Microstructures and properties of 80W-20Fe alloys prepared using laser melting deposition process

Tungsten alloys have wide applications due to their high melting point and high density. Traditional fabrication techniques of tungsten alloys, such as liquid phase sintering, usually cause distortion and a large material waste. Laser melting deposition (LMD) additive manufacturing has been considered as a promising new technique to realize the near net forming of tungsten alloys with little heat influence. In this study, thin wall 80W-20Fe alloy samples have been prepared by using LMD. Full dense samples can be obtained when the input volume energy density is larger than 150 J/mm3. As to the microstructure, besides tungsten and iron phases, Fe7W6 intermetallics can also be observed in the prepared samples, as a result of peritectic reaction during non-equilibrium solidification. The intermetallics are distributed as Fe7W6 shells surrounding tungsten phases, or Fe7W6 fragments scattered in the iron matrix. Tungsten phases exist in two forms: the tungsten particles and the tungsten dendrites. The former are un-melted or partially melted raw tungsten powders, while the latter originate from the precipitation of supersaturated tungsten in the liquid iron. With the increasing of input energy density, more tungsten will dissolves in liquid iron, thus leading to an increased proportion of tungsten dendrites after solidification. The formations of Fe7W6 intermetallics and tungsten dendrites significantly increase the hardness and brittleness of prepared tungsten alloys.