Role of Suzuki segregation and compositional complexity in governing plastic deformation of Co–Ni–Cr–Mo medium-entropy alloys

This study investigates the role of multi-element effects on the plastic deformation behavior of a Co–Ni–Cr–Mo medium-entropy alloy (SPRON510, hereafter CNCM) through direct comparison with a binary Co–35Ni alloy with comparable stacking fault energy (SFE). The configurational entropy of CNCM, including minor elements such as Fe, Nb, and Ti, is approximately 1.37R, classifying it as a medium-entropy, multi-principal element alloy. Thermodynamic modeling and X-ray diffraction (XRD) confirm that both alloys exhibit similarly low SFE values (∼12–17 mJ/m 2 ). Despite this similarity, their deformation behaviors differ markedly. CNCM shows continuous dislocation accumulation with rolling reduction, reaching 4.5 × 10 16 m -2 after 90% reduction, significantly higher than that of Co–35Ni. Transmission electron microscopy (TEM) reveals the formation of fine deformation twins in CNCM, whereas Co–35Ni develops coarser twins and pronounced deformation bands. Texture analysis shows that Co–35Ni undergoes a typical transition to the Brass orientation, while CNCM retains the Goss orientation up to high reductions, indicating delayed texture evolution. These differences cannot be explained by SFE alone but are primarily attributed to Suzuki-effect-related solute segregation and dislocation locking, together with strong solute–dislocation interactions, lattice distortion, and twin-related barriers. The results highlight the importance of multi-principal element effects in modifying defect behavior and deformation pathways, particularly in suppressing recovery and promoting dislocation storage during heavy cold rolling. This study provides new insights into the deformation mechanisms of MEAs/MPEAs and offers guidelines for designing advanced alloys with improved strength–ductility balance.