347 MoS 2-Filled PEEK Composite as a Se lf-Lubricating Material  for Aerospace Applications 

Géraldine Theiler * and Thomas Gradt *  

Abstract 

At BAM, several projects were conducted in the pa st years dealing with the tribological properties of  friction couples at cryogenic temperature and in va cuum environment. Promising candidates for vacuum  application are MoS 2-filled PEEK/PTFE composites, whic h showed a friction coeffi cient as low as 0.03 in  high vacuum. To complete the tribological profile of these composites, further tests were performed in  ultra-high vacuum (UHV) at room temperature. In this paper, friction and stick slip behavior, as well as outgassing characteristics during the test are presented.   Introduction 

Ultra-high vacuum, a wide temperature range, pres ence of atomic oxygen, and limited applicability of  liquid lubricants, make open space an extremely hostile environment for tribologically stressed components in satellites. In most of  these systems, self-lubricating materials must be employed. These  include lamellar solids, soft metals, and polymers. Solid lubricants usually are applied as thin film  (sputtering), bonded film (with organic binder), or mi xed in a polymer matrix (Polyimide and PTFE) [1].  MoS 2 is the most widely used solid lubricant in va cuum environment and has bee n successfully used in  space applications for many years. In vacuum, MoS 2 films exhibit extremely low friction, but in the  presence of humid air, friction and wear rate increase significantly.   Since many space mechanisms must be ground tested before launch, sometimes in atmospheric air, there has been much research perform ed to improve the performance of MoS 2 under atmospheric  conditions [2]. One method is the co-deposition of MoS 2 with metal [2] or DLC [3]. Good performance was  obtained with WC/DLC/WS 2 coatings in vacuum and air [4]. Another approach is to optimize MoS 2-filled  polymer composites.   At BAM, the tribological behavior of MoS 2-filled PEEK composites was investigated in the temperature  range between -80°C and +160°C in high vacuum [5, 6 ]. Particularly in the lower temperature range and  at higher loads, the composites showed high wear resistance and friction coefficients as low as PVD  coatings. To complete the tribological profile of th ese composites, further tests were performed in ultrahigh vacuum at lower sliding speed. In this paper, fr iction and stick slip behavior, as well as outgassing  characteristics during tests are presented.    Experimental  

Tests were performed with a pin-on-flat configuration in oscillating sliding at room temperature in a UHV  tribometer [Fig. 1]. The spherical  polymer pins used in these ex periments were made of PEEK composite  filled with 10% by volume carbon fibers, 10%  by volume PTFE and 10% by volume MoS 2. The  counterface material was X5CrNi1810 steel (similar to AISI 304), with a roughness R a ≅ 0.2 µm. Test  parameters are summarized in Table 1.                                                     * Federal Institute for Materials Research and Testing (BAM), Berlin, Germany  

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272