Exploration of potential of solid lubricants and short fibers in Polyetherketone (PEK) composites Jayashree Bijwe a,n , Sanjeev Sharma a , Mohit Sharma a,b , Tushar Parida c , Prakash Trivedi c a Industrial Tribology Machine Dynamics and Maintenance Engineering Centre, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India b Leibniz-Institut f¨ ur Polymerforschung Dresden, Hohe Straße 6, 01069 Dresden, Germany c Gharda Chemicals Ltd., Dombivili East, 421203 Mumbai, India article info Article history: Received 15 September 2012 Received in revised form 18 January 2013 Accepted 21 January 2013 Available online 29 January 2013 Keywords: Fiber reinforced composites Polyetherketone (PEK) composites Solid lubricants Adhesive wear Short fiber reinforcement abstract Polyetherketone (PEK) is one of the least explored specialty thermoplastic polymers for its tribo-utility. It exhibits continuous operating temperature up to 280 1C and under short-term loads it can function up to 350 1C. In literature, hardly anything is reported on the adhesive wear performance of PEK and its composites. Three composites based on PEK containing short fibers of carbon/glass along with various solid lubricants were developed and characterized for thermal and mechanical properties. The tribo- properties were studied under varying loads and speeds by sliding a composites pin against a mild steel disc as a counter face. The studies were focused to examine the role of these ingredients on enhancing pressure  velocity limit (PV limit ), which is an indication of utility of a tribo-polymer in severe operating conditions. The performance assessment was done according to multiple parameters; such as magnitude of coefficient of friction (m) and its fluctuations with time, PV limit , compatibility with the counter-face, specific wear rate (K 0 ), etc. Very low K 0 ( E10 16 m 3 /Nm), very low m (0.04–0.20) and very high PV limit values ( 495.2 MPa m/s) were reported for these composites. White graphite (hexa boron nitride—hBN) proved to be the most efficient solid lubricant. The wear mechanisms using scanning electron microscopy of worn surfaces of pins and discs were studied. It was interesting to observe that glass fibers in the composite showed extremely good performance instead of showing abrasion and high m. A very different friction and wear mechanism was claimed to be responsible for this. A synergism between lubricating action of two lubricants and layer of molten glass on the disc was the main reason for the enhanced performance. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Polyaryletherketones (PAEKs) form a family of high perfor- mance specialty thermoplastics with an excellent combination of thermal and mechanical properties, apart from very good resis- tance to chemicals and solvents. PEK (polyetherketone), PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PEKEKK (polyetherketone–ether ketone–ketone) etc. are the typical mem- bers of this family (Table 1 and Fig. 1) [1–12]. These semi- crystalline aromatic polymers exhibit special features; such as high mechanical strength even at elevated temperatures, very good resistance to abrasion, chemicals and radiation; low moist- ure absorption, good impact strength, low tendency to creep, good tribological properties (generally in composite form), etc. The major engineering tribo-application areas are; dry bearings, gears, oil drilling components such as compressor rings, seals, valve parts etc. Amongst these PEEK is the most explored polymer in recent years in the form of tribo-composites containing fibers (short, long and woven) of various types (glass, Aramid, carbon etc.), fillers, nano-fillers etc. [2,3,7,8,10–12]. Friedrich et al. have demonstrated the beneficial effect of solid lubricants and short fiber reinforcement on wear performance of PEEK composites. They suggested that the modification in melting and glass transi- tion temperature of PAEKs family by varying ether to ketone ratio affect its tribo utility [3]. Wear performance of functionally graded PEEK composites with PTFE solid lubricant is studied in detail. Solid lubricant (PTFE) at the bulk and surface region significantly increased the tribological performance of PEEK components [13]. Solid lubricant—MoS 2 in combination of PEEK/PTFE composites showed potential for improving tribologi- cal performance particularly in high vacuum situations [14]. As compared to PEEK, very limited work is reported on the tribology of PEKK [3,7], PEK and their composites [4–7,9]. PEK exhibits continuous operating temperature of 280 1C and under short-term loads, it can function up to 350 1C. Chemical structure (Fig. 1) indicates that the phenylene rings are linked at Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/wear Wear 0043-1648/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.wear.2013.01.059 n Corresponding author. Tel.: þ91 11 26591280; fax: þ91 11 26596222. E-mail address: jbijwe@gmail.com (J. Bijwe). Wear 301 (2013) 810–819