Effects of solute concentrations on kinetic pathways in Ni-Al-Cr alloys

TL;DR

This study investigates how solute concentrations influence the formation and evolution of y'-precipitates in Ni-Al-Cr alloys using atom-probe tomography, classical nucleation theory, and computational models.

Contribution

It provides detailed insights into the kinetic pathways and nucleation behavior of y'-precipitates influenced by solute concentrations in Ni-Al-Cr alloys.

Findings

Supersaturation drives nucleation behavior.

Precipitate radii follow classical coarsening predictions.

Precipitate number densities deviate from models.

Abstract

The kinetic pathways resulting from the formation of coherent L12-ordered y'-precipitates in the g-matrix (f.c.c.) of Ni-7.5 Al-8.5 Cr at.% and Ni-5.2 Al-14.2 Cr at.% alloys, aged at 873 K, are investigated by atom-probe tomography (APT) over a range of aging times from 1/6 to 1024 hours; these alloys have approximately the same volume fraction of the y'-precipitate phase. Quantification of the phase decomposition within the framework of classical nucleation theory reveals that the y-matrix solid-solution solute supersaturations of both alloys provide the chemical driving force, which acts as the primary determinant of the nucleation behavior. In the coarsening regime, the temporal evolution of the y'-precipitate average radii and the y-matrix supersaturations follow the predictions of classical coarsening models, while the temporal evolution of the y'-precipitate number densities of both alloys do not. APT results are compared to equilibrium calculations of the pertinent solvus lines determined by employing both Thermo-Calc and Grand-Canonical Monte Carlo simulation.