Inclusion of nano silicon particle in SS316L through LPBF and its responses on corrosion behaviour

Abstract

In this research work, laser powder bed fusion (LPBF) based stainless steel 316L (SS316L) was fabricated and its corrosion behaviour was analysed for the oil-gas piping application. The Field Emission Scanning Electron Microscopy (FESEM) analysis of the LPBF SS316L specimen revealed the presence of 1–2 μm size honeycomb structure and 2–10 μm size tabular structures. Nano-size particles in the range of 100 nm–500 nm were formed between the two tabular cells as well as their boundary regions in the LPBF SS316L specimen. The energy-dispersive X-ray spectroscopy (EDS) analysis of the nanoparticle confirmed the presence of Si with a percentage of 1.4% along with 15.9% of Cr and 1.6% of Mo that have the characteristic of dispersion strengthening of the LPBF SS316L specimen. In addition, the δ-ferrite phase was observed in tabular structure boundaries and intercellular regions of solute in the LPBF SS316L specimen. Moreover, among the three crystallographic orientations {001}{101}and {111}, no domination behaviour was observed from the Electron Backscatter Diffraction (EBSD) study. The Transmission Electron Microscopy (TEM) analysis confirmed the presence of nano twin structures that had a span of several nm on the FCC austenite unit cell. These twins came under the {111} category twining that often occurred in FCC metals. A potentiodynamic polarization test was conducted on the LPBF SS316L specimen at five different time periods (i.e., 0, 7, 15, 34 and 56 h) and it was assessed that the 0 and 15 h immersion specimens exhibited superior corrosion resistance compared with other LPBF SS316L specimens. The Nyquist plot revealed that the 0 and 15 h immersion specimens offered the highest resistance value of 1846.1Ω and 1720.3 Ω, respectively against corrosion. The Bode plots of the LPBF SS316L specimen followed a similar trend as the Nyquist plots.