Processing of nanostructured bulk Fe-Cr alloys by severe plastic deformation

TL;DR

This study explores how severe plastic deformation techniques can process Fe-Cr alloys, overcoming thermodynamic limitations and producing nanocrystalline microstructures, with implications for magnetic material applications.

Contribution

It demonstrates that SPD methods, especially high-pressure torsion, can produce homogeneous nanocrystalline Fe-Cr alloys despite thermodynamic challenges.

Findings

HPT yields homogeneous nanocrystalline microstructures in AM alloys.

BM powders and powder blends show excessive hardening and phase formation.

SPD techniques can surpass equilibrium processing limits in Fe-Cr alloys.

Abstract

The processing of binary alloys consisting of ferromagnetic Fe and antiferromagnetic Cr by severe plastic deformation (SPD) with different chemical compositions has been investigated. Although the phase diagram exhibits a large gap in the thermodynamical equilibrium at lower temperatures, it is shown that techniques based on SPD help to overcome common processing limits. Different processing routes including initial ball milling (BM) and arc melting (AM) and a concatenation with annealing treatments prior to high-pressure torsion (HPT) deformation are compared in this work. Investigation of the deformed microstructures by electron microscopy and synchrotron X-ray diffraction reveal homogeneous, nanocrystalline microstructures for HPT deformed AM alloys. HPT deformation of powder blends and BM powders leads to an exorbitant increase in hardness or an unusual fast formation of a $\sigma$-phase and therefore impede successful processing.