Hierarchical eutectoid nano-lamellar decomposition in an Al0.3CoFeNi complex concentrated alloys

Sriswaroop Dasari (1) , Bharat Gwalani (2) , Abhinav Jagetia (1) , Vishal Soni (1) , Stéphane Gorsse (3) , Rajarshi Banerjee (1)

1 Advanced Materials and Manufacturing Processes Institute
2 Physical and Computational Sciences Directorate
3 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux

This paper reports a novel eutectoid nano-lamellar (FCC + L12)/(BCC + B2) microstructure that has been discovered in a relatively simple Al0.3CoFeNi high entropy alloy (HEA) or complex concentrated alloy (CCA). This novel eutectoid nano-lamellar microstructure presumably results from the complex interplay between Al-mediated lattice distortion (due to its larger atomic radius) in a face-centered cubic (FCC) CoFeNi solid solution, and a chemical ordering tendency leading to precipitation of ordered phases such as L12 and B2. This eutectoid microstructure is a result of solid-state decomposition of the FCC matrix and therefore distinct from the commonly reported eutectic microstructure in HEAs which results from solidification. This novel nano-lamellar microstructure exhibits a tensile yield strength of 1074 MPa with a reasonable ductility of 8%. The same alloy can be tuned to form a more damage-tolerant FCC + B2 microstructure, retaining high tensile yield stress (~900 MPa) with appreciable tensile ductility (>20%), via annealing at 700 °C. Such tunability of microstructures with dramatically different mechanical properties can be effectively engineered in the same CCA, by exploiting the complex interplay between ordering tendencies and lattice distortion.

Domaines: Matériaux

Sriswaroop Dasari, Bharat Gwalani, Abhinav Jagetia, Vishal Soni, Stéphane Gorsse, et al.. Hierarchical eutectoid nano-lamellar decomposition in an Al0.3CoFeNi complex concentrated alloys. Scientific Reports, 2020, 10, 4836 (15 p.). ⟨10.1038/s41598-020-61538-6⟩. ⟨hal-02558742⟩