A comparative study of continuous-wave versus pulsed-wave laser emission in direct laser metal deposition of SS316L thin walls

Direct Laser Metal Deposition (DLMD), as a Directed Energy Deposition (DED) technique, can operate either continuous-wave (CW) or pulsed-wave (PW) laser emission, resulting in distinctly different thermal histories during material deposition. Although both laser modes are widely employed in additive manufacturing, a direct comparison of their influence on thin-walled structures fabricated specifically by the DLMD process remains limited. This study fabricated thin-walled structures of stainless steel 316 L (SS316L) using a Direct Laser Metal Deposition (DLMD) system operating in both continuous wave (CW) and pulsed wave (PW) modes to compare their microstructure, microhardness, and geometrical features (including penetration depth, bead width, maximum width, and height). Microstructural evaluation was conducted using optical microscopy (OM), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS). OM and FESEM images revealed that the solidification morphology for both CW and PW thin walls consisted of cellular, columnar, and equiaxed dendritic structures, with the PW thin wall exhibiting a finer grain size. The average grain size was 4.75 μm for the CW-DLMD sample and 3.2 μm for the PW-DLMD sample. The results indicate that the thin wall fabricated with the CW laser exhibited larger geometrical dimensions than its PW counterpart. Furthermore, microhardness distribution analysis indicated that hardness values generally decreased with increasing distance from the substrate for both sample types. The average microhardness was 168 HV for the CW thin wall and 213 HV for the PW thin wall.