Influence of precipitate and grain sizes on the brittle-to-ductile transition in Fe–Al–V bcc-L21 ferritic superalloys

P.a. Ferreirós; U.A. Sterin; P.R. Alonso; A.j. Knowles; G.H. Rubiolo

doi:10.1016/j.msea.2022.144031

Influence of precipitate and grain sizes on the brittle-to-ductile transition in Fe–Al–V bcc-L2₁ ferritic superalloys

P.a. Ferreirós, U.A. Sterin, P.R. Alonso, A.j. Knowles, G.H. Rubiolo

Metallurgy and Materials

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Abstract

The limiting factors to achieving a wide application of bcc-superalloys are the high brittle-to-ductile transition temperatures (BDTT). The understanding of the mechanisms controlling the BDTT and how to optimise the microstructure in polycrystalline bcc-superalloys remains a concern today.

In the present work, the influence of grain and coherent precipitates sizes on strength and brittle-to-ductile transition temperature (BDTT) are studied in a Fe₇₈Al₁₀V₁₂ (A2+L2₁) ferritic superalloy, toward application in high-efficiency power plants. Additionally, the A2 matrix behaviour was evaluated in a derived single-phase-bcc Fe₈4Al₈V₈ alloy. Thermal ageing and coarsening treatments were applied to produce samples with different precipitate and grain sizes. Tensile tests were carried out at different temperatures and strain rates to assess the variation of the yield stress. Charpy impact tests were used to measure the BDTT in both alloys, which was substantially reduced with grain size refinement, and precipitate coarsening. It was found that the increase in cleavage stress by precipitation strengthening follows the same behaviour that the increase in yield stress for coherent strengthened bcc-superalloys. Integration into a physical-based model, which identified a novel interplay with cleavage stress, provides enhanced BDTT predictive capability for ferritic superalloys.

Original language	English
Article number	144031
Number of pages	7
Journal	Materials Science and Engineering A
Volume	856
Early online date	21 Sept 2022
DOIs	https://doi.org/10.1016/j.msea.2022.144031
Publication status	Published - 20 Oct 2022

Bibliographical note

Funding Information:
The authors gratefully acknowledge the Centre for Electron Microscopy (University of Birmingham) for their support & assistance in this work. This research used internal founding of the Comisión Nacional de Energía Atómica. A.J. Knowles gratefully acknowledges funding from EPSRC [EP/T016566/1], UKRI Future Leaders Fellowship [MR/T019174/1] and Royal Academy of Engineering Research Fellowship, UK. U.A. Sterin was supported by Instituto Sabato & CONICET fellowships.

Publisher Copyright:
© 2022 The Authors

Keywords

Ageing
Brittle-to-ductile transition
Fe-Al-V
Impact test
Precipitate size
Superalloy

ASJC Scopus subject areas

Materials Science(all)
Condensed Matter Physics
Mechanics of Materials
Mechanical Engineering

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Cite this

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title = "Influence of precipitate and grain sizes on the brittle-to-ductile transition in Fe–Al–V bcc-L21 ferritic superalloys",

abstract = "The limiting factors to achieving a wide application of bcc-superalloys are the high brittle-to-ductile transition temperatures (BDTT). The understanding of the mechanisms controlling the BDTT and how to optimise the microstructure in polycrystalline bcc-superalloys remains a concern today.In the present work, the influence of grain and coherent precipitates sizes on strength and brittle-to-ductile transition temperature (BDTT) are studied in a Fe78Al10V12 (A2+L21) ferritic superalloy, toward application in high-efficiency power plants. Additionally, the A2 matrix behaviour was evaluated in a derived single-phase-bcc Fe84Al8V8 alloy. Thermal ageing and coarsening treatments were applied to produce samples with different precipitate and grain sizes. Tensile tests were carried out at different temperatures and strain rates to assess the variation of the yield stress. Charpy impact tests were used to measure the BDTT in both alloys, which was substantially reduced with grain size refinement, and precipitate coarsening. It was found that the increase in cleavage stress by precipitation strengthening follows the same behaviour that the increase in yield stress for coherent strengthened bcc-superalloys. Integration into a physical-based model, which identified a novel interplay with cleavage stress, provides enhanced BDTT predictive capability for ferritic superalloys.",

keywords = "Ageing, Brittle-to-ductile transition, Fe-Al-V, Impact test, Precipitate size, Superalloy",

author = "P.a. Ferreir{\'o}s and U.A. Sterin and P.R. Alonso and A.j. Knowles and G.H. Rubiolo",

note = "Funding Information: The authors gratefully acknowledge the Centre for Electron Microscopy (University of Birmingham) for their support & assistance in this work. This research used internal founding of the Comisi{\'o}n Nacional de Energ{\'i}a At{\'o}mica. A.J. Knowles gratefully acknowledges funding from EPSRC [EP/T016566/1], UKRI Future Leaders Fellowship [MR/T019174/1] and Royal Academy of Engineering Research Fellowship, UK. U.A. Sterin was supported by Instituto Sabato & CONICET fellowships. Publisher Copyright: {\textcopyright} 2022 The Authors",

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AU - Ferreirós, P.a.

AU - Sterin, U.A.

AU - Alonso, P.R.

AU - Knowles, A.j.

AU - Rubiolo, G.H.

N1 - Funding Information: The authors gratefully acknowledge the Centre for Electron Microscopy (University of Birmingham) for their support & assistance in this work. This research used internal founding of the Comisión Nacional de Energía Atómica. A.J. Knowles gratefully acknowledges funding from EPSRC [EP/T016566/1], UKRI Future Leaders Fellowship [MR/T019174/1] and Royal Academy of Engineering Research Fellowship, UK. U.A. Sterin was supported by Instituto Sabato & CONICET fellowships. Publisher Copyright: © 2022 The Authors

PY - 2022/10/20

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N2 - The limiting factors to achieving a wide application of bcc-superalloys are the high brittle-to-ductile transition temperatures (BDTT). The understanding of the mechanisms controlling the BDTT and how to optimise the microstructure in polycrystalline bcc-superalloys remains a concern today.In the present work, the influence of grain and coherent precipitates sizes on strength and brittle-to-ductile transition temperature (BDTT) are studied in a Fe78Al10V12 (A2+L21) ferritic superalloy, toward application in high-efficiency power plants. Additionally, the A2 matrix behaviour was evaluated in a derived single-phase-bcc Fe84Al8V8 alloy. Thermal ageing and coarsening treatments were applied to produce samples with different precipitate and grain sizes. Tensile tests were carried out at different temperatures and strain rates to assess the variation of the yield stress. Charpy impact tests were used to measure the BDTT in both alloys, which was substantially reduced with grain size refinement, and precipitate coarsening. It was found that the increase in cleavage stress by precipitation strengthening follows the same behaviour that the increase in yield stress for coherent strengthened bcc-superalloys. Integration into a physical-based model, which identified a novel interplay with cleavage stress, provides enhanced BDTT predictive capability for ferritic superalloys.

AB - The limiting factors to achieving a wide application of bcc-superalloys are the high brittle-to-ductile transition temperatures (BDTT). The understanding of the mechanisms controlling the BDTT and how to optimise the microstructure in polycrystalline bcc-superalloys remains a concern today.In the present work, the influence of grain and coherent precipitates sizes on strength and brittle-to-ductile transition temperature (BDTT) are studied in a Fe78Al10V12 (A2+L21) ferritic superalloy, toward application in high-efficiency power plants. Additionally, the A2 matrix behaviour was evaluated in a derived single-phase-bcc Fe84Al8V8 alloy. Thermal ageing and coarsening treatments were applied to produce samples with different precipitate and grain sizes. Tensile tests were carried out at different temperatures and strain rates to assess the variation of the yield stress. Charpy impact tests were used to measure the BDTT in both alloys, which was substantially reduced with grain size refinement, and precipitate coarsening. It was found that the increase in cleavage stress by precipitation strengthening follows the same behaviour that the increase in yield stress for coherent strengthened bcc-superalloys. Integration into a physical-based model, which identified a novel interplay with cleavage stress, provides enhanced BDTT predictive capability for ferritic superalloys.

KW - Ageing

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KW - Impact test

KW - Precipitate size

KW - Superalloy

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