Fabricating a single-crystal-like β grain structure of a near-β Ti alloy with unique variant selection by laser powder bed fusion

A near-β Ti alloy with a highly anisotropic single-crystal-like β grain structure was fabricated on a polycrystalline pure-Ti substrate by laser powder bed fusion (LPBF) using a flat-top laser with bidirectional scanning and 90° hatch rotation. The as fabricated specimen had an acicular microstructure with 12 α variants. β-annealing followed by air-cooling revealed the growth of columnar β grains with a <001> orientation in the build direction from the center outward with increasing height, which formed a highly anisotropic β grain structure with a <001> orientation in the build direction and <100> or <010> orientation along the scan direction with low-angle grain boundaries (LAGBs) in the β matrix. The predominant <2-1-10>-oriented and minor <10-12>-oriented α phases precipitated from the <001>-oriented β matrix according to the Burgers orientation relationship. The <10-12>-oriented α phase was found to form on some LAGBs. Notably, a single α variant was widely distributed without forming multiple variant clusters across the highly anisotropic β grain structure.