On the role of grain morphology in the mechanical behavior of laser powder bed fusion metastable β titanium alloy

A metastable titanium alloy Ti–3Al–6Fe–6V–2Zr (wt. %, Ti3662) was fabricated by laser powder bed fusion (LPBF), and high resolution digital image correlation (HRDIC) coupled with multiscale characterizations were employed, in order to uncover the effect of microstructural characteristics on the mechanical behavior of LPBF Ti3662 alloy. Results show that the LPBF Ti3662 alloy exhibits near equiaxial microstructure with fine β grain size and weak texture, due to the strong growth restriction effect from Fe addition. Mechanical tests and HRDIC results demonstrate that microstructural heterogeneity with a chessboard-like pattern has a pronounced influence on the microstrain evolution and mechanical properties of LPBF Ti3662. Strain localization is observed at the interfacial zones between the fine and coarse grains, and the irregular prior β grain morphology with rugged grain boundaries is significant in mitigating the adverse effect of grain boundary α phase. This is attributed to the successful suppression of strain localization and cracking at precipitate-free zones near the irregular grain boundaries. This study demonstrates that the irregular grain morphology is beneficial for the mechanical properties of metastable titanium alloy, whereas the heterostructure formed during LPBF causes strain localization. © 2024 Elsevier B.V.