Effect of geometrical morphologies, support structure and adding second phase on the microstructure of tungsten fabricated by selective laser melting

In order to further explore the application of W and W alloy fabricated by selective laser melting (SLM), W with different geometrical morphologies, support structure and second phase combination were prepared, and the corresponding microstructure characteristics were also investigated. The grain morphology and size distribution were significantly depend on the heat dissipation conditions caused by different geometrical morphologies, support structure and second phase combination. With the specimen size increases from 1D-2 to 3D, the average grain size increases, the percentage of large grains increases, and the dislocation density decreases. Because no remelting occurred in 2D specimen due to no overlap in the corresponding position, more prone to epitaxial growth and formed elongated cellular grains. Increase the height of support structure could decrease the cooling rate, especially the center area, which induced the grain size along with the reduction of cracks. The crack in pure W during SLM was related to the high thermal stress caused by high cooling rate as well as the recrystallization and epitaxial growth of W phase during SLM. Adding the second phase such as Cu or Cu10Sn could reduce the grain size of W phase remarkably, and crack was severely restrained in W phase simultaneously. This could be attributed to that grain refinement of W phase could decrease the DBTT and the second phase combination also breaks the epitaxial growth of W phase.