RESUMEN
The effect of temperature on the localized corrosion resistance and passive film characteristics of laser powder-bed fusion (LPBF) 316L (UNS S31603) was studied in a buffered 3.5 wt% NaCl solution at 25, 50, and 75 °C. DC techniques such as cyclic potentiodynamic polarization showed lower passive current densities, high breakdown potentials, and a higher resistance to initial breakdown compared with wrought 316L samples at all temperatures. However, LPBF 316L was more susceptible to metastable pitting at potentials before film breakdown and higher damage accumulation post film breakdown. AC techniques, such as Mott-Schottky analysis and electrochemical impedance spectroscopy, showed that the formed passive film was more robust on the LPBF 316L samples at all temperatures, accounting for the higher initial resistance to pitting. However, with increasing temperatures, the film formed had an increasing concentration of defect density. Passive compositions at the various test temperatures studied using X-ray photoelectron spectroscopy (XPS) showed that the LPBF samples showed higher amounts of Cr and Fe oxides and hydroxides compared with the wrought samples, which made the passive films on the LPBF samples more compact and protective. Investigation of the pits formed on the LPBF showed the preferential regions of attack were the melt-pool boundaries and cell interiors due to their being depleted of Cr and Mo when compared with the boundaries and matrix.
RESUMEN
In this work, the passivation and localized corrosion of selective laser melted (SLM) stainless steel 316 L when exposed to high pressures of CO2 with the presence of H2S and Cl- at 25 °C and 125 °C were studied. Depletion of Cr/Mo was observed at the cell interiors and melt-pool boundaries (MPBs) compared to the cell boundaries. Volta potential differences obtained from scanning Kelvin probe force microscopy (SKPFM) showed that the MPBs were 8-20 mV lower than the matrix, while the cell interiors were 20-50 mV lower than the cell boundaries. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky tests indicated a more defective passive film at 125 °C, and X-ray photoelectron spectroscopy (XPS) confirmed the formation of a less protective film with an increased S/O ratio at 125 °C than 25 °C. Initiation of localized corrosion was observed at the MPBs and pits formed after a week of immersion were wider by an order of magnitude at 125 °C than 25 °C, with evidence of cell-interior dissolution. While passivity was observed even at elevated temperatures, local chemical heterogeneities compromised the stability of the film and contributed to localized corrosion in SLM SS316L.
RESUMEN
Currently, permanent vascular stents are fabricated using titanium and stainless steel implants that are nondegradable and offer high stability, but they have certain disadvantages. For example, the prolonged exposition of aggressive ions in the physiological media and the existence of defects in the oxide film create conditions for corrosion to occur, thus triggering unwanted biological events and compromising the mechanical integrity of the implants. Moreover, when the implant does not need to be permanent, there is the need to submit the patient for a second surgery for implant removal. As a solution for nonpermanent implants, biodegradable magnesium alloys have been deemed a promising substitute, for example, for cardiovascular-related applications and the construction of orthopedic devices. A biodegradable magnesium alloy (Mg-2.5Zn) reinforced by zinc and eggshell was employed in this study as an environment-conscious magnesium (eco) composite (Mg-2.5Zn-xES). Disintegrated melt deposition (DMD) was used to fabricate the composite. Experimental studies were conducted to investigate the biodegradation performance of Mg-Zn alloys containing 3 and 7 wt % eggshell (ES) in simulated body fluid (SBF) at 37 °C. Different corrosion techniques were used to study the corrosion behavior of the Mg-2.5Zn-xES composites, including weight loss measurements, hydrogen evolution, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning vibrating electrode technique (SVET). Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were employed to scrutinize the corroded surfaces' morphology and composition. The outcomes indicated that Mg-2.5Zn-3ES possesses the lowest degradation activity.