Surface Morphology, Relative Density, Microhardness and Microstructure of Tungsten Fabricated by Laser Powder Bed Fusion

This study investigates the effects of laser power and scanning rate on the surface morphology, relative density, microhardness and microstructure of pure tungsten fabricated by laser powder bed fusion (LPBF). Increasing the laser power or decreasing the scanning rate effectively suppresses spheroidisation and enhances densification, achieving a maximum relative density of ~98%. However, excessive laser power intensifies Marangoni convection, leading to surface protrusions that reduce density. Microstructural analysis reveals that the laser-scanned surface is dominated by fine columnar grains (390–480 HV), whereas the side surface comprises coarser columnar grains with lower hardness (~390 HV). Electron backscatter diffraction analysis confirms that the side surface contains a high proportion of grains exceeding 100 μm and reveals a significant peak (~41.8%) at ~3.5° for low-angle grain boundaries, indicating substantial internal stress and microstrain. Pole figures show a weak preferred orientation (maximum texture intensity of 3.161). Phase analysis shows no significant phase transformation after LPBF, while internal stress and microstrain increase notably.