Search

Ballistic impact experiments are conducted on a CrMnFeCoNi high-entropy alloy (HEA) using spherical steel projectiles, to investigate the penetration behavior in a wide range of impact velocities (∼ 800 to 2300 m s−1). Penetration processes are captured by high-speed camera. Postmortem samples are characterized via three-dimensional laser scanning, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and microhardness tests. Both depth and diameter of impact crater show a nearly linear increase with increasing impact velocity. Penetration induces increased hardness; hardness is the same near the crater bottom and the sidewall, and the peak hardness (∼ 400 Hv 1.0) is independent of impact velocity. The penetration-induced hardening is caused by multiple deformation defects including dislocations, twins and kink bands (KBs). Quantitative analysis further reveals that KB boundaries have a 5–50° misorientation angle, and their density decreases with increasing misorientation angle. KB boundary density is higher near the crater bottom than near the crater sidewall, while this trend is inverse for twinning boundary density. A finite element method model based on measured static and dynamic mechanical properties reproduces experimental observations and is used for interpreting deformation mechanisms. [Display omitted] • Both crater depth and diameter increase linearly with increasing impact velocity. • More kink bands (KBs), but less twins are observed near crater bottom than near sidewall. • KB boundary density decreases with increasing boundary misorientation from 0 to 50°. • Simulation interprets well the different deformation mechanisms in different regions. [ABSTRACT FROM AUTHOR]

The effects of strain rate on mechanical properties, microstructural evolution and underlying deformation mechanisms of two kinds of interstitial CrMnFeCoNi high entropy alloys (HEAs), (CrMnFeCoNi) 99.5 C 0.5 and (CrMnFeCoNi) 99.0 C 1.0 , are investigated under quasi-static and dynamic tension. Dynamic loading is carried out via a split Hopkinson tension bar system. The pre- and post-deformation microstructures are characterized with electron back scatter diffraction and transmission electron microscopy. Both yield strength and work hardening increase remarkably with increasing strain rate. Plastic deformation in both alloys under quasi-static and dynamic loading are dominated by dislocations, stacking faults, kink bands and deformation twins. Twinning is activated easier under dynamic loading, and twin density decreases with increasing carbon content due to the increased stacking fault energy. The Khan-Liu constitutive model can describe the experimental results for these two interstitial HEAs in a wide strain range. • Both volume fraction and size of the carbides increase with the increase of C content. • The increase of C content and strain rate lead to the increase in σ Y and σ UT. • Twin density decreases with increasing C content due to the increased SF energy. • The Khan-Liu constitutive model is used to describe the deformation. [ABSTRACT FROM AUTHOR]