Investigation of powder bed laser fusion additive manufacturing of 93W, 5.6Ni, 1.4Fe tungsten heavy alloys

Tungsten exhibits a variety of interesting properties with significant potential for advanced applications but is currently limited by the difficulty of forming complex shapes for end-use parts. Additive manufacturing using powder bed laser fusion techniques may offer an alternative method of forming tungsten parts with greater design flexibility. To investigate this potential, two 93W, 5.6Ni, 1.4Fe tungsten heavy alloy (WHA) powders were densified using a Renishaw AM 400 laser melting system to >99.8% theoretical density and the resulting microstructures assessed. High densification was possible utilizing long exposure times to maximize melting at low laser powers, low to moderate laser powers to avoid overheating the Fe Ni phase, and small point distances, hatch distances, and layer heights to maximize remelting. SEM investigation of the resulting microstructure revealed two distinct phases: nearly pure W and ∼ 90% W-rich W-Ni-Fe. This was believed to be the result of complete melting of the Ni Fe powder and either dissolution of tungsten within the liquid Ni Fe matrix or partial melting of the tungsten powder. High cooling rates in the additive manufacturing process resulted in a tungsten-rich W-Ni-Fe matrix phase compared to traditional liquid phase sintered WHA alloys. Microhardness testing was conducted to begin assessment of resulting mechanical properties, with extremely high hardness values being measured when compared with expected literature values. Fine microstructure and high W content in the matrix phase contribute to these high hardness values, but further investigation is needed.