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In this work, the influence of amount (30 and 40 wt.%) of short glass fibers (SGF) in two composites containing synthetic graphite (10 wt.%) and Polyaryl ether ketone (PAEK) (60 wt.% and 50 wt.%) on thermal, mechanical and tribological performance was studied. The theme was to investigate wear-mechanical property correlation. Although the higher amount of SGF led to higher mechanical properties, tribological properties were not in tune to this. Overall, friction coefficient (µ) and specific wear rate (K0) for the composites were in the range 0.04–0.08 and 3–8 × 10−16 m3/Nm respectively and decreased with increase in applied PV values till failure was observed. PVlimit was indicated at 112 and 100 MPa m/s for 30 wt.% and 40 wt.% SGF filled composites respectively. The mechanical properties of the composite with 40 wt.% GF (CGF40) proved superior to a composite with 30 wt.% GF (CGF30).

While designing the ambitious advanced composites based on PAEK (50 wt%), glass fibers (30 wt %) and natural graphite (10 wt %), it was proposed to include one more solid lubricant (10 wt %) from the category of metal chalcogenides. Particles of MoS2 and WS2 in micron and nano-sizes were selected for inclusion in combination with natural graphite. The themes for investigations were; which one is the better performer amongst MoS2 and WS2, and nano-particles can impart beneficial effect or not; and the last how efficient would be these tribo-composites in terms of friction, wear resistance and PVlimit values. The composites were characterized in detail for physical, mechanical, thermal and tribological performance. The WS2 proved more beneficial till moderate PV conditions but not for severe conditions as compared to MoS2. The composites proved excellent tribo-materials in terms of low friction (∼0.04), wear rate (2.2 × 10−16 MPa m/s) and PVsafe values (84 MPa m/s). The chemistry of the counterface surface was studied using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) while the morphology of the worn pins surface and counterface surface was observed using a combination of 3D profilometer and scanning electron microscopy.

In the present study, tribo-potential of a combination of two solid lubricants (SLs) viz. a special graphite i.e. thermographite (TG) and hexa boron nitride (hBN) in a series of composites with fixed amount of short glass fibers (GF 30 wt %) and Polyaryletherketone (PAEK- 50 wt%) was investigated under severe operating condition (Load 900 N (Pressure-28 MPa), speed >1.6 m/s) against mild steel disc till the composites failed. All the composites showed excellent performance under very high PV (pressure and velocity) values and the performance depended mainly on operating parameters and amount of two SLs in the composites. It was observed that 20% of a single SL (either TG or hBN) did not show very good results, although TG inclusion proved better than hBN. When these two SLs (20%) were used in combination, synergistic effect was observed and best performance was exhibited by a composite containing 5% hBN and 15% TG with the highest PV limits of 102.2 MPa m/s (900 N, 3.65 m/s) along with very low μ (0.04) and specific wear rate (5.68 × 10−16 m3/Nm), followed by composite with 10% TG and 10% hBN. Combination of 15% hBN and 5% TG stood next in performance. Synergism in tribo-performance due to combination of two SLs was reported for oils and friction materials but not for high performance anti-friction materials. Such composites have excellent potential as materials for dry bearings, gears etc. The Scanning electron microscopy (SEM) and Energy Dispersive X-ray analysis (EDAX) studies on worn surfaces proved beneficial to understand how the fiber-matrix bonding was affected due to different combinations of SLs and how it affected wear performance.

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.

The three composites based on poly (aryl ether ketone) (PAEK) (60 wt %) as a matrix, glass fibers (30 wt %) as a reinforcement and particulate graphite 10 wt % as a solid lubricant were developed with identical composition but differing in the size and hence surface area of graphite particles. The theme of research was to study the influence of size of particles on physical, mechanical and tribological performance of the composites. Graphite particles possess a layer lattice structure which provides efficient lubrication and also enhanced thermal conductivity. The distribution of graphite particles and glass fibers in the bulk of composites was observed using X-ray micro-tomography. All the composites exhibited excellent tribo-performance indicating μ ≈ 0.04, and wear rate ≈10−16 m3/Nm apart from very high PVlimit values (≈112 MPa m/s). Composite containing graphite with smallest particle size (4 μm) performed best, followed by the one with medium size (15 μm). Scanning electron microscopy (SEM), as well as energy dispersive x-ray (EDAX) studies were conducted to observe the transfer film distribution and the wear mechanism. Postmortem analysis on the worn surfaces were performed by Raman spectroscopy. Chemical composition of the lubricating film on the worn disc surface was studied using x-ray photoelectron spectroscopy (XPS).

Graphite is one of the most widely used solid lubricants in both, anti-friction and friction materials. The influence of particles in the composite mainly depends on its size, amount, its combination with fibers and other fillers etc. No efforts were done to optimize the amount of graphite to achieve very low friction and wear. A series of Polyaryl ether ketone (PAEK) composites with GF (short glass fibers) and increasing amount of graphite particles (10, 15, 20 and 25 wt %) were developed and characterized for various properties such as physical, mechanical, thermal along with adhesive wear performance in severe operating conditions (high pressure and velocity (PV)). Inclusion of graphite led to deterioration in strength and modulus but increase in thermal conductivity. The composites showed very low μ (friction coefficient) in the range of 0.04 and K0 (specific wear rate) (∼2 × 10−16 m3/Nm). Composite with 15 wt % graphite proved to be significantly superior by showing highest PVlimit value (154 MPa m/s) and very low μ (0.04) and K0 (1.91 × 10−16 m3/Nm). The typical inferences were supported by various techniques such as Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), 3D profilometer, Raman spectroscopy on the worn surfaces.