Microstructural Evolution and Mechanical Properties of Non-Equiatomic (CoNi)74.66Cr17Fe8C0.34 High-Entropy Alloy.

You Sub Kim,Sun Ig Hong,E-Wen Huang,Jayant Jain,Takuro Kawasaki,Soo Yeol Lee,Hobyung Chae,Stefanus Harjo

doi:10.3390/ma15041312

Abstract

In this study, we manufactured a non-equiatomic (CoNi)74.66Cr17Fe8C0.34 high-entropy alloy (HEA) consisting of a single-phase face-centered-cubic structure. We applied in situ neutron diffraction coupled with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) to investigate its tensile properties, microstructural evolution, lattice strains and texture development, and the stacking fault energy. The non-equiatomic (CoNi)74.66Cr17Fe8C0.34 HEA revealed a good combination of strength and ductility in mechanical properties compared to the equiatomic CoNiCrFe HEA, due to both stable solid solution and precipitation-strengthened effects. The non-equiatomic stoichiometry resulted in not only a lower electronegativity mismatch, indicating a more stable state of solid solution, but also a higher stacking fault energy (SFE, ~50 mJ/m2) due to the higher amount of Ni and the lower amount of Cr. This higher SFE led to a more active motion of dislocations relative to mechanical twinning, resulting in severe lattice distortion near the grain boundaries and dislocation entanglement near the twin boundaries. The abrupt increase in the strain hardening rate (SHR) at the 1~3% strain during tensile deformation might be attributed to the unusual stress triaxiality in the {200} grain family. The current findings provide new perspectives for designing non-equiatomic HEAs.

Highlights

Multi-component alloys, called high-entropy alloys (HEAs) are composed of at least four elements and form a solid solution with a single-phase crystal structure [1,2,3,4,5]
The nonequiatomic (CoNi)74.66Cr17Fe8C0.34 exhibited a relatively higher ultimate tensile strength (UTS) and moderate ductility compared to the equiatomic CoNiCrFe and single-phase nonequiatomic FCC HEAs [36]
The strain hardening rate (SHR) of (CoNi)74.66Cr17Fe8C0.34 showed unusual behavior at the very early stage of deformation, such that the SHR suddenly dropped down to the strain of 1% and abruptly increased up to the strain of 3%, after which the SHR gradually decreased until fracture

Summary

Introduction

Multi-component alloys, called high-entropy alloys (HEAs) are composed of at least four elements and form a solid solution with a single-phase crystal structure [1,2,3,4,5]. HEAs play an important role as the second phase in the manufacturing of new alloys, since they improve strength-ductility synergy [6] These properties come from their lattice structure distortion, sluggish diffusion kinetics, the cocktail effect and the evolution of deformation twinning [3,7,8,9,10,11,12]. Many HEA researchers have demonstrated that the formation of HEAs is not highly dependent on the maximum configurational entropy via equiatomic ratios of elements They reported that entropy is not the most dominant factor in the strength of solid solution-strengthened HEAs [15,18,19]. These arguments led to more active research on non-equiatomic HEAs, compared to equiatomic HEAs [20]

Methods

Results

Discussion

Conclusion