Abstract
Rhenium plays a critical role in single-crystal superalloys –its addition to first generation alloys improves creep life by a factor of at least two, with further benefits for fatigue performance. Its use in alloys such as PWA1484, CMSX-4 and Rene N5 is now widespread, and many in this community regard Re as the “magic dust”. In this paper, the latest thinking concerning the origins of the “rhenium-effect” is presented. We start by reviewing the hypothesis that rhenium clusters represent barriers to dislocation motion. Recent atom probe tomography experiments have shown that Re may instead form a solid solution with Ni at low concentrations ( ′ interfaces, which require non-conservative climb and thus an associated vacancy flux.
Highlights
Rhenium additions are essential for the high-temperature properties of single-crystal superalloys
After describing the beneficial effects of Random CMSX−4 γ phase (Re) additions to the high-temperature a Corresponding author: a.mottura@bham.ac.uk properties of Ni-based superalloys, we examine all the available experimental evidence and discuss its significance in conjunction to recent modelling efforts
The authors proposed the evidence collected proved the presence of Re clusters, 1–1.5 nm in size, that contained up to 90 at.% Re [4, 19], suggesting this would be expected when considering the large miscibility gap in the established Ni-Re binary phase diagram [20, 21]. It follows that these clusters would act as powerful barriers against dislocation glide when compared to distributed Re atoms in solid solution with Ni
Summary
Rhenium additions are essential for the high-temperature properties of single-crystal superalloys. Re has been so important to the industry that single-crystal superalloys are commonly grouped into generations based on their Re content: first-generation Re-free alloys gave way to secondgeneration alloys in the 1990s, containing 2–3 wt.% Re, superseded by third-generation alloys in the 2000s, containing 5–6 wt.% Re. Since the advent of third-generation alloys, engine manufacturers have opted to reduce Re content in their alloys, primarily due to cost concerns: Re is one of the most expensive transition metals. The high price means that Re alone can be, depending on the alloy, responsible for over half of the raw material cost needed to produce turbine blades. The use of Re poses a risk due to the fact that the majority of Re reserves are clustered in a limited number of countries
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