Introduction & Motivation In order to achieve climate targets and reduce emissions of climatically harmful emissions, industrial processes have to become more climate-friendly. Power plants and waste incineration plants produce CO 2 as well as sulfur oxides (SO x ) through the combustion of fossil fuels. The latter can be removed from exhaust gases by means of a desulfurization process. These processes produce byproducts (slurry) that largely contain abrasive particles such as gypsum [1]. To ensure the effectiveness of the process, these operations take place in an aqueous solu- Aus Wissenschaft und Forschung 34 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 Tribological Method Development of Abrasive Resistant Polymer Coatings for Industrial Applications Martin Tockner, Archim Wolfberger, Youping Huang, Gerald Pinter, Andreas Hausberger* Eingereicht: 8.11.2022 Nach Begutachtung angenommen: 20.1.2023 Dieser Beitrag wurde im Rahmen der 63. Tribologie-Fachtagung 2022 der Gesellschaft für Tribologie (GfT) eingereicht. Maschinenhersteller stehen vor der Herausforderung, dass Bauteile, die mit aggressiven Medien in Kontakt stehen, extreme Anforderungen an Korrosions- und Verschleißbeständigkeit erfüllen müssen. Ausreichenden Schutz bieten in vielen Fällen gefüllte Beschichtungen auf Polymerbasis. Im Zuge dieser Arbeit wurden derartige Coatings im labormaßstab hergestellt und hinsichtlich ihrer tribologischen Performance auf modellbis hin zu einem bauteilähnlichen Niveau tribologisch geprüft. Um Informationen über die auftretenden tribologischen Einflüsse hinsichtlich Harz oder Partikelgröße zu erhalten, wurden, rotatorische Ballon-Disk-Prüfungen durchgeführt. Auf Basis dieser Erkenntnisse wurde die vielversprechendste Beschichtung ausgewählt und mit weiteren, anwendungsnahen Testmethoden geprüft. Die Ergebnisse, die anhand der Prüfkette produziert wurden, zeigten eine generell gute Verschleißresistenz der Beschichtungen gegenüber metallischer Gegenkörper im geschmierten Zustand. Darüber hinaus konnte auch durch die Weiterentwicklung der Modellversuche, hin zu anwendungsorientierten Versuchen, die Grundlagen zur Übertragbarkeit der Ergebnisse geschaffen werden. Schlüsselwörter Verschleißbeständigkeit, Ball-on-Disk, Beschichtungen, metallische Gegenkörper, aggressive Medien Machine manufacturers face the challenge that components in contact with aggressive media must fulfill extreme requirements in terms of corrosion and wear resistance. In many cases, filled polymer-based coatings provide sufficient protection. In the course of this work, such coatings were produced and tribologically tested with respect to their tribological performance from model to component-like levels. To obtain information on the occurring tribological influences with regard to used resin or particle size, rotational ball-on-disk tests were carried out. Based on these findings, the most promising coating was selected and tested using application-oriented test methods. The obtained results showed a generally good wear resistance of the coatings against metallic counterparts in lubricated states. In addition, the further development of the model tests, towards applicationoriented tests, also provided the basis for the transferability of the results. Keywords wear resistance, ball-on-disk, coatings, metallic counterparts, aggressive media Kurzfassung Abstract * DI Martin Tockner 1 DI Dr. Archim Wolfberger 1 DI Youping Huang 2 Doc. DI Dr. Andreas Hausberger 1 Univ.-Prof. DI Dr. Gerald Pinter 3 1 Polymer Competence Center Leoben GmbH Roseggerstraße 12, 8700 Leoben, Österreich 2 Andritz AG, Stattegger Straße 18, 8045 Graz, Österreich 3 Lehrstuhl für Werkstoffkunde und Prüfung der Kunststoffe, Montanuniversität Leoben Otto Glöckel-Straße 2, 8700 Leoben, Österreich TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 30 Seite 34 tion and at elevated temperatures. Thus, machine elements like pumps are exposed to an aggressive and abrasive environment due to the continuous circulation of slurry [2]. To prevent high costs for maintenance and premature failure polymer-based coatings filled with ceramic particles became more relevant in recent years. The reinforcement of a relatively soft polymer coating with an extremely hard phase (ceramic fillers) has many benefits from a tribological point of view. Hard phases increase protection against scratching from counterface or debris [3]. The matrix holds the hard phase in place and takes over a supporting (protective) function of the substrate as well as the fillers. The role of a protective shield is performed by the fillers, which thus bear the majority of tribological loads [4]. The focus of this work is the assessment of the tribological properties (friction behavior and wear resistance) for self-developed coatings. For this purpose, the tribological performance was tested simultaneously in a laboratory study with a Ball-on-Disk (BoD) model setup. This test setup was subsequently further developed into a Ball-on-Tube (BoT) and a Ball-on-Wheel (BoW) in order to form the basis for the transferability of the results to the application case. Materials In the present work, three different resin/ hardener systems were used as matrices (systems 1 - 3, see Table 1). Systems 1 and 3 need higher temperatures for full curing (hot-curing systems) and, system 2 cures at room temperature (cold-curing). Additionally, there are disparities between the different systems concerning mix viscosity, glass transition temperature (T g ), a chemical resistance. Table 1 provides a short overview of the characteristic properties of the used resin systems. To enhance the abrasion resistance ceramic fillers were incorporated into the resin matrix. Due to the brittleness of ceramics only a handful of engineering ceramics, like silicon carbide (SiC), zirconium oxide (ZrO 2 ), or aluminum oxide (Al 2 O 3 ), are suitable for tribological applications [5]. Silicon carbides (SiC) are used in this study due to their chemical resistance, outstanding hardness, and low costs [6,7]. To test the influence of the incorporated fillers three different grain sizes of SiC were used (Table 2). In the subsequent course of this work, aluminum oxide (Al 2 O 3 ) was added as well to improve the adhesion of the coating to the substrate and enhance the mechanical and tribological properties [8]. Within the frame of this work, three test methods were used to evaluate the tribological performance. Figure 1 illustrates schematically these setups and the load configuration. First, Ball-on-Disk (BoD) tests were carried out to get an impression of the tribological performance and the influences of the essential coating components (Figure 1a). Therefore, SiC/ epoxy samples were cast into aluminum shells. The bottom side of the cast sample was tested to ensure proper surface quality and comparable conditions for all tests. Next, the coating was spread on a metallic surface for a Ball-on-Tube (BoT) setup (Figure 1b). The metallic substrate has a circular recess with a depth of 2 mm where the coating was Aus Wissenschaft und Forschung 35 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 System 1 System 2 System 3 Curing type hot curing cold curing hot curing Mix viscosity ~ 1000 mPas ~ 400 mPas ~ 700 mPas Pot life ~ 2 h ~ 1 h < 1 h Glass transition temperature, T g ~ 90 °C ~ 30 °C ~ 70 °C Tensile strength good medium good Chemical resistance very good medium good Advantages resistance viscosity adhesion Table 1: Data sheet of used resin systems. Filler material Grain size SiC small 24 - 50 μm SiC medium 242 - 300 μm SiC large 600 - 850 μm Table 2: Used silicon carbide (SiC) fillers and range of grain size distri bution. (a) (b) (c) Figure 1: Schematic illustration of used test setups and the load situation. (a) Ball-on-Disk (BoD), (b) Ball-on-Tube (BoT) and (c) Ball-on-Wheel (BoW). The grey area marks the epoxy/ SiC specimen. TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 30 Seite 35 Results & Discussion In this paragraph the approach for the developed testing methods is described. In the primary part, influences of the individual components (e.g. resin system, grain sizes, etc.) and boundary conditions are examined in more detail. These investigations were done by the BoD setup. Based on the results a specific coating was selected for further tests with more application-oriented test configurations. Therefore, the BoT and hereafter the BoW configuration was used to test the coating and compare the results. The next subsections present the results of the tribological examination with the BoD setup. The following parameters were varied to be able to give a prediction about the influence of each parameter and the final coating: • influence of the used resin system and lubrication state, • influence of the particle size (SiC grain size), • influence of additional aluminum oxide Al 2 O 3 . Influence Resin System & Lubrication State The impact of the lubrication state was determined for all three resin systems. For the investigations, resins with SiC medium and with a filler content of 0.7 were prepared and tested in dry as well as water-lubricated conditions. The resulting temporal courses of the tribological examinations for both lubrication states are depicted in Figure 3. System 1 and system 3 show similarities in terms of running-in and long-term behavior in dry environments. By the same token, both resins exhibit a drop in the COF to a comparable level within the running-in phase. During the running-in, excessive resin at the surface was removed from the running surface and exposed SiC particles. The tribological load is mainly carried by these particles which results in higher COFs because of higher friction resistance owing to abrasive wear of the counterpart and SiC asperities. Since SiC possesses high hardness the counter body gets mainly grinded during this stage (Figure 6b) Aus Wissenschaft und Forschung 36 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 applied. The metallic surface was degreased with acetone and pretreated by sandblasting to guarantee sufficient adhesion between the coating and the substrate surface. In contrast to the BoD tests, the spread surface was tested. Lastly, a Ball-on-Wheel (BoW) test method was chosen (Figure 1c). In this case, the coating was applied on a cylinder with a circumferential groove. The BoW setup simulates the coating on a curved surface. While the BoW is the closest to the real application and was also the most sophisticated setup in terms of sample preparation. The tests were carried out on a Universal-Mechanical- Tester (UMT-2) manufactured by Bruker Corp. (USA). In Figure 2 the used setup is depicted. To simulate wet or moist environments a constant supply of water was implemented. Drop-by-drop lubrication was used for the BoD and BoT configuration because of simple practicability and satisfactory lubrication film formation ((5) in Figure 2). The water supply consists of a reservoir and a pipette tip, which drizzled the sample surface with dist. water constantly. This kind of lubrication was used for the BoD and BoT tests. BoW tests were conducted with immersion lubrication because the BoW test setup has the equipment for permanent lubrication. Finally, Table 3 provides an overview of the used test parameters. As a counterpart, a polished stainless steel (100Cr6) ball with a diameter of 6 mm was used. Parameter Value Vertical force 5 N Circumferential speed 0.125 m/ s Test duration 4 h Lubrication Dry or drop/ splash lubrication with dist. water Figure 2: Universal-Mechanical-Tester (UMT-2) with implemented water supply for Ball on Disk and Ball on Tube tests. The blue arrows indicate the applied load and the movement of the samples. Table 3: Test parameters of the tribological investigations. TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 30 Seite 36 and producees wear debris. High tribological stresses support the transfer of material on the sample surface. This happens because wear particles dwell in the tribological contact and form a tight, consistent layer (transfer film) on the sample surface. The layer covers rough SiC asperities and acts as a load-bearing interface which results in a smoother running-surface and lower COFs. As depicted in Figure 3a, instabilities for system 2 (red line) were observed until approximately 10 000 s. It can be assumed that these instabilities are caused by repeated peeling off and rebuilding of a transfer film. Resin systems 1 and 3 are hot curing systems and cure at evaluated temperatures, whereas system 2 cures at room temperature. Due to the dissimilar curing mechanisms variations in the mechanical properties are obvious. As mentioned in Table 1, system 2 has the lowest mechanical properties and the lowest glass transition temperature. The glass transition temperature of a polymer (T g ) is the temperature at which the mobility of the polymer backbone chains in amorphous areas changes. Consequently, the mechanical properties of a resin decrease when the temperature exceeds the glass transition temperature [9,10]. In tribological contacts, the glass transition temperature of the polymer can be exceeded due to the dissipation of frictional energy. This leads to local deterioration of the mechanical properties (e.g. Young’s modulus). Determination of the Shore D hardness offers that system 2 is the softest material (41 ± 1), followed by system 1 (78 ± 1) and system 3 (82 ± 1.3). Besides Shore D values, the T g also indicates that system 2 may lose mechanical stability because of local softening during testing as a result of frictional heat up. This leads to fluctuations in the COF and the poor formation of a stable transfer film which were observed for tests with system 2. Systems 1 and 3 have comparable mechanical properties and Shore D hardness levels which lead to an analogical COF and tribological behavior after runningin. Figure 3b exhibits the COFs for lubricated conditions. Since water act as a lubricant, in this case, fluctuations in the COF are less pronounced compared to dry conditions. However, the results reveal that the fluid has an impact on the tribological performance of the coating. In general, cold-curing epoxy resins possess lower mechanical properties and are less chemically stable. Lapique and Redford [11] found that water acts as a plasticizer for cold-curing systems. Hence, the material gets softer and the matrix has issues providing enough support for the SiC particles. Due to the cooling effects of the permanent drop lubrication mechanical instabilities caused by exceeding the glass transition temperature were not observed. Figure 4 shows the damage analysis of the worn sample surfaces. The appearance of the wear tracks of system 1 and system 3 are comparable for dry conditions. Both show a uniform and shiny surface appearance whereas the surface of system 2 exhibits a more particle-structured surface. This suggests that system 1 and system 3 form a uniform transfer film during tribological loading. In general, the formation of a transfer film decreases friction and gives the tribological system more stability during the application [12,13]. System 2 lacks of a continuous transfer film, which results in higher friction forces and volatile measurement curves. An energy-dispersive X-ray (EDX) analysis of the wear track revealed that the transfer film mainly consists of iron (Fe) and other elements which can be assigned to the counterpart as well as silicon (Si) from the filler. The image of the EDX analysis is depicted in Figure 5. Since Si is also present beside Fe it can be concluded that the transfer layer mainly consists of a mixture of crushed SiC filler particles, debris from the counterpart, and epoxy resin. System 1 and system 3 show similar results for lubricated conditions (Figure 4e & f). The constant water supply ensures that the specimen surface remains free of any wear particles. Thus, the running-in phases, as seen Aus Wissenschaft und Forschung 37 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 Figure 3: Temporal courses of the COFs tested with a BoD setup for system 1, 2 and 3 in (a) dry and (b) lubricated conditions. TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 30 Seite 37 Influence of the particle size Another investigated factor within this work was the influence of the SiC grain size on the tribological behavior. Based on the promising results in the previous section the investigations were exclusively done with system 1 Aus Wissenschaft und Forschung 38 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 in Figure 3, distinguish clearly from dry (a) to lubricated conditions (b). The wear debris remains easier between the counterpart and the sample surface if no lubricant is present. Thus, the formation of a transfer film was prevented because water impeded the adhesion of the material. However, lubricated tests reveal that system 2 has issues binding the filler to the matrix due to softening and swelling. Figure 6 displays an overview of a heavily worn sample (system 2). SiC particles were torn out and increased the wear of the samples as well as the counterpart drastically. This pattern was only observed for system 2. This implies that due to the lower mechanical strengths and softening effects, system 2 has an insufficient filler-matrix bonding if water is present. System 1 System 2 System 3 Dry Lubricated (d) (e) (f) (a) (b) (c) holes SiC particles running track Figure 4: Damage analysis of the running surface of (a) system 1 dry, (b) system 2 dry, (c) system 3 dry, (d) system 1 lubricated, (e) system 2 lubricated, (f) system 3 lubricated. (a) (b) (c) Si Fe Figure 5: (a) SEM image of the running surface, (b) EDX spectrum of iron (Fe), and (c) EDX spectrum of silicon (Si) of an exemplary test of system 1. Red areas flag the respective element. (a) (b) Figure 6: (a) Heavily worn sample and (b) counterpart due to the tribological load (system 2). TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 30 Seite 38 and a degree of filling of 0.7. Figure 7 shows the COFs and the mean values of the measured COFs. As indicated above, the running-in and the formation of the load-bearing interface or the transfer film are linked to the distribution of the fillers at the sample surface. In this case, the formation of the running surface needs longer for medium-sized particles as seen in Figure 3a. Nonetheless, the diagram in Figure 7 indicates no clear tendency for different particle sizes concerning friction performance. Small as well as large particles exhibit low and comparable COF levels. Figure 8 displays the damage analysis of the worn samples. All samples show a transfer film of the counterpart to the sample surface. The formation of the transfer film plays an important role in terms of resulting COF. As can be seen from Figure 7 the formation of the transfer film took longer for medium-sized particles (red line). This sample exhibits more scattering and a volatile course, especially in the first half of the test. Thus, it can be deduced that the formation is a dynamic process of reduction and renewal of the transfer layer until stable conditions are reached. Samples with small and large particles exhibit a comparable appearance of the wear tracks which was expected from measured COFs. Both formed a uniform transfer film resulting in lower friction and less wear. Based on the results obtained with the BoD tests, a coating was defined for further tests. The selected coating consists of system 1 filled with small SiC particles and a filling degree of 0.7. Due to better processability and handling, small particles were used instead of large particles. Furthermore, small particles create smoother surfaces which cause less hydrodynamic drag in the final application. Further investigations reveal that system 1 and system 3 perform on a comparable level concerning friction and wear. Due to better processability and a higher T g , system 1 was chosen as the basis resin system over system 3. System 2 exhibits unsatisfying results regarding filler/ resin adhesion. Moreover, the low T g and mechanical properties have been pointed out as limitations for the performance of the coating. Addition of Aluminum Oxide (Al 2 O 3 ) Although the mixture was previously defined, the effects of additional aluminum oxide were investigated as well. Al 2 O 3 is widely used in coatings to enhance the corrosive resistance and adhesion strength to metallic surfaces Aus Wissenschaft und Forschung 39 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 Figure 7: (a) Presentation of the COFs for system 1 with small, medium and large SiC particles, and (b) mean COFs of the particular particle size. (a) (b) (c) Transfer film Transfer film Transfer film Figure 8: Worn sample surfaces filled with (a) small, (b) medium, and (c) large SiC particles. TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 30 Seite 39 of Al 2 O 3 being about 3 times smaller compared to SiC (10 µm vs. approx. 30 µm), it is obvious that smaller particles occupy the interspaces between bigger SiC particles. This leads, in general, to improvements in mechanical properties (e.g. fracture stress), especially when particles with smaller grain sizes are added [17]. Thus, it has turned out that the most promising coating consists of system 1 with a degree of filling of 0.7 and a SiC/ Al 2 O 3 ratio of 90/ 10 wt.%. Application Oriented Test Methods This section covers the assessment of the BoT and the BoW test method compared to the results observed with the BoD setup. With the variety of sample preparation (spreading) and geometry (curved surface), steps were taken regarding the actual use case. For this purpose, the above-defined coating mixture was selected and tested with all three setups. Figure 10 presents the resulting Aus Wissenschaft und Forschung 40 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 [8,14]. Since Al 2 O 3 possesses high hardness it is also a proper choice as filler for coatings in high abrasive environments [15,16]. For these investigations, system 1 was used as matrix material and the amount of added Al 2 O 3 varied between 5 wt.%, 10 wt.%, and 20 wt.% whereby the amount of Al 2 O 3 refers to the total SiC/ Al 2 O 3 ratio. This test series was carried out with a BoD configuration and in lubed conditions. Figure 9 shows the COF against the test duration and the mean values of each test. From the table in Figure 9a, it can be seen that the added Al 2 O 3 has little impact on the tribological behavior. Likewise, the COFs show similar COF levels for different SiC/ Al 2 O 3 ratios. However, a multimodal particle distribution shows promising results in terms of enhancing mechanical properties and adhesion of the coating to the substrate [8,17]. Thus, a hybrid particle composition was selected for further evaluation of the test chain. Due to the grain size Figure 10: (a) COF vs. test duration for a BoD, BoT, and BoW configuration. (b) Obtained COFs of the individual tests and mean COFs for each test setup. Figure 9: (a) COFs against test duration for SiC samples filled with 5 wt.%, 10 wt.% and 20 wt.% Al 2 O 3 , and small SiC particles. (b) average COFs for each test configuration. TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 31 Seite 40 COFs of each test setup as well as the temporal courses of the COFs. The resulting COFs in Figure 10b reveal a drop of friction by around 15 - 20 %. The average COFs for BoT and BoW are on a comparable level. The reason for the higher COF of may be related to the method of sample preparation. BoD specimens were cast, whereas BoT and BoW specimens were applied via a coating process. In Figure 10a, the temporal progressions of the friction coefficients are shown to get a better understanding of how friction develops over the test duration. The BoD and the BoT setup exhibit similar characteristics but the BoT setup has a lower friction level over the whole test duration. For the BoW setup, a sharp decrease in friction force was detected at the beginning of the test. The COF remains at a relatively high level but decreases after about 4 000 s to around 0.2. The worn surfaces of each test configuration are illustrated in Figure 11. BoD (Figure 11a) exhibits a transfer film at the sample surface. Although the test was performed in wet conditions a smooth surface with a transfer film was formed. BoT gives similar results but a higher amount of epoxy resin remained at the surface which results in a smoother surface appearance of the wear track (white circles in Figure 11b). The transfer film was not as incisive as it was in the BoD tests. Nevertheless, wear tracks and the formation of a transfer film were visible for BoW test samples as well (Figure 11c). However, due to slight irregularities in the thickness of the coating, wear and the formation of the transfer film were partially more pronounced in areas with higher loads. Summary & Outlook In the course of this work, in-house developed coating samples were prepared and tribological characterized concerning the influence of the grain size, the resin system, and the lubrication state. Subsequently, the enhancement effect of Al 2 O 3 on the tribological properties was studied. Furthermore, the initial BoD test method and sample preparation were extended by developing a BoT and a BoW test setup to be more application-oriented. Promising results were shown in the comparison of BoD and BoT. The COFs of the BoD and BoT tests showed similarities in the course as well as in the observed wear patterns. The findings for the BoW tests show parallels to the previous test methods concerning friction. However, differences in the wear pattern were observed which is most likely related to sample preparation. A multi-modal particle size distribution of the fillers has proved to be a promising approach to increase the wear performance of a coating for further investigations [17]. Furthermore, there is still space for enhancements of the coating by using grafted particles to increase the matrixparticle adhesion. It should be noted that the sample preparation turned out as a crucial step for reliable and comparable results. Therefore, the applicability and processability of the coating should also be revised in the future, so that even more complex specimen geometries can be coated and tested. References [1] X. Li, Y. Mao, and X. Liu, “Flue gas desulfurization gypsum application for enhancing the desalination of reclaimed tidal lands,” Ecological Engineering, vol. 82, pp. 566- 570, 2015. [2] C. G. Duan and V. I. A. Karelin, Abrasive erosion & corrosion of hyraulic machinery, Imperial College Press, London, 2002. [3] K. Holmberg and A. Matthews, Coatings Tribology: Properties, Mechanisms, Techniques and Applications in Surface Engineering, Elsevier Science & Technology Books, Amsterdam, Netherlands, 2009. [4] F. Gruen, I. Godor, and W. Eichlseder, “Test methods to characterise differently designed tribomaterials,” Tribotest, vol. 14, no. 3, pp. 159-176, 2008. [5] K. G. Budinski, Friction, wear, and erosion atlas, CRC Press, Boca Raton, 2014. [6] Y. Zhou, K. Hirao, Y. Yamauchi et al., “Tribological Properties of Silicon Carbide and Silicon Carbide-Graphite Composite Ceramics in Sliding Contact,” Journal of the American Ceramic Society, vol. 86, no. 6, pp. 991-1002, 2003. [7] A. Agrawal, Advanced in silicon carbide processing and applications, Artech House, 2004. Aus Wissenschaft und Forschung 41 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 (a) (b) (c) epoxy resin Figure 11: Damage analysis of the samples tested with (a) BoD, (b) BoT, and (c) BoW configuration. TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 31 Seite 41 and frictional properties of epoxy resin,” SN Applied Sciences, vol. 2, no. 3, 2020. [14] L. Zhai, G. Ling, J. Li et al., “The effect of nanoparticles on the adhesion of epoxy adhesive,” Materials Letters, vol. 60, 25-26, pp. 3031-3033, 2006. [15] L. Rama Krishna, K. Somaraju, and G. Sundararajan, “The tribological performance of ultra-hard ceramic composite coatings obtained through microarc oxidation,” Surface and Coatings Technology, 163-164, pp. 484-490, 2003. [16] D. Bazrgari, F. Moztarzadeh, A. A. Sabbagh-Alvani et al., “Mechanical properties and tribological performance of epoxy/ Al 2 O 3 nanocomposite,” Ceramics International, vol. 44, no. 1, pp. 1220-1224, 2018. [17] R. Prehn, Tribologisch optimierte polymere Hochleistungsverbundwerkstoffe für den Einsatz unter abrasiven Bedingungen, PhD Thesis, Technischen Universität Kaiserslautern, 2006. Aus Wissenschaft und Forschung 42 Tribologie + Schmierungstechnik · 69. Jahrgang · 5-6/ 2022 DOI 10.24053/ TuS-2022-0043 [8] J. D. Oliveira, R. C. Rocha, and A. G. d. S. Galdino, “Effect of Al 2 O 3 particles on the adhesion, wear, and corrosion performance of epoxy coatings for protection of umbilical cables accessories for subsea oil and gas production systems,” Journal of Materials Research and Technology, vol. 8, no. 2, pp. 1729-1736, 2019. [9] G. W. Ehrenstein, Polymer-Werkstoffe: Struktur - Eigenschaften - Anwendung, Hanser, München, 2011. [10] W. Grellmann and S. Seidler, Polymer testing, Hanser Publishers, Cincinnati, 2013. [11] F. Lapique and K. Redford, “Curing effects on viscosity and mechanical properties of a commercial epoxy resin adhesive,” International Journal of Adhesion and Adhesives, vol. 22, no. 4, pp. 337-346, 2002. [12] S. Bahadur, “The development of transfer layers and their role in polymer tribology,” Wear, vol. 245, 1-2, pp. 92-99, 2000. [13] L. Guo, H. Yan, Z. Chen et al., “Graphene oxide grafted by hyperbranched polysiloxane to enhance mechanical TuS_5_6_2022.qxp_TuS_5_6_2022 09.02.23 16: 31 Seite 42