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

Abstract

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 〈21¯1¯0〉-oriented and minor 〈101¯2〉-oriented α phases precipitated in the 〈001〉-oriented β matrix according to the Burgers orientation relationship. The 〈101¯2〉-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.

Keywords

• Laser powder bed fusion
• Titanium
• Texture
• Precipitation
• Variant selection