Load Partitioning and Strain Compatibility in a Non-Equiatomic Dual-Phase AlCoCrFeNi High-Entropy Alloy Processed by Forging

The tensile and compressive behavior of hot-forged Al5Co35Cr30Fe20Ni5 high-entropy alloy (HEA) has been studied at room temperature. The forged HEA has a dual-phase microstructure consisting of a predominant face-centered cubic (FCC) matrix and a body-centered cubic (BCC) phase. The BCC phase embeds a low volume fraction of ordered BCC nanoparticles (B2 structure). During forging, the BCC phase recrystallizes more easily than the FCC phase. Yielding is controlled by the deformation of the FCC phase, although BCC grains assume an additional part of the load transferred by FCC grains, even during the elastic regime. During the onset of plastic deformation, slip is activated preferentially in the FCC phase in those grains that are favorably oriented for slip in planes (111). Dislocation pile-ups at FCC/BCC interfaces induce dislocation slip in the BCC phase. In the BCC phase, B2 particles act as effective obstacles to dislocation motion through the Orowan mechanism. As the deformation proceeds, dislocation activity causes an increase in the misorientation in both phases, resulting in the formation of subgrains whose boundaries are effective for blocking dislocation motion. The combination of high strength and ductility arises from the dual-phase FCC–BCC microstructure of the alloy. The load borne by the BCC phase partially relieves the stress applied to the FCC matrix, enabling the latter to continue deforming.