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

Selective laser melting of pure tungsten has always been a challenge due to its intrinsic properties such as high melting point, high surface tension and dynamic viscosity. In order to reveal the physical phenomenon during SLM-processed pure tungsten, a transient mesoscale model was developed by finite volume method (FVM). The temperature evolution and thermodynamic behavior within the molten pool were investigated. The simulation results demonstrated that the peak temperature and cooling rate were enhanced as the laser power increased. The peaking temperature and cooling rate reached 5742 K and 4.66 \(\:\times\:\) 10 ⁷ K/s using a high laser power of 350 W, respectively. Accordingly, the long liquid lifetime of 182 µs was obtained. At a high laser power of 350 W, the velocity vectors within the molten pool were intensified obviously, generating a strong mass transfer. A regular molten pool with a large width of 62 µm was obtained, which was favorable to metallurgical bonding with adjacent scanning tracks. The laser power played an important role in influencing the surface morphologies of SLM-processed tungsten parts. At a relatively low laser power of 200 W, the scanning track was discontinuous with a large number of unmelted particles. Simultaneously, the corresponding SLM-processed tungsten parts were observed with large pores. However, as a high laser power of 350 W was applied, the top surface of scanning track was continuous with regular liquid flow. Under this situation, the corresponding SLM-processed tungsten part was nearly free of pores. Moreover, the cracks were inevitable regardless of the applied laser powers and the formation mechanism of cracks was revealed. Based on the simulation results of SLM-processed tungsten, the available methods used to reduce the cracks were proposed.