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

Fractal Characterization of the Mass Loss of Bronze by Erosion-Corrosion in Seawater

The fractal approach is one of the nondestructive techniques for analyzing corrosion's effects on different materials. This article utilizes it to analyze the erosion-corrosion produced by cavitation on two types of bronze introduced into an ultrasonic cavitation field to investigate the differences between their behavior in saline water. The aim is to check the hypothesis that the fractal/multifractal measures significantly differ for the studied materials that belong to the same class (bronze) as a step in applying fractal techniques to distinguish between two materials. The study emphasizes the multifractal characteristics of both materials. While the fractal dimensions do not significantly differ, the highest multifractal dimensions correspond to the sample of bronze with Sn.

Artificial Intelligence Models for the Mass Loss of Copper-Based Alloys under Cavitation

Cavitation is a physical process that produces different negative effects on the components working in conditions where it acts. One is the materials' mass loss by corrosion-erosion when it is introduced into fluids under cavitation. This research aims at modeling the mass variation of three samples (copper, brass, and bronze) in a cavitation field produced by ultrasound in water, using four artificial intelligence methods-SVR, GRNN, GEP, and RBF networks. Utilizing six goodness-of-fit indicators (R², MAE, RMSE, MAPE, CV, correlation between the recorded and computed values), it is shown that the best results are provided by GRNN, followed by SVR. The novelty of the approach resides in the experimental data collection and analysis.

Effect of Cavitation Intensity on the Cavitation Erosion Behavior of 316L Stainless Steel in 3.5 wt.% NaCl Solution

In this study, the cavitation erosion behavior of 316L stainless steel under different cavitation intensities in 3.5 wt.% NaCl solution was investigated with scanning electron microscopy and various electrochemical tests. Results indicated that cavitation intensity corresponding to CE amplitude of 5 μm was lower than that of the mechanical bearing capacity of passive films. When subjected to cavitation erosion (CE), Open circuit potential (OCP) shifted to the noble direction instantaneously, which was mainly attributed to enhanced oxygen transfer of the cathode due to stirring effects of CE. By contrast, high cavitation intensities corresponding to CE amplitudes of 25 μm and 55 μm exceeded the mechanical bearing capacity of passive films, causing significantly reduced OCP associated with metal dissolution of the anode from mechanical damage. Potentiostatic polarization and Mott–Schottky tests showed that 316L SS subjected to low cavitation intensities displayed good repassivation properties. However, repassivation performance was markedly weakened when high cavitation intensity was applied, resulting in weaker protection of the passive films with high carrier density.

Ultrasonic-assisted electrodeposition of Cu-Sn-TiO2 nanocomposite coatings with enhanced antibacterial activity

Copper-based coatings are known for their high antibacterial activity. In this study, nanocomposite Cu-Sn-TiO₂ coatings were obtained by electrodeposition from an oxalic acid bath additionally containing 4 g/dm³ TiO₂ with mechanical and ultrasonic agitation. Ultrasound treatment was performed at 26 kHz frequency and 32 W/dm³ power. The influence of agitation mode and the current load on the inclusion and distribution of the TiO₂ phase in the Cu-Sn metallic matrix were evaluated. Results indicated that ultrasonic agitation decreases agglomeration of TiO₂ particles and allows for the deposition of dense Cu-Sn-TiO₂ nanocomposites. It is shown that nanocomposite Cu-Sn-TiO₂ coatings formed by ultrasonic-assisted electrodeposition exhibit excellent antimicrobial properties against E. coli bacteria.

The influence of semiconducting properties of passive films on the cavitation erosion resistance of a NbN nanoceramic coating

To alleviate the cavitation damage of metallic engineering components in hydrodynamic systems operating in marine environments, a NbN nanoceramic coating was synthesized on to a Ti-6Al-4V substrate via a double cathode glow discharge technique. The microstructure of the coating consisted of a ~13 μm thick deposition layer of a hexagonal δ'-NbN phase and a diffusion layer ~2 μm in thickness composed of face-centered cubic (fcc) B1-NaCl-structured (Ti,Nb)N. The NbN coating not only exhibited higher values of H/E and H²/E than those measured from NbN coatings deposited by other techniques, but also possessed good adhesion to the substrate. The cavitation erosion resistance of the NbN coating in a 3.5 wt% NaCl solution was investigated using an ultrasonic cavitation-induced apparatus combined with a range of electrochemical test methods. Potentiodynamic polarization measurements demonstrated that the NbN coated specimens demonstrated both a higher corrosion potential (E_corr) and lower corrosion current density (i_corr) than the uncoated substrate. Mott-Schottky analysis, combined with the point defect model (PDM), revealed that, for a given cavitation time, the donor density (N_D) of the passive film on the NbN coating was reduced by 1 ~ 2 orders of magnitude relative to the uncoated Ti-6Al-4V, and the diffusivity of the point defects (D₀) in the passive film grown on the NbN coating was nearly one order of magnitude lower than that on the uncoated substrate. In order to better understand the experimental observations obtained from Mott-Schottky analysis and double-charge layer capacitance measurements, first-principles density-functional theory was employed to calculate the energy of vacancy formation and the adsorption energy for chloride ions for the passive films present on both the NbN coating and bare Ti-6Al-4V.

Ultrasound-assisted electrodeposition and synthesis of alloys and composite materials: A review

The development of electrodeposited materials with improved technological properties has been attracting the attention of researchers and companies from different industrial sectors. Many studies have demonstrated that the electrodeposition and synthesis of alloys and composite materials assisted by ultrasound may promote the de-agglomeration of particles in the electrolytic solution due to microturbulence, microjets, shock waves, and breaking of Van der Waals forces. The sonoelectrochemical technique, in which the ultrasound probe acts as a working electrode, also has been used for the formation of nanostructures in greater quantity, in addition to accelerating the electrolysis process and eliminating the reaction products on the electrode surface. Regarding the morphological aspects, the acoustic cavitation promotes the formation of smooth and uniform surfaces with incorporated particles homogeneously distributed. These changes have a direct impact on the composition and physical properties of the material, such as corrosion resistance, magnetization, wear, and microhardness. Despite the widespread use of acoustic cavitation in the synthesis of nanostructured materials, the discussion of how process variables such as acoustic power, frequency, and type of ultrasound device, as well as their effects still are scarce. In this sense, this review discusses the influence of ultrasound technology on obtaining electrodeposited coatings. The trends and challenges in this research field were reviewed from 2014 to 2019. Moreover, the effects of process variables in electrodeposition and how these ones change the technological properties of these materials were evaluated.

Corrosion and material alterations of a CuZn38Pb3 brass under acoustic cavitation

An alloy that is exposed to cavitation may experience mechanical cavitation damages as well as accelerated corrosion. In the present paper, the evolution of corrosion erosion behavior of brass samples (CuZn38Pb3) during continuous exposure to ultrasonic cavitation in a salt solution (NaCl) was investigated. Various samples were sonicated for times between 0 min and 5 h. The average surface roughness and the effective surface area of the samples were measured by confocal microscopy, and the surfaces were inspected by scanning electron microscopy. Different erosion behavior of the phases present on the surface is discussed. Complementary to the surface inspection, the corrosion behavior of the samples before, during and after sonication was investigated through open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The results show that at the initial times of sonication preferably the lead islets were removed from the brass surface, resulting in a change in the open circuit potential. α and β' phases showed ductile and brittle behavior under sonication, respectively. The corrosion rate of the alloy under cavitation increased as the sonication time increased, mainly related to the increase in effective surface area and the rise of plastic deformation of the surface material.