Thermodynamic analysis of oxidation during selective laser melting of pure titanium

When a pure titanium component is fabricated in a selective laser melting (SLM) process using titanium powder, the oxygen concentration of the SLM sample increases compared to the initial powder. The purpose of this paper is to study the reason for increasing oxygen concentration after SLM.

To understand this phenomenon, the authors analyzed the oxidation behavior during the SLM process thermodynamically.

Based on the laser parameters used in this study, the temperature of the Ti melt during the SLM process was expected to rise to 2,150°C. Based on the thermodynamic analysis, the equilibrium oxygen partial pressure for oxidation was 2.32 × 10⁻¹⁹ atm at 2,150°C when the dissolved oxygen concentration in the titanium is 0.2 wt.%. However, the oxygen partial pressure inside the SLM chamber was 1 × 10⁻³ atm, which is much higher than the equilibrium oxygen partial pressure. Therefore, oxidation occurred during the SLM process, and the oxygen concentration of the SLM sample increased compared to the initial powder.

Most studies on fabricating Ti components using additive manufacturing (AM) have been focused on how the changes in the microstructures and mechanical properties depend on the process parameters. However, there are a few studies that analyzed the oxygen concentration change of Ti during the AM process and its causes. In this study, the authors analyzed the oxidation behavior during the SLM process thermodynamically.