Enhanced dynamic deformability and strengthening effect via twinning and microbanding in high density NiCoFeCrMoW high-entropy alloys

Abstract

High density alloys with enhanced deformability and strength are urgently required in energy, military and nuclear industries, etc. In this work, we present a new kind of NiCoFeCrMoW high entropy alloys (HEAs) which possess higher densities and sound velocities than copper. We systematically investigate the phase structure, quasi-static tensile, dynamic compression and related deformation mechanism of these HEAs. It is shown that single FCC or FCC + μ dual phases were formed in the HEAs depending on Mo and W content and annealing temperature. Excellent quasi-static tensile and dynamic compression properties have been achieved for these HEAs, e. g. Ni30Co30Fe21Cr10W9 HEA annealed at 1573 K exhibited a yield and ultimate tensile strength and elongation of ∼364 MPa, ∼866 MPa and ∼32%, respectively, in quasi-static test; a yield strength of ∼710 MPa and no fracture under the dynamic strain rate of 4100 s−1. Superior strain rate sensitivity (SRS) of yield strength than that of previously reported FCC HEAs have been evidenced. The dynamic stress-strain constitutive relation can be described by the modified Johnson-Cook model. As for the dynamic deformation mechanism, it is envisaged that the regulation of stacking fault energy and Peierls barrier in current HEAs resulted in occurrences of abundant nanoscale deformation twins and microbands during high strain rate compression. The synergistic microbanding and twinning effectively contributes to the enhanced dynamic deformability and strengthening effect. Besides, the interactions of dislocations with precipitates, stacking faults (SFs) with twins, and between SFs also contribute to extraordinary work-hardening capacity.