Abstract: α-titanium and its alloys with a dual-phase structure (α+β) were deformed dynamically under strain rate of about 104 s-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate (9×105 s-1) deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations in the bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products (α2) had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10 μm in diameter observed within the bands are proposed to be the results of recrystallization.

Key words: Localized shear bands, Microstructure, Dislocations, Twinning, Phase transformation...