A high-strength precipitation hardened cobalt-free high-entropy alloy

Matthew Luebbe; Jiaqi Duan; Fan Zhang; Jonathan Poplawsky; Hans Pommeranke; Maalavan Arivu; Andrew Hoffman; Mario Buchely; Haiming Wen

doi:10.1016/j.msea.2023.144848

A high-strength precipitation hardened cobalt-free high-entropy alloy

Matthew Luebbe, Jiaqi Duan, Fan Zhang, Jonathan Poplawsky, Hans Pommeranke, Maalavan Arivu, Andrew Hoffman, Mario Buchely, Haiming Wen

Materials MicroAnalysis

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Abstract

Recent studies on precipitation-hardened high-entropy alloys (HEAs) demonstrate their high strength and thermal stability, making them promising materials for high-temperature structural applications such as nuclear reactors. However, many existing HEAs contain cobalt (Co), which is unsuitable for nuclear applications because of the long-term activation issue of Co. Co is also expensive and considered a critical material for other applications. Therefore, it is desired to exclude Co from the composition. A Co-free (Fe_0.3Ni_0.3Mn_0.3Cr_0.1)₈₈Ti₄Al₈ HEA was developed and studied in this work. In contrast to previous Co-free HEAs, this alloy is close to equiatomic in its composition and promises a more pronounced high-entropy effect. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and synchrotron-based, high-energy X-ray diffraction were used to characterize this alloy and revealed a complex four-phase structure, with an FCC matrix, γ’ precipitates, and a network of B2 and χ phase particles. This structure granted 2151 MPa compressive strength and good thermal stability, but with limited ductility and slow precipitation kinetics. A strengthening analysis of the alloy shows that the B2 and χ provided the most significant strengthening contribution, adding 312 MPa and 788 MPa respectively. The strengthening effect from the nanoscale γ′ is also considerable, adding 608 MPa in total. This study lays the foundation for the continued development of high-strength Co-free HEAs with improved and satisfactory ductility.

Original language	English
Article number	144848
Journal	Materials Science and Engineering: A
Volume	870
DOIs	https://doi.org/10.1016/j.msea.2023.144848
State	Published - Apr 12 2023

Funding

This research was partially financially supported by the U.S. Nuclear Regulatory Commission Faculty Development Program (award number NRC 31310018M0044 ). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. APT research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. The authors would like to thank James Burns for assistance in performing APT sample preparation and running the APT experiments. We characterized the peak-aged alloy using EDS in both the SEM and TEM. A complicated microstructure of an FCC matrix and two other precipitating phases with elemental segregation were observed, as shown by the SEM data in Fig. 5. The first phase is a NiAl-enriched and FeCr-depleted B2 phase which appears lighter than the matrix under secondary electron SEM imaging. The second phase is an FeCr-enriched and NiAl-depleted χ (or Chi) phase that appears both darker than the matrix and slightly upraised from the matrix, indicating that it has a higher abrasion resistance to mechanical polishing. Notably, these two phases grow adjacent to each other in a network structure. Examples of the two phases are labeled in Fig. 5a and 5c-f. TEM data support these SEM findings, as shown in Fig. 6. The higher resolution of TEM enables elemental distribution to be more clearly observed than SEM. Specifically, while Mn appears to be homogeneous under SEM, TEM data demonstrated a slight preference for B2. Ti, which appears to be enriched in both B2 and χ under SEM, appears to show a slight preference for χ instead of B2 at a smaller scale.This research was partially financially supported by the U.S. Nuclear Regulatory Commission Faculty Development Program (award number NRC 31310018M0044). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. APT research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. The authors would like to thank James Burns for assistance in performing APT sample preparation and running the APT experiments.

Funders	Funder number
Center for Nanophase Materials Sciences
U.S. Department of Energy
U.S. Nuclear Regulatory Commission	NRC 31310018M0044
Office of Science
Argonne National Laboratory	DE-AC02-06CH11357
Oak Ridge National Laboratory
Federal Communications Commission

Keywords

High-entropy alloy
Mechanical properties
Microstructure
Precipitation strengthening
Strengthening mechanisms

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10.1016/j.msea.2023.144848

Cite this

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title = "A high-strength precipitation hardened cobalt-free high-entropy alloy",

abstract = "Recent studies on precipitation-hardened high-entropy alloys (HEAs) demonstrate their high strength and thermal stability, making them promising materials for high-temperature structural applications such as nuclear reactors. However, many existing HEAs contain cobalt (Co), which is unsuitable for nuclear applications because of the long-term activation issue of Co. Co is also expensive and considered a critical material for other applications. Therefore, it is desired to exclude Co from the composition. A Co-free (Fe0.3Ni0.3Mn0.3Cr0.1)88Ti4Al8 HEA was developed and studied in this work. In contrast to previous Co-free HEAs, this alloy is close to equiatomic in its composition and promises a more pronounced high-entropy effect. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and synchrotron-based, high-energy X-ray diffraction were used to characterize this alloy and revealed a complex four-phase structure, with an FCC matrix, γ{\textquoteright} precipitates, and a network of B2 and χ phase particles. This structure granted 2151 MPa compressive strength and good thermal stability, but with limited ductility and slow precipitation kinetics. A strengthening analysis of the alloy shows that the B2 and χ provided the most significant strengthening contribution, adding 312 MPa and 788 MPa respectively. The strengthening effect from the nanoscale γ′ is also considerable, adding 608 MPa in total. This study lays the foundation for the continued development of high-strength Co-free HEAs with improved and satisfactory ductility.",

keywords = "High-entropy alloy, Mechanical properties, Microstructure, Precipitation strengthening, Strengthening mechanisms",

author = "Matthew Luebbe and Jiaqi Duan and Fan Zhang and Jonathan Poplawsky and Hans Pommeranke and Maalavan Arivu and Andrew Hoffman and Mario Buchely and Haiming Wen",

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AU - Luebbe, Matthew

AU - Duan, Jiaqi

AU - Zhang, Fan

AU - Poplawsky, Jonathan

AU - Pommeranke, Hans

AU - Arivu, Maalavan

AU - Hoffman, Andrew

AU - Buchely, Mario

AU - Wen, Haiming

PY - 2023/4/12

Y1 - 2023/4/12

N2 - Recent studies on precipitation-hardened high-entropy alloys (HEAs) demonstrate their high strength and thermal stability, making them promising materials for high-temperature structural applications such as nuclear reactors. However, many existing HEAs contain cobalt (Co), which is unsuitable for nuclear applications because of the long-term activation issue of Co. Co is also expensive and considered a critical material for other applications. Therefore, it is desired to exclude Co from the composition. A Co-free (Fe0.3Ni0.3Mn0.3Cr0.1)88Ti4Al8 HEA was developed and studied in this work. In contrast to previous Co-free HEAs, this alloy is close to equiatomic in its composition and promises a more pronounced high-entropy effect. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and synchrotron-based, high-energy X-ray diffraction were used to characterize this alloy and revealed a complex four-phase structure, with an FCC matrix, γ’ precipitates, and a network of B2 and χ phase particles. This structure granted 2151 MPa compressive strength and good thermal stability, but with limited ductility and slow precipitation kinetics. A strengthening analysis of the alloy shows that the B2 and χ provided the most significant strengthening contribution, adding 312 MPa and 788 MPa respectively. The strengthening effect from the nanoscale γ′ is also considerable, adding 608 MPa in total. This study lays the foundation for the continued development of high-strength Co-free HEAs with improved and satisfactory ductility.

AB - Recent studies on precipitation-hardened high-entropy alloys (HEAs) demonstrate their high strength and thermal stability, making them promising materials for high-temperature structural applications such as nuclear reactors. However, many existing HEAs contain cobalt (Co), which is unsuitable for nuclear applications because of the long-term activation issue of Co. Co is also expensive and considered a critical material for other applications. Therefore, it is desired to exclude Co from the composition. A Co-free (Fe0.3Ni0.3Mn0.3Cr0.1)88Ti4Al8 HEA was developed and studied in this work. In contrast to previous Co-free HEAs, this alloy is close to equiatomic in its composition and promises a more pronounced high-entropy effect. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and synchrotron-based, high-energy X-ray diffraction were used to characterize this alloy and revealed a complex four-phase structure, with an FCC matrix, γ’ precipitates, and a network of B2 and χ phase particles. This structure granted 2151 MPa compressive strength and good thermal stability, but with limited ductility and slow precipitation kinetics. A strengthening analysis of the alloy shows that the B2 and χ provided the most significant strengthening contribution, adding 312 MPa and 788 MPa respectively. The strengthening effect from the nanoscale γ′ is also considerable, adding 608 MPa in total. This study lays the foundation for the continued development of high-strength Co-free HEAs with improved and satisfactory ductility.

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KW - Mechanical properties

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A high-strength precipitation hardened cobalt-free high-entropy alloy

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