Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Improving tribological performance of chemically bonded phosphate ceramic coatings reinforced by graphene nano-platelets Da Bian a , Thirumala Vasu Aradhyula b , Yongxin Guo a , Yongwu Zhao a, ⁎ a College of Mechanical Engineering, Jiangnan University, Wuxi 214100, Jiangsu, China b College of Mechanical Engineering, National Chung Cheng University, Chiayi 62102, Taiwan ARTICLE INFO Keywords: Graphene nano-platelets Chemically bonded phosphate ceramic coatings Wear Friction coefficient ABSTRACT To improve tribological performance of chemically bonded phosphate ceramic coatings, the graphene nano- platelets (GNPs) were selected as the reinforcement. Tribological experiment and the analysis of SEM, EDS and Raman were conducted to clarify the mechanism of graphene on the improvement of tribological performance. It was found that, the worn surface of the coating with GNPs is smoother than the one without GNPs, and these GNPs were extruded out and adhered to the worn surface forming the lubricating tribofilm. Besides, the wear volume decreases with the introduction of GNPs. The reason behind this is that these GNPs can lead to the absorption of the fracture energy, which further can improve the mechanical property of the ceramic. This improvement makes the ceramic more tolerant to damage during the wear. Additionally, the decrease of the internal stress of contact surface because of the large contact surface induced by the smooth worn surface results in the lower wear. The friction coefficient shows the similar trends with the wear volume. The lubricant effect of the adhered lubricating tribofilm stemming from the weak interfacial shear strength between graphene platelets dominantly leads to the decrease in friction coefficient. Besides, the smaller internal stress induced by the smooth surface also contributes to the low friction coefficient because of the direct proportionality between the interfacial shear strength and the contact pressure. 1. Introduction The ceramic coatings have attracted considerable scientific interests for minimizing corrosion and wear in mechanical assemblies because of their excellent wear and corrosion resistance [1–4]. Particularly, the tribological behaviors of a ceramic coatings are of great importance for mechanical assemblies and coating applications [5,6]. To further reduce the friction and wear of a ceramic coating, several methods have been reported in the ceramic design. One of the most widely-used and effective methods is incorporation of reinforcements such as fibers [7], carbon nanotubes [8–10], and nano-particles [11] into the ceramic matrixes. Among the availed choices, graphene emerged as an excellent reinforcement for the ceramic design because of its superior mechan- ical strength, low chemical reactivity, and flexibility [12–15]. Yazdanl et al. [16] found the graphene reinforced Al 2 O 3 composites showed better wear resistance than pure Al 2 O 3 ceramic. Moreover, graphene played an important role in forming the lubricant film on the worn surface. Harshit et al. found that GNPs/SiO 2 composites showed excellent wear resistance because the presence of graphene-based lubricant film on the worn surface. Belmonte et al. [17] reported that the graphene/composite showed a good wear resistance and a small friction coefficient because of the lubricating tribofilm induced by the graphene. Hvizdos et al. [18] also found that, with the introduction of graphene, the Si 3 N 4 -graphene nanocomposites did lead to a better wear resistance. However, according to their study, graphene did not participate in lubricating process. Gómezet al. [19] prepared GNPs reinforced Y 2 O 3 -Al 2 O 3 -SiO 2 glass coatings. The coating showed a high wear resistance attributed to the progressive exfoliation of graphene stacks and their incorporation to debris as lubricant. According the above researches, the mechanism of graphene on tribology is different when the graphene are applied into in different ceramics. The chemically bonded phosphate ceramic coatings are easily prepared at low curing temperature and low cost. Besides the fact that the chemically bonded phosphate ceramic coatings possess good adhesion and hardness, they also have little defects, such as pores. To minimize the friction coefficient and wear, in present paper, we applied the GNPs into a chemically bonded phosphate ceramic coatings to investigate the influence of graphene on the coating. The tribological behaviors of the composites were investigated and the wear mechanism http://dx.doi.org/10.1016/j.ceramint.2017.06.116 Received 5 June 2017; Received in revised form 19 June 2017; Accepted 19 June 2017 ⁎ Corresponding author. E-mail address: Zhaoyw@jiangnan.edu.cn (Y. Zhao). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2017 Published by Elsevier Ltd. Please cite this article as: Bian, D., Ceramics International (2017), http://dx.doi.org/10.1016/j.ceramint.2017.06.116