Enhancing work hardening and ductility in additively manufactured β Ti: roles played by grain orientation, morphology and substructure

• Published in: Journal of materials science & technology Vol. 105; pp. 131 - 141
• Main Authors: Zafari, Ahmad, Lui, Edward Wen Chiek, Li, Mogeng, Xia, Kenong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.04.2022
• Subjects: Anisotropy; Equiaxed microstructure; Laser powder bed fusion; Slip band; Work hardening; β titanium; Equiaxed microstructure; Laser powder bed fusion; Slip band; Work hardening; Anisotropy; β titanium
• ISSN: 1005-0302; 1941-1162
• DOI: 10.1016/j.jmst.2021.08.006

A metastable β Ti alloy was additively manufactured by laser powder bed fusion (LPBF). Tensile testing along the build direction of the as-LPBF material (LPBF-0°) revealed significant work softening immediately following yielding with no uniform deformation. By contrast, substantial work hardening and uniform elongation well over 10% were achieved perpendicular to the build direction (LPBF-90°). Similar effects were obtained in the build direction after super transus heat treatment (LPBF-0°+HT) although the strength was slightly lowered. In addition, the yield drop phenomenon observed in both orientations of the as-LPBF materials disappeared after HT. The enhanced work hardening ability, and thus ductility, can be attributed to increased interactions of slip bands/slip bands owing to additional {112} slip systems becoming operative in LPBF-0°+HT and LPBF-90° while LPBF-0° was dominated by {110} only. The other variations after HT may be related to the coarsening of grain structure and removal of specific substructures in the as-LPBF microstructure. •Tensile anisotropy in an LPBF-fabricated β Ti was studied•Work hardening and ductility were much improved perpendicular to build direction•Super transus heat treatment transformed columnar β grains to equiaxed•The equiaxed β structure exhibited enhanced work hardening and ductility•Substructural features in LPBF microstructure led to strengthening and yield drop