Substitutional effects of Al and Mn on the microstructure and mechanical response of Cantor-derived high-entropy alloys for nuclear structural applications

Abstract

As global energy demands rise, nuclear energy offers a clean and sustainable solution, albeit with safety concerns. Designing next-generation nuclear reactors requires advanced materials with stringent properties, and Cantor-derived high-entropy alloys (HEAs) recently emerged as promising alternatives to conventional nuclear structural-alloys. Among these, Al_0.3CoCrFeNi is widely studied but is metastable, posing challenges for nuclear applications where stable and low void swelling single-phase FCC-alloys are preferred. Guided by empirical parameters and CALPHAD, we design and develop a novel Cantor-derived FCC-stable Mn_0.3CoCrFeNi HEA as a potential substitute for Al_0.3CoCrFeNi. The microstructure and mechanical behaviors of Al_0.3CoCrFeNi and Mn_0.3CoCrFeNi under uniaxial quasi-static and dynamic strain-rates were evaluated in three processing conditions—as-cast (AC), homogenized and cold-rolled (CR), and homogenized, cold-rolled and annealed (CRA)—as a first experimental installment towards Mn_0.3CoCrFeNi candidacy. AC-Mn_0.3CoCrFeNi exhibits unique “casting twin boundaries” and suppressed cell-structure. While the hardness and yield strength of the AC and CRA samples for both alloys are comparable, those of CR-Mn_0.3CoCrFeNi surpasses CR-Al_0.3CoCrFeNi due to higher prior-deformation twins and dislocation density in the former. Unique Type A serration-dynamic strain aging (DSA) is observed in AC and CRA-samples of both HEAs under room temperature/low strain-rate conditions, and it delays instability onset. Meanwhile, DSA suppression in CR samples and those under high strain-rates are attributed to increased dislocation-dislocation and phonon drag-dislocation interactions, respectively. Additionally, Mn_0.3CoCrFeNi demonstrates a superior strain-hardening rate under all conditions due to Mn_0.3CoCrFeNi's lower stacking fault energy and critical twinning stress. These findings establish Mn_0.3CoCrFeNi as a mechanically-superior candidate for nuclear structural applications.