Direct observations of nucleation in a nondilute multicomponent alloy

TL;DR

This study investigates the nucleation process of gamma-prime in a nondilute Ni-Al-Cr alloy using atom-probe tomography, revealing the role of short-range order and Al diffusion in phase separation.

Contribution

It provides direct atomic-scale observations of gamma-prime nucleation pathways in a multicomponent alloy, highlighting the influence of short-range order and diffusion.

Findings

Cr atoms are initially randomly distributed.

Ni3Al short-range order domains form during quenching.

Gamma-prime nucleation occurs after SRO development.

Abstract

The chemical pathways leading to gamma-prime(L1_2)-nucleation from nondilute Ni-5.2 Al-14.2 Cr at.%, gamma(f.c.c.), at 873 K are followed with radial distribution functions and isoconcentration surface analyses of direct-space atom-probe tomographic images. Although Cr atoms initially are randomly distributed, a distribution of congruent Ni3Al short-range order domains (SRO), <R> =0.6 nm, results from Al diffusion during quenching. Domain site occupancy develops as their number density increases leading to Al-rich phase separation by gamma-prime-nucleation, <R>=0.75 nm, after SRO occurs.