Ni-Al alloys are good candidate materials for the turbine blades of high-efficiency gas turbines. The thermophysical properties of the liquid alloy are required for accurate modeling of the casting process. In this study, the densities of liquid Ni-Al alloys were measured over the entire composition range using the electromagnetic levitation technique under a static magnetic field. Surface oscillation and translational motion of the electromagnetically levitated droplet are suppressed by the static magnetic field, so an accuracy density can be obtained using the technique under a static magnetic field. Before the measurements, the liquidus temperatures of Ni-rich alloys were determined by differential scanning calorimetry. The liquidus temperatures were used as temperature calibration for the density measurements. For all of the compositions, the densities were measured with an experimental uncertainty of less than 1.9%, and they are a linear function of the temperature. The excess volume of the liquid alloys has a minimum value at 50 mol% Ni. The results are discussed from the viewpoint of the thermodynamics. The Ni-Al system shows a large negative excess volume with large negative enthalpy of mixing and excess Gibbs energy.

Aluminum nitride is a promising substrate material for AlGaN-based UV-LED. In order to develop a robust growth processing route for AlN single crystals, fundamental studies of solution growth experiments using Ni-Al alloy melts as a new solution system were performed. Al can be stably kept in solution the Ni-Al liquid even at high temperature; in addition, the driving force of the AlN formation reaction from solution can be controlled by solution composition and temperature. To investigate AlN crystal growth behavior we developed an in situ observation system using an electromagnetic levitation technique. AlN formation behavior, including nucleation and growth, was quantitatively analyzed by an image processing pipeline. The nucleation rate of AlN decreased with increasing growth temperature and decreasing aluminum composition. In addition, hexagonal c-axis oriented AlN crystal successfully grew on the levitated Ni-40 mol%Al droplet reacted at low driving force (1960 K), on the other hand, AlN crystal with dendritic morphology appeared on the sample with higher driving force (Ni-50 mol%Al, 1960 K). Thus, the nucleation rate and crystal morphology were dominated by the driving force of the AlN formation reaction. K E Y W O R D S aluminum nitride, crystal growth, nucleation, thermodynamicsThis is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. How to cite this article: Adachi M, Hamaya S, Yamagata Y, et al. In-situ observation of AlN formation from Ni-Al solution using an electromagnetic levitation technique. J Am Ceram Soc.

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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