Optimization of the magnetic properties of FePd alloys by severe plastic deformation

TL;DR

This study investigates how severe plastic deformation via high pressure torsion affects the nanostructure and magnetic properties of FePd alloys, demonstrating that controlled annealing enhances coercivity.

Contribution

It introduces a method to optimize FePd alloy magnetic properties by combining severe plastic deformation with specific annealing protocols.

Findings

Severe plastic deformation reduces grain size to 50-150 nm.

Low-temperature annealing after deformation maximizes coercivity.

Disordering during deformation is partially reversible through annealing.

Abstract

A FePd alloy was nanostructured by severe plastic deformation following two different routes: ordered and disordered states were processed by high pressure torsion (HPT). A grain size in a range of 50 to 150 nm is obtained in both cases. Severe plastic deformation induces some significant 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 materials were annealed to achieve nanostructured long range ordered alloys. The transformation proceeds via a first order transition characterized by the nucleation of numerous ordered domains along grain boundaries. The influence of the annealing conditions (temperature and time) on the coercivity was studied for both routes. It is demonstrated that starting with the disorder state prior to HPT and annealing at low temperature (400\degree C) leads to the highest coercivity (about 1.8 kOe).