Corrosion and wear properties of graphene based composite coatings

Nowadays, there is a lot of material loss due to corrosion, wear and breakage, and as a result, material degradation causes great economic losses. Preventing these losses is one of the biggest research areas of today's engineers. Different disciplines come together and bring out different ideas in a determined way. Adding different properties to an existing material without producing a new material is a very reasonable solution. Corrosion and cracks in the material start on the surface and can lead to material loss. Surface engineering reveals very different studies in this field. Chromium (Cr) coatings have been used very efficiently for a long time to improve surface properties. However, the production process is quite hazardous in terms of environmental factors and human health, and its use is limited. As an alternative to this method, current and outdated coatings have been developed and their development is continued by researchers. "Electroless coating is a chemical reduction process based on the catalytic reduction of a metallic ion from an aqueous solution containing a reducing agent without using electrical energy and without depositing the metal on the surface. It is used to obtain a more uniform coating thickness. Current coating is more widely used than electroless plating. A thicker coating layer is obtained at lower temperatures, around 50-60 ° C, at lower cost and in a shorter time. Another advantage is the density of the current, and the pulsed current delivered can be used as an additional parameter. Many materials, both anodic and cathodic, are coated with current "The main matrix is a metal, alloy, ceramic or polymer, and the particles can be spherical, angular, plate-like, layered or core-shell-like. In addition, their sizes can vary from millimeters to several nm. Nickel is widely used as a matrix in composite coatings because it is resistant to high temperatures, has high oxidation resistance, and also has a high alloying ability with other metals. It also reduces nickel (Ni) grain growth and electrocrystallization of grains and provides significant adhesion. Characteristic features of the nickel-phosphorus (Ni-P) alloy exhibited by nickel-based coatings; It is frequently applied in the coating industry due to its mature production process and controllable coating performance. It shows high hardness, good corrosion resistance and wear resistance in Ni-P alloy coatings. "Due to their affordable cost, mechanical and lubricating properties, flux nickel-phosphorus (Ni-P) coatings can be used for sensitive aluminum alloys, the quality of which depends on the adhesion behavior of aluminum. The formation of an oxide layer at the moment when the surface of the aluminum comes into contact with air significantly reduces the adhesion of the coatings. Therefore, appropriate pretreatments are carried out on aluminum alloys before the current coating process. Graphene has a hexagonal lattice structure and is a good solid lubricant due to the single layers of carbon atoms in the lattice. It has very high thermal and electrical conductivity due to the high electron movement at ambient temperature. This Due to the advantages, graphene is added to coatings as composite reinforcement. Graphene reinforced in a metal matrix can exhibit excellent wear and corrosion behavior. The ability to exhibit these properties is directly proportional to the effective homogeneous distribution of graphene in the solution. In their study, Uysal and colleagues applied Ni-W-TiO2 coating solution They reinforced GO(GO) and claimed that a significant decrease in the friction coefficient occurred (from 0. 6 to 0. 2). It is widely used in pulsed current (PC) coating technologies. Larger grains are observed when the intensity of the supplied current is low. A rapid decrease in ion concentration at high current results in the formation of a rough surface. The crystalline grain size is very suitable because the chemistry of the alloy offers a controllable production process using batch current, which has the advantages of dispersion, control of surface particles, improved powder morphology, good hardness and good wear resistance. Examining the production of nanocomposite coatings by electrolytically co-deposition of metallic and fine (small) ceramic particles in plating baths has been widely studied in recent years. Nanomaterials are produced by two basic technical methods: "bottom-up" and "top-down" techniques. In the bottom-up technique, the material develops from the bottom up (atom by atom, molecule by molecule, or cluster by cluster). In this technique, colloid dispersion is produced. The top-down technique starts with the bulk material and progresses towards the ideal state by engineering or etching it. This technique is similar to electron beam lithography in which patterns are used. Bottom-up and top-down techniques play an important role in the nanotechnology industry. The biggest advantage of both techniques is the creation of ultra-small structures with high purity. However, using the bottom-up method produces improved nanostructures such as less or defect-free, homogeneous, and long- and short-term assemblies; all of which result in thermally stable nanomaterials due to free Gibbs energy decreases. However, in the top-down technique, the material often suffers an increase in surface defects as the material is subjected to internal stress. Interest in electrolytic nanocomposite materials has increased rapidly over the last 20 years due to the properties of nanocomposite coatings such as high wear resistance, good corrosion and oxidation resistance at high temperatures, and self-lubrication on coated surfaces. In research on electrolytic nanocomposite coatings; Studies have been carried out to determine the optimum conditions such as composition of the bath, concentration of particles, temperature and current density for the production of coatings. Metal matrix composite coatings can be produced by electrodeposition, which is the deposition of polymeric or ceramic fine particles in an electrolytic bath metal matrix. Electrodeposition; It is a low-temperature process to produce nanocomposite coating in a simple step without a second process. Particles in the form of particles, fibers or whiskers can be used as secondary phase material. In this study, an aluminum surface with low oxidation resistance was coated with Ni-P-GO using the existing method and its electrochemical properties were examined. GO is one of the most popular solid lubricants in recent years. Steel bases were used in composite coating works. The surfaces of the substrates, which were cut in 3x3.5 cm dimensions, were prepared by sanding and polishing when necessary. Before coating, the substrates were subjected to alkaline and acidic cleaning processes. A solution with a concentration of 20% NaOH-80% H2O by volume was used for alkaline cleaning, and a solution with a concentration of 40%HCl-60%H2O by volume was used for acidic cleaning. After cleaning, the parts were rinsed abundantly with pure water and transferred to the plating bath without waiting. Phase analysis of the obtained samples was carried out using Rigaku brand D/MAX 2000 model XRD device. Potentiodynamic polarization (Tafel) analysis was applied to determine electrochemical properties and corrosion rates. Potentiodynamic polarization measurements were performed using the Gamry Interface 1000 Potentiostat. Tafel corrosion experiments were carried out in 3.5 wt% NaCl solution at room temperature. Corrosion tests were carried out using a classical three-electrode cell. Saturated calomel electrode (SCE), Pt, and samples with a working area of 1 cm2 were used as reference, counter, and working electrodes, respectively. The Tafel curve was obtained by potential scanning in the range −1.0 V to +1.0 V. In experimental studies, microhardness studies were carried out for coatings obtained from different bath compositions. Measured using Vickers hardness analysis to measure the hardness of the coating layer. At least 5 measurements were made on each sample. The hardness of the layer coated on the material was measured by immersing the section with a square pyramid-shaped tip under load for a certain period of time. In this study, a very good corrosion rate value (up to approximately 10 mpy) was obtained by adding Ni-P to the alloy matrix. It was applied in different operating cycles and with the increase of Ton time, the grain size decreased to approximately 28 nm. With increasing Tone duration, the hardness value was obtained as 592HV for the sample with the highest Tone duration. Considering the literature, these results are compatible with conventionally produced flow Ni-P coatings. The coating with the best wear properties was obtained in the sample produced under 80% duty cycle conditions. Another reason for the improvement of wear behavior is the increase in the hardness of composite coatings due to the high hardness of GO and the dispersion hardening effect it creates in the coating layer. The higher volume of GO particles in the coating layer added a high anticorrosive property to the coating. The reason for this is the protection that GO's honeycomb layers provide to the substrate, and this is another reason that can be attributed to the decreasing corrosion rate. Thanks to this honeycomb structure, ion transfer is delayed and accordingly, there is a decrease in the corrosion current density (Icorr) value and a shift in the corrosion potential towards the positive direction. The GO layer acts as an ionic barrier (anodic) on the surface, but the dominant factor in the decrease in corrosion rate is the decrease in metallic ionization kinetics.