The Effects of Morphology and Surface Oxidation of Stainless Steel Powder in Laser Based-Powder Bed Fusion
This work therefore addresses three grades of 316L stainless steel powder with regard to the surface oxide characteristics and processability in AM, a vacuum induction melted and inert gas atomized (VIGA) grade, an air-melted and nitrogen gas atomized (GA) grade and a water-atomized (WA) grade. The chemical surface characterization revealed that the two gas-atomized powders had comparable oxidation states, with minor differences in particulate coverage between the two grades. Since the GA powder contained more Si, it was found in higher concentrations in the oxide particulates. The WA grade, however, had a larger surface coverage of particulates (rich in Cr and Si), yet had a thinner oxide layer surrounding the particulates compared to the gas atomized grades. However, the particulate features on the WA grade did not seem to affect the printability, as densities of > 99.95% were reached without discernible defects in the microstructure. While the printability was comparable with the GA grade at a layer thickness of 20 µm, the limitation of the WA powder were noticed at a higher layer thicknesses (40 µm), where up to about 1 vol.% of porosity was obtained.
Furthermore, LB-PBF processing of WA powder was found to result in a rather homogenous precipitation of nanometric oxide inclusions within the microstructure. Consequently, this work investigated whether the oxide inclusions could contribute to an oxide dispersion strengthening effect. The average size of these oxides was found to be 56 nm, with an average number density of 2.8 × 1015 m-3. The oxides were observed to be amorphous with a characteristic core-shell structure. Concerning the mechanical strength, the WA samples had slightly reduced yield strength (~500 MPa) in comparison to the GA samples (~600 MPa). Hence, no oxide dispersion strengthening effect was observed, as the average size and number density of oxides was not optimized.
316L stainless steel
laser based-powder bed fusion
Chalmers, Industri- och materialvetenskap, Material och tillverkning
Riabov, D., Hryha E., Rashidi M., Bengtsson, S., Nyborg L., Effect of Atomization on Surface Oxide Composition in 316L Stainless Steel Powders for Additive Manufacturing
Factors Affecting Printability of 316L Powders Using the DMLS Process
Proceedings of World PM 2018,; (2018)
Paper i proceeding
Riabov D., Rashidi M., Hryha E., Bengtsson S., Effect of the powder feedstock on the oxide dispersion strengthening of 316L stainless steel produced by laser powder bed fusion
Metallurgi och metalliska material
Thesis for the degree of licentiate of engineering / Department of Materials Science and Engineering, Chalmers University of Technology: IMS-2020-4
Chalmers tekniska högskola
VDL, Chalmers Tvärgata 4C
Opponent: Dr. Seshendra Karamchedu, Uddeholms AB, Sweden