Defect Formation Mechanism and Suppression Strategy in Additively Manufactured Tungsten Grid Thin-Wall Structures Via Laser Powder Bed Fusion

Tungsten grid thin-wall structures are extensively utilized as ray filtering parts in medical equipment and nuclear industries. In this work, tungsten grid thin-wall structures with a wall thickness of approximately 100 mu m were fabricated via laser powder bed fusion (LPBF) additive manufacturing technology. Post-treatments were employed to suppress the defects generated in LPBF-printed tungsten grid thin-wall structures, and the mechanisms of the defect formation and suppression were discussed. The adhesions attached to the wall surface were effectively eliminated by employing chemical corrosion and sandblasting, resulting in improved values of top and lateral surface roughness at 6.4 mu m and 1.65 mu m, respectively. The thin-wall structure annealed at 1400 degrees C presented the highest relative density of 98.28 % and unique microstructure with its lateral surface exhibiting elongated columnar grains in thin wall areas. Micro-defects including pores and cracks were observed around grain boundaries. The micro-defects deteriorated when annealed below the recrystallization temperature of 1300 degrees C, whereas they were effectively suppressed when annealed at 1400 degrees C. Consequently, this sample group exhibited exceptional mechanical properties. The stress experienced during the initial collapse in compression testing of the thin-wall structures annealed at 1400 degrees C was calculated to be 100.61 MPa. Subsequently, through a nano-indentation testing, the hardness and Young's modulus were measured as 9.15 GPa and 153.41 GPa respectively in thin-wall area, while in intersection area they were measured as 9.96 GPa and 381.44 GPa. The enhancement in mechanical properties of annealed tungsten grid thin-wall structures was attributed to gas pore release, diffusion densification and reduced residual stress.