Extremely high strength and work hardening ability in a metastable high entropy alloy

Abstract

Design of multi-phase high entropy alloys uses metastability of phases to tune the strain accommodation by favoring transformation and/or twinning during deformation. Inspired by this, here we present Si containing dual phase Fe42Mn28Co10Cr15Si5 high entropy alloy (DP-5Si-HEA) exhibiting very high strength (1.15 GPa) and work hardening (WH) ability. The addition of Si in DP-5Si-HEA decreased the stability of f.c.c. (γ) matrix thereby promoting pronounced transformation induced plastic deformation in both as-cast and grain refined DP-5Si-HEAs. Higher yet sustained WH ability in fine grained DP-5Si-HEA is associated with the uniform strain partitioning among the metastable γ phase and resultant h.c.p. (ε) phase thereby resulting in total elongation of 12%. Hence, design of dual phase HEAs for improved strength and work hardenability can be attained by tuning the metastability of γ matrix through proper choice of alloy chemistry from the abundant compositional space of HEAs.

Metastability-assisted fatigue behavior in a friction stir processed dual-phase high entropy alloy

“…Thus, the present work is focused on examining fatigue behavior of the metastable DP-5Si-HEA under constant stress cycles. As reported in our recent work [19], multi-pass FSP on the same HEA system showed very high YS and near ultrafine microstructure. Stresscontrolled, fully reversible bending fatigue tests were performed for the same processing condition.…”

“…Figure 1(a) shows an electron backscatter diffraction (EBSD) inverse pole figure (IPF) map for the nugget region after FSP, where a fully recrystallized microstructure with an average grain size of 1.97 ± 1.03 µm was obtained by multi-pass FSP. Multiple passes promote not only chemical homogeneity but also adaptive phase stability [4,19] while the consecutive decrease in tool rotation rate leads to severe refinement of grains leading to homogenous very fine grained microstructure. Accordingly, multi-pass of DP-5 Si-HEA resulted in very fine grained microstructure with almost ∼ 96% f.c.c.…”

“…Further, the addition of Si in Fe 42 Mn 28 Cr 15 Co 10 Si 5 (DP-5Si-HEA) altered the γ phase stability and assisted in grain refinement during FSP (to an average grain size of ∼ 1.97 µm from as-cast grain average grain size of ∼ 100 µm). As a result, YS of DP-5Si-HEA was observed to be exceptionally high (950 MPa) with an ultimate tensile strength (UTS) of 1.15 GPa [19]. These enhanced mechanical properties were attributed to the exceptional work hardening ability of the material through controlled transformation and twinning-assisted deformation [19].…”

“…As a result, YS of DP-5Si-HEA was observed to be exceptionally high (950 MPa) with an ultimate tensile strength (UTS) of 1.15 GPa [19]. These enhanced mechanical properties were attributed to the exceptional work hardening ability of the material through controlled transformation and twinning-assisted deformation [19]. Adaptive deformation accommodation is a result of extreme metastability of the γ matrix attained by adding Si [19].…”

“…These enhanced mechanical properties were attributed to the exceptional work hardening ability of the material through controlled transformation and twinning-assisted deformation [19]. Adaptive deformation accommodation is a result of extreme metastability of the γ matrix attained by adding Si [19]. Hence, whether the flexible microstructural evolution that resulted from metastability-based phase stability in DP-5Si-HEA is beneficial for improving fatigue crack resistance is indeed worth exploring.…”