The Changes of Rheological Behavior of Ti-6Al-4V Alloy Powders for Additive Manufacturing by Powder Oxidation

Abstract

Laser Powder Bed Fusion (L-PBF) has recently attracted significant attention as a new method for fabricating three-dimensional metallic parts with complex structures. For energy saving and cost reduction, the reuse of feedstock powders has been recommended for L-PBF. However, it is reported that the powder surface is usually oxidized during L-PBF process. Even though the influence of oxygen content on the mechanical properties of L-PBF builds has been investigated by some researchers, the effect of surface oxidation on the powder flowability is still controversial. In order to control the oxygen content and the homogeneity of oxidized powders, a powder oxidation approach using a wet mixing process with aqueous hydrogen peroxide was developed in this study. By taking Ti-6Al-4V alloy powder as a model material, the relationship between powder oxidation and flowability was experimentally investigated. The Ti-6Al-4V powders were successfully oxidized via the wet mixing process without changing their morphology or particle size distribution. However, the oxidized powders had better flowability rather than the raw powders. As demonstrated by STEM-EDS mappings, the surface oxide layer of oxidized powder was continuous, and its thickness was increased by approximately 30 nm comparing with the raw powder. This result indicates that the improved flowability was mainly attributed to the decrease in van der Waals force caused by the increased surface roughness of the powders. This research offers the potential of utilizing the wet mixing process with aqueous hydrogen peroxide for adjusting oxygen contents of Ti alloy powders.