Navegando por Palavras-chave "Solidification"

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    Directionally solidified dilute Zn-Mg alloys: Correlation between microstructure and corrosion properties
    (Elsevier Science Sa, 2017) Vida, Talita Almeida; Conde, Ana; Freitas, Emmanuelle Sá; Arenas, Maria Angeles; Cheung, Noe; Brito, Crystopher Cardoso de [UNIFESP]; Damborenea, Juan José de; Garcia, Amauri; Universidade Federal de São Paulo (UNIFESP)
    ZinceMagnesium (Zn-Mg) alloys have been addressed as potential biodegradable biomaterials. These alloys enable to overcome the main drawbacks of Mg, its high corrosion rate and hydrogen evolution. Moreover, homogeneous corrosion degradation is also an interesting issue to ensure the success of load-bearing biodegradable implants. In this work, two directionally solidified dilute alloys, Zn-0.3wt-% Mg and Zn-0.5wt-%Mg were studied. Both alloys having different microstructural morphologies (cellular and dendritic arrays) depending of the distance to the cooling bottom were evaluated to correlate their microstructural features with corrosion properties. Kinetics and corrosion mechanism have been evaluated by means of DC and AC electrochemical techniques in low chloride containing solution, 0.06 M NaCl. Coarser microstructures are shown to promote higher corrosion rate. Like Zn the corrosion mechanism occurs throughout a multistep dissolution process involving the formation of intermediate monovalent Zn-I, and soluble zinc hydroxychloride compounds resulting of the reaction of zincate ions with chloride ions. (C) 2017 Elsevier B.V. All rights reserved.
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    Microstructure characterization of a directionally solidified Mg-12wt.%Zn alloy: Equiaxed dendrites, eutectic mixture and type/morphology of intermetallics
    (Elsevier Science Sa, 2018) Verissimo, Nathalia Carolina; Brito, Crystopher Cardoso de [UNIFESP]; Afonso, Conrado Ramos Moreira; Spinelli, José Eduardo; Cheung, Noe; Garcia, Amauri; Universidade Federal de São Paulo (UNIFESP)
    Over the last years, magnesium and its alloys have deserved special attention due to their good mechanical properties and promising biomedical applications. In the present investigation the Mg-12 wt.% Zn alloy has been directionally solidified (DS) under an extensive range of cooling rates. Based on the scarceness of characterization works related to both the morphology of the eutectic mixture and the development of equilibrium and non-equilibrium intermetallic particles (IMCs) in Mg-Zn alloys, a number of analyses are performed emphasizing and discussing such aspects. Rod and lamellar eutectic spacings are experimentally correlated with the growth rate and the cooling rate. The volume fraction of rod-like eutectic is shown to increase with the decrease in cooling rate during solidification. The characterization on the DS Mg-12 wt.%Zn samples is carried out using X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopies, which allowed the identification of two different non equilibrium IMCs, MgZn2 and Mg4Zn7, which are distributed as nanoparticles throughout the alpha-Mg matrix. The Mg-Zn eutectic morphologies (lamellar and rod-like) are found to be constituted by alpha-Mg/Mg21Zn25 phases, the latter being formed by the decomposition of the eutectic IMC Mg51Zn20 through a eutectoid reaction. (C) 2017 Elsevier B.V. All rights reserved.