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In this work, Al-20Si-5Fe-2Ni/ZrB2 composites with 0-20 wt% ZrB2 were fabricated by spark plasma sintering. The effects of ZrB2 content on the microstructure, mechanical properties and high-temperature tribological behavior of the composites were investigated. The results indicate that Si, Al5FeSi, and ZrB2 particles are uniformly distributed in the aluminum matrix. The density, hardness, and compressive strength increase with increasing ZrB2 content. The friction coefficient and wear rate are dependent on the ZrB2 content and test temperature. At a certain temperature, the friction coefficient increases with an increase in ZrB2 content, whereas the wear rate shows a reverse trend. Due to the improvement in thermal stability and high-temperature softening resistance, the composite shows improved wear resistance and increased transition temperature from mild wear to severe wear. [ABSTRACT FROM AUTHOR]

The (CrAlTiNbV)N x coatings are fabricated by controlling the substrate bias via magnetron sputtering method. Under low substrate bias, the coating tends to form a loose columnar crystal structure with (200) preferred orientation. However, when the substrate bias increases, the coating transforms into a dense nanocrystalline structure, and the (111) orientation is enhanced. As the substrate bias increases, the residual stress and hardness of the coating gradually increase, while the adhesion strength decreases slightly. Friction tests show that the coating possesses the lowest average friction coefficient (about 0.06) and wear rate (8.7 × 10-9 mm3/N·m) in 4050# aviation lubricant, which is achieved under the substrate bias of -96 V and -126 V, respectively. [ABSTRACT FROM AUTHOR]

As is well known, it is hard to prepare ceramic-Ag composites, owing to the lower melting temperature of silver. In this paper, Si 3 N 4 -based composites reinforced with in situ formation of Ag particles were successfully fabricated by sintering Si 3 N 4 and AgNO 3 , and their microstructure, elevated-temperature mechanical and tribological properties were investigated. It can be found that Ag particles about 1 µm were uniformly dispersed into the Si 3 N 4 matrix and there was no outflow of silver during the sintering. Meanwhile, S 3 N 4 /Ag composite containing 5.1 wt% silver exhibited the best fracture toughness, 7.05 MPa m 1/2 and 6.12 MPa m 1/2 at 25 °C and 600 °C, respectively, and the plastic deformation and crack bridging of silver were responsible for the high toughness. Besides, the friction coefficient and wear rate of composites were continuously reduced as the silver content increases. Especially at 200 °C, the friction coefficients reached the lowest value due to the formation of an amorphous silicon oxide film. And the wear resistance was enhanced by the cooperative strengthening effect of silver toughening and lubricating. [ABSTRACT FROM AUTHOR]

Al matrix composites reinforced with Ti 3 AlC 2 and Cu coated Ti 3 AlC 2 were prepared by hot-press sintering approach. It was confirmed that Ti 3 AlC 2 displayed poor wettability with Al, resulting in the poor interfacial bonding strength between Ti 3 AlC 2 and Al matrix. However, Al 2 Cu layer could be formed due to the reaction between Cu and Al during the sintering process, when Cu coated Ti 3 AlC 2 was incorporated in Al matrix. Because of the formation of enhanced Al 2 Cu interface, the mechanical and tribological properties were significantly improved. The Al 2 Cu layer could bridge Ti 3 AlC 2 particle and Al matrix effectively, which contributed to absorbing energy when load was applied, to provide better mechanical properties. Moreover, Ti 3 AlC 2 particle could exhibit powerful pinning effect to inhibit two-body abrasion and adhesion wear, which was favorable for forming smooth tribo-oxidation surface to yield low friction coefficient. The wear mechanism was believed to be oxidation and fatigue wear. [ABSTRACT FROM AUTHOR]

Ag films, deposited by arc ion plating, had been exposed for 43.5 h in real low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard the China Shenzhou-7 manned spaceship. The structure, morphology, composition and tribological property of the Ag films after the space environment exposure (SEE) were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscope (XPS) and ball-on-disk tribometer, respectively. Depth XPS and XRD analysis revealed that after the SEE, the surface layer of Ag films was partially oxidized to Ag 2 O, the cracking and flaking phenomena could be observed from the film surface by FESEM, and so the Ag films lose its metallic shine and became gray. As a result, the tribological performance was deteriorated and the high/unstable friction was obtained. [ABSTRACT FROM AUTHOR]