Phase Evolution and Thermal Stability of Low-Density MgAlSiCrFe High-Entropy Alloy Processed Through Mechanical Alloying

An equiatomic MgAlSiCrFe high-entropy alloy was synthesized by mechanical alloying. The alloying behavior, phase evolution, phase composition and thermal stability of as-milled nanostructured powders of HEA were ascertained through X-ray diffraction and transmission electron microscopy, scanning electron microscopy and differential scanning calorimetry (DSC), respectively. The milling of elemental powders for 60 h led to the formation of HEA with a major BCC phase having lattice parameter of 0.2887 +/- 0.005 nm very close to that of the alpha-Fe and a minor fraction of undissolved Si. The nanocrystalline HEA powder formed during milling has crystallite size of 19 +/- 0.8 nm. The STEM-EDS mapping of these milled powders confirms the homogenous elemental distribution after 60 h of mechanical alloying. The DSC thermogram of 60 h milled HEA powder shows the thermal stability of milled powder up to similar to 400 degrees C. The exothermic heating events observed in the DSC thermogram correspond to phase transformation of MgAlSiCrFe HEA powder, and it may be correlated with the phases observed through the ex situ XRD of HEA powders annealed at different temperatures up to 700 degrees C. After annealing the 60 h milled powder, various phases along with parent BCC phase have evolved, i.e., B2 type Al-Fe phase, FCC phases (Al-Mg solid solution), Cr5Si3, Mg2Si, Al13Fe4. Further, the experimental findings were correlated with various thermodynamic parameters for understanding the phase evolution and stability.