Carbon Doped Co40Cr20Ni20Fe10Mn10 High Entropy Alloy: Microstructure and Mechanical Properties
摘要
The Co-rich Co40Cr20Ni20Fe10Mn10 high-entropy alloy (HEA) offers superior properties over the equiatomic CoCrFeMnNi (Cantor) alloy; however, its relatively low yield strength constrains its structural applications. This study investigates the influence of minor carbon additions (0.5 at.%) on the microstructure and mechanical properties of this alloy system. Nominal Co40Cr20Ni20Fe10Mn10 (C-free) and Co39.5Cr20Ni20Fe10Mn10C0.5 (C-doped) HEAs were synthesized via vacuum arc remelting (VAR), homogenized at 1200 °C for 5 h, cold-rolled with a 77% thickness reduction, and subsequently annealed at 1000 °C for 90 min to achieve recrystallization and grain refinement. The alloys were characterized using X-ray diffraction (XRD), optical microscopy (OM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and uniaxial tensile testing. Post-homogenization, both alloys exhibited a single-phase face-centered cubic (FCC) structure; however, the C-doped alloy additionally contained M23C6 carbide precipitates. Carbon addition induced pronounced grain refinement (10.9 μm vs. 48.9 μm), and significantly improved yield strength (395 MPa vs. 230 MPa) and ultimate tensile strength (907 MPa vs. 687 MPa), albeit with reduced ductility (66% vs. 92%). The strength enhancement was attributed to grain boundary pinning, Orowan strengthening, and reduced stacking fault energy and increased stacking fault probability (2.7 × 10–2 vs. 1.55 × 10–2), promoting mechanical twinning. These findings demonstrate that interstitial carbon doping, in combination with Co enrichment, effectively tailors the microstructure and achieves a superior strength–ductility synergy in Co-rich HEAs, positioning them as promising candidates surpassing Cantor-based alloys for advanced structural applications.