Microstructural evolution and mechanical properties of ternary Al–Fe–Nb alloy under free fall condition

Abstract

Ternary Al55Fe40Nb5 alloy was rapidly solidified in 3 m drop tube to investigate its solidification evolution and mechanical properties at high cooling rates and undercoolings. The microstructure of this alloy was composed of the primary FeAl dendrite, the (FeAl + Nb(Fe, Al)2) eutectic and the composite of FeAl, FeAl2 and Nb(Fe, Al)2 phases. As the alloy droplet diameter varied from 1200 to 80 μm, the growth morphology of primary FeAl phase evolved from coarse dendrite to refined dendrite, and finally into equiaxed grain. Meanwhile, the eutectic and the composite exhibited a regular to anomalous microstructure transition, and the Nb(Fe, Al)2 phase changed from aggregation growth to uniform distribution. Consequently, the homogenous reticulate-shaped particulate structure formed. The microscopic structures of the three intermetallic compound phases were explored by HRTEM technique. Under the influences of large undercooling and cooling rate, the grain refinement of primary phase and the homogenous distribution of three phases led to the increase of Vickers microhardness for this rapidly solidified alloy.