Systematic study of the interplay between laser beam shape, energy input, and hatch spacing in PBF-LB/M of Ti-6Al-4V: experiments and numerical modeling

Programmable laser beam shaping tailors the spatial irradiance distribution in laser powder bed fusion (PBF-LB/M), enabling control over melt-pool geometry and defect formation. However, the coupled effects of beam shape, hatch spacing (track overlap), and energy input on densification and microstructural development remain insufficiently understood. Accordingly, Ti-6Al-4V is studied using single-track experiments, cube builds, and 3D transient multiphysics simulations across three ring-type beam profiles ranging from relatively core-weighted to strongly ring-dominated. Single tracks spanning a power–speed matrix (linear energy density, P/v) quantified melt-pool width, depth, and molten area and mapped stability regimes (fragmentation, necking, stable) and transition thresholds with increasing energy input. Cube specimens mapped relative density versus beam mode, areal energy density AEDh = P/(v h) (J/mm2), hatch spacing h, and geometric ratios h/d (d: effective beam diameter) and W/h (W: melt-pool width). Near-full density (~99.9%) was achieved for all profiles at AEDh ≥ 2.8–3.0 J/mm2; relatively more core-weighted profiles reached this at lower AEDh, whereas ringdominated profiles required higher input to suppress lack-of-fusion. Density dropped when h/d≳1, while W/h≳ 1.2 preserved high density. Microstructure and Vickers microhardness (HV0.2) were assessed across AEDh. All conditions exhibited martensitic α′ microstructures, and microhardness remained ≈360–395 HV0.2, converging once near-full density was reached. Simulations showed that ring-dominated density loss arises from insufficient inter-track remelting depth (cusp formation) despite lateral overlap, requiring higher overlap ratios for full fusion. Thermal gradients (G) and solidification rates (R) placed all cases in the columnar growth regime; higher G/R in more core-weighted profiles is consistent with stronger grain continuity than the more refined ringdominated structures.

Subjects

Additive manufacturing

Hatch spacing

Laser beam shaping

Multiphysics simulation

PBF-LB/M

Ti-6Al-4V

DDC Class

621: Applied Physics

Funding(s)

RMIT European Doctoral Innovators Programme

Lizenz

https://creativecommons.org/licenses/by/4.0/

Publication version

publishedVersion

Name

1-s2.0-S0264127526011925-main.pdf

Type

Main Article

Size

47.72 MB

Format

Adobe PDF

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Systematic study of the interplay between laser beam shape, energy input, and hatch spacing in PBF-LB/M of Ti-6Al-4V: experiments and numerical modeling