Dislocation-induced breakthrough of strength and ductility trade-off in a non-equiatomic high-entropy alloy

Abstract

In conventional metallic materials, strength and ductility are mutually exclusive, referred to as strengthductility trade-off. Here, we demonstrate an approach to improve the strength and ductility simultaneously by introducing micro-banding and the accumulation of a high density of dislocations in single-phase high-entropy alloys (HEAs). We prepare two compositions (Cr 10 Mn 50 Fe 20 Co 10 Ni 10 and Cr 10 Mn 10 Fe 60 Co 10 Ni 10 ) with distinctive different stacking fault energies (SFEs) as experimental materials. The strength and ductility of the Cr 10 Mn 50 Fe 20 Co 10 Ni 10 HEA are improved concurrently by grain refinement from 347.5 ± 216.1 μm to 18.3 ± 9.3 μm. The ultimate tensile strength increases from 543 ± 4 MPa to 621 ± 8 MPa and the elongation to failure enhances from 43 ±2% to 55 ±1%. To reveal the underlying deformation mechanisms responsible for such a strength-ductility synergy, the microstructural evolution upon loading is investigated by electron microscopy techniques. The dominant deformation mechanism observed for the Cr 10 Mn 50 Fe 20 Co 10 Ni 10 HEA is the activation of micro-bands, which act both as dislocation sources and dislocation barriers, eventually, leading to the formation of dislocation cell structures. By decreasing grain size, much finer dislocation cell structures develop, which are responsible for the improvement in work hardening rate at higher strains ( > 7%) and thus for the increase in both strength and ductility. In order to drive guidelines for designing advanced HEAs by tailoring their SFE and grain size, we compute the SFEs of Cr 10 Mn x Fe 70-x Co 10 Ni10 (10 ≤ x ≤ 60) based on first principles calculations. Based on these results the overall changes on deformation mechanism can be explained by the influence of Mn on the SFE.

Hierarchical crack buffering triples ductility in eutectic herringbone high-entropy alloys

“…Although the directionally solidified EHEA has a high content of hard, low-ductility B2 phase (~41 vol%) (15,22,23), it nonetheless exhibits a large uniform elongation of ~50%. Its elongation is comparable to that of widely studied, high-ductility, fully homogenized face-centered cubic high-entropy alloys (HEAs) (24)(25)(26)(27). The resulting strength-ductility combination, and especially the uniform ductility, in the directionally solidified EHEA outperforms that of any other as-cast eutectic and neareutectic HEAs (14,15,19,20,22,23,(28)(29)(30)(31)(32)(33) (Fig.…”

Effects of Cold Rolling and Annealing Treatment on Microstructure and Properties of CoFeNiMnV High‐Entropy Alloys

“…A large number of dislocations in crystals are entangled with each other, which results in the obstruction of the mutual movement of materials and the improvement of the yield strength of materials. Bailey–Hirsch can be used to express the corresponding dislocation strengthening where M is the Taylor factor of ≈3.06 [ 64 ] ; α is the material constant of the FCC metal (≈0.2 [ 65 ] ); G is the shear modulus of the CoFeNiMn system HEA (81 GPa) [ 66 ] ; and b is the Burgers vector (for FCC structure alloys, , where a is the lattice constant (based on the data in Table 4)); The dislocation density can be estimated by the following equation [ 67 ] where ε is the lattice strain, D is the grain size, ρ is the dislocation density, b is the Burgers vector, and for the FCC structure, , where a is the lattice parameter. The values of the various parameters mentioned previously, and the calculated values of dislocation density and lattice stress are summarized in Table 4.…”

“…where a is the lattice constant (based on the data in Table 4)); The dislocation density can be estimated by the following equation [67] ρ…”

Nonlinear deformation and elasticity of BCC refractory metals and alloys

“…Carefully tuning these parameters enables control over the ductility. Point defects, dislocations and other microstructure effects will also affect the ductility of the system [33][34][35][36][37][38], but are out of the scope of this work.…”