Effects of a tungsten addition on the morphological evolution, spatial correlations, and temporal evolution of a model Ni-Al-Cr superalloy

TL;DR

This study investigates how adding tungsten to a Ni-Al-Cr superalloy influences precipitate morphology, distribution, and evolution at high temperature, revealing changes in microstructure and coarsening behavior.

Contribution

It provides new insights into the effects of tungsten addition on precipitate evolution, morphology, and kinetics in Ni-Al-Cr superalloys at elevated temperatures.

Findings

W addition increases microhardness and precipitate volume fraction.

W causes earlier spheroidal-to-cuboidal transition of precipitates.

Coarsening kinetics follow t1/3 and t-1/3 laws, but deviations suggest non-stationary states.

Abstract

The effect of adding 2 at.% W to a model Ni-Al-Cr superalloy on the morphological evolution, spatial correlations and temporal evolution of g'(L12)-precipitates at 1073 K is studied with scanning electron microscopy and atomic force microscopy. Adding W yields a larger microhardness, earlier onset of spheroidal-to-cuboidal precipitate morphological transition, larger volume fraction (from ~20 to 30%), reduction in coarsening kinetics by one third and a larger number density (Nv) of smaller mean radii (<R>) precipitates. The kinetics of <R> and interfacial area per unit volume obey t1/3 and t-1/3 relationships, respectively, which is consistent with coarsening driven by interfacial energy reduction. The Nv power law dependencies deviate, however, from model predictions indicating that a stationary-state is not achieved. Quantitative analyses with precipitate size distributions, pair correlation functions, and edge-to-edge interprecipitate distance distributions gives insight into 2D microstructural evolution, including the elastically driven transition from a uniform g'-distribution to one-dimensional <001>-strings to eventually clustered packs of g'-precipitates in the less densely packed Ni-Al-Cr alloy.