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The microstructural evolution in localized shear deformation was investigated in an 8090 Al -Li alloy by split Hopkinson pressure bar (strain rate of approximately 10 3 s − 1) at ambient temperature and 77 K. The alloy was tested in the peak-, over-, under-, and natural-aged conditions, that provide a wide range of microstructural parameters and mechanical properties. Two types of localized shear bands were distinguished by optical microscopy: the deformed shear band and the white-etching shear band. They form at different stages of deformation during localization. There are critical strains for the occurrence of deformed and white-etching localized shear deformation, at the imposed strain rate. Observations by transmission electron microscopy reveal that the white-etching bands contain fine equiaxed grains; it is proposed that they are the result of recrystallization occurring during localization. The deformed-type bands are observed after testing at 77 K in all heat treatment conditions, but they are not as well defined as those developed at ambient temperature. Cracking often occurs along the localized shear at ambient temperature. The decrement in temperature is favorable for the nucleation, growth and coalescence of the microcracks along the shear bands, inducing fracture.

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Abshact: Tantalum tubular speci mens, emkdded in a q p r thick-~Yall cylinders, n m collapsed quasiuniformly by detonating the eyl&;e in with the copper cylinder. The microstrtmur f m : (i) dislocations and elongated dislocation cetls, (ii) subpins; (iii) dyna~~cally rmydlkd mi cro-. and (N) statically mqslahd p m whose grain sizes wae pmhded using conventional grain-grmu2h lanetics. The evolution mecharusm of the microstructure fium elongated dislocation cells, subpins, to micrograins is proposed Grainscale l o a b t i o n was observed Ductile fracture along shear bands was produced by the residual tensile hoop stresses near the ~n t r a l hole region upon unloading. RQum6: Des tchantillons tubulaires en tantale, entoures par des cylindres a paroi epaisse ont subi une implosion de f a~o n symttrique par la detonation d'un explosif place de f a~o n co-axiale avec le cylindre en cuivre. La microstructure est constituee de : (i) dislocations et cellules de dislocations allongees; (ii) sous-grains; (iii) micrograins produits par recristallisation dynamique; (iv) grains generes par recristallisation statique dont la taille de grains a ete prCvue par la cinetique conventionnelle de croissance des grains. Un mecanisme est propose pour I'Cvolution de la microstructure des cellules allongees, sous-grains, et micrograins. Une localisation de la deformation a I'echelle des grains a ete observee. La rupture ductile le long des bandes de cisaillement est due aux contraintes residuelles engendries dans I'orifice interieur apres dechargement.