Agglomeration behavior of alumina inclusions and calcium aluminate inclusions on molten nickel-based superalloy surface

Understanding the interactive forces of inclusions on the surface of molten nickel-based superalloys and finding methods to disperse these inclusions help improve performance and service life. The aggregation behavior of aluminum oxide (Al₂O₃) and calcium aluminate inclusions with different sizes and spacings on the surface of molten nickel-based superalloys was observed in-situ using a high-temperature confocal laser scan microscope. The attractive force acted on Al₂O₃ inclusions with radii of 3.5–6 μm was found ranging from 6.2 × 10^–18 to 3.6 × 10^–15 N, and that of CaO·2Al₂O₃ (CA2) inclusions with radii of 3–5.5 μm ranging from 3.5 × 10^–19 to 8.3 × 10^–15 N. The capillary force acted on inclusions on the surface of nickel-based superalloy was calculated based on the Kralchevsky–Paunov model and investigated as a function of inclusion size, spacing, and composition. The calculated results were in the same trend as the experimental results. The capillary force acted on inclusions was also affected by their contact angle, the density, surface energy, and oxygen content of the molten alloy. It decreased with increasing alloy density and decreasing contact angle between inclusion with alloy. Thus, the attractive force acted on Al₂O₃ inclusions was smaller on the surface of molten nickel-based superalloy than that of molten steel. Decreasing the oxygen content in the molten nickel-based alloy could increase its surface energy, and the attractive force acted on the inclusions would decrease. When the oxygen content in the molten nickel-based alloy decreased from 0.05 to 0.0001 wt.%, the capillary force acted on the Al₂O₃ inclusions decreased from 1.7 × 10⁻¹⁸ to 3.6 × 10⁻¹⁹ N, reduced by 79% (1.4 × 10^–18 N).