In order to improve the dispersibility of halloysite nanotubes (HNTs) in polytetrafluoroethylene (PTFE), the modification of HNT surfaces was studied with three types of modifiers (polymethyl methacrylate [PMMA], sodium dodecyl sulfate [SDS] and carboxylic acid). The modified HNTs were characterized by Fourier-transform infrared (FTIR) spectrometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and contact angle measurements. The HNTs were used to reinforce the mechanical properties of PTFE. The mechanical results indicated that the tensile strength of the modified HNT-filled PTFE nanocomposites (F-HNT/PTFE) improved to an acceptable degree and Young's modulus increased significantly. The tribological results showed that the wear rate of F-HNT/PTFE decreased by 21–82 and 9–40 times compared to pure PTFE and the pristine F-HNT/PTFE, respectively.

The NiAl matrix composite coatings containing silver and molybdenum were prepared by atmospheric plasma spraying and their tribological properties were investigated in details from 25 to 900 °C. The X-ray diffraction (XRD), micro-Raman, scanning election microscopy (SEM) and transmission election microscopy (TEM) were used to analyze the composition and microstructure of composite coatings. The X-ray diffraction (XRD) results shown that molybdenum and silver were exist in single-phase, but not alloyed in composite coatings. The addition of silver could effectively improve the tribological properties of composite coatings at the wide range of temperature. The silver, nickel and molybdenum could occur the tribo-chemical reaction and form silver molybdates and nickel molybdates lubricating films inside the wear track of composite coatings at high temperature. The friction process promoted the formation of the silver molybdates. The silver molybdates, nickel molybdates and NiO were the main components in composite coatings at high temperature, which could effectively improve tribological properties of composite coatings.

Four types of W-doped graphite-like carbon (W-GLC) films were deposited under different W target currents by magnetron sputtering method. The effects of W content on the microstructure and properties of the W-GLC films were analyzed via various characterization techniques. The results show that the microstructure of the W-GLC films tends to be loose, while the surface roughness distinctly increases with the increase in the W target current. Moderate W-doping can considerably improve the mechanical properties and wear resistance of the film, which will subsequently decrease as the W content becomes excessive. Moreover, the friction coefficient of the W-GLC films does not show a distinct change, but significantly increases when the W target current increases from 0.9 A to 1.2 A. In particular, when the W target current is 0.6 A, the friction coefficient and the wear rate of the W-GLC film are 0.02 and 3.8 × 10−17 m3/N·m, respectively, exhibiting excellent tribological properties.

Ni-based composites with in situ formed Al2O3 and TiC ceramic phases were fabricated by hot pressing technology and that with directly added Al2O3 and TiC particles (ex situ) were also fabricated for comparison. The antioxygenic property and tribological properties of the composites were comparatively studied. The results show that the high-temperature oxidation resistance of the composite with in situ formed Al2O3 and TiC ceramic is superior to that of ex situ composite, and the friction coefficient of in situ composite is lower than that of ex situ composite in the wide temperature range from 400 °C to 1000 °C. The lowest friction coefficient was about 0.19 at 1000 °C and the wear rate of the composites are in the order of magnitude of 10−6 mm3/(N m) at high temperatures. The differences in tribological properties of in situ/ex situ composites are attributed to the formation of the glaze layer composed of MoO3, TiO2, Al2TiO5, NiAl2O4, and NiO on the worn surfaces and the difference of the distribution of the ceramics in the matrix.

In the recent years, carbon fiber reinforced polymer (CFRP) composites have formed a very important class of tribo-engineering materials in nonlubricated condition. The usage of CFRPs has been growing at a substantial rate that leads to the increasing amount of waste generated from end-of-life components and manufacturing scrap. In the present paper, the role of as-received (rCF-AR) and cryogenic treated (rCF-T) recycled carbon fiber (rCF) reinforcements were investigated on the tribological behavior of epoxy composites by using a micro pin-on-disc tribotester apparatus under dry sliding condition. The wear behavior of the composites was analyzed based on three different sliding velocities and loads at a constant sliding distance. The results showed that the reinforcement effect of rCF-T as compared to rCF-AR has enhanced the wear resistance of epoxy composite, which is attributed to the improved adhesion between the treated rCFs and epoxy matrix.