Thermal Conductivities of Fe-Ni Melts Measured by Non-contact Laser Modulation Calorimetry
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NTRODUCTION
NUMERICAL simulations have been developed to improve casting, welding, and three-dimensional printing processes of Fe-Ni based alloys, such as stainless steels, Hastelloy, Inconel, permalloy, and Invar alloys.[1–4] These alloys are widely used in automobiles, electrical power plants, and the aerospace industry, owing to their superior properties such as high corrosion resistance, high heat resistance, and low thermal expansion coefficient. To perform precise numerical simulations, accurate thermophysical properties of Fe-Ni melts should be established as input parameters. However, it is difficult to measure the thermophysical properties of high-temperature Fe-Ni melts because of their high chemical reactivity with container materials. To solve this problem, our group has developed an experimental apparatus called PROSPECT, which consists of electromagnetic levitation (EML) within a static magnetic field and enables non-contact, containerless measurements.[5–10] A static magnetic field is applied to suppress convection, surface oscillation, and translational motion of the droplet. This approach enables highly accurate
MANABU WATANABE, MASAYOSHI ADACHI, MASAHITO UCHIKOSHI, and HIROYUKI FUKUYAMA are with the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, 980-8577, Japan. Contact e-mails: w-manabu@mail. tagen.tohoku.ac.jp, [email protected] Manuscript submitted November 15, 2018. Article published online April 30, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
measurements of density, emissivity, heat capacity, and thermal conductivity of metallic melts. In particular, suppression of convection in the liquid sample is important for measuring thermal conductivity with high accuracy. The density, normal spectral emissivity at 807 nm and heat capacity of Fe-Ni melts have previously been successfully measured using PROSPECT from 1488 K to 1937 K, from 1484 K to 1959 K, and from 1503 K to 1996 K, respectively.[9,10] In this study, we measured the thermal conductivity of the Fe-Ni melts using PROSPECT. Thermal conductivity data measured in this study are compared with evaluated values from Wiedemann–Franz law.
II.
PRINCIPLE OF LASER MODULATION CALORIMETRY
Details of the principle of laser modulation calorimetry for EML have been previously presented,[5,7] therefore, a brief explanation is given here. The top of the levitated sample was heated by a modulated laser at a power of P0(1 + cos xt) with angular frequency (x). The temperature response was measured at the bottom of the sample by a pyrometer. The unsteady-state heat conduction equation for the levitated sample in a spherical coordinate system is expressed as: @T 1 @ 1 @ @T 2 @T ¼j 2 r sin h þ 2 qCP @t r @r @r r sin h @h @h þ Qðr; hÞ: ½1 VOLUME 50A, JULY 2019—3295
Here, q is density, CP is mass heat capacity at constant pressure, j is thermal conductivity, Q(r, h) is heat generated by induction current, and r and h denote the radial distance and polar angle, respectively. The values of
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