Superb strength and ductility balance of a Co-free medium-entropy alloy with dual heterogeneous structures

doi:10.1016/j.jmst.2021.05.023

Abstract

Abstract:

In present work, we successfully fabricated a novel Co-free non-equiatomic Ni₄₆Cr₂₃Fe₂₃Al₄Ti₄ medium-entropy alloy with dual heterogeneous structures, i.e. three-levels grain structures and heterogeneous L1₂ precipitates. Experimental results revealed the dual heterogeneous structures lead to remarkable strength-ductility synergy properties in this Co-free medium-entropy alloy, showing high yield strength and ultimate tensile strength of ~1203 MPa and ~1633 MPa, respectively, remaining an excellent ductility of ~28.7%. Further analyses about strengthening and deformation mechanisms indicated precipitation hardening and hetero-deformation induced hardening contribute the majority strength enhancement, meanwhile deformation-induced hierarchical stacking-faults networks, high density Lomer-Cottrell locks and microstructure features of heterogeneous grains and precipitates substantially facilitate the high work-hardening capacity and excellent tensile ductility. This work not only offers fundamental understanding of the strength and deformation mechanisms of the dual heterogeneous structural material, but also provides useful strength design strategy for low-price high performance high/medium-entropy alloys

Key words: Dual heterogeneous structures, Medium-entropy alloy, Co-free, Strength-ductility synergy properties

Wenjie Lu, Kang Yan, Xian Luo, Yuetang Wang, Le Hou, Pengtao Li, Bin Huang, Yanqing Yang. Superb strength and ductility balance of a Co-free medium-entropy alloy with dual heterogeneous structures[J]. J. Mater. Sci. Technol., 2022, 98: 197-204.

Figures/Tables 9

Fig. 1. Microstructure investigation of 1323 K/15 min annealed Al4Ti4 MEA, (a) IPF image showing heterogeneous grain structure, (b) DF image showing large precipitates randomly distribute in matrix, (c) and (d) SADPs along [001] and [110] zone axis, respectively.

Fig. 2. Microstructure investigation of 973 K/8 h aged Al4Ti4 MEA sample, (a) IPF image, inset (a1) and (a2) show grain size distribution and grain boundaries misorientation, respectively, (b) TEM BF image, showing a twinned NG at the lower part of a UFG, (c) and (d) SADP and HRTEM of NT structur, (e) DF image showing heterogeneous precipitates distribution, (f), (g) and (h) SADPs along [100], [110] and [111] zone axes, respectively, which confirmed those precipitates both have L12 superlattice, (i) and (j) HAADF-STEM images along [100] zone axe, which verified those heterogeneous precipitates both coherent with fcc matrix, (k)-(o) EDS mappings showing constitution element distribution of the red rectangle in (e).

Table 1 Chemical compositions of different phase in this DHS Al4Ti4 MEA sample (at.%).

Phases	Compositions (at.%)
	Ni	Cr	Fe	Al	Ti
Large L1₂	70.15	5.45	6.22	5.38	12.85
Fine L1₂	62.17	11.73	12.74	5.44	7.92
Matrix	41.07	25.91	27.34	3.08	2.78

Fig. 3. Mechanical properties of solid-solution Ni50Cr25Fe25 MEA, (a) typical engineering stress-strain curve, (b) work-hardening rate.

Fig. 4. Mechanical properties of the DHS Al4Ti4 MEA sample, (a) representative engineering stress-strain curve, the inset is LUR curve, and (b) work-hardening rate curve.

Fig. 5. DHS Al4Ti4 MEA shows superb strength-ductility synergy in comparison with relative literatures.

Fig. 6. Calculated HDI hardening effects of this DHS Al4Ti4 MEA.

Fig. 7. Deformation characters in solid-solution Ni50Cr25Fe25 MEA after tensile testing, (a) BF image, inset is the corresponding SADP, (b) HRTEM image of red rectangle region in (b).

Fig. 8. Deformation characters in the DHS Al4Ti4 MEA after tensile test, (a) high-density hierarchical SFs (yellow arrows) at two {111} slip plans, (b) HRTEM showing intersecting SFs (white dash line) and LC locks (red dot).

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