Surface Characterization of Titanium Powders with X-ray Photoelectron Spectroscopy

Abstract

Electron Beam Melting (EBM)is a near-net-shape additive manufacturing technology developed by Arcam AB, where Ti-6Al-4V alloy powder is commonly used to manufacture medical implants and components for the aerospace industry. Although Arcam has developed special specifications of some parameters for the powders, the powders from different manufacturers do not behave in the same way in the EBM process. Differences also have been detected for powder that have been reused in the process. It is believed that the variations in the behaviour in the process arise due to differences in the native oxide surface layer of the powder particles. Therefore, the aim of this project was to characterize the surface oxides on Ti-6Al-4V powders in order to compare powders from different manufacturers, new and recycled powders as well as powder before and after an anti-satellite treatment made to reduce small particles (satellites) on the powder surfaces. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to obtain information about the chemical composition, the in-depth distributions, the chemical states of the elements in the surface oxide, the oxide thickness, as well as the shape and the morphology of the powder particles. The results showed that the surface oxide contained titanium mostly in the form of TiO2 and aluminium in the form of Al2O3 in all samples. The vanadium was impoverished at the powder surface whereas the aluminium content was enriched. Yttrium was also found on the powder surfaces from one manufacturer. The investigation of the new and recycled particles showed that the vanadium content was higher on the outermost surface. Furthermore, the powder surface was rougher, and, after several cycles of recycling, the surface oxide was thicker. The anti-satellite treatment did not affect the chemical composition, the chemical state or the oxide thickness.