Investigation on the stress corrosion cracking susceptibility of an alloy 718 prepared by laser powder bed fusion assessed by microcapillary method

The study focused on evaluating the stress corrosion cracking (SCC) behaviour of alloy 718 processed by laser powder bed fusion (L-PBF), also called selective laser melting (SLM), with different laser powers, in a solution containing chloride, using the microcapillary method under constant tensile load. An analysis of the surface defects, hardness, and microstructure of the samples under examination was carried out and a correlation was sought between these results and those obtained by electrochemical investigations. The polished surface of the samples was observed under the optical microscope, as was the electro-etched surface. Vickers hardness measurements were carried out. Electrochemical polarization tests were used to evaluate the resistance of the passive layer on the surface of the material. Potentiodynamic and galvanostatic polarization tests were performed. The tests were carried out on as-printed samples and samples under tensile load. The results were compared with conventionally produced counterparts. The microstructure and stress corrosion cracks were observed under the scanning electron microscope (SEM). The 115W laser power produced samples with a lower defect density; therefore, the highest resistance to localized corrosion was found. L-PBF samples under tensile load showed corrosion and SCC resistance superior to that of conventional material. In the L-PBF samples, submicronic cracks were detected adjacent to the boundaries of the subgrain, and the mechanisms that led to their appearance were explained as a synergistic effect of various microstructural factors, specifically, the greater corrosion resistance of the subgrain boundary and the high concentration of dislocations in the adjacent area. The fine microstructure of the L-PBF samples generated much smaller cracks than those observed on the conventional material, which explains the increased resistance to SCC observed in electrochemical tests.