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-entropyalloy (HEA) has been studied at room temperature. The forged HEA has a dual-phasemicrostructure consisting of a predominant face-centered cubic (FCC) matrix and a bodycenteredcubic (BCC) phase. The BCC phase embeds a low volume fraction of ordered BCCnanoparticles (B2 structure). During forging, the BCC phase recrystallizes more easily thanthe FCC phase. Yielding is controlled by the deformation of the FCC phase, although BCCgrains assume an additional part of the load transferred by FCC grains, even during theelastic regime. During the onset of plastic deformation, slip is activated preferentially in theFCC phase in those grains that are favorably oriented for slip in planes (111). Dislocationpile-ups at FCC/BCC interfaces induce dislocation slip in the BCC phase. In the BCCphase, B2 particles act as effective obstacles to dislocation motion through the Orowanmechanism. As the deformation proceeds, dislocation activity causes an increase in themisorientation in both phases, resulting in the formation of subgrains whose boundaries areeffective for blocking dislocation motion. The combination of high strength and ductilityarises from the dual-phase FCC–BCC microstructure of the alloy. The load borne by theBCC phase partially relieves the stress applied to the FCC matrix, enabling the latter tocontinue deforming.