Enhancement of Microstructural and Tensile Isotropy for Ti–6Al–4V and Ti–6Al–2Sn–2Zr–2Mo–2Cr Alloys Deposited with Wire Arc Additive Manufacturing and Interlayer Peening

The wire arc additive manufacturing (WAAM) deposition of Ti–6Al–4V (Ti64) and Ti–6Al–2Sn–2Zr–2Mo–2Cr (Ti62222) alloys produce long columnar grains, indicating tensile anisotropy in various directions. Therefore, this study applied interlayer peening (ILP) during WAAM to modify the solidification morphology. The index of plane anisotropy (IPA) of the as-built Ti64 deposit was 30%, whereas that of the ILP Ti64 alloy was 1%, indicating the significant effect on modifying the solidification morphology and reducing the IPA of the Ti64 deposit. However, the IPA of the as-built Ti62222 alloy was 79%, whereas that of the ILP Ti62222 alloy was 72%, indicating anisotropy in the mechanical properties despite the ILP process. In Ti64 alloy, ILP resulted in larger D_ILP (3.2 mm) than D_remelt (1.87 mm), which impeded the growth of columnar β grains and nucleated the equiaxed β grains during subsequent layer deposition. However, in Ti62222 alloy, owing to its higher hardness and Yield Strength, D_ILP (2.2 mm) and D_remelt (1.97 mm) were approximately the same, thus allowing the growth of columnar β grains to continue during subsequent layer deposition.