Scan-Strategy Dependent Microstructural Modulation in L-PBF Ti-6Al-4V Components Through Selective Rescanning

Laser Powder Bed Fusion (L-PBF) can enable in situ microstructural tailoring of metallic components by precisely controlling the layer-wise processing parameters. Layer rescanning is one such strategy used to induce localized microstructural modification. In this study, we investigated the effect of a lattice-based selective rescanning approach applied to different base scan strategies for Ti-6Al-4V samples. The lattice regions were selectively rescanned at 50% reduced laser power relative to the initial scan along the same laser path. Relative density, porosity, martensitic α′ morphology, phase fraction, and Vickers microhardness were compared with those of non-rescanned reference counterparts. Different scan strategies, including unidirectional, stripes, and chess, exhibited distinct responses to selective rescanning, resulting in localized variations in martensitic phase formation and hardness values. The extent of localized microstructural modification and hardness enhancement was strongly governed by the underlying scan strategy. Selective rescanning using the stripes strategy yielded the largest contrast between non-rescanned and rescanned regions. The unidirectional strategy showed strong effects of rescanning, but the heat-affected zones extended to the non-rescanned regions. In contrast, the chess strategy exhibited comparatively moderate changes owing to its inherent thermal-management characteristics. These findings demonstrate that selective rescanning can provide an effective, localized approach for tailoring microstructure and hardness enhancement in L-PBF Ti-6Al-4V, with its effectiveness strongly dependent on the underlying scan strategy.