DEENP - Artigos publicados em periódicos

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Browsing DEENP - Artigos publicados em periódicos by Author "Barros, André dos Santos"

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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.
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    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.
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    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.
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    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 .
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    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.
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    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.