Mo triggered TWIP/TRIP effect synergistically improves mechanical properties of Co35Cr25Fe20Ni20

Abstract

In this study, the strength-ductility paradox of high-entropy alloys was overcome by modulating the twin-induced plasticity (TWIP)/phase-transformation-induced plasticity (TRIP) effect through Mo atoms, while ensuring that it remains the single solid solution phase. With the increase of Mo atoms leads to a reduction in grain size, the reduction from 11.05 μm for Mo0 to 7.15 μm for Mo5 exhibits obvious grain refinement effect. Meanwhile, the addition of Mo improves the mechanical properties, from Mo0 yield strength of 326 MPa, tensile strength of 751 MPa, to Mo5 yield strength of 547 MPa, tensile strength of 998 MPa, maintains an elongation of 55 %. The formation of deformation twins (DTs) and hexagonal close-packed (hcp) phases improves not only the strength but also the work-hardening capacity. At the same time, these structures also ensured ductility with the help of TWIP and TRIP effects. Molecular dynamics simulations revealed that the formation of the hcp phase is associated with intrinsic stacking faults (ISFs) and DTs. The interlocking of ISFs and the appearance of DTs provide nucleation sites for the formation of hcp. Besides, the addition of Mo facilitates the charge redistribution of the matrix alloy, enhancing the overall Bader charge transfer. This explained that Mo can result in local lattice distortion, which is one of the important factors for the strength enhancement of Mo atoms. At the same time, this charge redistribution inevitably affects the chemical short-range ordered (CSRO) structure. The Warren-Cowley parameters confirmed that Mo increases MoCo, MoFe, and MoNi clusters, and more chemical short-range structures enhanced the stacking faults energy (SFE), it favours the generation of deformation twins.