Endüstri ve araştırma alanında tercih edilen polimer esaslı kompozit kaplamalar, seramik bazlı nano partiküller, karbon nanotüpler, karbon fiberler vb. gibi çeşitli dolgu maddelerinin ilavesiyle özelliklerinin iyileştirilmesi ve geliştirilmesi imkanı sunar. Termoset malzeme olan epoksi, üstün mekanik özellikleri, termal kararlılığı, solvent direnci ve işlenme kolaylılığı gibi sahip olduğu özellikler nedeniyle yaygın olarak tercih edilen kaplama malzemelerinden biridir. Sürtünme kuvvetinin arttırılması, yüksek sıcaklıklarda çalışma verimliliği gibi çeşitli özelliklerinin arttırılması için incelemeler ve uygulamalar yapılmaktadır. Bu çalışmada epoksi bazlı polimer kaplamanın özelliklerinin iyileştirilmesi için iki çeşit katkı malzemesi kullanılmıştır. Bu malzemelerden biri teknoloji, sanayi, bilim ve çeşitli alanlarda değerli bir gelecek potansiyeline sahip olan pulcuklu grafitten elde edilen indirgenmiş grafen oksittir. Diğer malzeme ise endüstriyel alanlarda kimyasal, fiziksel, termal özellikleri açısında güçlü fonksiyonel gruplara sahip olan politetrafloroetilen (PTFE)'dir. Litetatürde de uygulanan deneysel çalışmalara göz önüne alınarak indirgenmiş grafen oksit ve PTFE bileşiminde ki sinerjitik etkinin tribolojik özelliklerinin iyileştirilmesi amaçlanmıştır. Bu amaç doğrultusunda pulcuklu grafitten indirgenmiş grafen oksit ve PTFE polimer esaslı kompozite takviye malzemesi amacıyla kullanılmıştır. Kaplamaların altlık malzeme olarak kullanılan AISI 420-B martenzitik çelik yüzeyine; epoksi bazlı kaplama, grafitten indirgenerek üretilen %1 oranında RGO (redüklenmiş grafen oksit) ilaveli epoksi, %1 oranında RGO ve %10 oranında PTFE ilaveli epoksi bazlı polimer kompozit kaplamalar gerçekleştirilmiştir. Kaplama yüzeylerin Taramalı Elektron Mikroskobu (SEM) ve X-Işını Difraktometresi (XRD) yardımıyla mikroyapı ve faz analizi, Fourier transform kızılötesi spektroskopisi (FT-IR), temas açısı, yapışma mukavemeti (Cross-cut deneyi) ve tribolojik özellikleri incelenmiştir. Elde edilen sonuçlar doğrultusunda epoksi, %1 RGO ilaveli epoksi, %1 oranında RGO ve %10 oranında PTFE ilaveli epoksi bazlı polimer kompozit altlık malzeme ile uyum sağlamış ve homojen yapıdadır. Yapışma mukavemeti ASTM D-3359 standardına göre değerlendirilmiş olup sırasıyla 5B ve 4B özelliği göstermektedir. Tüm kaplamalar için çıkan sonuçlar %0 pullanma ve %5'in altında pullanma olarak değerlendirilmiştir. Uyumlu fonksiyonel gruplara sahip olan kaplamalarda; fulleren, PTFE, epoksi fazlarının varlığı tespit edilmiştir. Yapılan çalışmalara göre hidrofobik özellik gösteren kaplamalarda, özellikle PTFE ilavesinin sürtünme katsayısının büyük oranda azalttığı tespit edilmiştir.
Polymer-based composite coatings, which are preferred in industry and research, offer the possibility to improve and enhance their properties with the addition of various fillers such as ceramic-based nanoparticles, carbon nanotubes, carbon fibers, etc. Epoxy, a thermosetting material, is one of the widely preferred coating materials due to its superior mechanical properties, thermal stability, solvent resistance and ease of processing. Investigations and applications are carried out to improve various properties such as increasing the friction force, operating efficiency at high temperatures. In this study, two types of additives were used to improve the properties of epoxy-based polymer coating. Reduced graphene oxide derived from flaky graphite, which has a valuable future potential in technology, industry, science and various fields. The other material is polytetrafluoroethylene (PTFE), which has strong functional groups in terms of chemical, physical and thermal properties in industrial fields.Based on previous experimental studies, it is aimed to improve the tribological performance of the synergistic effect between reduced graphene oxide and PTFE. For this purpose, graphene oxide reduced from flaky graphite, and PTFE was used as reinforcement material for polymer based composite. Epoxy based coating, 1% RGO (reduced graphene oxide) added epoxy, 1% RGO and 10% PTFE added epoxy, epoxy based polymer composite coatings were applied on the surface of AISI 420-B martensitic steel used as the base material of the coatings. Before the coating process, the substrate sample surfaces were sanded with 60, 180, 400, 800, 1000 grit sandpaper and polished with 0.3 μm Al2O3. Before coating, the surface of the steel substrate was cleaned using ethanol, acetone and distilled water. The solution phase prepared for epoxy coating constitutes the main body of the entire coating. For this reason, it is used as the main solution in every type of coating. For epoxy coating without additives, dimethylformamide (DMF), dimethylbenzene and acetone were added and magnetic stirring was performed. Then epoxy resin and carboxymethyl cellulose (CMC) as binding agent were added. After magnetic stirring for a certain period of time, it was stirred in an ultrasonic mixer to obtain homogeneous dissolution. The resulting solution was subjected to ball milling. After these processes were completed, epoxy coating was applied on the sample whose surface was prepared metallographically. For the preparation of the epoxy coating sample with the addition of reduced graphene oxide, the epoxy coating solution was first prepared. As mentioned above, the same steps were applied first. Dimethylformamide, dimethylbenzene, and acetone were mixed using. Carboxymethyl cellulose and epoxy were added after magnetic mixing of the prepared solution. After stirring in a magnetic stirrer, 1% graphene oxide reduced from flaky graphite was added to the solution. The ultrasonically stirred solution was subjected to ball milling. The RGO-added epoxy polymer composite solution was applied to the cleaned sample for coating. When preparing the epoxy polymer composite coating solution with 1% reduced graphene oxide and 10% polytetrafluoroethylene (PTFE), the materials used as the main body are the same. In this process, polytetrafluoroethylene and reduced graphene oxide were combined in separate processes for easy dissolution. In the first step, reduced graphene oxide was dissolved by the addition of dimethylformamide. On the other hand, polytetrafluoroethylene material was also dissolved with ethanol. These separately soluble additives are combined to obtain a homogeneous coating. It was subjected to magnetic mixing followed by ultrasonic mixing. Ball milling was carried out for the completed solution. The solution was then applied as a coating material on the cleaned sample. In the experimental part, microstructures and tribobological properties of epoxy coating, epoxy coating with reduced graphene oxide addition and epoxy polymer composite coatings obtained by adding polytetrafluoroethylene to reduced graphene oxide addition were investigated. Microstructure images of each coating surface were taken by Scanning Electron Microscopy (SEM). In addition, microstructure images of RGO-added and RGO+PTFE-added coating solution powder were also analyzed. Energy Dispersive Spectrometry (EDS) investigations were performed for elemental analysis of the coating samples. Phase analysis was performed with the help of X-Ray Diffractometer (XRD), which enables the determination of the phases contained in epoxy polymer composite coatings. Fourier transform infrared spectroscopy (FT-IR) was applied for the detection of organic groups in the coatings. On the other hand, the contact angle was measured to observe the wettability of the coating surfaces. In this process, which is carried out with the help of a pure water drop, it is aimed to determine whether the coated surface shows hydrophobic or hydrophilic properties. Cross-cut test was applied to test the adhesion strength of epoxy polymer composite coating surfaces. Adhesion strength was evaluated according to ASTM D-3359 standard. A wear test was performed to examine the tribological properties of the coated surfaces. Abrasion testing is used to test the resistance to controlled abrasion of various material surfaces in a laboratory environment. In this study, wear tests were performed under constant load for base material, epoxy coating, epoxy polymer composite coating with reduced graphene oxide addition and epoxy polymer composite coating with polytetrafluoroethylene addition in addition to reduced graphene oxide addition. Wear rate and friction coefficients were compared. SEM and EDS analyses for epoxy coating, epoxy polymer composite coating with 1% reduced graphene oxide addition, and epoxy polymer composite coating with 10% polytetrafluoroethylene addition to reduced graphene oxide; It was observed that the epoxy coating was compatible with the substrate, porosity-free and homogeneous, but the outer part was slightly rough and peaks belonging to oxygen elements were found on the surface. The presence of C and O atoms in the epoxy polymer composite coating with RGO addition, and the presence of C, F, O atoms in the epoxy composite coating with RGO + PTFE addition were determined by EDS analysis. When FT-IR results are analyzed, RGO-added epoxy has C=C, C=O, C-O functional groups, indicating high oxidation of RGO. RGO+PTFE added epoxy was found to contain O-H, C-H, C-H, C=C functional groups. When XRD results are analyzed, the presence of epoxy and α -Fe phase in epoxy based coating, the presence of fullerene, α -Fe, epoxy phases in RGO doped epoxy coating, and the presence of PTFE, epoxy, fullerene phases in RGO+PTFE doped epoxy coating. FT-IR, where we examined the presence of functional groups, and the detection of phases in the coatings examined by XRD showed that the coating process was successful. When the contact angle results were analyzed, it was determined that the epoxy coating with RGO and RGO+PTFE addition showed more hydrophobic properties than the epoxy coating without additives. A cross-cut test was performed to determine whether the adhesion between the coating and the substrate was appropriate and sufficient. The result of this test was evaluated according to ASTM D-3359 standard. When the results for all coatings are evaluated, the flaking rate is below 5%. The materials showed 5B and 4B properties according to the standard. In order to investigate the tribological properties of each coating sample and the effect of additives; a wear test based on the reciprocating motion of a steel ball at room temperature, under a constant load of 10N. The coating with the addition of RGO resulted in a constant coefficient of friction when evaluated together with the sliding distance, while the addition of PTFE with antifriction effect was found to reduce the coefficient of friction.
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