Formation and morphology of twinning in titanium under high strain rate deformation

The dynamic behavior of pure titanium was studied in planar impact experiments using a 25-mm pneumatic gun, at impact velocities of 150-550 m/sec. The sample free surface velocity was monitored by VISAR. Softly recovered samples were characterized utilizing XRD, and optical, SEM and TEM microscopy. Metallographic examination of the cross section areas of the impacted samples revealed impact-oriented twins with significantly lower concentration in the direct vicinity of the spall plane. TEM studies revealed dense dislocation areas and twins in the samples, with profound secondary twins and ordered dislocations cells near the spall plane. The results allow estimating the relative contribution of twinning mechanisms in shock-induced plastic deformation of titanium. The differences in the morphology of the area near the spall plane, in contrast to the rest of the sample, implies on alternative deformation mechanisms depending on the loading history.