Compositional Dependence of Normal Spectral Emissivity of Molten Cu-Fe Alloy
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RODUCTION
LIQUID-PHASE separation occurs in immiscible alloys, such as Cu-Fe and Cu-Co alloys, exhibiting a metastable miscibility gap in the undercooled state. In this state, the homogeneous melt is separated into two liquid phases, i.e., Cu-rich and Fe-rich phases in the Cu-Fe system.[1–7] Solidified Cu-based binary alloys with phase separation structures have attracted growing attention because the alloys express various electric, magnetic, and mechanical characteristics depending on the structures. In addition, such a Cu-Fe alloy has been used as a model material for investigating the kinetics of liquid-phase separation similar to a Cu-Co alloy. Thermophysical properties are important to develop and optimize manufacturing processes of metals and alloys. Emissivity is especially required for analyzing the radiative heat transfer in the molten metal processing at high temperature. The normal spectral emissivity of pure Cu[8–14] and pure Fe[15–18] was measured, and the normal spectral emissivity of molten Cu-Fe alloy had been reported by Smith and Chipman[19] and Mori et al.[20] focusing on the composition dependence,
EITA SHOJI, RYUJI TAKAHASHI, SHOSEI ISOGAI, NAOTO ITO, MASAKI KUBO, and TAKAO TSUKADA are with the Department of Chemical Engineering, Tohoku University, 6-6-07, Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, 980-8579, Japan. Contact e-mail: [email protected] HIROYUKI FUKUYAMA is with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi, 980-8577, Japan. Manuscript submitted March 3, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
similar to this study. However, the composition of Fe in previous studies[20] was higher than 20 at pct, such that the emissivity of molten Cu-Fe alloy at a relatively low composition, i.e., less than 10 at pct, is unknown. The current author’s research group has developed an electromagnetic levitator (EML) superimposed with a static magnetic field (SMF) and measured the thermophysical properties, e.g., the normal spectral emissivities of molten silicon,[21] iron,[15] nickel,[15] copper,[11] and Cu-Co,[22] and the thermal conductivities of silicon,[23] Cu,[24] and Cu-Co[25] in wide ranges of temperature including the undercooled conditions. The EML allows us to avoid the chemical reactions of a molten sample with a crucible. Furthermore, the SMF can suppress translational and surface oscillations of a levitated sample, and avoid convection in the molten sample, which often become error sources in the measurement. In this study, the normal spectral emissivity of molten Cu-Fe alloy was measured using the EML with SMF, and the compositional and temperature dependences were investigated. In particular, the compositional dependence at low Fe at pct was focused because Terzieff and Gasser demonstrated that the electric resistivity of molten Cu-Fe alloy, which is closely related to the emissivity, increased markedly with the addition of a small amount of Fe, i.e., 2 or 4 at pct.[26] II.
EXPERIMENT
The Cu-Fe alloy samples were Cu
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