Decomposition process in a FeAuPd alloy nanostructured by severe plastic deformation

TL;DR

This study investigates the microstructural evolution and phase decomposition in a FeAuPd alloy subjected to severe plastic deformation, revealing nanostructure stability and phase transformations that enhance alloy hardness.

Contribution

It provides new insights into the decomposition mechanisms and microstructural stability of FeAuPd alloys processed by severe plastic deformation.

Findings

Nanostructure grain size reduced to 50-100nm by high pressure torsion.

Decomposition into lamellar phases occurs during aging at 450°C.

Nanoscale grains and phase mixture significantly increase alloy hardness.

Abstract

The decomposition process mechanisms have been investigated in a Fe50Au25Pd25 (at.%) alloy processed by severe plastic deformation. Phases were characterized by X-ray diffraction and microstructures were observed using transmission electron microscopy. In the coarse grain alloy homogenized and aged at $450 ^{circ}\mathrm{C}$, the bcc \alpha-Fe and fcc AuPd phases nucleate in the fcc supersaturated solid solution and grow by a discontinuous precipitation process resulting in a typical lamellar structure. The grain size of the homogenized FeAuPd alloy was reduced in a range of 50 to 100nm by high pressure torsion. Aging at $450 ^{circ}\mathrm{C}$ this nanostructure leads to the decomposition of the solid solution into an equi-axed microstructure. The grain growth is very limited during aging and the grain size remains under 100nm. The combination of two phases with different crystallographic structures (bcc \alpha-Fe and fcc AuPd) and of the nanoscaled grain size gives rise to a significant hardening of the alloy