Alec Davis ICOTOM19 conference presentation

Simulation and texture investigation of a novel recrystallisation mechanism in Ti-6Al-4V during wire-arc AM with inter-pass deformation. High deposition rate Wire-Arc Additive Manufacture (WAAM) of Ti-6Al-4V is attractive to industry for near-net shape production of large-scale components. However, WAAM leads to the development of undesirable coarse columnar β grains which, as a consequence of the larger heat source, grow epitaxially throughout components. To break up the β-grain structure, a cold deformation step can be introduced, between deposition passes, to induce recrystallisation on heating during the α→β transformation. This inter-pass deformation process produces small, equiaxed, β grains, even when low strains are employed. In single β crystal simulations of the thermomechanical history, starting with a coarse conventional α microstructure, the more expected behaviour occurred, with limited β recrystallisation produced largely by lattice rotation. In contrast, with a fine AM starting transformation microstructure, as well as a high level of recrystallisation, a unique texture was observed, which was consistent with the deformation-induced annealing twinning produced during the α→β transformation.