The effectiveness of combining rolling deformation with Wire-Arc Additive Manufacture on β-grain refinement and texture modification in Ti-6Al-4V

In Additive Manufacture (AM), with the widely used titanium alloy Ti-6Al-4V, the solidification conditions typically result in undesirable, coarse-columnar, primary 13 grain structures. This can result in a strong texture and mechanical anisotropy in AM components. Here, we have investigated the efficacy of a new approach to promote beta grain refinement in Wire-Arc Additive Manufacture (WAAM) of large scale parts, which combines a rolling step sequentially with layer deposition. It has been found that when applied in-process, to each added layer, only a surprisingly low level of deformation is required to greatly reduce the beta grain size. From EBSD analysis of the rolling strain distribution in each layer and reconstruction of the prior beta grain structure, it has been demonstrated that the normally coarse centimetre scale columnar beta grain structure could be refined down to <100 mu m. Moreover, in the process both the 3 and a phase textures were substantially weakened to close to random. It is postulated that the deformation step causes new beta orientations to develop, through local heterogeneities in the deformation structure, which act as nuclei during the alpha -> beta transformation that occurs as each layer is re-heated by the subsequent deposition pass. (C) 2016 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license