Influence of severe straining and strain rate on the evolution of dislocation structures during micro-/nanoindentation in high entropy lamellar eutectics. (October 2018)

• Record Type: Journal Article
• Authors: Maity, T.; Prashanth, K.G.; Balcı, Ö.; Kim, J.T.; Schöberl, T.; Wang, Z.; Eckert, J.
• Is Part Of: International journal of plasticity. Volume 109(2018:Oct.)
• Page Start: 121
• Page End: 136
• Publication Date: 2018-10
• Subjects: Eutectic high entropy alloys -- Strengthening mechanism -- Deformation mechanism -- Dislocations -- Plasticity -- Micro-/nanoindentation; Plasticity -- Periodicals; Plasticité -- Périodiques; Plasticity; Periodicals; 620.11233
• DOI: 10.1016/j.ijplas.2018.05.012
• Languages: English
• ISSNs: 0749-6419

Abstract

Abstract: Eutectic high entropy composites (EHECs) can exhibit an excellent combination of high strength and high ductility; however, the mechanisms responsible for the strength-ductility trade-off remain unpredicted. The influence of strain rate ( ε ˙ ) on the severe deformation imposed by high-pressure torsion (HPT) was used to evaluate the deformation mechanisms for a series of CoCrFeNiNb x ( x molar ratio, 0 ≤ x ≤ 0.80) EHECs. Systematic and detailed micro-/nanoindentation investigations were performed and the results suggest that strain hardening (Taylor hardening) and grain-boundary strengthening ( H-P strengthening) are the predominant strengthening mechanisms. Nanoindentation at different loading conditions (varying ε ˙ ) revealed that the measured hardness in the eutectic regime increases gradually because of dislocation-lamellae-interface interactions. Based on the deformation mechanisms operating at different strain rates ( ε ˙ ), the density of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs), determined by the Nix-Gao approach, are used to explain the strain hardening phenomena. The results reveal that a large volume fraction of lamellae-interfaces accommodate more dislocations upon straining these EHECs. Lamellae-interface GNDs ( ρ G G ) are activated at higher strain rates and can be effectively stored, thereby improving the global strain and strain hardening. Highlights: Study the deformation mechanism of high entropy lamellar eutectic composites using micro-/nanoindentation studies. Hardness increase due to dislocation-lamellae-interface (L-I) interactions. Large volume fraction of L-I interfaces accommodates more dislocations upon straining the eutectic high entropy composites. Lamellae-interface GNDs ( ρ G G ) are activated at higher strain rates, hence improving the global strain and strain hardening.