Effect of process parameters on surface integrity in laser powder bed fusion of Ti-6Al-4V alloy.

Abstract

Laser powder bed fusion (LPBF) printing of Ti-6Al-4V often suffers from surface defects such as weld traces, unmelted particles, spatter, and porosity that degrade surface integrity and induce significant residual stresses due to a higher thermal gradient. This study aims to elucidate the evolution of surface topography and residual stresses as a function of build height and process energy input during LPBF fabrication. Ti-6Al-4V samples were produced at volumetric energy densities ranging from 21.8 to 65.4 J·mm⁻³ by varying laser power and scanning speed. Focus variation microscopy measurements show propagation of surface irregularities extending over several tens of layers. Higher energy densities resulted in stable melt pools and reduced surface roughness. The computed and measured residual stresses agreed well for the sound builds. In contrast, notable deviation was observed for the conditions that exhibited high porosity. Overall, the findings show that residual stress evolution in LPBF significantly influences surface morphology, which further supports the importance of process energy optimization to achieve a sound part.