Dynamic tensile behavior and deformation mechanism of carbon interstitial Fe40Mn40Co10Cr10 high entropy alloy

Carbon interstitial solid solution strengthening is an effective strategy to simultaneously enhance the strength and ductility of face-centered cubic high entropy alloys (HEAs). However, majority of studies have confined to quasi-static condition. In this study, the dynamic and quasi-static tensile mechanical behaviors of Fe₄₀Mn₄₀Co₁₀Cr₁₀ and (Fe₄₀Mn₄₀Co₁₀Cr₁₀)_96.7C_3.3 HEAs were investigated at room temperature. The results show that high strain rate can significantly improve the strength of both Fe₄₀Mn₄₀Co₁₀Cr₁₀ and (Fe₄₀Mn₄₀Co₁₀Cr₁₀)_96.7C_3.3 HEAs. The yield strength of Fe₄₀Mn₄₀Co₁₀Cr₁₀ and (Fe₄₀Mn₄₀Co₁₀Cr₁₀)_96.7C_3.3 increases from 245 MPa and 437 MPa at strain rate of 1 × 10⁻³ s⁻¹ to 530 MPa and 815 MPa at strain rate of 8 × 10³ s⁻¹. Moreover, the ultimate tensile strength of Fe₄₀Mn₄₀Co₁₀Cr₁₀ and (Fe₄₀Mn₄₀Co₁₀Cr₁₀)_96.7C_3.3 reaches to 1073 MPa and 1413 MPa at strain rate of 8 × 10³ s⁻¹, respectively. Whereas, the ductility of both HEAs declines remarkedly, with uniform elongation decreasing from 46.2 % and 67.4 % at strain rate of 1 × 10⁻³ s⁻¹ to 7.9 % and 25.2 % at strain rate of 8 × 10³ s⁻¹. The thermally activated dislocation motion and the phonon drag effects jointly contribute to the striking increment of yield strength with increasing strain rate. The temperature rise during dynamic deformation gives rise to stacking fault energy increasing, which inhibits the deformation twinning, resulting in the reduction of strain hardening rate and thus the reduced ductility. In particular, with the assistance of C solid solution, (Fe₄₀Mn₄₀Co₁₀Cr₁₀)_96.7C_3.3 exhibits enhanced twinning formation capability and superior resistance to shear bands formation than Fe₄₀Mn₄₀Co₁₀Cr₁₀, which enables a better combination of strength and ductility upon dynamic loads. These findings provide deep insights into dynamic deformation behavior of carbon interstitial face-centered cubic HEAs.