Effects of ruthenium on phase separation in a model Ni–Al–Cr–Ru superalloy

Abstract

The temporal evolution of a Ni–10.0Al–8.5Cr–2.0Ru (at.%) alloy aged at 1073 K was investigated using transmission electron microscopy (TEM) and atom-probe tomography. The γ′(L1₂)-precipitate morphology is spheroidal through 256 h of ageing as a result of adding Ru, which decreases the lattice parameter misfit between the γ′(L1₂)- and γ(f.c.c.)-phases. The addition of Ru accelerates the compositional evolution of the γ′(L1₂)- and γ(f.c.c.)-phases, which achieve their equilibrium compositions after 0.25 h. Initially, Ru accelerates the partitioning of Ni and Cr to the γ(f.c.c.)-phase, and the partitioning of Al to the γ′(L1₂)-phase, but after 0.25 h, Ru, which partitions to the γ(f.c.c.)-phase, decreases the partitioning of Ni and increases the partitioning of Al and Cr. The temporal evolution of the average radius, ⟨R(t)⟩, number density, volume fraction of the γ′(L1₂)-precipitates, and the supersaturations of Ni, Al, Cr, and Ru in the γ(f.c.c.)- and γ′(L1₂)-phases are compared in detail with predictions of coarsening models and PrecipiCalc simulations. Based on a spline function fitting procedure of the concentration profiles between the γ′(L1₂)- and γ(f.c.c.)-phases, it is demonstrated that the temporal evolution of the normalized interfacial width, δ/⟨R(t)⟩ vs. ⟨R(t)⟩, of each element, decreases with increasing ageing time: δ is the interfacial width.

Keywords:

• Ni–Al–Cr–Ru alloy
• effects of Ru
• coarseniing kinetics
• atom-probe tomography
• transmission electron microscopy

Acknowledgements

This research was sponsored by the National Science Foundation (NSF) under grant DMR-0804610. The TEM studies were performed in the EPIC facility of the NUANCE Center at Northwestern University. The NUANCE Center is supported by NSF-NSEC, NSF-MRSEC, the Keck Foundation, the State of Illinois and Northwestern University. Atom-probe tomographic measurements were performed in the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph was purchased and upgraded with funding from NSF-MRI (DMR-0420,532) and ONR-DURIP (N00014-0400,798, N00014-0610539, NOOO14-0910,781) grants. Ms. Gillian Hsieh’s contributions to this article constitute portions of her senior thesis in the Department of Material Science and Engineering: she was also supported by a NSF REU during one summer. Dr Jou at Questek Inovations LLC is kindly thanked for help with PrecipiCalc simulations, Dr Chantal K. Sudbrack is thanked for performing the JMat Pro calculations and reading the manuscript, Drs Christopher Booth–Morrison and Yaron Amouyal are thanked for helpful discussions and Dr Carelyn Campbell (NIST) for diffusivity databases.