Strength-ductility synergy and superior strain-hardening ability of Ni38Co25Fe13Cr10Al7Ti7 multi principal element alloy through heterogeneous L12 structure modulation

In this paper, heterogeneous L12 particles were successfully introduced into Ni38Co25Fe13Cr10Al7Ti7 MPEA by two-stage aging treatment. Compared with the homogeneous particles, the heterogeneous L12 particles strengthened alloy exhibits enhanced strength-plasticity synergy. The tensile elongation is 23.2%, which is higher than all samples with the homogeneous particles, and the yield strength remains at 942 MPa, which is equivalent to the micro particles (972 MPa) with the highest yield strength in the homogeneous particles. Further analysis of the strengthening and deformation mechanisms revealed that precipitation hardening, and heterogeneous deformation-induced hardening were the main factors for the enhanced strength. The deformation-induced layered fracture networks, high-density Lomo-Cottrell locks, and heterogeneous L12 particles microstructure characteristics significantly improve the strain hardening ability; GNDs accumulate at the heterogeneous interface to alleviate the stress concentration at the GBs and improve the tensile plasticity of the MPEA with heterogeneous L12 particle structure. The heterogeneous L12 particle structure obtained through two-stage aging treatment without severe mechanical deformation has attractive engineering application potential. These properties of Ni38Co25Fe13Cr10Al7Ti7 MPEA with heterogeneous L12 particle structure have important enlightening and practical value.