Weakening the Anisotropic Property and Refining Prior-β Grains via Hammer Peening Treatment During Wire Arc Additively Manufacturing of Ti-6Al-4V

In Wire Arc Additive Manufacturing (WAAM), solidification grain morphology in titanium alloy tends to be columnar rather than equiaxed due to heat dissipation and repeated thermal cycles. This study demonstrates improved microstructure and anisotropic properties in Ti-6Al-4V specimens fabricated by WAAM and treated with hammer peening, resulting in a transition from columnar grains to fine equiaxed grains (~300 μm) in both single-pass and four-bead WAAM walls. The anisotropic elongation decreased by approximately 7%, and tensile strength along the building direction decreased by ~50 MPa for a single-pass wall. Additionally, small and large equiaxed prior-β grains appeared alternately due to the combined effect of hammer peening and welding deposition. The region can be categorized into three parts (MAX, MED, MIN) based on the degree of plastic strain characterized by KAM mapping of EBSD data. In current WAAM parameters, the ratio of strong (~1.5 mm) deformation field (MAX) is about 50% within one deposition layer (MAX+MIN), suggesting a new approach for producing equiaxed prior-β grains. We expect that this method will be applicable for transforming the prior-β grains from columnar to equiaxed. Furthermore, the distribution of plastic strain and phase transformation mechanisms offers innovative approaches to optimize the hammer peening process, with potential applications to optimize the process for more complex components in the aerospace and power plant industries.