Very high strain rate deformation twinning behaviour of Ti–6Al–4V

Abstract

Equiaxed fine-grained and coarse-grained samples of h.c.p. α phase Ti–6Al–4V with trace amounts of retained b.c.c. β phase were ballistically tested at room temperature. The deformed microstructures were characterised by electron back scattered diffraction. The extensive deformation twinning observed in the α phase in both samples was limited to the {1 0 -1 2} and {1 1 -2 1} tensile twinning modes. These two deformation twinning types have very different morphologies: thin {1 1 -2 1} deformation twins span multiple α phase grain boundaries, while the wider {1 0 -1 2} deformation twins are usually limited to individual grains, reorienting almost entire grains to a twinned orientation. Both {1 0 -1 2} and {1 1 -2 1} deformation twins are able to propagate across low angle α lath boundaries, but only the {1 1 -2 1} deformation twinning types can propagate across high angle α grain boundaries.