On the deformation behavior of CoCrNi medium entropy alloys: Unraveling mechanistic competition

• Published in: International journal of plasticity Vol. 159; p. 103442
• Main Authors: Gupta, Ankit, Jian, Wu-Rong, Xu, Shuozhi, Beyerlein, Irene J., Tucker, Garritt J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2022
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2022.103442

•Role of deformation mechanisms is resolved from the amount of strain accommodation.•Partial dislocation slip is the dominant intragranular mechanism during initial loading.•Twinning and perfect slip should be the dominant mechanism under continued loading.•Tensile simulations suggest twinning to be more pronounced with short-range ordering.•Maximum strength occurs at a smaller grain size in the structure with short-range ordering. Recently, CoCrNi medium entropy alloys (MEA) have been the subject of numerous investigations due to their unique mechanical properties such as an exceptionally high strength-ductility combination. The resulting superior toughness of CoCrNi MEAs is attributed to an interplay of multiple deformation mechanisms, such as twinning, and partial and perfect dislocation glide. The current understanding of MEA deformation mostly stems from an indirect analysis of the defect evolution in deformed microstructures, where the contributions of individual mechanisms are assessed from the relative concentrations of associated defect structures. Here, we propose that the mechanistic contributions to microstructural deformation are more properly reflected by the percentages of total strain accommodation. Using atomistic simulations, the mechanical response of nanocrystalline CoCrNi MEA under uniaxial tension is investigated as function of grain size and chemical short-range ordering (SRO). The contributions of deformation mechanisms are resolved directly from the amount of strain accommodation by leveraging continuum based kinematic metrics. It is found that during initial loading, deformation occurs by partial dislocation slip, in agreement with experimental observations. Under continued loading, the governing deformation mechanisms transition to twinning and perfect dislocation slip. Furthermore, the grain size that corresponds to the maximum strength is found to decrease in presence of SRO. [Display omitted]