The predicted rate-dependent deformation behaviour and multistage strain hardening in a model heterostructured body-centered cubic high entropy alloy. (October 2021)

• Record Type: Journal Article
• Authors: Peng, Jing; Li, Li; Li, Fang; Liu, Bin; Zherebtsov, Sergey; Fang, Qihong; Li, Jia; Stepanov, Nikita; Liu, Yong; Liu, Feng; Liaw, Peter K
• Is Part Of: International journal of plasticity. Volume 145(2021)
• Publication Date: 2021-10
• Subjects: High-entropy alloy -- Multistage strengthening mechanism -- Multiple phase transformation -- Strain rate -- Constitutive model; Plasticity -- Periodicals; Plasticité -- Périodiques; Plasticity; Periodicals; 620.11233
• DOI: 10.1016/j.ijplas.2021.103073
• Languages: English
• ISSNs: 0749-6419

Abstract

Highlights: Rate-dependent deformation behaviour of the heterostructured BCC HEA is for the first time investigated at atomic scale. A large number of edge dislocations generated are extremely different from screw dislocations invariably observed in traditional BCC alloys. The microstructure-based constitutive model with a single parameter set is established in heterostructured BCC HEA. The effects of multistage strengthening mechanisms on strength and strain hardening are quantitatively determined. Abstract: Heterostructured high-entropy alloys (HEAs) exhibit a good combination of strength and ductility. However, the deformation mechanisms and related mechanical properties of the heterogeneous nanostructured body-centred cubic (BCC) HEAs remain largely unrevealed. Here, we report the effect of the strain rate on the mechanical properties and microstructural evolution in the heterostructured Al3 CoCrCuFeNi HEA with the gradient grain size ranging from 9 nm at the surface to 45 nm in the center using the large-scale atomic simulations. Based on the characterization of microstructure evolution from the atomic simulation, a microstructure-based constitutive model that utilizes a single parameter set is established to study the effects of the multiple strengthening mechanisms at various deformation stages on the strength and strain hardening of the heterostructured HEA under different strain rates. The results show that the plastic deformation mechanisms are strongly influenced by the strain rate in the range of 1 × 10 6 to 1 × 10 10 s −1 . The dislocation and deformation twin are the main deformation mechanisms at the strain rate less than 1 × 10 8 s −1 . The deformation twinning cooperated with multiple phase transformations plays a pivotal role at the strain rate of 1 × 10 9 s −1 . The multiple phase transformations are the dominant plastic deformation model at the strain rate of 1 × 10 10 s −1, which is different from the classic plastic-deformation mode, including the dislocation and deformation twin in traditional alloys. This phenomenon is ascribed to various types of atomic interactions and atomic-size mismatches, which produce strong lattice distortion. In particular, a large number of edge dislocations are observed, which is extremely different from screw dislocations invariably generated in traditional BCC alloys, and thus, could be responsible for high strength. Furthermore, the stress-strain response of the Al3 CoCrCuFeNi HEA is derived from the individual contributions of the lattice distortion, dislocation, grain boundary, deformation twin, phase transformation, and back-stress strengthening mechanisms. The heterogeneous grain boundaries and lattice distortion contribute the most to the yield strength, and the dislocation, deformation twin, phase transformation, and back stress dominate the strain hardening. Therefore, these results highlight a new design strategy of HEAs to tailor their mechanical properties based on the partition of the multistage strengthening mechanisms by the heterostructure. Graphical abstract: Image, graphical abstract