Inhomogeneity of negative enthalpy enables excellent mechanical properties in nanosized single crystals of multi-principal element alloys

Abstract

Many nanosized metals with limited dislocation nucleation and multiplication usually exhibit poor plasticity. Previous studies have demonstrated that multi-principal element alloys (MPEAs) can achieve a combination of strength and plasticity. However, whether these mechanical properties extend to their nanosized counterparts and how nanosized MPEAs accommodate plastic deformation remains unknown. Using a homemade in-situ device, we captured the atomic-scale tensile process and measured the stress-strain curve of Fe 48 Mn 32 Co 10 Cr 10 nanosized single crystals (NSCs). We find that NSCs achieve a strength of ~3 GPa and a uniform elongation of ~20%. We show that this combination arises from the inhomogeneous distribution of enthalpy, which produces a broad spectrum of energy barriers for the nucleation of full dislocations, partial dislocations, and nanotwins. Consequently, dislocations and nanotwins are randomly generated throughout MPEA NSCs, effectively suppressing local stress concentration and leading to both high strength and large uniform elongation.