The effects of energy density and heat treatment on the properties of 3D printed tungsten

Abstract A large temperature gradient led to rapid temperature changes in the selective laser melting (SLM) process, resulting in high residual stress and micro-cracks, which were the main challenges faced by the 3D printing of tungsten (W) materials. On the other hand, the volumetric energy density had a significant effect on the density of the pure W structural component fabricated by SLM. It was difficult to eliminate defects in the formed parts solely by optimizing SLM technology parameters. The crystalline W powder with a concentrated grain size was used as the raw material, and substrate preheating was adopted to prepare the W structural component with a lattice structure by selective laser melting (SLM). The processed samples were subsequently subjected to heat treatment at 1100℃, 1400℃, 1700℃and 1900℃ for 2 hours. The mechanical properties and microstructure of the specimens at different heat treatment temperatures were analyzed. The results indicate that the optimal volumetric energy density for obtaining a theoretical density of 96.2% is around 972 J/mm3. After the heat treatment at 1700℃, the samples achieved the best mechanical performance, with an ultimate compressive strength and microhardness reaching 1200 MPa and 457HV, respectively. The fracture morphology shows cleavage fracture characteristics, and microcracks were largely eliminated after the heat treatment at 1700℃, indicating strong metallurgical bonding between layers and particles.