Variant Selection of Additive-Manufactured Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Titanium Alloy

In this study, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) titanium alloy samples are fabricated via arc-wire directed energy deposition (AW-DED) and laser powder bed fusion (L-PBF). The variant-selection (VS) mechanism of the α grain boundary (α GB ) and the intragranular microstructure are characterized via electron backscatter diffraction, and the related formation mechanisms are discussed. The continuous α GB maintained Burgers orientation relationships with one of the adjacent lamellas in the AW-DED sample and the adjacent acicular α' laths in the l-PBF sample as much as possible, respectively. For the intragranular microstructure, the VS of the colony and basket-weave microstructures maintained a common {11 2 ¯ 0} pole with one of their adjacent microstructures in the AW-DED sample. The VS of the acicular α' lath in the intragranular region is maintained as the common {0001} pole and {11 2 ¯ 0} pole section as much as possible with the adjacent acicular α' lath. Type-2 (60°/[11 2 ¯ 0]) boundaries dominated the colony microstructure and the basket-weave microstructure because of their low cooling rate in the AW-DED sample. By contrast, type-4 (63.26°/[ 10 ‾ 5 5 3 ¯ ]) boundaries are composed of the acicular α' lath owing to their high cooling rate in the l-PBF sample during deposition.