The application of single-phase face-centered cubic (FCC) medium entropy alloys (MEAs) in the engineering industry is often hindered by the challenge of insufficient strength. In this study, a novel non-equiatomic ratio Ni40Co30Cr20Al5Ti5 MEA was successfully fabricated. Through the well-designed mechanical heat treatment processing, we introduced a heterogeneous grain structure comprising 67.4% fine grain and 32.6% coarse grain. Additionally, heterogeneous size L12 phases consisting of 18.7% submicron precipitates and 11.7% nano-sized precipitates, were incorporated into the alloy. Tensile tests conducted at room temperature revealed that the double heterogeneous structure alloy demonstrated remarkable strength–ductility synergy. It exhibited a yield strength of 1200 MPa, an ultimate tensile strength of 1560 MPa and a total elongation of 33.6%. The exceptional strength of the alloy can be primarily attributed to heterogeneous deformation induced strengthening, grain boundary strengthening and precipitation strengthening. The excellent ductility is mainly attributed to the high-density stacking faults and Lomer–Cottrell locks. This study not only contributes to the clarification of the strengthening and deformation mechanism of double heterogeneous structure alloys but also provides an effective strategy for the development of high-performance alloys with high strength and ductility. 

Double heterogeneous structures induced excellent strength-ductility synergy in Ni40Co30Cr20Al5Ti5 medium-entropy alloy

High- and medium-entropy alloys (HEAs/MEAs), also called as multicomponent alloys, are a new class of materials that break through the traditional alloy design concept based on single principal element. However, they do not break away from the magic spell of strength–ductility trade-off. Therefore, designing HEAs/MEAs with both high strength and high ductility still remains a great challenge nowadays. This article provides a review on the recent progress in mechanical properties of face-centered cubic (FCC) HEAs/MEAs. First, several traditional strengthening strategies are briefly reviewed, focusing on the strengthening mechanisms and the optimized mechanical properties. Subsequently, various novel strategies for achieving strength–ductility synergy in HEAs/MEAs are summarized, which include lowering the stacking fault energy, regulating the short-range order, promoting transformation-induced plasticity, and constructing heterogeneous microstructures. The basic ideas and related underlying mechanisms from these strategies are discussed. Finally, the current challenges and the future outlooks are emphasized and addressed systematically. In brief, the present review is expected to provide a useful guide for the design of HEAs/MEAs with superior mechanical properties. 

Strategies for achieving strength‐ductility synergy in FCC high‐ and medium‐entropy alloys

High-density dislocations and nano-twinning are known to significantly influence the work hardening ability of materials, presenting a potent approach for enhancing their overall strength. Here, a superior tensile strength-ductility synergy in a FeCoCrNiMo0.2 high entropy alloy (HEA) with high density dislocation and nano-twinning was achieved by employing cryo-rolling followed by subsequent annealing. Through electron microscope observation, the effects of geometrically necessary dislocation density and nano-twinning on tensile strength and plasticity are elucidated. The microstructure analysis reveals a substantial presence of dislocations and nano-twinning within the deformed grains following short-time annealing at 600 °C and 800 °C. The strategic presence of nano-twins serves as effective impediments to dislocation slip, resulting in the storage of dislocations within the grains, which contributes to the alloy's superior strength-ductility synergy and remarkable work hardening ability. Impressively, the obtained tensile strength-ductility matching exhibits yield strength and ductility values of 992.1 MPa/0.19 and 719 MPa/0.39, respectively. Upon increasing the annealing temperature to 1000 °C, high-density annealing twins emerge in the recrystallized grains, accompanied by a concomitant reduction in the geometrically necessary dislocation density due to dislocation rearrangement and annihilation. Furthermore, a small amount of topological close-packed (TCP) phase and L12 phase precipitation during annealing are observed, contributing to increased work hardening ability of the alloy. The findings underscore the importance of microstructural engineering as a valuable strategy for optimizing the mechanical properties of HEAs with a face-centered cubic structure. 

Achieving excellent strength-ductility synergy via high density dislocation and nano-twinning in cryo-rolled FeCoCrNiMo0.2 high-entropy alloy

We describe the development of a non-equiatomic CoCrFeNi 2 Al 0.3 Ti 0.25 high entropy alloy (HEA). Both high-density nano-lamellar precipitates and ultrafine grain structure are simultaneously introduced by cold rolling then annealing at 600–800 ° C for 1 h. The HEA annealing at 700 ° C (CR-700) exhibits ultra-high yield strength ( σ y ) of 1900 ± 15 MPa, ultimate tensile stress of 2074 ± 17 MPa and excellent total elongation ( ε t e ) of 16.7 ± 1.5. This succeeds in overcoming the strength-ductility trade-off that often hampers the development of high-performance alloys. Compared with the as-cast alloy, σ y of the CR-700 HEA increases by 171% and ε t e decreases by 54%. The ultra-high strength is mainly attributed to the synergistic strengthening effects of both nano-lamellar precipitates and ultrafine grains. The high coherent FCC/L1 2 interface facilitates the transmission of dislocations, which eliminates the stress concentration during deformation and effectively maintains uniform deformation. Meanwhile, high-density stacking faults and Lomer-Cottrell locks are formed during the deformation process. These promote the multiplication of dislocations and further improves the work-hardening ability. The combination of high-density nano-lamellar precipitates and ultrafine grain structure can potentially be applied to other conventional alloys. This work provides a new strategy for fabricating materials with ultra-high strength and excellent ductility. 

Ultra-high strength and excellent ductility high entropy alloy induced by nano-lamellar precipitates and ultrafine grain astructure

Effect of Silicon addition on the corrosion resistance of Al0.2CoCrFe1.5Ni high-entropy alloy in saline solution

Excellent strength-ductility combination in Co36Cr15Fe18Ni18Al8Ti4Mo1 multi-principal element alloys by dual-morphology B2 precipitates strengthening

A novel high-strength and high-ductility CoCrNi medium entropy alloy by Ti/Mo co-doping

A never-ending challenge for materials scientists is to design alloys with excellent strength-ductility combinations. Here, a systematic study on B2 precipitation and mechanical behaviors of a high Co and Al content high entropy alloy (HEA) annealed at 700–1000 °C was investigated. The alloy annealed at 700 °C (denoted as A700) exhibited a high yield strength of 1820 ± 22 MPa and an ultimate tensile strength of 1884 ± 21 MPa, which can be mainly attributed to the dislocation, ultra-fine grain and B2-strengthening. With the annealed temperature increasing to 900 °C (denoted as A900), the FCC matrix has been full-recrystallized, and the grain size of FCC matrix increases from 0.21 μm to 2.8 μm. The volume fraction of the B2 phase decreases slightly from 58% to 53%. As a result, the A900 alloy displays a yield strength of 1038 ± 17 MPa and tensile ductility of 28 ± 2.3%. The deformation and strengthening mechanisms are investigated by microstructural characterization and theoretical calculations. This work will provide a basis for the composition and structural design of B2-strengthened HEAs. 

Investigating the strengthening and deformation behavior of B2-strengthened high entropy alloys with high Co and Al contents

High-pressure and high-temperature induced densely discontinuous nanoprecipitates in multi-principle element alloy

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