Microstructural deformation mechanisms in adiabatic shear bands in Ti6Al4V are studied
using traditional TEM and selected area diffraction, and more advanced microstructural
characterisation techniques such as energy dispersive X-ray spectroscopy, high angle
annular dark field STEM and conical dark field TEM.
The shear bands under investigation are induced in Ti6Al4V samples by high strain rate
compression of cylindrical and hat-shaped specimens in a split Hopkinson pressure bar
setup. Samples from experiments interrupted at different levels of deformation are used to
study the evolution of the microstructure in and nearby the shear bands.
From the early stages of adiabatic shear band formation, TEM revealed strongly elongated
equiaxed grains in the shear band. These band-like grains become narrower towards the
centre of the band and start to fraction even further along their elongated direction to
finally result in a nano-crystalline region in the core. In fully developed shear bands, twins
and a needle-like martensite morphology are observed near the shear band.