Containerless measurements of the liquid-state density of Ni–Al alloys for use as turbine blade materials

Abstract

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.