Leveraging a coarse yet strong matrix in L12-strengthened high-entropy alloy through simplified thermomechanical processing

Abstract

High-entropy alloys (HEAs), characterized by their unique design concept without a distinct major element, offer a versatile alloy design window while ensuring outstanding properties. In this study, the FeCoCrNi–AlTi alloy system, which exploits L12 phase with slow ripening kinetics due to the coherent interface with the FCC phase, has been researched to increase strength via precipitation. This system has been widely studied to improve mechanical properties through microstructure optimization, especially in a direction that suppresses discontinuous precipitation while enhancing strength. Herein, we propose a novel processing method utilizing hot-rolling followed by direct aging for a newly designed (FeCoNi)79.5Cr10.5Al5Ti5 (at%) HEA. The coarse yet strong FCC matrix, generated via hot-rolling, proves advantageous in the subsequent direct aging, as revealed through careful microstructural characterization of both continuous and discontinuous precipitates. A high yield strength of 1065.5 ± 0.4 MPa, a uniform elongation of 14.2 ± 0.0%, and a total elongation of 27.5 ± 0.9% are simultaneously achieved, due to maintaining high dislocation density and promoting continuous precipitation, whereas discontinuous precipitation is suppressed and occupies little area fraction of ∼8%. Careful discussions are provided regarding the impact of the newly proposed processing on the precipitation mechanism, and how the resulting microstructure influences the strengthening mechanisms. This work demonstrates the effectiveness of a simplified thermomechanical process, providing valuable insights into microstructure control in HEAs.