DEENP - Departamento de Engenharia de Produção
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/556
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6 resultados
Resultados da Pesquisa
Item 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, NoéAl-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.Item 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, NoéThe 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.Item 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, NoéBi-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.Item 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, NoéIn 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.Item Corrosion behavior of an AleSneZn alloy : effects of solidification microstructure characteristics.(2021) Barros, André dos Santos; Cruz, Clarissa Barros da; Garcia, Amauri; Cheung, NoéDue 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.Item 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, NoéThe 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 .