Charpy impact toughness of Cu–Fe–Mn-based immiscible medium-entropy alloys

doi:10.1016/j.msea.2022.144464

Materials Science and Engineering: A

Volume 862, 18 January 2023, 144464

https://doi.org/10.1016/j.msea.2022.144464 Get rights and content

Abstract

Impact toughness at ambient and cryogenic temperatures was investigated with systematic fracture analyses for CuFeMn and Al₁₅(CuFeMn)₈₅ (at%) immiscible medium-entropy alloys. These two types of alloys exhibited different impact toughness behavior at different temperatures, while exhibiting higher impact toughness values than those of dual-phase steels with a similar strength level.

Introduction

Material scientists are always eager to develop stronger and more ductile metallic materials for improved performance in various structural applications. However, improving strength of metallic materials usually accompanies the ductility sacrifice by traditional methods, known as strength–ductility trade-off. Recently, heterostructuring has been a novel metallurgical strategy for improving both strength and ductility of metallic materials, stemming from the large strain gradient by strain incompatibility between hard and soft domains promoting hetero-deformation-induced (HDI) hardening effect [[1], [2], [3], [4], [5], [6]]. Various kinds of microstructural heterogeneities, comprising crystal structures [1,3], grain sizes [4,5], and elemental distribution [1,6], can be considered as the strengthening factor triggering the HDI hardening in metallic materials. In particular, since the multi-principal element alloys, known as high-entropy alloys (HEAs) and medium-entropy alloys (MEAs), with no single dominant element in contrast to conventional alloys, have emerged, a wide variety of microstructural heterogeneities in this novel type of alloys offers new alloying design concept for hetero-structured materials with strength–ductility synergy [7,8].

One novel design strategy for the hetero-structured MEAs was recently suggested as utilizing an immiscible nature of Cu and Fe in a wide range of temperatures, called immiscible medium-entropy alloys (IMMEAs) [1]. The addition of Mn in the Cu–Fe binary system, which is easily dissolved in both Cu and Fe, promotes solid solution strengthening of a CuFeMn IMMEA (configurational mixing entropy, ΔS_conf = 1.10R, R is a gas constant) consisting of Cu- and Fe-rich FCC phases [9]. To induce the microstructural heterogeneity of not only the elemental distribution but the crystal structures between the two phases, an Al₁₅(CuFeMn)₈₅ (at%) IMMEA (ΔS_conf = 1.36R) comprising Fe-rich FCC and Cu-rich BCC phases has been developed [1]. The strength–ductility combination of the IMMEAs is better than those of conventional single-phase HEAs/MEAs, originating from the HDI strengthening [1]. On the other hand, it has been often considered as the enhancement of strength–ductility combination leading to improved impact toughness of materials, which is a crucial property for cryogenic or harsh applications [10,11]. However, it is questionable whether the IMMEAs possess good impact toughness because the phase interfaces are vulnerable to crack initiation [12].

In this study, Charpy impact tests were performed on two different IMMEAs at 298 K and 77 K. The relationship between microstructure and impact toughness of the alloys was systematically investigated, and the temperature-dependent ductile-brittle transition (DBT) was figured out by a fractography study.

Section snippets

Experimental

The equiatomic CuFeMn and non-equiatomic Al₁₅(CuFeMn)₈₅ (at%) IMMEAs were produced with high-purity (99.99%) element pellets by vacuum induction melting (VTC200, Indutherm, Germany). The ingots were homogenized at 1073 K for 6 h followed by water quenching [1,9]. Then, cold rolling at ambient temperature reduced the thickness of the ingots from 23 mm to 11 mm (reduction ratio: 52.2%) to break the cast coarse microstructures. The as-rolled samples were annealed at 1073 K for 1 h and immediately

Results and discussion

Fig. 1 shows the initial microstructures of the 0Al and 15Al. Both the alloys are separated into Cu- and Fe-rich phases according to EDS mapping in Fig. 1(a and e) due to the immiscible property of Fe and Cu [1]. The 0Al comprises dual FCC phases while the 15Al shows Fe-rich FCC and Cu-rich BCC phases in Fig. 1(d) because Al addition increases the BCC fraction according to the phase diagram of the 0Al and 15Al [1]. Average grain sizes of both phases in the 0Al are measured to be 9.5 μm, whereas

Conclusion

This study introduces the impact toughness of the two kinds of IMMEAs having different constituent phases on the basis of the fractured microstructures. At 298 K, both IMMEAs exhibit good impact toughness as compared with those of various commercial steels. In particular, the impact toughness of the 15Al is superior at 298 K. Whilst both IMMEAs exhibit higher static toughness at 77 K than those at 298 K, the impact toughness of the 15Al at 77 K is deteriorative in contrast to the static

Originality statement

I write on behalf of myself and all co-authors to confirm that the results reported in the manuscript are original and neither the entire work, nor any of its parts have been previously published. The authors confirm that the article has not been submitted to peer review, nor has been accepted for publishing in another journal. The authors confirm that the research in their work is original, and that all the data given in the article are real and authentic. If necessary, the article can be

CRediT authorship contribution statement

Jungwan Lee: Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft. Jeong Min Park: Conceptualization, Data curation, Formal analysis, Methodology, Visualization, Writing – original draft, Writing – review & editing. Jongun Moon: Investigation, Methodology, Validation, Writing – review & editing. Hyojin Park: Formal analysis, Methodology. Hyoung Seop Kim: Conceptualization, Funding acquisition, Project administration, Resources, Supervision,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP)(NRF–2021R1A2C3006662, NRF-2022R1A5A1030054). This work was also supported by Principal R&D Project (PNK8290) of the Korean Institute of Materials Science (KIMS), and Basic Research Program (PICO190) of Korea Institute of Machinery and Materials (KIMM).

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Charpy impact toughness of Cu–Fe–Mn-based immiscible medium-entropy alloys

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Originality statement

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgments

Acta Mater.

Comput. Mater. Sci.

J. Alloys Compd.

Prog. Mater. Sci.

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J. Alloys Compd.

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J. Nucl. Mater.

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Mater. Char.

Mater. Sci. Eng., A

Intermetallics

J. Nucl. Mater.

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Scripta Mater.

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Mater. Sci. Eng., A