Influence of particle size on surface oxide of 316L stainless steel powders for hot isostatic pressing

The powder oxide state is essential for resilient powder metallurgy components using Hot Isostatic Pressing (HIP) process. In fact, it can affect the behaviour of the powder during the different additive manufacturing processes. However, the oxide layer properties as a function of particle size are not well known yet. This work summaries a detailed surface characterization of different 316L particles' size of a gas atomization powder to permit a better understanding and control of additive manufacturing processes. X-ray photo-electron spectroscopy (XPS), Raman spectroscopy, Transmission Electron Microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) were combined to characterize the surface condition of the powders. The results show an evolution of the oxide thickness in function of the particle's size. This oxide appears like an amorphous micro-structure. An evolution of its composition can be observed through the oxide. The main composition is iron oxide (FeO and Fe3O4 types), chromium oxide (Cr2O3 type) and manganese oxide ( Mn2O3 type). In addition, nanometric nodules of manganese oxide ( MnO type) were observed on the particles' surface by TEM and Scanning Electron Microscope (SEM). These variations can explain behaviour difference between small and large particles.