Microstructural evolution in adiabatic shear localization in stainless steel
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Shear bands were generated under prescribed and controlled conditions in stainless steel (Fe- 18%Cr-8%Ni). Hat-shaped specimens, deformed in a Hopkinson bar were used, yielding strain rates of approximately 104s-1 and shear strains that could be varied between 1 and 100. Specimens recovered from the collapse of thick-walled cylinders were also investigated. Microstructural characterization was performed by electron backscattered diffraction (EBSD) with orientation imaging microscopy(OIM), and transmission electron microscopy (TEM). The shear-band thickness was approximately 8 µm. This low-stacking fault energy alloy deforms, at the imposed strain rates (outside of the shear band), by planar dislocations and stacking fault packets, twinning, and occasional martensitic phase transformations at twin-twin intersections. EBSD reveals gradual lattice rotations of the grains approaching the core of the band. A  fiber texture (with the  direction perpendicular to both shear direction and shear plane normal) develops both within the shear band and in the adjacent grains. The formation of this texture, under an imposed global simple shear, suggests that rotations take place concurrently with the shearing deformation. This can be explained by compatibility requirements between neighboring deforming regions. EBSD could not reveal the deformation features at large strains because their scale was below the resolution of this technique. Transmission electron microscopy reveals a number of features that are interpreted in terms of the mechanisms of deformation and recovery/recrystallization postulated. They include the observation of grains with sizes in the nanocrystalline domain. The microstructural changes are described by an evolutionary model, leading from the initial grain size of 15 µm to the final submicronic (sub)grain size. Calculations are performed on the rotations of grain boundaries by grain-boundary diffusion, which is 3 orders of magnitude higher than bulk diffusion at the deformation temperatures. They indicate that the microstructural reorganization can take place within the deformation times of a few milliseconds.
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Meyers, M.A.; Xu, Y.B.; Xue, Q.; Pérez-Prado, M.T.; McNelley, T.R. (Elsevier, 2003);Shear bands were generated under prescribed and controlled conditions in an AISI 304L stainless steel (Fe-18%Cr-8%Ni). Hat-shaped specimens were deformed in a Hopkinson bar at strain rates of ca 104 s-1 and shear strains ...
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