High strength and deformation stability achieved in CrCoNi alloy containing deformable oxides

Abstract

• The spreading lattice distortion in CrCoNi-O high entropy solution locally relieved the severe interfacial mismatch and led to nanoscale variation of interfacial strain at the matrix-oxide interface. • Dislocations slip transferred from solid solution phase to ceramic phase, enabling the ceramic phase with significant deformability. • The yield strength of the dual-phase samples was twice of the single-phase CrCoNi-O alloy; strong strain hardening was obtained with ultra-high deformation stability, whereas the single-phase CrCoNi-O sample exhibited catastrophic shear localization. Hard secondary phases usually strengthen alloys at the expense of ductility. In this work, we made a dual-phase CrCoNi-O alloy containing a face centered cubic matrix and chromium oxide. On one side, the dispersed chromium oxide nano-particles impeded dislocation movement and increased the strength of the alloy. On another side, the spreading lattice distortion in CrCoNi-O high entropy solution locally relieved the severe interfacial mismatch and led to nanoscale variation of interfacial strain at the matrix-oxide interface, which facilitated dislocations’ transmission from one phase to another. Consequently, unlike the strong but brittle oxide nanoparticles used before, the oxide phase here can afford significant dislocation activities during material's plastic deformation. Comparing the mechanical properties of CrCoNi-O alloys with and without chromium oxide particles, it was found that the yield strength of the dual-phase samples was twice of the single phase CrCoNi-O alloy and strong strain hardening was obtained with ultra-high deformation stability. High density of nanotwins formed in dual-phase samples under high stress, resulting in significant strain hardening according to the well-known twinning-induced plasticity (TWIP) effect. Our results shed light on optimizing the combination of strength and plasticity of compounds by modulating the variation of interfacial strain field based on the spreading lattice distortion.