Non-Equilibrium Solidification Behavior and Microstructure Evolution of Undercooled Fe7(CoNiMn)80B13 Eutectic High-Entropy Alloy
WANG Yeqing, FU Ke, ZHAO Yongzhu, SU Liji, CHEN Zheng()
School of Material Science and Physics, China University of Mining and Technology, Xuzhou 221116, China
Cite this article:
WANG Yeqing, FU Ke, ZHAO Yongzhu, SU Liji, CHEN Zheng. Non-Equilibrium Solidification Behavior and Microstructure Evolution of Undercooled Fe7(CoNiMn)80B13 Eutectic High-Entropy Alloy. Acta Metall Sin, 2025, 61(1): 143-153.
Eutectic high-entropy alloys show excellent properties, such as casting property, mechanical properties, corrosion resistance properties, and so on. They are usually consisted of two kinds of phases, which would be compete with each other in the non-equilibrium solidification process. Fe7(CoNiMn)80B13 eutectic high-entropy alloy has complex phase transition and microstructure evolution behavior during the non-equilibrium solidification process. In order to reveal the non-equilibrium solidification characteristics and microstructure evolution mechanism, Fe7(CoNiMn)80B13 eutectic high-entropy alloy was undercooled by the molten glass fluxing method in this work. The results show that the solidification path and microstructure of undercooled Fe7(CoNiMn)80B13 eutectic high-entropy alloy can be divided into 5 categories. At low undercooling (ΔT < 57 K), the cooling curve has only one recalescence phenomenon. The corresponding solidification microstructure is primary B-rich phase + peritectic α-(Fe, Co, Ni, Mn) phase + eutectic structure. At medium undercooling (ΔT = 57~111 K), there are two recalescence phenomena on the cooling curve. The corresponding solidification microstructure can be divided into two types: the first is primary M23B6 dendrite + secondary α-(Fe, Co, Ni, Mn) halo + regular eutectic; the second is primary α-(Fe, Co, Ni, Mn) dendrite + regular eutectic. At high undercooling (ΔT = 139~198 K), the cooling curve shows a single recalescence phenomenon again. The corresponding solidification microstructure can be divided into two types: the first is a mixture of B-rich phase + M23B6 + α-(Fe, Co, Ni, Mn) three phases, and the second is M23B6 + α-(Fe, Co, Ni, Mn) anomalous eutectic. Note that the type of primary phase transited for twice with the increase of undercooling: B-rich phase→M23B6 phase→α-(Fe, Co, Ni, Mn) phase. In addition, the orientation relationship of two eutectic phases in regular eutectic at low undercooling is consistent with that of two phases in anomalous eutectic at high undercooling.
Fig.1 Temperature-time profiles of the undercooled Fe7(CoNiMn)80B13 eutectic high-entropy alloys (ΔT—undercooling, Tm—melting temperature)
Fig.2 XRD spectra of the as-cast Fe7(CoNiMn)80B13 eutectic high-entropy alloys and with different ΔT
Fig.3 SEM back-scattered electron (BSE) images (a-d) and EDS line scanning result (e) of the Fe7(CoNiMn)80B13 eutectic high-entropy alloys with ΔT = 23 K (a, b) low (a) and high (b) magnifications, dendrites + fine structure (c) locally enlarged image of region 1 in Fig.3b, eutectic structure (d) locally enlarged image of region 2 in Fig.3b, net structure
ΔT / K
Region
Fe
Co
Ni
Mn
023
Average
10.0
41.1
40.5
08.4
Dark phase
14.7
55.3
24.8
05.2
Light phase
11.7
47.3
33.8
07.2
057
Average
09.7
38.9
38.4
12.9
Dark phase
14.7
56.4
20.7
08.2
090
Average
08.4
31.3
29.5
30.8
Dark phase
16.7
43.9
11.9
27.5
Light phase
12.0
37.5
20.4
30.1
139
Average
10.2
41.0
36.7
12.0
P1
11.6
42.6
33.7
11.0
P2
04.4
19.6
53.6
23.4
P3
14.3
52.8
21.6
07.3
198
Average
09.2
40.7
38.5
11.6
Dark phase
04.3
26.4
50.1
19.2
Light phase
12.8
46.5
33.0
07.7
Table 1 EDS analysis results of the Fe7(CoNiMn)80B13 eutectic high-entropy alloys with different ΔT
Fig.4 SEM-BSE images of the Fe7(CoNiMn)80B13 eutectic high-entropy alloys under ΔT = 57 K (a-c), ΔT = 90 K (d-f), ΔT = 139 K (g-i), and ΔT = 198 K (j-l) with different magnifications (The microstructure at the region I in Fig.4a is magnified in Fig.4b, and those at the regions II and III in Fig.4f represent two kinds of eutectic structure with different lamellar spacing. EDS results of regions P1-P3 in Fig.4i are listed in Table 1. The area enclosed by dashed lines in Fig.4j show the clustered eutetic structures)
Fig.5 EBSD analysis results of the eutectic structure in Fe7(CoNiMn)80B13 eutectic high-entropy alloys under ΔT = 57 K (a) phase map (b) EBSD map (Inset is the inverse pole figure (IPF) map of single α-(Fe, Co, Ni, Mn) phase) (c) pole figures of α-(Fe, Co, Ni, Mn) solid solution phase in crystal plane groups {100}, {110}, and {111}, respectively (Circles represent coincident orientations between M23B6 phase and α-(Fe, Co, Ni, Mn)) (d) pole figures of M23B6 phase in crystal plane groups {100}, {110}, and {111}, respectively
Fig.6 EBSD analysis results of the anomalous eutectic structure in Fe7(CoNiMn)80B13 eutectic high-entropy alloys under ΔT = 198 K (a) phase map (b) EBSD map (Inset is the IPF map of single α-(Fe, Co, Ni, Mn) phase) (c) pole figures of α-(Fe, Co, Ni, Mn) phase in crystal plane groups {100}, {110}, and {111}, respectively (d) pole figures of M23B6 phase in crystal plane groups {100}, {110}, and {111}, respectively
Fig.7 Solid-liquid interfacial morphologies of Fe7(CoNiMn)80B13 eutectic high-entropy alloys under ΔT = 23 K (a), ΔT = 111 K (b), and ΔT = 154 K (c) (Red dashed lines and red arrow in Fig.7a show the solid-liquid interface and the growing direction of the solid phase, respectively. Circles with yellow, blue, and green colors in Fig.7b represent three nucleation points in the melt)
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