Diode area melting of Ti6Al4V: effects of multi-laser processing on microstructure and residual stress

Laser Powder Bed Fusion (LPBF) is a widely adopted additive manufacturing technique for producing geometrically complex metallic components. While this process yields fine microstructures that are beneficial for strength, the associated rapid thermal cycles generate steep temperature gradients and high residual stresses, which may lead to warping, cracking, and dimensional instability. Diode Area Melting (DAM) employs arrays of low-power diode lasers operating at a wavelength of 808 nm. The diode beams are integrated into a customised optical head that traverses the powder bed in the X–Y plane, enabling a broader thermal interaction area and reducing local cooling rate. In this study, single-layer Ti6Al4V samples were processed by DAM using 3, 4, and 5 aligned 808 nm diode lasers, each operating at 5 W. The effects of laser number and scanning speed (100, 150, 200, and 250 mm/min) on surface roughness, melt pool geometry, microstructure, simulated cooling rate, and residual stress were systematically investigated. DAM produced lower simulated cooling rates (2211–8400 K/s) than those typically reported for LPBF (10⁴–10⁷ K/s), leading to coarser HCP lath spacings (0.8–1.3 μm) and evidence of retained β. Near-surface tensile residual stresses of up to 138.2 MPa were measured. The simulated lower cooling rates and reduced residual stress indicate that DAM may provide improved control over solidification behaviour and stress evolution.