An insight into the evolution of corrosion resistant coatings on titanium during bipolar plasma electrolytic oxidation in sulfuric acid

Cleaning Strategies of Synthesized Bioactive Coatings by PEO on Ti-6Al-4V Alloys of Organic Contaminations

The effect of various cleaning methods on coating morphology and their effectiveness in removing organic contaminants has been studied in this research. Bioactive coatings containing titanium oxides and hydroxyapatite (HAP) were obtained through plasma electrolytic oxidation in aqueous electrolytes and molten salts. The cleaning procedure for the coated surface was performed using autoclave (A), ultraviolet light (UV), radio frequency (RF), air plasma (P), and UV-ozone cleaner (O). The samples were characterized using scanning electron microscopy (SEM) with an EDS detector, X-ray photoelectron spectroscopy (XPS), X-ray phase analysis (XRD), and contact angle (CA) measurements. The conducted studies revealed that the samples obtained from molten salt exhibited a finer crystalline structure morphology (275 nm) compared to those obtained from aqueous electrolytes (350 nm). After applying surface cleaning methods, the carbon content decreased from 5.21 at.% to 0.11 at.% (XPS), which directly corresponds to a reduction in organic contaminations and a decrease in the contact angle as follows: A > UV > P > O. This holds true for both coatings obtained in molten salt (25.3° > 19.5° > 10.5° > 7.5°) and coatings obtained in aqueous electrolytes (35.2° > 28.3° > 26.1° > 16.6°). The most effective and moderate cleaning method is ozone treatment.

An Accurate Model of the Corrosion Current Density of Coatings Using an Adaptive Network-Based Fuzzy Inference System

Corrosion resistance coating is fabricated using epoxy/glass flake (E/GF) composites and is utilized to prolong the lifespan of cold-rolled steel (CRS) metal substrates. An in situ synthesis approach was adopted to prepare the composite coating at different levels of synthesis parameters, including a load of filler and coating thickness. In addition, this work shows the effects of the chemical functionalization of the filler on the corrosion protection property of the epoxy/functional glass flake (E/FGF) composite coatings. The effects of the modification of the filler, as well as the other synthesis parameters, on the corrosion resistance property are evaluated using a potentiodynamic polarization technique. Here, the corrosion resistance property is evaluated based on the observed current density. The primary goal of this work is to present an accurate model of corrosion current density (CCD). By using measured data, a precise model, which simulates the corrosion resistance properties of the coatings, has been created by an adaptive network-based fuzzy inference system (ANFIS) in terms of glass flake loading, chemical functionalization, and coating thickness. The obtained results revealed good agreement between ANFIS-based modelling and the measured dataset. The root mean square errors of the prediction model were 8.1391 × 10−8 and 0.0104 for training and testing, respectively. The coefficient of determination (R2) values of the ANFIS output were found to be 1.0 and 0.9997 for training and testing, respectively. To prove the superiority of the ANFIS-based model of CCD, the achieved results were compared with an analysis of variance (ANOVA). ANOVA utilizes a linear regression approach to get the model. Thanks to ANFIS, compared with ANOVA, the values of R2 are increased by 10% and 18.6% for the training and testing phases, respectively. Finally, the accuracy of the ANFIS model of corrosion current density is validated experimentally.

Addition of Organic Acids during PEO of Titanium in Alkaline Solution

This research study describes recent advances in understanding the effects of the addition of organic acids, such as acetic, lactic, citric and phytic acids, on the process of plasma electrolytic oxidation (PEO) on Ti using an alkaline bath. As the plasma developed over the workpiece is central to determine the particular morphological and structural features of the growing oxide, the focus is then on the inter-relationships between the electrolyte and the resultant plasma regime established. In situ optical emission spectroscopy (OES) allowed us to verify a marked plasma suppression when adding low-molecular-weight anions such as acetates, resulting in short-lived and well-distributed discharges. Conversely, when more bulky anions, such as lactates, citrates and phytates, were considered, a less efficient shielding of the electrode caused the build-up of long-lasting and destructive sparks responsible for the formation of thicker coatings, even >30 µm, at the expense of a higher roughness and loss of compactness. Corrosion resistance was tested electrochemically, according to electrochemical impedance spectroscopy (EIS), and weight losses evidenced the coatings produced in the solution containing acetates to be more suitable for service in H2SO4.

Investigation of Biocompatible PEO Coating Growth on cp-Ti with In Situ Spectroscopic Methods

The problem of the optimization of properties for biocompatible coatings as functional materials requires in-depth understanding of the coating formation processes; this allows for precise manufacturing of new generation implantable devices. Plasma electrolytic oxidation (PEO) opens the possibility for the design of biomimetic surfaces for better biocompatibility of titanium materials. The pulsed bipolar PEO process of cp-Ti under voltage control was investigated using joint analysis of the surface characterization and by in situ methods of impedance spectroscopy and optical emission spectroscopy. Scanning electron microscopy, X-ray diffractometry, coating thickness, and roughness measurements were used to characterize the surface morphology evolution during the treatment for 5 min. In situ impedance spectroscopy facilitated the evaluation of the PEO process frequency response and proposed the underlying equivalent circuit where parameters were correlated with the coating layer properties. In situ optical emission spectroscopy helped to analyze the spectral line evolutions for the substrate material and electrolyte species and to justify a method to estimate the coating thickness via the relation of the spectral line intensities. As a result, the optimal treatment time was established as 2 min; this provides a 9-11 µm thick PEO coating with Ra 1 µm, 3-5% porosity, and containing 75% of anatase. The methods for in-situ spectral diagnostics of the coating thickness and roughness were justified so that the treatment time can be corrected online when the coating achieves the required properties.

Hybrid Organic-Inorganic Materials on Metallic Surfaces: Fabrication and Electrochemical Performance

In recent years, hybrid organic-inorganic (HOI) materials have attracted massive attention as they combine the unique properties of organic and inorganic compounds. In this review, we focus on the formation of HOI materials and their electrochemical performance that can be controlled by microstructural design depending upon their chemical composition. This overview outlines the recent strategies of preparing HOI materials on metallic surface via wet-electrochemical systems, such as plasma electrolysis (PE) and dip chemical coating (DCC). The corresponding electrochemical behavior for short and long term exposures is also summarized.