Multiscale investigation of pore and crack formation during selective laser melting of pure tungsten: simulation and experimental validation

Abstract

Selective laser melting (SLM) of pure tungsten remains challenging due to its intrinsic properties, including high melting point, high surface tension, and high dynamic viscosity. To reveal the physical phenomena involved in the SLM of pure tungsten, a transient mesoscale model was developed using the finite volume method (FVM). The temperature evolution and thermodynamic behavior within the molten pool were investigated. The simulation results demonstrated that both the peak temperature and the cooling rate increased with higher laser power. At a high laser power of 350 W, the peak temperature and cooling rate reached 5742 K and 4.66 × 10⁷ K/s, respectively. Correspondingly, a long liquid lifetime of 184 µs was obtained. At 350 W, the velocity vectors within the molten pool were significantly intensified, generating strong mass transfer. A regular molten pool with a large width of 62 µm was formed, which favored metallurgical bonding with adjacent scanning tracks. Laser power played a crucial role in determining the surface morphologies of SLM-processed tungsten parts. At a relatively low laser power of 200 W, the scanning track was discontinuous and contained numerous unmelted particles. Simultaneously, the corresponding SLM-processed parts exhibited large pores. However, when a high laser power of 350 W was applied, the top surface of the scanning track became continuous with regular liquid flow, and the corresponding part was nearly pore-free. Moreover, cracks were inevitable across all applied laser power levels, and its formation mechanism was revealed. Based on the simulation results, potential methods for reducing cracks were proposed.