Dual heterogeneous structures lead to ultrahigh strength and uniform ductility in a Co-Cr-Ni medium-entropy alloy

Abstract

Alloys with ultra-high strength and sufficient ductility are highly desired for modern engineering applications but difficult to develop. Here we report that, by a careful controlling alloy composition, thermomechanical process, and microstructural feature, a Co-Cr-Ni-based medium-entropy alloy (MEA) with a dual heterogeneous structure of both matrix and precipitates can be designed to provide an ultra-high tensile strength of 2.2 GPa and uniform elongation of 13% at ambient temperature, properties that are much improved over their counterparts without the heterogeneous structure. Electron microscopy characterizations reveal that the dual heterogeneous structures are composed of a heterogeneous matrix with both coarse grains (10∼30 μm) and ultra-fine grains (0.5∼2 μm), together with heterogeneous L12-structured nanoprecipitates ranging from several to hundreds of nanometers. The heterogeneous L12 nanoprecipitates are fully coherent with the matrix, minimizing the elastic misfit strain of interfaces, relieving the stress concentration during deformation, and playing an active role in enhanced ductility.

In situ atomistic mechanisms of detwinning in nanocrystalline AuAg alloy

“…Particularly for those alloys containing more than three types of solution atoms, such as medium-entropy or highentropy alloys, the detwinning mechanism should be different from those observed in the current study and in pure metals. As shown in previous studies, there are noticeable fluctuations in the elemental distribution in medium-or high-entropy alloys [51,54,[56][57][58]. This local chemical ordering can cause the nucleation energy and dislocation motion pathways to vary between regions [59,60], which would affect the detwinning model.…”

Ultrahigh strength and ductility in newly developed materials with coherent nanolamellar architectures

“…Fourth, the fully recrystallized and uniform microstructure promotes the homogeneous deformation, leading to stable mechanical properties of the CNL alloy. This contrasts with non-uniform structured materials, which usually induce inhomogeneous deformation, resulting in large variations of mechanical properties 58 . In addition, the delicate composition design endows our materials with extra advantages compared with other existing ultrahigh-strength materials.…”

The Influence of Metastable Cellular Structure on Deformation Behavior in Laser Additively Manufactured 316L Stainless Steel

“…As expected, the dislocation structures are associated with variation of SFE due to the local chemical fluctuation in the MCS [11,15,25]. Burgers vector in red in Figure 7b indicates that the immobile stair-rod dislocations are generated via a 6 [121] + a 6 112 → a 6 011 , which are known as Lomer-Cottrell locks [50,51]. The Lomer-Cottrell lock is possible to enhance the strain hardening as the dislocation reactions [51].…”

“…Burgers vector in red in Figure 7b indicates that the immobile stair-rod dislocations are generated via [50,51]. The Lomer-Cottrell lock is possible to enhance the strain hardening as the dislocation reactions [51].…”