Progress in Organic Coatings 74 (2012) 50–58 Contents lists available at SciVerse ScienceDirect Progress in Organic Coatings j ourna l ho me p ag e: www.elsevier.com/locate/porgcoat Tribological and mechanical properties of amorphous and semi-crystalline PEEK/SiO 2 nanocomposite coatings deposited on the plain carbon steel by electrostatic powder spray technique M. Hedayati a,∗ , M. Salehi a , R. Bagheri b , M. Panjepour a , F. Naeimi c a Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran b Department of Chemical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran c Department of Material Science, Lenjan Branch, Islamic Azad University, Isfahan, Iran a r t i c l e i n f o Article history: Received 22 March 2011 Received in revised form 18 July 2011 Accepted 28 September 2011 Available online 22 October 2011 Keywords: PEEK-based nanocomposite coatings Electrostatic powder spraying Adhesion strength Crystalline structure Hardness Tribological behavior a b s t r a c t One of the main practical limitations of polymer coatings is dependency of their mechanical and physi- cal properties on the crystallinity of polymer matrix. In this research, the effect of the presence of silica nanoparticles on microhardness, interfacial adhesion strength and tribological behavior of amorphous and semi-crystalline polyether–ether–ketone (PEEK) coatings were examined. The coatings were pre- pared by a combination of ball milling and electrostatic powder spraying methods. The results showed that the semi-crystalline pure PEEK coating had higher hardness, lower adhesion strength, coefficient of friction (COF) and wear rate than the amorphous one. However, the incorporating of PEEK with surface modified silica nanoparticles led to an increase in the coatings microhardness and interfacial adherence. The wear rates of both the semi-crystalline and amorphous nanocomposite coatings were lower than the pure ones but their COF were slightly higher. It was also found that, compared with the pure coatings, the sensitivity of the mechanical and tribological properties of the nanocomposite coatings to the crystalline structure of the PEEK matrix are less pronounced. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Polymeric protective coatings have become important since 1930s and are used in a wide range of applications including pas- sivation, wear resistance and chemical resistance [1–3]. PEEK, is a semi-crystalline thermoplastic that widely used as one of the highest performing polymers. It offers a unique combination of properties such as, exceptional abrasion resistance, good friction and wear behavior as well as excellent thermal stability. Due to these properties, PEEK has become one of the most attractive poly- mers for tribological coatings in automotive or aerospace industries [4–7]. However, one of the main practical limitations of these coat- ings is dependency of their mechanical and physical properties (such as hardness, adherence to the substrate and tribological per- formance) to the crystallinity of PEEK [8]. In the several previous studies conducted by Coddet and his co-workers [8–12] in the university of Belfort in France, the corre- lation of crystallization behavior and mechanical and tribological properties of thermal sprayed PEEK coatings were investigated. They subjected the amorphous flame sprayed PEEK coatings to ∗ Corresponding author. Tel.: +98 9132171193. E-mail address: m.hedayati@ma.iut.ac.ir (M. Hedayati). the isothermal annealing treatment under the different holding times and temperatures to gain the semi-crystalline coatings with the different crystallinity. They reported that the semi-crystalline coatings exhibited a higher Knoop hardness but weaker adhe- sion to substrate than the amorphous one [8,9]. They also found that the semi-crystalline coatings exhibited lower COF and wear rates [8,10–12]. To overcome this limitation, in this research, SiO 2 nanoparticles were incorporated in the PEEK matrix and the mechanical and tribological properties of amorphous and semi- crystalline PEEK based composite coatings were studied. Several coating techniques such as printing method [12–14] or electrophoretic [15,16] were developed to prepare PEEK-based composites coatings. Zhang et al. [12–14], investigated the struc- ture and tribological performance of PEEK and PEEK/SiC and PEEK/graphite microcomposite coatings deposited by printing technique. However, dispersion of the filler particles in the poly- mer matrix using these techniques is not very good especially when the filler content is high. As for PEEK-based composites, obtaining a homogeneous distribution and dispersion of filler particles in the PEEK matrix is very difficult by spraying method [12]. Because of this, no work has been reported on the preparation of PEEK-based composite coatings by means of spraying methods. In the present work, electrostatic powder spraying which is the most common technique used for powder coating was utilized 0300-9440/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2011.09.014