Characterization of a marginal glass former alloy solidified in gas atomized powders

Al90Sm10, a marginal glass former, was rapidly solidified using high pressure gas atomization (HPGA). Rapid solidification is a non-equilibrium process, with different degrees of departure from full equilibrium constituting a microstructural hierarchy that correlates with increasing solidification rate. In accordance with this the resultant HPGA powders show a variety of microstructures according to their particle diameters, corresponding to degree of undercooling, with an amorphous structure appearing at high cooling rates. Five distinct phases and microstructures have been identified at different undercoolings; Al solid solution, tetragonal Al11Sm3, two different orthorhombic phases, and an amorphous phase which exists in company with a high number density of Al nanocrystals. The product phases of the rapid solidification were identified and analyzed using high energy transmission X-ray diffraction (HEXRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and thermal analysis (DSC). The results of the study will be helpful in identifying metastable phase hierarchy and glass formation during vitrification of marginal glass formers.