Nanosecond laser polishing of laser powder bed fusion manufactured Haynes 230: Surface quality improvement and surface microstructure evolution

Additive manufacturing through laser powder bed fusion (LPBF) enables the production of geometrically complex nickel-based superalloy components. However, it results in poor surface quality, partially melted powder particles, and surface irregularities, that limits their performance in critical applications. This study investigates nanosecond laser polishing as an advanced post-processing technique for improving the surface quality of LPBF-manufactured Haynes 230, a high-temperature Ni-Cr-W superalloy. Eighteen LPBF-manufactured samples were polished using a nanosecond pulsed fiber laser while systematically varying laser power (25-170 W), pulse duration (2611420 ns), pulse frequency (150-400 kHz), and scanning speed (900-2400 mm/s) to establish a comprehensive processing window. Surface roughness parameters (arithmetic mean height Sa and maximum height Sz) were measured using confocal microscopy, while remelted layer thickness, microstructure, and microhardness were analyzed through metallographic observations and Vickers microhardness testing. Laser polishing significantly improved the surface finish, achieving a maximum reduction in Sa of 90.9%, decreasing from 18.98 μm to 1.72 μm under optimal parameters of 110 W, 150 kHz, 1420 ns, and 900 mm/s. The remelted layer thickness ranged from 24 to 129 μm, increasing with higher laser power and lower scanning speeds. Excessive power levels (170 W) resulted in subsurface cracking and porosity, whereas optimal conditions produced a smooth, crack-free surface and average microhardness of remelted layer ranging approximately from 274 to 383 HV. This work provides the systematic investigation of nanosecond laser polishing of LPBF-manufactured Haynes 230 and establishes practical correlations between laser parameters, energy intensity, and resulting surface morphology. The findings provide valuable guidelines for optimizing laser-based surface finishing of nickel-based superalloys used in high-temperature applications.