Navegando por Autor "Garcia, Amauri"

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Corrosion behavior of an AleSneZn alloy : effects of solidification microstructure characteristics.
(2021) Barros, André dos Santos; Cruz, Clarissa Barros da; Garcia, Amauri; Cheung, Noé
Due to its strong influence on service life of manufactured parts, corrosion resistance is an important factor to consider when designing Al alloys for engineering applications. With this in mind, the present study focuses on understanding the role of microstructure features in the corrosion behavior of an Al-10wt.%Sn-5wt.%Zn alloy. Samples with different microstructural length scales were subjected to corrosion tests, which were performed using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. An equivalent circuit analysis was also carried out. The results revealed a relatively high electrochemical activity of the studied alloy. Furthermore, coarsening in microstructure showed a slight tendency towards improvements in the corrosion resistance, that is, coarser microstructures composed by Al-rich dendrites surrounded by SneZn constituent particles were comparatively less prone to corrosion degradation than finer ones. Finally, the proposed equivalent circuit model is shown to have good agreement with the experimental EIS measurements.
Dry sliding wear features of an Al-20Sn-5Zn alloy affected by microstructural length scales.
(2022) Cota, André Barros; Cruz, Clarissa Barros da; Botelho, Tamires; Silva, Maria Adrina Paixão de Souza da; Casteletti, Luiz Carlos; Garcia, Amauri; Cheung, Noé
Al-Sn-Zn alloys are attractive options for use as wear-resistant materials. While Sn promotes self-lubricating characteristics, Zn strengthens the Al-rich matrix. Conventionally, the manufacturing of these alloys involves casting. However, there is still a paucity of studies that associate the solidification microstructure with the wear resistance of these alloys. Inspired by such considerations, this work aims at investigating the wear behavior of an Al-20Sn-5Zn [wt.%] alloy produced by a directional solidification technique. A set of samples with different microstructure length scales was subjected to ball cratering tests using a normal contact load of 0.25 N and six test times. The results show that the dependence of the wear behavior on the microstructure length scale becomes more expressive for longer sliding distances. It was found that coarser microstructures provide an improved wear resistance. In view of that, a possible spectrum of specific wear rates was determined as a function of the sliding distance, considering different microstructure length scales. Finally, experimental equations are proposed to represent a possible range of wear volume and wear coefficient according to the dendrite arm spacings.
Effect of microstructure features on the corrosion behavior of the Sn‐2.1 wt%Mg solder alloy.
(2020) Cruz, Clarissa Barros da; Lima, Thiago Soares; Soares, Marco César Prado; Feitosa, Emmanuelle Sá Freitas; Fujiwara, Eric; Garcia, Amauri; Cheung, Noé
The Sn–Mg eutectic alloy is a potential replacement for the traditional Sn-38.1 wt%Pb solder alloy, since lead has been banned because of its risk to human health and the environment. However, studies in the literature related to the Sn-2.1 wt%Mg alloy are restricted to mechanical, electrical and thermal properties. Therefore, this study aims to evaluate the corrosion behavior of this alloy, as a function of the microstructural arrangement obtained from directional solidifcation performed in a transient heat extraction regime. The thermal solidifcation parameters (solidifcation growth rate and cooling rate) were determined along the length of the casting for correlations with microstructural features. The resulting microstructure was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray difraction. Subsequently, the electrochemical impedance spectroscopy, linear polarization, equivalent circuit and evolution of hydrogen release analyzes were performed to evaluate the corrosion behavior of the samples in a 0.5 M NaCl solution at 25 °C. Interphase spacing and Mg2Sn fraction were found to infuence the corrosion behavior, showing higher corrosion resistance for a more refned microstructure.
Interface evaluation of a Bi–Zn eutectic solder alloy : effects of different substrate materials on thermal contact conductance.
(2021) Azeredo, Rudimylla Septimio; Cruz, Clarissa Barros da; Xavier, Marcella Gautê Cavalcante; Lima, Thiago Soares; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
Industry is searching for ways of improving the process control required for the manufacture of electronic circuitry. In this respect, a numerical mathematical model for thermal contact conductance of solder/substrate couples is developed based on an inverse heat conduction problem. The intention of this research is combining the model results and wetting experiments in order to determine if there is a compromise between them in the matter of the Bi–Zn eutectic alloy. Substrate materials considered as priority for the electronics industry were tested. It was found that the heat transfer coefficients (h) and the contact angles (θ) might be related to each other. The Bi–Zn/copper, Bi–Zn/nickel, Bi–Zn/Invar and Bi–Zn/steel couples, in this order, generated θ varying from the smallest to the largest as well as h from the largest to the smallest. Microstructural coarsening effect has been realized with higher spacing between Zn fibers (λZn) referring to a condition of worse heat extraction imposed by an alloy/substrate couple during solidification.
Interfacial heat transfer and microstructural analyses of a Bi- 5% Sb lead- free alloy solidified against Cu, Ni and low-C steel substrates.
(2021) Lima, Thiago Soares; Cruz, Clarissa Barros da; Xavier, Marcella Gautê Cavalcante; Reyes, Rodrigo André Valenzuela; Bertelli, Felipe; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
Bi-Sb system alloys demonstrate high corrosion resistance and good wettability, becoming promising for use as lead-free solder alloys. The simplicity of the phase diagram is also a characteristic of this system, which is isomorphous forming the (Bi,Sb) phase. While extensive research has been performed on heat flow in couples of microelectronics surfaces with eutectic and peritectic alloys, literature regarding the issues of interfacial heat transfer between isomorphous alloys and microelectronics substrates is nonexistent. In this regard, the present research work demonstrates not only the application of a numerical mathematical model for thermal interface conductance but also wetting and interfacial reaction layer results in the formation of phases for the Bi- 5 wt% Sb alloy in different substrate materials. After carrying out the mentioned analyzes in three different conditions, Bi-Sb/copper, Bi-Sb/nickel and Bi-Sb/low-C steel, the wetting angle is shown not to be the predominant factor in controlling the interfacial heat transfer. Instead, the phases forming the interfacial layer from each of the tested substrates have a role in the heat transfer coefficients (h). In the case of the steel substrate, there is no layer formation, which allows greater contact conductance, whereas Bi-Sb/copper and Bi-Sb/nickel couples generate smaller h, being reasonably similar to each other.
Interplay of wettability, interfacial reaction and interfacial thermal conductance in Sn-0.7Cu solder alloy/substrate couples.
(2020) Lima, Thiago Soares; Cruz, Clarissa Barros da; Silva, Bismarck Luiz; Brito, Crystopher Cardoso de; 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 sup-pression of the undesirable thermal contraction since the hexagonal Cu6Sn5 intermetallics is stable at temperatures below 186C in the presence of nickel.
Length scale of solidification microstructure tailoring corrosion resistance and microhardness in T6 heat treatment of an Al–Cu–Mg alloy.
(2020) Barros, André dos Santos; Cruz, Clarissa Barros da; Silva, Maria Adrina Paixão de Souza da; Cheung, Noé; Garcia, Amauri; Rocha, Otávio Fernandes Lima da; Moreira, Antônio Luciano Seabra
The combined effects of solidification microstructure refining scale and T6 heat treatment conditions on corrosion behaviour and Vickers microhardness of an Al–3 wt-% Cu–0.5 wt-% Mg alloy were studied. Then, representative samples having quite distinct primary dendritic spacings were solution treated at 495°C for 3 h and artificially aged at 200°C during different times. It was found that the feature of finer solidification microstructure having higher corrosion current density and higher microhardness can be inherited to subsequent T6 heat treatments. In contrast to the as-cast condition, the aging times of 0.5 and 1 h were shown to promote lower corrosion rates without corrosion occurring at the central region of Al-rich matrix. On the other hand, the aging time of 3 h led to a significant decrease in both the corrosion resistance and the microhardness. Finally, a comparative analysis with other works from the literature was also conducted.
Microstructural and segregation efects afecting the corrosion behavior of a high‐temperature Bi‐Ag solder alloy in dilute chloride solution.
(2021) Azeredo, Rudimylla Septimio; Cruz, Clarissa Barros da; Silva, Bismarck Luiz; Garcia, Amauri; Spinelli, José Eduardo; Cheung, Noé
In electronic devices the solder joint is exposed not only to the air but also to moistures and other corrosive media such as chlorine and sulfur compounds. Bi–Ag alloys meet the melting temperature requirement to be classifed as high-temperature solders, therefore, knowledge of corrosion behavior is important for a long-term reliability of Bi–Ag solder connections. However, corrosion studies of Bi–Ag alloys are quite restricted in the literature. In this study, the role of the representative length scale of the microstructure as well as of the efects of Ag segregation on the resulting corrosion behavior of Bi–4 wt% Ag alloy samples are investigated. Cyclic potentiodynamic polarization and electrochemical impedance spectroscopy measurements were performed, and an equivalent circuit was also proposed to simulate the electrochemical corrosion behavior. All the used techniques indicated a tendency of better corrosion resistance associated with the sample having coarser microstructure and less Ag content.
Microstructure growth morphologies, macrosegregation, and microhardness in Bi–Sb thermal interface alloys.
(2020) Lima, Thiago Soares; Cruz, Clarissa Barros da; Barros, André dos Santos; Garcia, Amauri; Cheung, Noé
Due to the rising demand for thermal management technologies within the electronics industry, there has been an increased emphasis on developing new thermal interface materials (TIMs) with enhanced performance. Despite Bi-based alloys having exhibited promising potential as TIMs in microelectronics cooling applications, understanding the microstructure evolution of these alloys and the consequent effects on the resulting properties still remains an essential task to be accomplished. Herein, a directional solidification technique is used to investigate microstructural features and Vickers microhardness of Bi(5–20) wt% Sb alloys with a focus on the roles of alloy composition, solidification thermal parameters, and macrosegregation. The results show the formation of aligned Bi-rich den-drites in a broad range of cooling rates from about 0.2 to 25 C s1. In contrast, as the alloy Sb content increases, two morphological transitions in the Bi-rich matrix are shown to occur as follows: trigonal pattern ! irregular shape ! trigonal pattern. Then, primary and secondary dendritic arm spacings are related to growth and cooling rates through experimental equations. Finally, the occurrence of macrosegregation along the length of the Bi–20 wt% Sb alloy casting is shown to be a key factor associated with the variation of microhardness.
Plate-like growth in a eutectic Bi–Ni alloy : effects of morphological microstructure evolution and Bi3Ni intermetallic phase on tensile properties.
(2020) Cruz, Clarissa Barros da; Lima, Thiago Soares; Kakitani, Rafael; Barros, André dos Santos; Garcia, Amauri; Cheung, Noé
The development of efficient thermal interface materials (TIMs) has become an emerging demand mainly driven by the continual rise in power dissipation of high-performance microprocessors. In this context, Bi-based alloys are among the promising types of TIMs for electronic packaging applications. However, the influence of the microstructural arrangement on mechanical strength of Bi–Ni alloys remains barely understood. To overcome this issue, this study aims to develop quantitative microstructure features-tensile properties correlations for a Bi–0.28 wt.%Ni alloy solidified in a wide range of cooling rates (T). ̇ In addition to the phase diagram calculated by the Thermo-Calc software (SSOL6 database) and differential scanning calorimetry analysis, the characterization of the Bi3Ni intermetallic compound is carried out using X-ray diffraction and SEM microscopy with energy disper- sive X-ray spectroscopy. Wavy instabilities in the plate-like morphology of the Bi matrix are shown to occur for T ̇ ≤ 0.13 ◦C/s. Besides that, more significant variations in yield and ultimate tensile strengths, y and u, respectively, are associated with a certain range of microstructural spacings between Bi plates () from 47.6 to 135.2m. Hence, Hall–Petch type relations are proposed to describe the variation of both y and u as a function of .
Solidification microstructure-dependent hydrogen generation behavior of AleSn and AleFe alloys in alkaline medium.
(2021) Konno, Camila Yuri Negrão; Cruz, Clarissa Barros da; Costa, Thiago Antônio; Barros, André dos Santos; Goulart, Pedro Roberto; Garcia, Amauri; Cheung, Noé
This work deals with the development of quantitative correlations of hydrogen evolution performance with solidification microstructural and thermal parameters in Ale1Sn, Al e2Sn, Ale1Fe, and Al-1.5Fe [wt.%] alloys. The cellular growth as a function of growth and cooling rates is evaluated using power type experimental laws, which allow determining representative intervals of microstructure length scale for comparison purposes with the results of immersion tests in 5 wt%NaOH solution. For both Al alloys systems, hydrogen evolution becomes slower as the alloy solute content increased. However, for a given alloy composition, whereas a more homogeneous distribution of Sn-rich particles promotes faster hydrogen generation using AleSn alloys, coarsening of Al6Fe IMCs (intermetallic compounds) fibers favors hydrogen production using AleFe alloys. When solidification conditions that result in a range of cellular spacings within 16 and 19 mm are considered, the specific hydrogen production of the Al-1wt.%Fe alloy is higher than that of the other studied alloys.
Thermal conductance at Sn‐0.5mass%Al solder alloy/substrate interface as a factor for tailoring cellular/dendritic growth.
(2022) Oliveira Junior, Ricardo; Cruz, Clarissa Barros da; Barros, André dos Santos; Bertelli, Felipe; Spinelli, José Eduardo; Garcia, Amauri; Cheung, Noé
The use of Al for replacing high-cost alloying metals, like Ag, Bi, and Cu, as the second major element in Sn-based alloys, arises as a promising alternative for the development of low-cost Pb-free solder alloys. To date, however, the interfacial characteristics of Sn–Al solder joints in electronic substrates remain barely explored. Thus, the present study focuses on an understanding of the mechanisms afecting the heat transfer efciency between a Sn–Al eutectic alloy and two types of substrates, establishing correlations with the microstructure evolution. Results of solidifcation experiments coupled with mathematical modeling demonstrate an interfacial thermal conductance between the Ni substrate and the Sn-0.5mass%Al alloy higher than that observed for the Sn–Al/Cu couple. Furthermore, Al-rich intermetallics are shown to occur at the interfacial reaction layers for both tested conditions. While dendritic and dendritic/cellular morphologies predominate in the solidifcation of the Sn–Al eutectic alloy in a Cu substrate, the better heat extraction through the Ni substrate induces the growth of refned high-cooling rate cells. Then, growth laws relating the length scale of the Sn-matrix, represented by cellular or primary dendritic spacings, to solidifcation thermal parameters such as cooling rate and growth rate are proposed.