Characterization of rapidly solidified Nd-Al and Nd-Ag eutectic alloys in drop tube

Abstract

Nd-14.2 at%Al and Nd-20.0 at%Ag eutectic alloys were containerlessly solidified in an 8 m drop tube. The droplets were undercooled during the free fall in about 1 s under reduced gravity condition in He atmosphere. The cooling rates at the solidification temperature were computed as a function of droplet size by making use of heat balance calculations. They were ranging between 40 × 103 and 0.8 × 103 K s-1 for droplets in size range of 100-900 μm diameters. Nusselt, Reynolds, and Prandtl numbers of the droplets were calculated. Microstructures of the alloys were analyzed and eutectic spacings were determined. Microhardnesses of the droplets with different sizes were measured to reveal a dependence on the cooling rates with which the droplets are solidified. Nd-14.2 at%Al and Nd-20.0 at%Ag eutectic alloys are solidified in an 8 m drop tube and droplets in diameter of 100-900 μm are produced. The cooling rates, Nusselt, Reynolds, and Prandtl numbers are determined by heat balance calculations. Microstructures are analyzed, shown in the figure and eutectic spacings are determined. Microhardness is measured to reveal the cooling rate dependence of the droplets.