Design and development of high performance tribo-composites based on synergism in two solid lubricants

The paper presents on the synergistic effect of two solid lubricants viz. thermo-graphite (TG) and hexa boron nitride (hBN – white graphite) in the composites when performance was evaluated in adhesive (against smooth mild steel disc) and in abrasive (against SiC paper) wear modes. The basic composition of matrix PEK (polyether ketone) (50%) and short glass fibers (30%) was kept constant and composites were designed with increasing amount of hBN (0, 5, 10, 15 and 20%) with simultaneous decrease of TG (20, 15, 10, 5 and 0). The composites were characterized for mechanical and tribological properties (in adhesive and abrasive wear modes). It was observed that the composites showed very good tribo-potential (very low wear rate and low friction) in adhesive wear mode. However, any of the SLs did not show great potential when included in isolation. Both showed synergism when existed in the composite in combination. The optimum amount was wear mode specific. For adhesive wear mode 15% TG and 5% hBN worked best while for abrasive wear mode 10% of each worked best. Overall TG proved better choice than hBN. Natural graphite proved superior to TG in adhesive wear mode, while trend was opposite for abrasive wear mode. The Lancaster–Ratner factor was observed to be responsible for controlling wear behavior.