 wt%Ag, eutectic—2.5 wt%Ag and hypereutectic—4.0 wt%Ag) were directionally solidified under upward unsteady state heat flow conditions. Both time-dependent hi profiles and wetting behavior represented by contact angles (θ) were determined for the three alloys examined. The dependence of θ on the alloy Ag content is assessed experimentally. Also, thermal readings collected during directional solidification of the Bi 1.5, 2.5 and 4.0 wt% Ag alloys are used with a view to permitting hi versus time (t) profiles to be computed. It is shown that along a first solidification stage (t < 16 s) the hi values followed the trend experimentally observed by the contact angles for the three alloys examined, while for t > 16 s the volumetric expansion of the Bi-rich phase is shown to have a dominant role inducing a sudden increase in hi. For each alloy a couple of time-dependent hi expressions is needed to represent the entire solidification progress
Tailoring morphology and size of microstructure and tensile properties of Sn-5.5 wt.%Sb-1 wt.%(Cu,Ag) solder alloys
(Springer, 2017-10-12) Dias, Marcelino; Costa, Thiago A.; Soares, Thiago; Silva, Bismarck Luiz; Cheung, Noé; Spinelli, José Eduardo; Garcia, Amauri
Transient directional solidification experiments, and further optical and scanning electron microscopy analyses and tensile tests, allowed the dependence of tensile properties on the micromorphology and length scale of the dendritic/cellular matrix of ternary Sn-5.5Sb-1Ag and Sn-5.5Sb-1Cu alloys to be determined. Extensive ranges of cooling rates were obtained, which permitted specific values of cooling rate for each sample examined along the length of the casting to be attributed. Very broad microstructural length scales were revealed as well as the presence of either cells or dendrites for the Ag-containing alloy. Hereafter, microstructural spacing values such as the cellular spacing, λ c, and the primary dendritic spacing, λ 1, may be correlated with thermal solidification parameters, that is, the cooling rate and the growth rate. While, for the Cu-containing Sn-Sb alloy, the β-Sn matrix is characterized only by the presence of dendritic arrangements, the Ag-containing Sn-Sb alloy is shown to have high-velocity β-Sn cells associated with high cooling rate regions, i.e., positions closer to the bottom of the alloy casting, with the remaining positions being characterized by a complex growth of β-Sn dendrites. Minor additions of Cu and Ag increase both the yield and ultimate tensile strengths when compared with the corresponding values of the binary Sn-5.5Sb alloy, with a small reduction in ductility. This has been attributed to the homogeneous distribution of the Ag3Sn and Cu6Sn5 intermetallic particles related to smaller λ 1 characterizing the dendritic zones of the ternary Sn-Sb-(Cu,Ag) alloys. In addition, the Ag-modified Sn-Sb alloy exhibited an initial wetting angle consistent with that characterizing the binary Sn-5.5Sb alloy
The application of an analytical model to solve an inverse heat conduction problem: transient solidification of a Sn-Sb peritectic solder alloy on distinct substrates
(Elsevier, 2019-12) Curtulo, Joanisa P.; Dias, Marcelino; Bertelli, Felipe; Silva, Bismarck Luiz; Spinelli, José Eduardo; Garcia, Amauri; Cheung, Noé
Three distinct alloy/substrate couples were considered. In order to treat the reaction interface problem effectively, sheets of commercially pure copper (Cu), electrolytic nickel (Ni) and low carbon steel were chosen so that solidification of a Sn-Sb peritectic alloy could be evaluated comprehending very different conditions. A straightforward view of the mechanisms affecting the heat transfer efficiencies was consistent with a number of techniques applied in the present investigation, which includes directional solidification experiments, analytical modelling, wettability analyses and characterization of the reactions between the alloy and the substrates. The proposed analytical model was perceptive to these reactions. For the Cu substrate, the motion of Cu towards the alloy was more effective as compared to the motion of Ni from the Ni substrate. As a consequence, the alloy/Cu interface presented a higher level of Kirkendall voids. The higher fraction of voids at the interface resulted in lower interfacial thermal conductance for the Sn-Sb/Cu couple. Hence, the present experimental-theoretical approach is useful to indicate the solder joint integrity in terms of the presence of empty spots. Despite the higher thermal conductivity of Cu and lower contact angle between the alloy and the Cu in comparison to the Ni substrate, the high porosity at the Cu interface during alloy soldering was shown to reduce the heat transfer capability
The role of eutectic colonies in the tensile properties of a Sn–Zn eutectic solder alloy
(Elsevier, 2020-01-01) Ramos, Lidiane Silva; Reyes, Rodrigo Valenzuela; Gomes, Leonardo Fernandes; Garcia, Amauri; Spinelli, José Eduardo; Silva, Bismarck Luiz
The growth of eutectic colonies in Sn–Cu, Sn–Zn and Sn–Ag–Cu eutectic alloys has already been reported in the literature. However, relationships between this kind of microstructure and mechanical properties remain undetermined for solders. The use of water-cooled copper (Cu) and AISI 1020 low-C steel molds and the eutectic Sn-9 wt.%Zn alloy make it possible to address this matter. The samples grown in the Cu mold demonstrated higher solidification rates than those developed in the low-C steel mold. Overall, the microstructure is constituted by Zn-lamellae embedded in a Sn-rich matrix. The Zn lamellae are not only uneven in thickness but also irregularly perforated. Due to Cu dissolution into the alloy, a small fraction of Cu5Zn8 intermetallic particles formed during solidification of the Sn-9 wt.%Zn alloy in the Cu mold. The contamination with Cu appears to be responsible for the improvement in the distribution of Zn-lamellae. The decrease in spacing between broken lamellae measured from SEM images, as well as a higher number of Zn particles per area, explain such occurrence. Ductility and tensile strength of different samples could allow the establishment of relationships among properties vs. eutectic colony spacing. For the Cu mold, the motion of Cu towards the alloy as well as higher solidification rates, allowed microstructures to be formed combining 60% of strain to fracture and 52 MPa of ultimate tensile strength. These achievements are mainly due to the finest spacings of both the eutectic colony (λχ = 36 μm) and the Zn lamellae (λL=0.9 μm), besides homogeneous distribution of Cu across the resulting microstructure
Transient unidirectional solidification, microstructure and intermetallics in Sn-Ni Alloys
(ABM, ABC, ABPol, 2018-04-12) Cruz, Clarissa Barros da; Kakitani, Rafael; Xavier, Marcella Gautê Cavalcante; Silva, Bismarck Luiz; Garcia, Amauri; Cheung, Noé; Spinelli, José Eduardo
The present research work examines the microstructural arrangements formed during the transient solidification of eutectic Sn-0.2wt.%Ni and hypereutectic Sn-0.5wt.%Ni alloys. Also, it examines their respective correlations with solidification thermal parameters: eutectic growth rate (VE) and eutectic cooling rate (ṪE); length scales of matrix and eutectic phases: microstructural spacings and the corresponding tensile properties: ductility and strength. Both alloys were directionally solidified upwards under unsteady-state regime, and characterized by optical and scanning electron microscopy. Concerning the hypereutectic Sn-0.5wt.%Ni, the increase in Ni content is shown to influence both thermal behavior and cellular spacing (λC). The NiSn4 intermetallics is present in the eutectic mixture of both alloys, whilst in the Sn-0.5wt.%Ni alloy the primary phase has been identified by SEM-EDS as the Ni3Sn4 intermetallics. A β-Sn morphological cellular/dendritic transition occurs in the 0.2wt.%Ni eutectic alloy for ṪE> 1.2K/s. Despite that, regular cells in the hypereutectic alloy (0.5wt.%Ni) turns into plate-like cells for ṪE> 1.4K/s. If considered a reference cellular spacing about 20μm (i.e.,λ(c-1/2=0.22), the samples associated with the Sn-0.5wt.%Ni alloy are shown to be associated with higher tensile strengths, but much lower ductility as compared with the corresponding results of the eutectic alloy
Wetting behavior of Sn–Ag–Cu and Sn–Bi–X alloys: insights into factors affecting cooling rate
(Elsevier, 2019) Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo
Based on two experimental approaches: transient directional solidification and drop shape analyses, the measurements of cooling rates and contact angles (θ) of several solders of interest became practical. Three Sn–0.7Cu–(1; 2 and 3Ag) and four Sn–34Bi–(0Cu; 0.1Cu; 0.7Cu; 2Ag) alloys are investigated to determine their wetting behavior, compare to each other and bring to light their ability (or not) to control the initial cooling rate. In the case of SAC alloys, increase in Ag means decrease in both θ and cooling rate. An opposite correlation between cooling rate and θ is observed when Sn–34Bi and the Sn–34Bi–0.1Cu alloys are compared

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Navegando por Autor "Garcia, Amauri"