Microstructure and electrochemical anodic behavior of Inconel 718 fabricated by high-power laser solid forming

Microstructures and Electrochemical Dissolution Characteristics of Additive-Manufactured Stainless Steel 304 on Different Sections at Low Current Density

Additive manufacturing (AM) is a burgeoning technology for fabricating complex components with high efficiency and low material waste. However, the surface of AM parts is rough owing to partially melted powders and severe surface fluctuation. Electrochemical machining (ECM) is a suitable postprocessing method to finish the surface of the AM parts, and the low current density is usually employed. Our study illustrates the electrochemical dissolution characteristics of the horizontal and vertical sections of the AM SUS 304 component under a low current density and the electrochemical finishing process to obtain smooth surfaces. Linear and fan-shaped melt pools are observed on the horizontal and vertical sections, respectively. Moreover, the melt pool boundaries are vulnerable to dissolution and separate the hollows, basins, and swellings formed after electrochemical dissolution. The two sections display similar current efficiency and polarization because of the single austenitic phase and the identical and uniform elemental content distribution. The top and side surfaces of the AM sample could be efficiently smoothened via ECM by eliminating the partially melted powders and significantly reducing the surface roughness. The numerous band humps make the top surface of the AM sample difficult to smoothen compared with the side surface under the point effect of the electric field.

An investigation on cavitation-corrosion behavior of Ni/β-SiC nanocomposite coatings under ultrasonic field

Ni/β-SiC nanocomposite coating was electroplated on the 17-4 PH SS (precipitation-hardening stainless steel) in modified Watt's bath. The role of cyclic-cavitation (Duty cycle: 50%) on corrosion behavior of Ni/β-SiC nanocomposite coating in 3.5 wt% NaCl solution was investigated using open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results of OCP tests demonstrated that cavitation led to positive shifts in the potential for Ni composite coating, while it caused the potential negative shifts in the case of 17-4 PH SS. The results of the polarization tests under cavitation condition exhibited positive shifts in potential and an increase in current density up to a specific anodic potential. In higher anodic potentials, the cavitation had a reverse effect on potential and current density. Moreover, it increased the overall corrosion current density. EIS measurements illustrated a severe reduction in electrochemical resistance of both 17-4 PH SS (from 228.15 kΩ.cm² to 14.85 kΩ.cm²) and Ni composite coating (from 20.19 kΩ.cm² to 5.00 kΩ.cm²) after 20 h of the cavitation tests. The cumulative mass loss measurements showed that the mass loss for the substrate (10.3 mg.cm^-2) was about five times more than that of Ni composite coating (2.3 mg.cm^-2). Also, in the coated specimen, the incubation time is increased and the growth slop of the accelerating period decreased under cavitation condition.