On the Effect of Environmental Exposure on Dwell Fatigue Performance of a Fine-Grained Nickel-Based Superalloy

Abstract

The influence of sulfur contamination on the corrosion-fatigue behavior of a polycrystalline superalloy used in aero-engines is considered. Samples tested under a variety of environmental conditions (including exposures to air, SO x gas, and salt) are characterized through a suite of high-resolution characterization methods, including transmission electron microscopy (TEM), secondary ion mass spectroscopy (nanoSIMS), and atom probe tomography (APT). The primary effect of sulfur contamination is to accelerate the crack growth rate by altering the failure mechanism. The SIMS and TEM analyses indicate Cr-Ti sulfide particle formation at grain boundaries ahead of and around oxidized cracks. The APT analysis suggests that these particles then oxidize as the crack propagates and are enveloped in chromia. The chromia is surrounded by a continuous layer of alumina within the cracks. All of the sulfur detected was confined within the particles, with no elemental segregation found at grain boundaries.

The effect of manganese and silicon additions on the corrosion resistance of a polycrystalline nickel-based superalloy

“…Another similar experiment was performed on a Ni-Cr-Al based turbine disc alloy (RR1000) performed at 750⁰C in air +300 ppmv SO2/3 and NaCl-Na2SO4 salts (both under static furnace exposures and under dynamic fatigue testing conditions) and in the absence of Nb, Ti-rich Cr sulfides formed instead [48], [49]. It is possible that Nb suppresses the formation of Cr3S2 as well, though more studies will be required to prove this.…”

Corrosion fatigue and damage tolerance in the nickel‐based superalloy RR1000 subjected to SO2 environments

“…A previous study employed advanced atom probe characterization techniques to identify sulphide reactions at subsidiary crack tips in specimens sourced from this same research project. 27 Notably, those samples related to identical corner cracks growing in a salt and SO 2 environment were characterized on a nearsurface plane. Irrespective of the precise crack tip damage mechanism, no significant effect on the rate of crack growth was reported because of the complex sulphidation reactions, and those findings are replicated by the current data.…”

“…It is impossible to conclude whether these sulphides formed concurrent with the crack advancing or developed behind the crack tip in the wake of cracking. A previous study employed advanced atom probe characterization techniques to identify sulphide reactions at subsidiary crack tips in specimens sourced from this same research project 27 . Notably, those samples related to identical corner cracks growing in a salt and SO 2 environment were characterized on a near‐surface plane.…”

A review on atom probe and correlative microscopy studies of corrosion in nickel-based superalloys

“…73 Correlative SEM, controlled electron channeling contrast imaging (cECCI), and APT (Figure 5) has revealed a high density of Cr, Co decorated dislocations, enabling rapid Cr, Co transport through pipe diffusion, and γ′ precipitate dissolution due to local chemical inhomogeneities. The investigation of crack tips using correlative microscopy with APT enabled the identification of alumina and chromia oxide intrusions ahead of crack tips 74 as well as the identification of layered oxide scales within the cracks, 12,75 offering new insights into the failure mechanisms. Using SEM and NanoSIMS (Figure 6a-b), Viskari et al 75 found that oxygen enters intergranular cracks without penetrating into the GB ahead of the crack tip, nor into the adjacent grains, as was verified by APT.…”

“…Through combination of APT with other investigation tools, a broad range of material properties can be characterized at varying length scales and with complementary precision, enabling further understanding of the mechanisms underpinning corrosion and stress-corrosion cracking. [11][12][13] This article discusses current scientific knowledge of nickelsuperalloys and the role of alloying additions on phase stability and corrosion resistance, with a particular emphasis on additions of W and Moknown for improving creep resistance. The use of correlative microscopy with atom probe tomography (APT) to understand key oxidation and corrosion mechanisms, including crack investigation is reviewed.…”