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Tribological behavior of graphene reinforced chemically bonded ceramic coatings
Ceramics International xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Tribological behavior of graphene reinforced chemically bonded ceramic coatings Bian Daa,b,1, Xu Ronglia,1, Guo Yongxina, Liu Yaxuana, Thirumala Vasu Aradhyulaa, Zhao Yongwua,b,∗, Wang Yongguangc,∗∗ a
College of Mechanical Engineering, Jiangnan University, Wuxi, 214100, Jiangsu, China Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology, Jiangnan University, Wuxi, 214100, Jiangsu, China c College of Mechanical Engineering, Soochow University, Suzhou, 215006, Jiangsu, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Graphene Coating High temperature Friction coefficient Wear
To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.
1. Introduction The wear is the main failure of contact surfaces, which provides a challenge for materials saving and energy saving. Besides, the wear also affects the precision of a system. Researchers concerted efforts in developing coatings, new materials and lubricants to reduce the wear and the friction coefficient of contact surfaces [1–6]. The application of coatings is an effective way to reduce the wear among them, especially under the serve condition. The chemically bonded ceramic coating attracted considerable interests because of its low heat treatment temperature, low cost, easy preparation, high corrosion resistance and good wear resistance performance [7–9]. In order to improve the wear resistance of chemically bonded ceramic coatings, lubricant materials have been introduced into coatings as reinforcements. Wilson et al. [10] found that the wear resistance of the chemically bonded ceramic coating is improved with the introduction of SiC. Martins et al. [1] prepared a chemically bonded phosphate ceramic coating containing TiO2, and the wear test showed that the wear rate of the coating with 20 wt% TiO2 was smaller than that of the coating without TiO2. Carbon nano materials, such as carbon
nanotubes and graphene, have become popular lubricant materials with the development of material engineering. Many researchers began to add carbon nano materials into chemically bonded ceramic coatings. Qin et al. [11] prepared the chemically bonded ceramic coatings reinforced by carbon nanotubes and graphene, and found that the friction coefficient and wear rate of the coating decreased with the increase of graphene. Bian et al. [12] also found that the wear rate and friction coefficient of the chemically bonded ceramic coating decreased with the increase of graphene because of the lubricant film formed by graphene. Colorado et al. [13] found the same result: the introduction of graphene could improve the wear resistance of chemically bonded ceramic coatings. Above results were drawn from the room temperature (RT). In other words, graphene could improve the wear resistance of chemically bonded ceramic coatings at RT. However, whether graphene can form a lubricant film to reduce the friction coefficient and wear rate of chemically bonded ceramic coatings at different temperatures still needs to clarify. In the present paper, the graphene reinforced chemically bonded ceramic coatings were prepared. Tribological experiments at different temperatures were carried out to investigate the mechanism for
∗
Corresponding author. College of Mechanical Engineering, Jiangnan University, Wuxi, 214100, Jiangsu, China. Corresponding author. E-mail addresses: [email protected] (Z. Yongwu), [email protected] (W. Yongguang). 1 These authors contributed equally to this work. ∗∗
https://doi.org/10.1016/j.ceramint.2019.10.180 Received 16 September 2019; Received in revised form 16 October 2019; Accepted 20 October 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Bian Da, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.10.180
Ceramics International xxx (xxxx) xxx–xxx
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Table 1 Compositions of raw materials for coatings. Sample
Alumina (wt %)
Zinc oxide (wt %)
graphene (wt %)
AP binder (wt %)
GCBC0 GCBC1 GCBC 2 GCBC 3
50 49.75 49.25 49
5 5 5 5
0.0 0.25 0.75 1.0
45 45 45 45
graphene to improve the wear resistance of chemically bonded ceramic coatings at different temperatures. 2. Materials and methods 2.1. Materials The chemically bonded ceramic coatings were prepared with commercially available aluminum phosphate binder (AP binder, Xinxiang Materials Tech Co., Ltd., China) and powders. The powders consisted of Al2O3 and ZnO, which were both purchased from Sinopharm Chemical Reagent Co., Ltd., China. The reinforcement graphene was purchased from Suzhou Tanfeng Graphene Technology Co., Ltd, China.
Fig. 1. Hardness of coatings.
W=
V (mm3/ N . m) F . L
Where V, F and L represent the wear volume, the applied force, and the sliding distance, respectively.
2.2. Preparation of coatings The coating was prepared with the AP binder, Al2O3, ZnO and graphene by the sol-gel method. Before adding the powders into the AP binder, the powders were mixed with a ball mill for 4 h. Then the mixed powders were added into the AP binder and stirred to form the sol solution. The compositions of raw materials for coatings are shown in Table 1. After stirring, the sol solution was deposited on the substrate (A3 steel) using an air-pressure driven nozzle, then dried at room temperature for 5 h and heat treated by the following process: 50 °C for 1 h, 100 °C for 2 h, 200 °C for 1 h and 280 °C for 1 h.
3. Results and discussions 3.1. Mechanical properties Fig. 1 shows the hardness of coatings with different contents of graphene. The average hardness of the coating without graphene is 402 kg•mm−2. However, with the introduction of graphene, the coating's hardness slightly increases. The biggest hardness value among the samples reaches to 459 kg•mm−2. Although the hardness slightly increases with the introduction of graphene, All E/H value of the coating obtained from the nano indentation is 0.054–0.06 because the elastic module value is much smaller than the hardness value. The KIC is calculated with the same E/ H value of 0.055. The KIC result is shown in Fig. 2. It can be seen from Fig. 2, the KIC obviously increases with the introduction of graphene. The KIC of the coating with 0.25 wt% graphene increases nearby 19% over that of the coating without graphene. In addition, KIC increases with the increase of graphene. The KIC of the coating with 0.75 wt%
2.3. Characterization of the coatings The morphology of the coating was investigated by the Scanning Electron Microscopy (SEM, ZEISS EVO18, Germany). The indentation experiment was conducted in the ambient condition using nano indenter (G200, Keysight, USA) with the load of 400 mN, and the tip type is the Berkovich diamond tip. The hardness of the coating was measured by a Vicker's microhardness tester (HVS-1000ZCM-XY, Shanghai Suoyan Precision Instruments, China) with 100gf load and dwelling time of 15s. Fracture toughness (KIC) was determined by Anstis equation at 300gf load. KIC is calculated according to the following equation [14]:
E 1/2 P KIC = 0.016 ⎛ ⎞ ⎝ H ⎠ C3/2 Where E, H, P and C represent the elastic modulus, hardness, load and crack length, respectively. The nano indention test was carried out to obtain the E/H value of the coating. The tribological behavior of the coating was evaluated by the high temperature ball-on-plate tribometer test (MFT-5000, RTEC, USA). The coatings were rotated and slid against the Si3N4 ball with diameter of 9 mm under the speed of 0.2 m/s and the applied load of 20 N. The tests were performed at RT, 200 °C and 500 °C for 20 min. In order to investigate the mechanism for graphene to improve the wear resistance of chemically bonded ceramic coatings at different temperatures, the worn surface was characterized by SEM and energy dispersive X-ray (EDX). The friction coefficient and wear rate of the coating were obtained to evaluate the tribological performance. The wear rate W can be calculated with the following equation:
Fig. 2. KIC of coatings. 2
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wear speeds up when the temperature increases, because the higher temperature stress caused by the increasing temperature and the stress from the tribological test result in more cracks and defects in the coating together leading to the larger wear rate. In addition, the wear rate obviously decreases when the graphene is added. For example, the wear rate of the coating with 0.75 wt% graphene at RT is around 8.5 × 10−4mm3/Nm which decreases by 38% over that of the coating without graphene. Furthermore, the wear rate decreases with increasing the graphene content. Combined with the front results of the hardness and fracture toughness, the harder surface with the addition of graphene shows higher wear resistance. Besides, the higher fracture toughness with the addition of graphene also improves the ability of anti-cracks, which also leads to the small wear rate. What deserves our attention is that with the same content of graphene, the wear rate of the coating at 200 °C is almost similar with that at RT. In contrast, the wear rate at 500 °C is much larger than those at RT and 200 °C. This phenomenon clarifies that the temperature has little effects on the wear rate when the temperature arises to 200 °C, however the temperature has a great effect on the wear rate when the temperature arises to 500 °C. In order to better understand the mechanism for graphene to improve the wear resistance of chemically bonded ceramic coatings at different temperatures, the worn surface morphology of the coating with 0.75 wt% graphene was investigated. Fig. 5 shows the worn surface of the coating at RT. As shown in Fig. 5(a), Obviously, there are many cracks on the worn surface, because ceramic is one kind of hard brittle materials which is prone to cracking under the cyclic stress from the tribological test. Although there are many cracks, no obvious debris can be found on the worn surface and the surface is smooth (see in Fig. 5(b)). This is because the bridge function of graphene improves the coating's ability to protect materials from exfoliating when cracks occur, which is agree with the result of the wear rate of the coating with graphene. The EDX result (rectangular frame shown in Fig. 5 (b)) is shown in Fig. 6. There is a peak corresponding to silicon occurring in the result of EDX. The silicon is transferred from the Si3N4 ball. In addition, the weight percent of carbon on the worn surface is obviously larger than 0.75 wt%, which means graphene adheres on the worn surface rather than spalls out during the tribological test. The graphene adhered on the worn surface can decrease the friction coefficient and wear, which is agree with the results of the friction coefficient and the wear rate. The worn surface morphology at 200 °C is shown in Fig. 7. At 200 °C, the surface is also smooth. Similar to the worn surface at RT, there are many cracks on the worn surface because of the cyclic stress. Besides, grooves can be found on the worn surface (See in Fig. 7(a)). At RT, only the cyclic stress can lead to cracks. However, besides of the cyclic stress, the temperature stress also results in cracks at 200 °C. with the combination of the cyclic stress and temperature stress, some cracks become larger to consume the energy, which form the grooves. Fig. 7(b) presents a X100 magnified morphology of the worn surface. No obvious debris can be found on the worn surface. The EDX result (rectangular frame shown in Fig. 7(b)) is shown in Fig. 8. The weight percent of carbon on the worn surface is larger than that at RT (2.29%). This means at 200 °C, graphene becomes easily to adhere on the worn surface, and the friction coefficient and the wear rate can decrease because of the lubricant of graphene, which is agree with the result of the friction coefficient: the COF of coatings with graphene achieves the lowest value at 200 °C rather than RT. Similar with the friction coefficient, the wear rate should also achieve the lowest value at 200 °C. However, the wear rate at 200 °C keeps almost similar with that at RT, even slightly larger than that at RT. The temperature is the main factor for this special phenomenon. As shown in Fig. 8, the weight percent of silicon on the worn surface at 200 °C is less than that at RT, which means the material transfer due to the sliding wear decreases because more graphene adheres on the worn surface. So, the larger wear rate at 200 °C is leaded by the temperature.
Fig. 3. The friction coefficient (COF) of coatings at different temperature.
graphene increases nearby 11% over that of the coating with 0.25 wt% graphene. The KIC of the coating with 1 wt% graphene also slightly increases compared to that of the coating with 0.75 wt% graphene. The increase of KIC means the crack resistance of the coatings is improved. This is because of the strength of graphene and the bridge function of graphene [15–18]. 3.2. Tribological performance The result of the friction coefficient (COF) of coatings, presented in Fig. 3, clearly shows that the COF decreases with the introduction of graphene at RT and 200 °C. this is mainly because of the lubricant function caused by graphene. However, the COF does not change with the introduction of graphene at 500 °C and keeps almost similar when the content of graphene increases, which means graphene loses its lubricant function at this temperature. Besides, the coating without graphene possesses the similar COF at all temperatures. However, the COF of coatings with graphene achieves the lowest value at 200 °C, and achieves the highest value at 500 °C. Above results mean that graphene's lubricant function is affected by the temperature, but COF of the coating without graphene has no relationship with the temperature. As can be seen in Fig. 4, the wear rate of the coating without graphene increases with the increase of the temperature, which means the
Fig. 4. The wear rate of coatings at different temperature. 3
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Fig. 5. The worn surface morphology of the coating with 0.75 wt% graphene at RT (a) X24 and (b) X100.
Fig. 6. The worn surface EDX of the coating with 0.75 wt% graphene at RT.
Fig. 7. The worn surface morphology of the coating with 0.75 wt% graphene at 200 °C (a) X25 and (b) X100.
The graphene adhered on the worn surface is decomposed at 500 °C. In order to investigate whether the graphene in the ceramic coating matrix is decomposed, the cross section of the coating after the tribological test at 500 °C is characterized. Fig. 11 shows the cross section of the coating. As observed in Fig. 11, the graphene structure is not destroyed during the tribological test at 500 °C and graphene is still well dispersed in the coating. This means that only the graphene on the worn surface is decomposed because of the high temperature. The graphene in the coating still keeps its own structure, which is the reason that the wear rate of the coating with graphene is smaller than that of the coating without graphene and the wear rate decreases with the increase of graphene at 500 °C.
Fig. 9 shows the worn surface morphology of the coating at 500 °C. Compared to worn surfaces at RT and 200 °C, the worn surface at 500 °C becomes rough. There are many grooves, which can be seen in Fig. 9(b). Besides, many materials are spalled out. The EDX result is shown in Fig. 10. At 500 °C, the weight percent of carbon decreases to 0.21%. This decrease is mainly caused by the decomposition of graphene [19,20]. The result reveals that the lubricant failure of graphene happens at 500 °C. The increase of the weight percent of silicon also shows the serious wear between two contact surfaces. This is the reason that the friction coefficient and the wear rate at 500 °C is much larger than those at RT. In addition of the lubricant failure of graphene, the larger temperature stress from the arising temperature (500 °C) also contributes to the larger wear rate. 4
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Fig. 8. The worn surface EDX of the coating with 0.75 wt% graphene at 200 °C.
Fig. 9. The worn surface morphology of the coating with 0.75 wt% graphene at 500 °C (a) X25 and (b) X100.
Fig. 10. The worn surface EDS of the coating with 0.75 wt% graphene at 500 °C.
4. Conclusions
and the graphene loses its lubricant function at 500 °C. (3) The wear rate of the coating decreases with the increase of graphene, and the wear rate at 200 °C is almost similar with that at RT. In contrast, the wear rate of all samples at 500 °C is much larger than those at RT and 200 °C. The wear rate at 200 °C keeps the same level with that at RT because of the lubricant function of graphene. The lubricant failure of graphene and temperature stress lead to the large wear rate at 500 °C. (4) The worn surfaces at RT and 200 °C are smooth, but the worn surface at 500 °C is rough.
Chemically bonded ceramic coatings reinforced with graphene were prepared with the sol-gel method. Tribological tests at different temperatures were carried out to investigate the mechanism for graphene to improve the wear resistance of chemically bonded ceramic coatings. (1) The hardness is slightly improved with the addition of graphene, and the fracture toughness is obviously improved; (2) The friction coefficient of the coating decreases with the introduction of graphene. Besides, when the graphene is added, the friction coefficient achieves the lowest value at 200 °C, and achieves the highest value at 500 °C, which is because that the graphene becomes easily to adhere on the worn surface as lubricant at 200 °C
Declaration of competing interest The authors declare that they have no known competing financial 5
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[2] J. Zhang, S. Yang, Z. Chen, M. Wyszomirska, J. Zhao, Z. Jiang, Microstructure and tribological behaviour of alumina composites reinforced with SiC-graphene coreshell nanoparticles, Tribol. Int. 131 (2019) 94–101. [3] B. Postolnyi, O. Bondar, K. Zaleski, E. Coy, S. Jurga, L. Rebouta, J. Araujo, Multilayer design of CrN/MoN superhard protective coatings and their characterisation, Advances in Thin Films, Nanostructured Materials, and Coatings, Springer, 2019, pp. 17–29. [4] D. Berman, A. Erdemir, A.V. Sumant, Graphene: a new emerging lubricant, Mater. Today 17 (2014) 31–42. [5] D. Berman, A. Erdemir, A.V. Sumant, Few layer graphene to reduce wear and friction on sliding steel surfaces, Carbon 54 (2013) 454–459. [6] Y. Guo, D. Bian, Y. Zhao, Preparation and corrosion behavior of chemically bonded ceramic coatings reinforced with ZnO-MWCNTs composite, Mater. Res. Express 6 (2019) 085021. [7] C. Wang, Y. Ye, X. Guan, J. Hu, Y. Wang, J. Li, An analysis of tribological performance on Cr/GLC film coupling with Si3N4, SiC, WC, Al2O3 and ZrO2 in seawater, Tribol. Int. 96 (2016) 77–86. [8] E. Colonetti, E.H. Kammer, A.D.N. Junior, Chemically-bonded phosphate ceramics obtained from aluminum anodizing waste for use as coatings, Ceram. Int. 40 (2014) 14431–14438. [9] D. Bian, Y. Zhao, Preparation and corrosion mechanism of graphene-reinforced chemically bonded phosphate ceramics, J. Sol. Gel Sci. Technol. 80 (2016) 30–37. [10] S. Wilson, H. Hawthorne, Q. Yang, T. Troczynski, Scale effects in abrasive wear of composite sol–gel alumina coated light alloys, Wear 251 (2001) 1042–1050. [11] L. Qin, D. Bian, Y. Zhao, X. Xu, Y. Guo, Study on the preparation and mechanical properties of alumina ceramic coating reinforced by graphene and multi-walled carbon nanotube, Russ. J. Appl. Chem. 90 (2017) 811–817. [12] D. Bian, T.V. Aradhyula, Y. Guo, Y. Zhao, Improving tribological performance of chemically bonded phosphate ceramic coatings reinforced by graphene nano-platelets, Ceram. Int. 43 (2017) 12466–12471. [13] H. Colorado, C. Hiel, H. Hahn, Chemically bonded phosphate ceramics composites reinforced with graphite nanoplatelets, Compos. Appl. Sci. Manuf. 42 (2011) 376–384. [14] G.R. Anstis, P. Chantikul, B.R. Lawn, D.B. Marshall, A critical evaluation of indentation techniques for measuring fracture toughness: I, direct crack measurements, J. Am. Ceram. Soc. 64 (1981) 533–538. [15] C.-H. Chang, T.-C. Huang, C.-W. Peng, T.-C. Yeh, H.-I. Lu, W.-I. Hung, C.-J. Weng, T.-I. Yang, J.-M. Yeh, Novel anticorrosion coatings prepared from polyaniline/ graphene composites, Carbon 50 (2012) 5044–5051. [16] L.S. Walker, V.R. Marotto, M.A. Rafiee, N. Koratkar, E.L. Corral, Toughening in graphene ceramic composites, ACS Nano 5 (2011) 3182–3190. [17] J. Liu, H. Yan, M.J. Reece, K. Jiang, Toughening of zirconia/alumina composites by the addition of graphene platelets, J. Eur. Ceram. Soc. 32 (2012) 4185–4193. [18] X. Zhao, Q. Zhang, D. Chen, P. Lu, Enhanced mechanical properties of graphenebased poly (vinyl alcohol) composites, Macromolecules 43 (2010) 2357–2363. [19] G. Gedler, M. Antunes, V. Realinho, J. Velasco, Thermal stability of polycarbonategraphene nanocomposite foams, Polym. Degrad. Stab. 97 (2012) 1297–1304. [20] S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S.T. Nguyen, R.S. Ruoff, Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide, Carbon 45 (2007) 1558–1565.
Fig. 11. The cross section of the coating after 500 °C tribological test.
interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors gratefully acknowledge the supports of the National Natural Science Foundation of China (Grant No.51675232), the Natural Science Foundation of Jiangsu Province (Grant No.BK20190611), the Fundamental Research Funds for the Central Universities (Grant No. JUSRP11942), the Mechanical Engineering Discipline Construction Funds of Jiangnan University (Grant No. 1075210372180 0101 007) and the national first-class discipline program of Light Industry Technology and Engineering (LITE2018-29). References [1] M.A. Martins, B.d.O. de Lima, L.P. Ferreira, E. Colonetti, J. Feltrin, A.D.N. Júnior, Preparation and photocatalytic activity of chemically-bonded phosphate ceramics containing TiO2, Appl. Surf. Sci. 404 (2017) 18–27.
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Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Tribological behavior of graphene reinforced chemically bonded ceramic coatings Bian Daa,b,1, Xu Ronglia,1, Guo Yongxina, Liu Yaxuana, Thirumala Vasu Aradhyulaa, Zhao Yongwua,b,∗, Wang Yongguangc,∗∗ a
College of Mechanical Engineering, Jiangnan University, Wuxi, 214100, Jiangsu, China Jiangsu Key Laboratory of Advanced Food Manufacturing Equipment and Technology, Jiangnan University, Wuxi, 214100, Jiangsu, China c College of Mechanical Engineering, Soochow University, Suzhou, 215006, Jiangsu, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Graphene Coating High temperature Friction coefficient Wear
To investigate tribological behavior of graphene reinforced chemically bonded ceramic coatings at different temperatures, tribological tests at room temperature, 200 °C and 500 °C were carried out. Results show that the fracture toughness and the hardness of the coating are improved with the introduction of graphene. Besides, the friction coefficient of the coating decreases with the addition of graphene at the room temperature and 200 °C. The coating without graphene achieves the similar friction coefficient at all temperatures. However, the coating with graphene achieves the lowest friction coefficient at 200 °C, and achieves the highest at 500 °C. In addition, the wear rate of the coating decreases with the increase of graphene. Besides, the wear rate at 200 °C is almost similar with that at room temperature. In contrast, the wear rate at 500 °C is much larger than those at room temperature and 200 °C. The mechanisms for graphene to decrease the friction coefficient and improve the wear resistance of chemically bonded ceramic coatings at evaluated temperatures are clarified.
1. Introduction The wear is the main failure of contact surfaces, which provides a challenge for materials saving and energy saving. Besides, the wear also affects the precision of a system. Researchers concerted efforts in developing coatings, new materials and lubricants to reduce the wear and the friction coefficient of contact surfaces [1–6]. The application of coatings is an effective way to reduce the wear among them, especially under the serve condition. The chemically bonded ceramic coating attracted considerable interests because of its low heat treatment temperature, low cost, easy preparation, high corrosion resistance and good wear resistance performance [7–9]. In order to improve the wear resistance of chemically bonded ceramic coatings, lubricant materials have been introduced into coatings as reinforcements. Wilson et al. [10] found that the wear resistance of the chemically bonded ceramic coating is improved with the introduction of SiC. Martins et al. [1] prepared a chemically bonded phosphate ceramic coating containing TiO2, and the wear test showed that the wear rate of the coating with 20 wt% TiO2 was smaller than that of the coating without TiO2. Carbon nano materials, such as carbon
nanotubes and graphene, have become popular lubricant materials with the development of material engineering. Many researchers began to add carbon nano materials into chemically bonded ceramic coatings. Qin et al. [11] prepared the chemically bonded ceramic coatings reinforced by carbon nanotubes and graphene, and found that the friction coefficient and wear rate of the coating decreased with the increase of graphene. Bian et al. [12] also found that the wear rate and friction coefficient of the chemically bonded ceramic coating decreased with the increase of graphene because of the lubricant film formed by graphene. Colorado et al. [13] found the same result: the introduction of graphene could improve the wear resistance of chemically bonded ceramic coatings. Above results were drawn from the room temperature (RT). In other words, graphene could improve the wear resistance of chemically bonded ceramic coatings at RT. However, whether graphene can form a lubricant film to reduce the friction coefficient and wear rate of chemically bonded ceramic coatings at different temperatures still needs to clarify. In the present paper, the graphene reinforced chemically bonded ceramic coatings were prepared. Tribological experiments at different temperatures were carried out to investigate the mechanism for
∗
Corresponding author. College of Mechanical Engineering, Jiangnan University, Wuxi, 214100, Jiangsu, China. Corresponding author. E-mail addresses: [email protected] (Z. Yongwu), [email protected] (W. Yongguang). 1 These authors contributed equally to this work. ∗∗
https://doi.org/10.1016/j.ceramint.2019.10.180 Received 16 September 2019; Received in revised form 16 October 2019; Accepted 20 October 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Bian Da, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.10.180
Ceramics International xxx (xxxx) xxx–xxx
B. Da, et al.
Table 1 Compositions of raw materials for coatings. Sample
Alumina (wt %)
Zinc oxide (wt %)
graphene (wt %)
AP binder (wt %)
GCBC0 GCBC1 GCBC 2 GCBC 3
50 49.75 49.25 49
5 5 5 5
0.0 0.25 0.75 1.0
45 45 45 45
graphene to improve the wear resistance of chemically bonded ceramic coatings at different temperatures. 2. Materials and methods 2.1. Materials The chemically bonded ceramic coatings were prepared with commercially available aluminum phosphate binder (AP binder, Xinxiang Materials Tech Co., Ltd., China) and powders. The powders consisted of Al2O3 and ZnO, which were both purchased from Sinopharm Chemical Reagent Co., Ltd., China. The reinforcement graphene was purchased from Suzhou Tanfeng Graphene Technology Co., Ltd, China.
Fig. 1. Hardness of coatings.
W=
V (mm3/ N . m) F . L
Where V, F and L represent the wear volume, the applied force, and the sliding distance, respectively.
2.2. Preparation of coatings The coating was prepared with the AP binder, Al2O3, ZnO and graphene by the sol-gel method. Before adding the powders into the AP binder, the powders were mixed with a ball mill for 4 h. Then the mixed powders were added into the AP binder and stirred to form the sol solution. The compositions of raw materials for coatings are shown in Table 1. After stirring, the sol solution was deposited on the substrate (A3 steel) using an air-pressure driven nozzle, then dried at room temperature for 5 h and heat treated by the following process: 50 °C for 1 h, 100 °C for 2 h, 200 °C for 1 h and 280 °C for 1 h.
3. Results and discussions 3.1. Mechanical properties Fig. 1 shows the hardness of coatings with different contents of graphene. The average hardness of the coating without graphene is 402 kg•mm−2. However, with the introduction of graphene, the coating's hardness slightly increases. The biggest hardness value among the samples reaches to 459 kg•mm−2. Although the hardness slightly increases with the introduction of graphene, All E/H value of the coating obtained from the nano indentation is 0.054–0.06 because the elastic module value is much smaller than the hardness value. The KIC is calculated with the same E/ H value of 0.055. The KIC result is shown in Fig. 2. It can be seen from Fig. 2, the KIC obviously increases with the introduction of graphene. The KIC of the coating with 0.25 wt% graphene increases nearby 19% over that of the coating without graphene. In addition, KIC increases with the increase of graphene. The KIC of the coating with 0.75 wt%
2.3. Characterization of the coatings The morphology of the coating was investigated by the Scanning Electron Microscopy (SEM, ZEISS EVO18, Germany). The indentation experiment was conducted in the ambient condition using nano indenter (G200, Keysight, USA) with the load of 400 mN, and the tip type is the Berkovich diamond tip. The hardness of the coating was measured by a Vicker's microhardness tester (HVS-1000ZCM-XY, Shanghai Suoyan Precision Instruments, China) with 100gf load and dwelling time of 15s. Fracture toughness (KIC) was determined by Anstis equation at 300gf load. KIC is calculated according to the following equation [14]:
E 1/2 P KIC = 0.016 ⎛ ⎞ ⎝ H ⎠ C3/2 Where E, H, P and C represent the elastic modulus, hardness, load and crack length, respectively. The nano indention test was carried out to obtain the E/H value of the coating. The tribological behavior of the coating was evaluated by the high temperature ball-on-plate tribometer test (MFT-5000, RTEC, USA). The coatings were rotated and slid against the Si3N4 ball with diameter of 9 mm under the speed of 0.2 m/s and the applied load of 20 N. The tests were performed at RT, 200 °C and 500 °C for 20 min. In order to investigate the mechanism for graphene to improve the wear resistance of chemically bonded ceramic coatings at different temperatures, the worn surface was characterized by SEM and energy dispersive X-ray (EDX). The friction coefficient and wear rate of the coating were obtained to evaluate the tribological performance. The wear rate W can be calculated with the following equation:
Fig. 2. KIC of coatings. 2
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wear speeds up when the temperature increases, because the higher temperature stress caused by the increasing temperature and the stress from the tribological test result in more cracks and defects in the coating together leading to the larger wear rate. In addition, the wear rate obviously decreases when the graphene is added. For example, the wear rate of the coating with 0.75 wt% graphene at RT is around 8.5 × 10−4mm3/Nm which decreases by 38% over that of the coating without graphene. Furthermore, the wear rate decreases with increasing the graphene content. Combined with the front results of the hardness and fracture toughness, the harder surface with the addition of graphene shows higher wear resistance. Besides, the higher fracture toughness with the addition of graphene also improves the ability of anti-cracks, which also leads to the small wear rate. What deserves our attention is that with the same content of graphene, the wear rate of the coating at 200 °C is almost similar with that at RT. In contrast, the wear rate at 500 °C is much larger than those at RT and 200 °C. This phenomenon clarifies that the temperature has little effects on the wear rate when the temperature arises to 200 °C, however the temperature has a great effect on the wear rate when the temperature arises to 500 °C. In order to better understand the mechanism for graphene to improve the wear resistance of chemically bonded ceramic coatings at different temperatures, the worn surface morphology of the coating with 0.75 wt% graphene was investigated. Fig. 5 shows the worn surface of the coating at RT. As shown in Fig. 5(a), Obviously, there are many cracks on the worn surface, because ceramic is one kind of hard brittle materials which is prone to cracking under the cyclic stress from the tribological test. Although there are many cracks, no obvious debris can be found on the worn surface and the surface is smooth (see in Fig. 5(b)). This is because the bridge function of graphene improves the coating's ability to protect materials from exfoliating when cracks occur, which is agree with the result of the wear rate of the coating with graphene. The EDX result (rectangular frame shown in Fig. 5 (b)) is shown in Fig. 6. There is a peak corresponding to silicon occurring in the result of EDX. The silicon is transferred from the Si3N4 ball. In addition, the weight percent of carbon on the worn surface is obviously larger than 0.75 wt%, which means graphene adheres on the worn surface rather than spalls out during the tribological test. The graphene adhered on the worn surface can decrease the friction coefficient and wear, which is agree with the results of the friction coefficient and the wear rate. The worn surface morphology at 200 °C is shown in Fig. 7. At 200 °C, the surface is also smooth. Similar to the worn surface at RT, there are many cracks on the worn surface because of the cyclic stress. Besides, grooves can be found on the worn surface (See in Fig. 7(a)). At RT, only the cyclic stress can lead to cracks. However, besides of the cyclic stress, the temperature stress also results in cracks at 200 °C. with the combination of the cyclic stress and temperature stress, some cracks become larger to consume the energy, which form the grooves. Fig. 7(b) presents a X100 magnified morphology of the worn surface. No obvious debris can be found on the worn surface. The EDX result (rectangular frame shown in Fig. 7(b)) is shown in Fig. 8. The weight percent of carbon on the worn surface is larger than that at RT (2.29%). This means at 200 °C, graphene becomes easily to adhere on the worn surface, and the friction coefficient and the wear rate can decrease because of the lubricant of graphene, which is agree with the result of the friction coefficient: the COF of coatings with graphene achieves the lowest value at 200 °C rather than RT. Similar with the friction coefficient, the wear rate should also achieve the lowest value at 200 °C. However, the wear rate at 200 °C keeps almost similar with that at RT, even slightly larger than that at RT. The temperature is the main factor for this special phenomenon. As shown in Fig. 8, the weight percent of silicon on the worn surface at 200 °C is less than that at RT, which means the material transfer due to the sliding wear decreases because more graphene adheres on the worn surface. So, the larger wear rate at 200 °C is leaded by the temperature.
Fig. 3. The friction coefficient (COF) of coatings at different temperature.
graphene increases nearby 11% over that of the coating with 0.25 wt% graphene. The KIC of the coating with 1 wt% graphene also slightly increases compared to that of the coating with 0.75 wt% graphene. The increase of KIC means the crack resistance of the coatings is improved. This is because of the strength of graphene and the bridge function of graphene [15–18]. 3.2. Tribological performance The result of the friction coefficient (COF) of coatings, presented in Fig. 3, clearly shows that the COF decreases with the introduction of graphene at RT and 200 °C. this is mainly because of the lubricant function caused by graphene. However, the COF does not change with the introduction of graphene at 500 °C and keeps almost similar when the content of graphene increases, which means graphene loses its lubricant function at this temperature. Besides, the coating without graphene possesses the similar COF at all temperatures. However, the COF of coatings with graphene achieves the lowest value at 200 °C, and achieves the highest value at 500 °C. Above results mean that graphene's lubricant function is affected by the temperature, but COF of the coating without graphene has no relationship with the temperature. As can be seen in Fig. 4, the wear rate of the coating without graphene increases with the increase of the temperature, which means the
Fig. 4. The wear rate of coatings at different temperature. 3
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Fig. 5. The worn surface morphology of the coating with 0.75 wt% graphene at RT (a) X24 and (b) X100.
Fig. 6. The worn surface EDX of the coating with 0.75 wt% graphene at RT.
Fig. 7. The worn surface morphology of the coating with 0.75 wt% graphene at 200 °C (a) X25 and (b) X100.
The graphene adhered on the worn surface is decomposed at 500 °C. In order to investigate whether the graphene in the ceramic coating matrix is decomposed, the cross section of the coating after the tribological test at 500 °C is characterized. Fig. 11 shows the cross section of the coating. As observed in Fig. 11, the graphene structure is not destroyed during the tribological test at 500 °C and graphene is still well dispersed in the coating. This means that only the graphene on the worn surface is decomposed because of the high temperature. The graphene in the coating still keeps its own structure, which is the reason that the wear rate of the coating with graphene is smaller than that of the coating without graphene and the wear rate decreases with the increase of graphene at 500 °C.
Fig. 9 shows the worn surface morphology of the coating at 500 °C. Compared to worn surfaces at RT and 200 °C, the worn surface at 500 °C becomes rough. There are many grooves, which can be seen in Fig. 9(b). Besides, many materials are spalled out. The EDX result is shown in Fig. 10. At 500 °C, the weight percent of carbon decreases to 0.21%. This decrease is mainly caused by the decomposition of graphene [19,20]. The result reveals that the lubricant failure of graphene happens at 500 °C. The increase of the weight percent of silicon also shows the serious wear between two contact surfaces. This is the reason that the friction coefficient and the wear rate at 500 °C is much larger than those at RT. In addition of the lubricant failure of graphene, the larger temperature stress from the arising temperature (500 °C) also contributes to the larger wear rate. 4
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Fig. 8. The worn surface EDX of the coating with 0.75 wt% graphene at 200 °C.
Fig. 9. The worn surface morphology of the coating with 0.75 wt% graphene at 500 °C (a) X25 and (b) X100.
Fig. 10. The worn surface EDS of the coating with 0.75 wt% graphene at 500 °C.
4. Conclusions
and the graphene loses its lubricant function at 500 °C. (3) The wear rate of the coating decreases with the increase of graphene, and the wear rate at 200 °C is almost similar with that at RT. In contrast, the wear rate of all samples at 500 °C is much larger than those at RT and 200 °C. The wear rate at 200 °C keeps the same level with that at RT because of the lubricant function of graphene. The lubricant failure of graphene and temperature stress lead to the large wear rate at 500 °C. (4) The worn surfaces at RT and 200 °C are smooth, but the worn surface at 500 °C is rough.
Chemically bonded ceramic coatings reinforced with graphene were prepared with the sol-gel method. Tribological tests at different temperatures were carried out to investigate the mechanism for graphene to improve the wear resistance of chemically bonded ceramic coatings. (1) The hardness is slightly improved with the addition of graphene, and the fracture toughness is obviously improved; (2) The friction coefficient of the coating decreases with the introduction of graphene. Besides, when the graphene is added, the friction coefficient achieves the lowest value at 200 °C, and achieves the highest value at 500 °C, which is because that the graphene becomes easily to adhere on the worn surface as lubricant at 200 °C
Declaration of competing interest The authors declare that they have no known competing financial 5
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[2] J. Zhang, S. Yang, Z. Chen, M. Wyszomirska, J. Zhao, Z. Jiang, Microstructure and tribological behaviour of alumina composites reinforced with SiC-graphene coreshell nanoparticles, Tribol. Int. 131 (2019) 94–101. [3] B. Postolnyi, O. Bondar, K. Zaleski, E. Coy, S. Jurga, L. Rebouta, J. Araujo, Multilayer design of CrN/MoN superhard protective coatings and their characterisation, Advances in Thin Films, Nanostructured Materials, and Coatings, Springer, 2019, pp. 17–29. [4] D. Berman, A. Erdemir, A.V. Sumant, Graphene: a new emerging lubricant, Mater. Today 17 (2014) 31–42. [5] D. Berman, A. Erdemir, A.V. Sumant, Few layer graphene to reduce wear and friction on sliding steel surfaces, Carbon 54 (2013) 454–459. [6] Y. Guo, D. Bian, Y. Zhao, Preparation and corrosion behavior of chemically bonded ceramic coatings reinforced with ZnO-MWCNTs composite, Mater. Res. Express 6 (2019) 085021. [7] C. Wang, Y. Ye, X. Guan, J. Hu, Y. Wang, J. Li, An analysis of tribological performance on Cr/GLC film coupling with Si3N4, SiC, WC, Al2O3 and ZrO2 in seawater, Tribol. Int. 96 (2016) 77–86. [8] E. Colonetti, E.H. Kammer, A.D.N. Junior, Chemically-bonded phosphate ceramics obtained from aluminum anodizing waste for use as coatings, Ceram. Int. 40 (2014) 14431–14438. [9] D. Bian, Y. Zhao, Preparation and corrosion mechanism of graphene-reinforced chemically bonded phosphate ceramics, J. Sol. Gel Sci. Technol. 80 (2016) 30–37. [10] S. Wilson, H. Hawthorne, Q. Yang, T. Troczynski, Scale effects in abrasive wear of composite sol–gel alumina coated light alloys, Wear 251 (2001) 1042–1050. [11] L. Qin, D. Bian, Y. Zhao, X. Xu, Y. Guo, Study on the preparation and mechanical properties of alumina ceramic coating reinforced by graphene and multi-walled carbon nanotube, Russ. J. Appl. Chem. 90 (2017) 811–817. [12] D. Bian, T.V. Aradhyula, Y. Guo, Y. Zhao, Improving tribological performance of chemically bonded phosphate ceramic coatings reinforced by graphene nano-platelets, Ceram. Int. 43 (2017) 12466–12471. [13] H. Colorado, C. Hiel, H. Hahn, Chemically bonded phosphate ceramics composites reinforced with graphite nanoplatelets, Compos. Appl. Sci. Manuf. 42 (2011) 376–384. [14] G.R. Anstis, P. Chantikul, B.R. Lawn, D.B. Marshall, A critical evaluation of indentation techniques for measuring fracture toughness: I, direct crack measurements, J. Am. Ceram. Soc. 64 (1981) 533–538. [15] C.-H. Chang, T.-C. Huang, C.-W. Peng, T.-C. Yeh, H.-I. Lu, W.-I. Hung, C.-J. Weng, T.-I. Yang, J.-M. Yeh, Novel anticorrosion coatings prepared from polyaniline/ graphene composites, Carbon 50 (2012) 5044–5051. [16] L.S. Walker, V.R. Marotto, M.A. Rafiee, N. Koratkar, E.L. Corral, Toughening in graphene ceramic composites, ACS Nano 5 (2011) 3182–3190. [17] J. Liu, H. Yan, M.J. Reece, K. Jiang, Toughening of zirconia/alumina composites by the addition of graphene platelets, J. Eur. Ceram. Soc. 32 (2012) 4185–4193. [18] X. Zhao, Q. Zhang, D. Chen, P. Lu, Enhanced mechanical properties of graphenebased poly (vinyl alcohol) composites, Macromolecules 43 (2010) 2357–2363. [19] G. Gedler, M. Antunes, V. Realinho, J. Velasco, Thermal stability of polycarbonategraphene nanocomposite foams, Polym. Degrad. Stab. 97 (2012) 1297–1304. [20] S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S.T. Nguyen, R.S. Ruoff, Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide, Carbon 45 (2007) 1558–1565.
Fig. 11. The cross section of the coating after 500 °C tribological test.
interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors gratefully acknowledge the supports of the National Natural Science Foundation of China (Grant No.51675232), the Natural Science Foundation of Jiangsu Province (Grant No.BK20190611), the Fundamental Research Funds for the Central Universities (Grant No. JUSRP11942), the Mechanical Engineering Discipline Construction Funds of Jiangnan University (Grant No. 1075210372180 0101 007) and the national first-class discipline program of Light Industry Technology and Engineering (LITE2018-29). References [1] M.A. Martins, B.d.O. de Lima, L.P. Ferreira, E. Colonetti, J. Feltrin, A.D.N. Júnior, Preparation and photocatalytic activity of chemically-bonded phosphate ceramics containing TiO2, Appl. Surf. Sci. 404 (2017) 18–27.
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