Unveiling the precipitation behavior and mechanical properties of Co-free Ni47-Fe30Cr12Mn8Al Ti3 high-entropy alloys

Abstract

• Effects of Al on precipitation behavior and mechanical properties of Co-free Ni 47- x Fe 30 Cr 12 Mn 8 Al x Ti 3 ( x = 3, 5, and 7 at.%) HEAs were studied. • Al as a BCC stabilizer in the current alloy system inhibits the formation of η phase while improves the formation of B2-ordered phase. • The precipitation behavior of L1 2 precipitates is enhanced due to the decreased FCC/L1 2 lattice mismatch with increasing Al content. • The Ni 42 Fe 30 Cr 12 Mn 8 Al 5 Ti 3 HEA shows a better combination of a yield strength of 661 MPa and tensile ductility of 29.7%. • This work provides references foundation for the optimization design on compositions of precipitated Co-free HEAs with excellent performance. Precipitate hardening is considered as an effective method to strengthen High- and medium-entropy alloys (HEAs and MEAs), especially the recently developed Co-free HEAs/MEAs. In this work, a systematic study on precipitation and mechanical behaviors of a Co-free HEAs with dilute amount of Al addition, Ni 47- x Fe 30 Cr 12 Mn 8 Al x Ti 3 ( x = 2 at.%, 5 at.% and 7 at.%), is presented. Results shown that the Ni 45 Fe 30 Cr 12 Mn 8 Al 2 Ti 3 has a face-centered cubic (FCC) + L1 2 + η three-phased structure. With increasing Al content, the formation of η phase is inhibited, accompanying with an enhanced formation of B2 phase, and FCC + L1 2 + B2 three-phased structure is thus observed in alloys with x = 5 and 7. The constrained lattice mismatch between FCC matrix and L1 2 precipitates is decreased with increasing Al content, leading to an enhanced precipitation behavior of L1 2 phase. As a result of microstructural evolution, the mechanical properties of the aged HEAs changed: the Ni 42 Fe 30 Cr 12 Mn 8 Al 5 Ti 3 alloy exhibits a better combination of a yield strength of 661 MPa and tensile ductility of 29.7% as compared to the 2 at.% Al alloyed HEA; and addition of Al beyond 5 at.% results in an increase of strength with a large expense of ductility. We believe that the present work is helpful for developing high-performance Co-free HEAs/MEAs strengthened by nanoprecipitates via composition optimizing.