Reduction of anisotropy in Ti-6Al-4V WAAM deposits by dual wire TIG using vibrations

Ti-6Al-4V is a widespread material in industrial sectors such as aerospace and defense. This alloy exhibits an excellent strength to weight ratio, especially as a wrought material. However, the use of direct energy deposition processes typically leads to unfavorable coarse columnar microstructures with a strong texture which reduces ductility and increases mechanical properties anisotropy. Multiple ways of refining the as-built microstructure have been studied such as melt pool shape control, hammer peening, inoculant additions or vibration. Refinement by vibration is generally obtained according to literature by vibrating the substrate and leads to heterogeneous results (due to: vibration node, attenuation). This study aims to increase the efficiency of vibration-induced refinement by directly vibrating the melt pool during deposition using dual wire-tungsten inert gas process. For this purpose, the second filler wire, which is positioned at the back of the melt pool, is vibrated in order to affect locally the solidification. High frequency vibration of the melt pool may produce cavitation within the liquid alloy, and increase dynamic nucleation. This dynamic nucleation promotes homogeneous nucleation of grains in the melt pool and disrupts epitaxial growth at the liquid/solid interface of the melt pool. The effect of vibration process parameters such as amplitude and frequency on the additive manufactured deposits will be presented. Anisotropic microstructure will be investigated with EBSD analysis.