Hetero-deformation promoted strengthening and toughening in BCC rich eutectic and near eutectic high entropy alloys

Heterostructured eutectic high-entropy alloys(EHEAs)have attracted significant attention owing to their novel properties,such as balanced combinations of strength and fracture toughness.However,the toughening/strengthening mechanisms of these EHEAs have not been thoroughly investigated.In this study,we developed a series of dual-phase Al_((18–2x))Co_(30)Cr_((11+x))Fe_((11+x))Ni_(3)0(x=-1,0,1)eutectic and neareutectic HEAs containing face-centered cubic(FCC)and body-centered cubic(BCC)phases.Despite the high amount of BCC,which is referred to as the brittle phase,newly developed EHEAs exhibited superior fracture toughness.Interestingly,we discovered that a fully eutectic HEA exhibited further improvements in both yield stress and fracture toughness,outperforming our off-eutectic and other previously reported HEAs.By combining experiments and theoretical models,we demonstrated that the synergistic increase in both strength and toughness in our fully eutectic HEA was derived from the high hetero-deformationinduced(HDI)strengthening/toughening associated with a high misorientation angle at the grain/phase boundaries.

Coherent interface driven super-plastic elongation of brittle intermetallic nano-fibers at room temperature

The intermetallic compound such as Ni_(2)Si has a brittle nature.Therefore,monolithic intermetallic compounds have not yet been prepared by mechanical downsizing.During mechanical drawing of bulk CuNi_(2)Si alloy at room temperature,we observed more than 400%plastic elongation of hard and brittle Ni_(2)Si intermetallic nano-fibers.The calculation based on the density functional theory reveals that the fully coherent interface induces strain on the intermetallic compound surrounded by the matrix,and lowers the intrinsic stacking fault energy below the level required to break an interatomic bond.The new interface between the Ni_(2)Si intermetallic and Cu matrix formed by the plastic deformation is as stable as the original coherent interface formed by precipitation,and the activation energy of the newly formed interface to slip is similar to that of the Cu matrix.All of these make plastic deformation of brittle Ni_(2)Si intermetallic possible by slip without failure.