Composition Dependence of Normal Spectral Emissivity of Liquid Ni–Al Alloys

Abstract

Ni-Al alloys are good candidates for the fabrication high-efficiency gas turbine blades. The Ni-Al system is also important as a solution for AlN crystal growth. To accurately model the casting process for turbine blade fabrication and design solution growth techniques for AlN, the thermophysical properties of the liquid alloy are required. In this study, the normal spectral emissivity of Ni-Al liquid alloys was measured using the electromagnetic levitation technique under a static magnetic field. Both the melting temperature of Cu and the eutectic temperature of the Ni-C system were used as fixed temperature points for spectrometer calibration to obtain the radiance of liquid Ni-Al alloys. The composition dependence of the normal spectral emissivity of liquid Ni-Al alloys had a maximum at ~40-50 mol%Al-Ni. The Ni-Al binary system had a stable intermetallic compound of NiAl with a melting temperature of 1 911 K. The short range chemical ordering could be attributed to strong bonding between Ni and Al atoms, which affected the scattering cross section of the conduction electrons even in the liquid state; hence, the normal spectral emissivity had a maximum at ~40-50 mol%Al-Ni.

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