Effects of powder surface conditions on the rheological behavior of Ti-6Al-4 V alloy powders for additive manufacturing

Laser powder-bed fusion (L-PBF) is a promising manufacturing process for fabricating metallic parts with tailored architectures. A feedstock powder with good flowability is required to homogeneously deposit the powder on the building substrate and obtain reliable and high-quality L-PBF products. Although the effects of powder morphology and particle size on flowability have been widely investigated, the relationship between powder surface conditions and rheological behaviors is not well established. Therefore, in this study, the surface conditions of Ti-6Al-4 V alloy powders were intentionally adjusted through conventional heat treatments under different gas atmospheres. The morphology and particle size distribution of the Ti-6Al-4 V powder heat treated at 773 K in air (Air773) and Ar (Ar773) atmospheres remained unchanged compared to those of the untreated powder. However, the quantity of surface oxides on the Air773 powder increased, enhancing the decoration of surface hydroxyl groups, as illustrated by water wettability tests. By contrast, the oxide layer of the Ar773 powder decomposed and dissolved into the matrix, resulting in the generation of fresh metallic surfaces. Consequently, the flowability of the Air773 powder increased, whereas that of the Ar773 powder tended to decrease, thereby deteriorating the quality of powder beds during the recoating process. The results prove that the cohesive strength of Ti-6Al-4 V powder is more strongly determined by metallic Ti-Ti interactions than by hydrogen bonds. Thus, the effective approach for adjusting the powder surface conditions presented in this study offers new insights into the potential for economically developing high-performance Ti alloy components by controlling the powder properties and L-PBF process.

Automated summary

This study intentionally adjusted the surface conditions of Ti-6Al-4 V alloy powders through heat treatments and investigated their effects on flowability. The results showed that the increase in surface oxides enhanced the flowability of the powders, while the decomposition of the oxide layer decreased flowability, thereby affecting the quality of the powder beds. The study demonstrated that metallic interactions are more important for the cohesive strength of the powders.