Unveiling microstructural origins of the balanced strength–ductility combination in eutectic high-entropy alloys at cryogenic temperatures

Figures & data

Figure 1. Typical eutectic lamellar microstructure of the as-cast Al₁₉Co₂₀Fe₂₀Ni₄₁ EHEA. (a) BSE-SEM image. (b) EBSD phase map (upper) and IPF (under). (c) HAADF-STEM image and EDS maps. (d) Two SAED patterns of B2 and L1₂ phases with superlattice diffraction spots marked by circles. (e, f) Enlarged TEM image of B2 and L1₂ phases and the corresponding SADP pattern. (g) HR-TEM image of B2 and L1₂ phases. The phase interface is marked by a white dotted line. The inset shows the corresponding FFT pattern, which helps get two lattice planes marked in each phase.

Figure 2. Tensile response of the as-investigated Al₁₉Co₂₀Fe₂₀Ni₄₁ EHEA (termed as Ni41) and the widely-reported AlCoCrFeNi_2.1 EHEA (Ni2.1; Ref. 10) at 77 and 298 K. The error bars are standard deviations of the mean. The inset shows the corresponding strain-hardening curves of the as-investigated Al₁₉Co₂₀Fe₂₀Ni₄₁ EHEA at 77 and 298 K.

Table 1. Similarities and differences between these two AlCoCrFeNi_2.1 (termed as Ni2.1) and Al₁₉Co₂₀Fe₂₀Ni₄₁ (Ni41) EHEAs [9–11,13,20,21].

	Phase	Lamellar thickness (μm)	Phase content (vol%)	Hardness (GPa)	Grain size (μm)	Interface feature	Interplanar spacing (Å)
Ni2.1	L12	∼1.15	65∼71	4.0∼6.0	43	K-S	d(111) = 2.06
	B2	∼0.81	29∼35	7.5∼12.0			d(110) = 2.08
Ni41	L12	∼0.92	∼55	∼4.2	35	K-S	d(111) = 2.06
	B2	∼0.73	∼45	∼5.6			d(110) = 2.03

Figure 3. Typical TEM images showing deformation microstructures of the as-investigated Al₁₉Co₂₀Fe₂₀Ni₄₁ EHEA under different strain conditions: (a) ∼3%, (b, c) ∼6% and (d, e) ∼12% at 77 K; (f) ∼16% at 298 K. g indicates the direction of the diffraction vector. All phase interfaces are marked by yellow dotted lines. (g and h) The corresponding SAEDs of L1₂ and B2 phase, respectively, at ∼3%, ∼6% and ∼12%. (I) EBSD phase map, KAM map, and the corresponding curve of KAM values from these locations marked by white line in the KAM map.

Figure 4. Deformation microstructures in the post-fracture AlCoCrFeNi_2.1 EHEA at 77 K. (a, b) STEM image and the enlarged STEM image showing a multi-slip dislocation scenario in the L1₂ phase. These two insets are the SAED patterns of B2 and L1₂ phases, respectively. (c) Upper STEM image and under HAADF-STEM image exhibiting dense Cr-rich precipitates and a few dislocation debris in the B2 phase.

Xiong T, Yang WF, Zheng SJ, et al. Faceted Kurdjumov-Sachs interface-induced slip continuity in the eutectic high-entropy alloy, AlCoCrFeNi2.1. J Mater Sci Technol. 2021;65:216–227.

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Shi PJ, Ren WL, Zheng TX, et al. Enhanced strength–ductility synergy in ultrafine-grained eutectic high-entropy alloys by inheriting microstructural lamellae. Nat Commun. 2019;10:489.

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