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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. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing (WAAM) technique has introduced a novel approach for producing complex Ti–6Al–4V parts with metric dimensions. However, the produced part leads to the development of a strong texture and anisotropic mechanical properties due to the formation of large columnar β grains. To resolve this issue, the plastic deformation of each deposited track through hammer peening was developed as a means to refine these large β grains. In this study, we have investigated an innovative approach to further enhance the efficiency of β grain refinement by minimizing the arc heat input associated with previous deposited layer, which is achieved by employing a C-type filler wire. Our findings reveal a notable enhancement in grain refinement efficiency through the utilization of a C-type filler wire with peening process, as compared to available conventional commercial round shape filler wire. Specifically, the employment of the C-type filler wire results in a reduced melt pool penetration depth of WAAM Ti–6Al–4V (3.3 mm), compared to the commercially available round shape (R-Type) filler wire (4.48 mm). Within the plastically deformed region by peening, fine and randomly oriented β grains are observed, extending to a depth of deformation reaching 844 ± 32.65 μm. Peening WAAM Ti–6Al–4V with the C-type filler wire leads to the development of isotropic mechanical properties in both horizontal and vertical directions, offering high strength due to the presence of small equiaxed β grains and thin α laths (0.56 ± 0.18 μm), in contrast to the use of conventional commercial round shape filler wire.

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.