Charpy impact behavior and fracture mechanisms in cost-effective ferrous medium-entropy alloy at ambient and cryogenic temperatures

Abstract

The cost-effective ferrous medium-entropy alloys (MEAs) exhibit excellent quasi-static tensile property especially at cryogenic temperature, whereas their impact property under high loading rate is still unclear. In this work, the tensile and Charpy impact behaviors of Fe₆₂Co₅Ni₁₀Cr₁₃Si₇Al₃ (at. %) ferrous MEA have been thoroughly investigated at 298 K and 77 K, respectively. The tensile mechanical response shows that as the temperature decrease from 298 K to 77 K, the prepared ferrous MEA comprising 86 vol% face-centered cubic (FCC) phase and 14 vol% body-centered cubic (BCC) phase shows significantly improved yield strength from 986 MPa to 1252 MPa and tensile strength from 1186 MPa to 2016 MPa, along with a comparable ductility. While outstanding combination of impact toughness and yield strength outperforms most other metallic materials, it is undeniable that the impact absorbed energy sharply decrease from 95.5 J at 298 K to 32.2 J at 77 K. The substantial reduced plastic zone ahead of crack tip coupled with the transition of micro-fracture mechanism from ductile dimples to a mixture of dimples and cleavages, which is not conducive to energy consumption during crack propagation, is responsible for the reduced impact toughness.