Rafael Parra Ribeiro

The possibility of inducing structural crosslinking and densification of plasma-deposited SiO_x networks by controlling low-energy reaction mechanisms was investigated. For this, films were deposited for 300 s from HMDSO (2%), O₂ (86%) and Ar (12%) mixtures at a working pressure of 15.7 Pa. A radiofrequency signal was used to excite the plasma in a configuration so as to not deliberately induce ion bombardment of the growing layers. The plasma excitation power was varied (100 to 300 W) to promote changes in the deposition mechanisms, which were investigated from deposition rate and layer thickness, chemical structure, elemental composition, topography, roughness, hardness, elastic modulus, corrosion potential, corrosion current density and porosity of the films. Under the experimental conditions studied, inorganic SiO_x thin films (x = 1.8–1.9) with a low carbon content were deposited. The increase in the applied power during the deposition process reduced the number of silanol groups in the coatings, due to dangling bonds recombination by structural crosslinks, which avoided hydroxyl incorporation and silanol formation. As a consequence, the structure became harder, more compact and corrosion resistant.

This study investigated the effects of plasma electrolytic oxidation (PEO) treatment in a Ca- and P-rich electrolyte on the surface of the Ti-6Al-4V alloy with distinct α/β phase proportions previously induced by heat treatments. The results revealed that the α/β phase proportions were successfully altered by the heat treatment temperatures, forming α phase plates surrounded by β phase precipitates. PEO-treated samples exhibited a thick and microsized porous TiO₂ coating in the anatase and rutile crystalline forms. The oxide layer was depleted by Al and V atoms, while Ca and P were gradually enriched along the coatings. Chemical analysis also indicated the absorption of water and organic molecules into the outer layer. PEO-treated samples had microscale roughness and thickness, hydrophilic behavior, and surface energy mainly formed by the dispersive component. The bulk’s elastic modulus decreased with β phase precipitation, while the alloying elements directly influenced the Vickers microhardness. The corrosion tests indicated a stable and protective layer in the PEO-treated samples, showing better corrosion resistance than untreated ones. Overall, the findings indicated that the α and β phase proportion significantly impacts the mechanical properties, while the PEO treatment acts in the corrosion protection and surface aspects, suggesting that combining both approaches could be a powerful tool in biomedical applications.

The possibility of inducing structural crosslinking and densification of plasma-deposited SiOx networks, by controlling low energy reaction mechanisms was investigated. For this, films were deposited for 300 s from HMDSO (2%), O2 (86%) and Ar (12%) mixtures at a working pressure of 15.7 Pa. A radiofrequency signal was used to excite the plasma in a configuration to not deliberately induce ion bombardment of the growing layers. Plasma excitation power was varied (100 to 300 W) to promote changes in the deposition mechanisms, which were investigated from deposition rate and layer thickness, chemical structure, elemental composition, topography, roughness, hardness, elastic modulus, corrosion potential, corrosion current density and porosity of the films. Under the experimental conditions studied, inorganic SiOx thin films (x=1.8-1.9) with low carbon content were deposited. The increase in the applied power during the deposition process reduced the number of silanol groups in the coatings, which became more compact, and consequently, harder and more corrosion resistant.

Ti and its alloys have been vastly employed in the manufacturing of biomedical implants for orthopedy and dentistry, especially the Ti-6Al-4V alloy (wt%), which is the most-used Ti alloy worldwide. However, the ion release of Al and V in the long term has been related to harmful effects on the human body. In this scenario, surface modification strategies, such as plasma electrolytic oxidation (PEO), have often been performed in Ti alloys to match the clinical needs. This study evaluated the effect of electrical AC parameters on the surface of the commercial Ti-6Al-4V alloy immersed in ZrO₂-rich electrolytic solution regarding the chemical, physical, structural, and topographical aspects. Then, the selected PEO-treated samples surpassed the electrochemical test in saline solution. The results indicated that the electrical AC parameters affect the duration and intensity of the oxidative reactions and plasma micro-discharge steps, resulting in porous and thick oxide layers. PEO treatment promoted bio-camouflage of the surface, enriching it with TiO₂, ZrO₂, and ZrTiO₄ compounds and depleting it of Al and V. After screening the PEO-treated samples and their corrosion behavior, the results indicated that the porous ZrO₂–TiO₂ ceramic coatings in the Ti-6Al-4V alloy can be a viable alternative for the manufacturing of biomedical implants.

Due to their lower cost and good mechanical and corrosion properties, ferrous materials such as stainless steel (SS) are commonly used as bio-materials, mainly as surgical instruments and implants. Surface treatments such as plasma electrolytic oxidation (PEO) can be a valuable tool to increase corrosion resistance and enhance the bio-compatibility of metallic materials. In this scenario, the current study evaluated the effect of electrolyte composition on the surface of SS304 submitted to PEO treatment. The variation in the amount of KOH and Ta(OH)₅ promoted significant changes in the surface characteristics, forming Fe-rich oxide plates, Ta-rich agglomerate particles, and an exposed substrate. The PEO-treated substrates were depleted of some alloying elements (Cr, Ni, and Mn), which, allied to the Ta-enrichment, affected the roughness, wettability, phase stability, micro-hardness, and corrosion resistance. All the PEO treatments presented a phase composition of single γ-Fe instead of a dual α + γ phase from the untreated substrate, which was understood in terms of the Ni_eq-Cr_eq diagram. The corrosion tests indicated that the PEO treatment significantly affected the corrosion parameters, having the presence of a non-uniform oxide layer. The findings show that it is possible to control the chemical and phase composition of SS304 material employing PEO treatment.

Fe-based materials have extensive applications in the building and automobile industries due to their excellent mechanical properties and low cost. However, their biomedical employment is restricted by the corrosion propensity when in contact with bodily fluids. In this study, single-step Plasma Electrolytic Oxidation, PEO, treatment in Ta-rich electrolyte was used, for the first time, to improve the corrosion resistance of low-carbon steel SAE 1020 for possible use as device implants. The effect of the applied voltage on the chemical and phase composition, topography, wettability, roughness, and corrosion properties were addressed. The results indicated that the Fe-based oxide coatings had a rough and hydrophilic surface, increasing the Ta content with the applied potential. The phase composition of the coatings was mainly composed of hematite (Fe₂O₃), with the Fourier-transform Infrared Spectroscopy, FTIR, spectrums indicating the presence of some absorbed water and organic molecules. The corrosion resistance of the PEO-treated samples was better than the substrate against saline solution (0.9% NaCl) due to the Fe₂O₃ growth decorated with Ta particles, especially the sample treated at 200 V. The results state that Ta-enriched Fe-based oxide coatings could significantly improve the applicability of low-carbon steel SAE 1020 as a low-cost biomaterial, particularly for medical devices.