Effect of Cu on Nanoscale Precipitation Evolution and Mechanical Properties of a Fe-NiAl Alloy.
The nucleation (to a limited extent), growth and coarsening behavior of Cu-rich precipitates in a concentrated multicomponent Fe– Cu-based steel aged at 500 C from 0.25 to 1024 h is investigated. The temporal evolution of the precipitates, heterophase interfaces, matrix compositions and precipitate morphologies are presented. With increasing time, Cu partitions to the precipitates, Ni, Al and Mn partition to the interfacial region, whereas Fe and Si partition to the matrix. Coarsening time exponents are determined for the mean radius, hR(t)i, number density, NV(t), and supersaturations, which are compared to the Lifshitz–Slyzov–Wagner (LSW) model for coarsening, modified for concentrated multicomponent alloys by Umantsev and Olson (UO). The experimental results indicate that the alloy does not strictly follow UO model behavior. Additionally, we delineate the formation of a Ni–Al–Mn shell with a stoichiometric ratio of 0.51:0.41:0.08 at 1024 h, which reduces the interfacial free energy between the precipitates and the matrix. 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.