Disordering and Ordering in a Severely Deformed FePd Alloy

A Fe50Pd50 alloy was severely deformed by High Pressure Torsion (HPT). For a processing temperature ranging from 20°C to 300°C, the Severe Plastic Deformation (SPD) induces a significant grain size reduction (in a range of 50 to 150 nm) but also a strong disordering of the long range ordered L10 phase. However, Transmission Electron Microscopy (TEM) data clearly show that few ordered nanocrystals remain in the deformed state. The deformed material was annealed to achieve a nanoscaled long range ordered structure. The transformation proceeds via the nucleation and growth of ordered domains along grain boundaries. Aging at lower temperature (400°C) gives rise to a smallest domain size and thus the highest coercivity.