Oxide Scale Formation in Novel γ‐γ′ Cobalt‐Based Alloys

Stewart, Colin A.; Rhein, Robert K.; Suzuki, Akihito; Pollock, Tresa M.; Levi, Carlos G.

doi:10.1002/9781119075646.ch105

Cited by 17 publications

(8 citation statements)

References 24 publications

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“…Ion plasma deposition (IPD) using five cathodes of different alloy compositions was used to create three libraries covering a spectrum of Co-Ni-Al-W-Cr-Ta alloy compositions with 234 samples. The combinatorial approach 51,52 was coupled with rapid oxide screening based on photo-stimulated luminescence spectroscopy (PSLS) 53 and the Calphad database 48 to outline regions of composition space giving rise to α-Al 2 O 3 scales and two-phase γ À γ 0 microstructures.…”

Section: Resultsmentioning

confidence: 99%

“…By utilizing a suite of modern research tools, including firstprinciples calculations 35,36,43,44,51 , high-throughput thermodynamic database calculations 40,48 , combinatorial alloy synthesis 51,52 and non-destructive characterization techniques 53 , we have rapidly explored a complex multicomponent space for Co-Ni alloy compositions that are favorable for AM and also possess favorable mechanical and environmental properties. A particular challenge for alloy design in the additive domain is the need to fabricate expensive powders in significant quantities (typically >100 kg); thus the computational suite of design tools was essential for efficient exploration and selection of a composition likely to be favorable for AM.…”

Section: Discussionmentioning

confidence: 99%

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A defect-resistant Co–Ni superalloy for 3D printing

et al. 2020

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Additive manufacturing promises a major transformation of the production of high economic value metallic materials, enabling innovative, geometrically complex designs with minimal material waste. The overarching challenge is to design alloys that are compatible with the unique additive processing conditions while maintaining material properties sufficient for the challenging environments encountered in energy, space, and nuclear applications. Here we describe a class of high strength, defect-resistant 3D printable superalloys containing approximately equal parts of Co and Ni along with Al, Cr, Ta and W that possess strengths in excess of 1.1 GPa in as-printed and post-processed forms and tensile ductilities of greater than 13% at room temperature. These alloys are amenable to crack-free 3D printing via electron beam melting (EBM) with preheat as well as selective laser melting (SLM) with limited preheat. Alloy design principles are described along with the structure and properties of EBM and SLM CoNi-base materials.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

A defect-resistant Co–Ni superalloy for 3D printing

et al. 2020

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“…[1][2][3] Thus, they are regarded as potential structural materials for future turbine engine applications. [4][5][6] Although this new alloy system was rediscovered just over 1 decade ago, [4] the knowledge regarding the effect of alloying elements, [7][8][9][10][11] oxidation, [12][13][14] and thermodynamic, [15][16][17][18] microstructural, [3,19,20] and mechanical properties [2,[21][22][23] has significantly increased since then. Despite the growing understanding, there are still open questions regarding this new class of alloys.…”

Section: Introductionmentioning

confidence: 99%

Design of a Co–Al–W–Ta Alloy Series with Varying γ′ Volume Fraction and Their Thermophysical Properties

Volz

Xue

Bezold

et al. 2021

Metall Mater Trans A

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The γ′ volume fraction is a key parameter in precipitation-strengthened Co- and Ni-base superalloys and mainly determines the alloys’ properties. However, systematic studies with varying γ′ volume fractions are rare and the influence on thermal expansion has not been studied in detail. Therefore, a series of six Ta-containing Co-based alloys was designed with compositions on a γ–γ′ tie-line, where the γ′ volume fraction changes systematically. During solidification, Laves (C14-type) and µ (D85-type) phases formed in alloys with high levels of W and Ta. Single-phase γ or two-phase γ/γ′ microstructures were obtained in four experimental alloys after heat treatment as designed, whereas secondary precipitates, such as χ (D019-type), Laves, and μ, existed in alloys containing high levels of γ′-forming elements. However, long-term heat treatments for 1000 hours revealed the formation of the χ phase also in the former χ-free alloys. The investigation of the thermal expansion behavior revealed a significant anomaly related to the dissolution of γ′, which can be used to determine the γ′ solvus temperature with high accuracy. Compared to thermodynamic calculations, differential scanning calorimetry (DSC) and thermal expansion analysis revealed a larger increase of the γ′ solvus temperatures and a lesser decline of the solidus temperatures when the alloy composition approached the composition of the pure γ′ phase.

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“…Initially, Co-base superalloys have been seen as highly promising alternatives, as pure Co outmatches the melting point of pure Ni by 40 °C [6][7][8]11]. Even though quite remarkable mechanical properties could be achieved since 2006, the oxidation resistance of Co-base superalloys at temperatures exceeding 800 °C still undoubtedly ranks behind their Ni-base counterparts and needs to be increased for serious competitiveness [5,[12][13][14][15][16]. Therefore, strategies to enable the growth of protective and sustainable oxide scales, e.g.…”

Section: Introductionmentioning

confidence: 99%

Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

et al. 2021

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The oxidation resistance of novel γ/γ’-strengthened Co-base superalloys is clearly outmatched by their Ni-base counterparts within the high-temperature regime. Therefore, surface modification strategies to foster protective alumina growth seem auspicious. This study elucidates the impact of fluorination and shot-peening on protective alumina formation at 900 °C for a quaternary Co-base model alloy (Co-Al-W-Ta system) which is well known for an exceptionally low inherent oxidation resistance. Time-resolved isothermal gravimetric analysis (TGA) in synthetic air, detailed electron microscopic analysis, and X-ray diffraction (XRD) were used. For polished samples, no pronounced enhancement of oxidation resistance could be obtained by halogenation. However, in case of shot-peened samples (halogen-free), an increased tendency for alumina formation is found compared to polished surfaces. The very early stages of oxidation were identified to be especially crucial with respect to sustainable protective scale growth. Most noteworthy is the observation of a strong synergistic effect derived by a combination of halogenation and shot-peening, leading to significantly increased oxidation resistance.

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Oxide Scale Formation in Novel γ‐γ′ Cobalt‐Based Alloys

Cited by 17 publications

References 24 publications

A defect-resistant Co–Ni superalloy for 3D printing

A defect-resistant Co–Ni superalloy for 3D printing

Design of a Co–Al–W–Ta Alloy Series with Varying γ′ Volume Fraction and Their Thermophysical Properties

Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

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