Effect of track spacing on porosity of metallic foam fabricated by laser melting deposition of Ti6Al4V/TiH2 powder mixture

We fabricated porous metallic materials using laser melting deposition, wherein a mixture of a metal powder and a foaming agent is sprayed while a high-energy laser is irradiated on it to melt and deposit it, resulting in foaming action. To fabricate the porous materials, we used a powder of Ti6Al4V alloy. TiH2, a foaming agent, was employed to create pores within the deposited material. The track spacing was varied to examine its effect on the foaming characteristics and the porosity and pore size and distribution of the deposited material. We also investigated the effects of representative process parameters, including the laser power, foaming agent content, and powder feed rate. The results showed that, when the track spacing was smaller than the width of the deposited beads, pores were generated by the foaming agent. In the opposite case, however, open-cell pores were created between the tracks. This was because the fluidity of the molten metal varied with the track spacing, confirming that the porosity can be adjusted by changing the track spacing. Moreover, as the laser power was decreased or the powder feed rate increased, the porosity increased. Hence, the porosity is related to the cooling rate of the molten metal.