Amorphous Bands Induced by Low Temperature Tension in a Non-Equiatomic CrMnFeCoNi Alloy

Abstract

Single-phase face-centered cubic multi-principal-element alloys (fcc MPEAs) comprising transition metal elements Cr, Mn, Fe, Co or Ni generally show strong temperature dependence of stacking fault energy (SFE) of {111} planes, the lower temperature the lower SFE. Through uniaxial tension at low temperature, we fabricate a non-equiatomic Cr26Mn20Fe20Co20Ni14 alloy with nanoscale microstructures including stacking faults bands, nano-twins, hexagonal-close packed (hcp) phase bands and amorphous bands. These nanostructures are characterized with strain level in terms of formation and interactions, and their thermal stability are investigated by subsequent tempering. We highlight the formation of extensive nanoscale amorphous bands and their much higher thermal stability above 650 oC as compared with the thermal stability of nano-twins and hcp bands. Amorphous bands ensure non-equiatomic Cr26Mn20Fe20Co20Ni14 alloy with the enhanced strength and good ductility after high temperature tempering. Amorphous bands can plastically co-deform with matrix. The interfaces between amorphous band and fcc matrix provide not only strong barriers for dislocation motion, strengthening materials, but also natural sinks of dislocations, disrupting stress concentrations and delaying decohesion and fracture initiation. Our results demonstrate that engineering amorphous bands could be an efficient strategy in remaining enhanced mechanical properties of fcc MPEAs at high temperature.