Progress in Organic Coatings 60 (2007) 39–44 Structures and tribological performances of PEEK (poly-ether-ether-ketone)-based coatings designed for tribological application G. Zhang a,∗ , W.-Y. Li a , M. Cherigui a , C. Zhang a , H. Liao a , J.-M. Bordes b , C. Coddet a a LERMPS-UTBM, Site de S´ evenans, 90010 Belfort cedex, France b Technical Center of Belchamp 25420 Voujeaucourt, PSA Peugeot Citroen, France Received 28 June 2006; received in revised form 24 January 2007; accepted 20 June 2007 Abstract Driven by economical and ecological reasons, thermoplastic-based coatings become a potential solution for anti-wear purpose. Two coating design concepts, flame spraying and printing PEEK (poly-ether-ether-ketone)-based coatings on Al substrate, were introduced in this paper. An amorphous PEEK coating was obtained by these two techniques. After being annealed, the coating presents a semi-crystalline structure. The friction and wear behaviors of PEEK-based coatings were investigated by means of ball-on-disc tests. The results show that PEEK coatings exhibit an excellent tribological performance with a relatively low coefficient of friction and wear rate. The semi-crystalline PEEK coating exhibits a lower friction coefficient and wear rate than the amorphous one. The additions of micron-sized particles such as SiC and graphite in PEEK coating can improve significantly the coating wear resistance. © 2007 Elsevier B.V. All rights reserved. Keywords: Flame spraying; Printing; PEEK coating; Wear 1. Introduction In automotive industry, continuous work has been carried out on pistons to meet the requirement of future engines. Weight savings are needed in future products without sacrificing the per- formance that motorists are looking for [1]. Recently, aluminum alloys are widely used as piston materials in auto-engines. However, under an operating temperature ranging from 120 to 150 ◦ C, the direct contact of the uncoated piston skirts with the sliding or oscillating counterparts results in severe wear, seizing and high coefficient of friction (COF) [2]. The friction reduction and wear resistance are the challenges for industrial applica- tions. In order to improve the surface tribological performance, polymer coatings were developed on metallic substrates [3,4]. PEEK (poly-ether-ether-ketone) has become one of the most attractive polymer materials and has been used as a bearing and sliding material in industrial applications due to its excel- ∗ Corresponding author. Tel.: +33 3 84 58 32 43; fax: +33 3 84 58 32 86. E-mail address: ga.zhang@utbm.fr (G. Zhang). lent thermal stability, good friction and wear resistance [5–10]. In these works, the studied bulk PEEK materials had semi- crystalline structures. Due to the high crystallizing speed and the low thermal conductivity of PEEK, to obtain an amorphous bulk PEEK is impossible. Due to the high service temperature (generally 200 ◦ C) and high degradation temperature (570 ◦ C [11]) of PEEK, PEEK coatings are of great significance for the application in engine pistons. In recent years, PEEK coatings have been prepared on a metallic substrate using thermal spraying techniques [4,12,13]. In a previous study [4], the feasibility of preparing PEEK coating by atmospheric plasma spraying (APS), high velocity oxygen-fuel (HVOF) and flame spraying (FS) was investigated following a technical route of “preheating + spraying + cooling”. The results showed that APS led to a degradation of PEEK coat- ing owing to the high temperature plasma. The PEEK coating prepared by HVOF had a large roughness. This is caused by the blowing force of high velocity flame. FS was suitable for the preparation of PEEK coating and a homogenous coating was obtained. The infrared spectra results indicated that little degradation of PEEK occurs after flame spraying. 0300-9440/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2007.06.004