Structural, mechanical and magnetic properties of Fe-40-at.% Al powders during mechanical alloying

Nanocrystalline Fe - 40at.% Al alloy powders were prepared by using a mechanical alloying (MA) process with a planetary high-energy ball mill. The structural and the morphological properties of the powders were investigated by means of X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. A disordered Fe(Al) solid solution with bcc crystal structure was formed after 10 h of MA. Longer MA durations introduced ordering in the alloyed powders. The final crystallite size was found to be as small as 5 nm whereas the internal strain was found to reach a final value of 2.1%. Also, the lattice parameter quickly increased to a maximum value of 0.2926 nm at 30 h of MA, and then decreased to a value of 0.2873 at 80 h of MA. SEM results showed variations in the shapes and the sizes of the particles in the powders at different stages. Furthermore, the microhardness values were found to increase gradually with increasing MA time due to work hardening, grain refinement and solid-solution formation. Magnetic properties such as the saturation magnetization (Ms) and the coercive field (Hc) were calculated from the hysteresis loops, and the results are presented as functions of the MA time.