Microstructure and Microtexture Evolution of Shear Localization in Dynamic Deformation with Different Strains in Anneale
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UCTION
SHEAR localization, which sometimes is referred to as adiabatic shear bands (ASBs), can occur in many metallic materials during dynamic deformation such as ballistic impact, penetration, high-speed machining, and explosion.[1] It is generally considered as an instability phenomenon in the case that thermal softening arising from the adiabatic temperature rise exceeds work hardening and strain-rate hardening. In most circumstances, the formation of shear localization can promote the initiation, growth and coalescence of microcracks, which will lead to catastrophic failure. At high strain rates, it has been found that the ASB formation is sensitive to the initial microstructure and texture state of materials.[2–4] The microstructure characterization and microtexture analyses are critical to understand the formation and evolution of shear localization. Microstructure investigation of the shear localization has been carried out extensively by transmission electron microscopy (TEM) during the past 20 years.[5–8] Dynamic recrystallization (DRX) has been observed within some ASBs and taken as a potential cause for LIN TANG and CONGKUN ZHAN, Graduate Students, ZHIYONG CHEN, Associate Professor, and XUYUE YANG and CHUMING LIU, Professors, are with the School of Materials Science and Engineering, Central South University, Changsha 410083, P.R. China. Contact e-mail: [email protected] Manuscript submitted February 14, 2012. Article published online September 26, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
adiabatic shear failure.[9] Hines and Vecchio[10] discussed the recrystallization kinetics within ASBs and demonstrated that the classic recrystallization mechanisms, such as the high-angle boundary migration mechanism and the subgrain coalescence mechanism, cannot account for DRX at high strain rates. The mechanisms known as rotational dynamic recrystallization (RDR) and progressive subgrain misorientation recrystallization (PriSM) are generally accepted as the reasonable mechanisms for DRX within ASBs.[11,12] The former is based on the dislocation energetics, whereas the latter is based on a ‘‘bicrystal’’ approach using crystal plasticity theory. The main difference between the two mechanisms is that the ultrafine grains with high-angle grain boundaries (HAGBs) are formed during deformation (RDR), whereas the misorientation increases during deformation and the grain boundaries refinement occurs during cooling (PriSM).[13] Due to the difficulty in preparing the TEM samples for ASBs as well as the relative small observation areas of TEM, the TEM technique should be combined with other advanced characterization tools for the measurement and systematic observations of the microstructures.[14] In addition, previous microstructure examinations have mainly focused on the substructures within shear bands at a specific deformation stage. Only a few literatures[15–17] examined microstructure at different stages of evolution with different strains. Microtexture analysis has been greatly facilitated since the electron backscatter d
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