Localized amorphism after high-strain-rate deformation in TWIP steel

Nanocrystalline steel obtained by mechanical alloying of iron and graphite subsequently compacted by high-pressure torsion

“…1(a) is still apparent, however the particles seem to be somewhat flattened from HPT. grain size in this shear band may seem surprising, however grain sizes near the amorphous limit of 1 nm have indeed been observed in shear bands in TWIP steel [43]. The hypothesis that the nature of the band is localized shear is substantiated by the fact that the ratio of band width to grain size is about (100 nm)/(2 nm) = 50, a ratio that has been observed in shear bands in iron with grain sizes between 80 and 268 nm [39].…”

Strain rate sensitivity and evolution of dislocations and twins in a twinning-induced plasticity steel

“…In an extreme case reported by Li et al [49], the TWIP steel sample can even be heated over the melting point when a high strain rate deformation at $10 5 s À1 is induced by ballistic impact loading. In the present model, the temperature increase during dynamic deformation is estimated by considering the energy input from the external work and the energy lost due to the heat conduction to the sample holders [50]:…”

Hydrostatic pressure effects on deformation mechanisms of nanocrystalline fcc metals

“…7, partial dislocation behaviors, formation of SFs and formation of dislocation networks are all enhanced with increasing hydrostatic pressure when the grain size is large (15 nm), which is consistent with results shown in GB thickening is observed to increase monotonically with increasing hydrostatic pressure for both grain sizes, and the NC Cu with grain size of 3 nm has the trend to become amorphous state after 10% strain compression when the hydrostatic pressure is as high as 80 GPa. The crystalline-to-amorphous transition has generally been observed during the high-strain-rate deformation processes [36][37][38]. Meyers et al [36] reported the first observation on crystalline-to-amorphous transition in stainless steel inside a shear band formed under dynamics loading, which was attributed to a non-equilibrium solid-state amorphization process rather than melting.…”

“…Amorphous structures were also observed by Zhang and Shim [37] in polycrystalline oxygen-free high conductivity copper severely deformed at high strain rate and liquid nitrogen temperature, in which they proposed that the amorphized regions were associated with the relative displacement between adjacent grains at their boundaries and the rotation of individual grains. More recently, a large region of amorphous phase was also identified in TWIP steel inside the shear band formed under high-strain-rate ballistic impact [38], and was attributed to melting inside the shear band. Although different mechanisms proposed [36][37][38], the high temperature rise due to adiabatic heating and extremely rapid cooling by heat dissipation should play an important role in the formation of amorphous region during the high-strain-rate deformation.…”

“…More recently, a large region of amorphous phase was also identified in TWIP steel inside the shear band formed under high-strain-rate ballistic impact [38], and was attributed to melting inside the shear band. Although different mechanisms proposed [36][37][38], the high temperature rise due to adiabatic heating and extremely rapid cooling by heat dissipation should play an important role in the formation of amorphous region during the high-strain-rate deformation. However, the deformation temperature in the present simulations was controlled at 1 K, the small grain size and the ultra-high hydrostatic pressure should be the main factors for forming the amorphous state, which gives a new way to produce crystalline-to-amorphous transition.…”