Comparative Study of Nickel-Based Super-Alloy Powders Atomized by Argon and Nitrogen

Abstract

This work allowed the study and comparison of the cooling rate, surface morphology, and microstructure of nickel-based super-alloy powders produced by the atomization of argon and nitrogen. The results show that the principal phase in argon and nitrogen atomized powders has an FCC structured γ-phase with γ′-strengthening phase. X-ray diffraction detected no apparent nitride or oxide on the powder surface. The interplanar spacing and lattice constant of γ-phase increase as the powder size decreases. Nitrogen- and argon-atomized powders are spherical, but argon- atomized powders have higher sphericity and smoother surfaces. Atomization by argon has produced a small number of satellite particles, whereas atomized nitrogen powders have more split particles. The proportion of special-shaped powder decreases with the decreasing powder particle size. The super-alloy powder with high sphericity can be effectively obtained by controlling the particle size. Because of the higher coefficient of thermal expansion, the trough of argon-atomized powders is higher than that of nitrogen-atomized powders with the same particle size. As the powder particle size decreases, the hollowness of the powders declines for both powders, with the argon- atomized powder falling more quickly. The cooling rate of melted alloy droplets has an essential effect on the surface characteristics of the powder. The dendrite morphology of argon-atomized powders is more evident than that of nitrogen-atomized powders. As the powder particle size decreases, the radial dendrites gradually disappear, with dendrites and cellular crystals dominating the powder surface. The cooling rate of the powder is calculated based on the surface secondary dendrite arm spacing. It is found that argon-atomized powders exhibit cooling rates from 2.09 × 10⁴ K ? s^–1 to 1.26 ? 10⁵ K ? s^–1, while nitrogen-atomized powders show higher cooling rates in the range between 2.71 ? 10⁴ K ? s^–1 and 1.86 ? 10⁵ K · s^–1. Because of the higher cooling rate, nitrogen- atomized powders have a lower secondary dendrite arm spacing than argon-atomized powders with similar particle sizes.