Optimum concentration of reinforcement and solid lubricant in polyamide 12 composites for best tribo-performance in two wear modes

In general polymers are used in the form of composites (fiber reinforced, solid lubricated or both) in tribo-applications, where they may encounter more than one type of wear situations or mechanisms to different extents. The area of investigating the optimum concentration of fillers for best combination of tribo-performance in different wear modes and mechanical strength is sparingly researched. In this paper, research findings on the influence of the contents of short carbon fibers (CF) and PTFE (particulate form) in Polyamide (PA) 12 on friction and wear behavior in two wear modes (adhesive and fretting) have been reported. With increase in contents of CF up to 30% (vol) most of the mechanical properties and tribo-performance improved in adhesive and fretting wear modes. With a view to enhance it further, PTFE was added step by step in the best performing composite (PA+30% CF). This boosted the tribo-performance further, however, at the cost of strength properties. With increase in PTFE percentage (10, 15 and 20% by vol), specific wear rate (K (o)) and friction coefficient (mu) both decreased appreciably in adhesive as well as fretting wear modes. The composite consisting of 30% CF and 20% PTFE showed lowest values for mu and K (o) rendering it the best tribo-combination for all practical purposes. The abrasive wear behavior of composites was also investigated. However, wear performance in this mode showed exactly opposite trends. Inclusion of fibers or combination of fibers and PTFE proved detrimental.