The present article describes the tribological properties of Mg-based hybrid composites reinforced with graphite nanofiber (GNF) and alumina short fiber (Alsub.2Osub.3sf) that were investigated. The ...Mg/GNF/Alsub.2Osub.3sf hybrid composites with varying volume fraction of fiber (10 vol.%, 15 vol.%, 20 vol.%) were developed. SEM observations indicate that the GNF cluster distributions within the array of the Alsub.2Osub.3sf network are found to be relatively good. The Taguchi design of the experiment has been applied to conduct the wear test, and the statistical analysis of variance (ANOVA) has been used to evaluate the influence of wear test parameters on the wear loss and coefficient of friction (COF) of the composites. The influence of wear test parameters such as volume fraction of fiber (VF), applied load (AL), sliding distance (SD), and sliding speed (SP) on the wear loss and COF of composites was analyzed under dry sliding conditions. The results of ANOVA indicate that the sliding distance was found to be the prominent factor affecting wear loss, and the applied load influenced the COF most significantly. Furthermore, the composites with 20 vol.% of fiber had lower wear loss than those with 10 vol.% and 15 vol.% of fiber. The COF of composites with 15 vol.% of fiber was found to be slightly lower compared to the 10 vol.% and 20 vol.% of fiber cases. The results imply that the hybridization of GNFs and Alsub.2Osub.3sf, as well as the formation of Mgsub.17Alsub.12 and Alsub.2MgCsub.2 precipitates enhanced the tribological properties of the Mg hybrid composites.
In the field of aerospace, core components require excellent wear resistance, lubrication and mechanical properties over a wide temperature range. In this study, three groups of CoCrFeNi high-entropy ...alloy (HEA)-based self-lubricating composites were designed with the addition of Ag, Ni/MoSsub.2 and Crsub.2Osub.3 using discharge-plasma-sintering technology. Their microstructure, phase composition, mechanical properties, friction and wear properties were analyzed. The results showed that, with the addition of Ag, the hardness and yield stress of HEA-Ni/MoSsub.2-Ag were reduced by 36 HV and 24 MPa, respectively, while the plastic strain was increased by 2%. With the addition of Crsub.2Osub.3, the hardness (382 HV) and yield stress (430 MPa) of HEA-Ni/MoSsub.2-Ag-Crsub.2Osub.3 reached their highest values, but the plastic strain reached its lowest value. HEA-Ni/MoSsub.2-Ag-Crsub.2Osub.3 had the smallest friction coefficient in which the friction coefficient at 800 °C was only 0.42. Additionally, it had a small wear rate of 3.2 × 10sup.−6 mmsup.3/Nm over a wide temperature range. At lower temperatures, Ni/MoSsub.2 and Ag were conducive to lubrication, and the wear resistance was improved by the presence of Crsub.2Osub.3. At high temperatures, a nickel oxide phase and a variety of silver molybdate phases were formed via a tribochemical reaction, which was vital to the high-temperature tribological properties.
Polypropylene (PP) grease is a type of lubricating grease with excellent low-temperature performance. The wear and friction performance of steel/steel couples lubricated with PP grease containing ...molybdenum disulfide (MoSsub.2), zinc dialkyldithophosphate (ZDDP) and MoSsub.2/ZDDP as additives at low temperatures was investigated using an Optimol SRV reciprocating tester. Compared with MoSsub.2 or ZDDP as single additives, the combination of MoSsub.2 and ZDDP resulted in outstanding tribological properties, especially for higher-load, longer-duration and low-temperature working conditions. The analysis of the wear surface indicated that MoSsub.2 not only adhered to the steel surfaces to form a solid film, but also combined with ZDDP to form a tribofilm. The active components of the additives reached the metal surfaces effectively, indicating that the polymer system did not interfere with the function of the additives. The rheological experiment results also showed that PP grease with additives can maintain stable viscoelasticity, viscosity recovery rates and ductility at low temperatures.
In this paper, MoSsub.2 nanosheets with an ultrathin structure were fabricated using a solvothermal method and further added into PAO oil, which was further combined with W-DLC coating to constitute ...a solid–liquid lubricating state. The influences of MoSsub.2 concentration, applied load and counter surfaces on the lubricating of the solid–liquid hybrid lubricating system were explored through a ball-on-disk tribometer. The friction results indicated that the steel/W-DLC and W-DLC/W-DLC tribopairs lubricated with ultrathin MoSsub.2 possessed better friction reduction and wear resistance behaviors in comparison to pure PAO oil. However, compared to the steel/steel couple case, the prepared MoSsub.2 nanosheets exhibited a more efficient lubricating effect for the W-DLC/W-DLC couple. The beneficial boundary lubricating impact of MoSsub.2 nanosheets on self-mated W-DLC coated rubbing surfaces could be attributed to the tribochemical reaction between MoSsub.2 and doping W element in DLC, resulting in a formation of a thin tribofilm at both counterparts. Meanwhile, the extent of graphitization of W-DLC film induced by friction was alleviated because of the lubrication and protection from the formation of MoSsub.2-based tribofilm at both counterparts.
In order to improve the tribological performance of PVD–MoSsub.2 coatings, which are frequently used as a solid lubricant for operating in challenging environments, e.g., in a vacuum, they can be ...modified with nitrogen. This work evaluates the tribological behavior and a possible compaction occurring during the initial tribological load in the rolling contact for pure and nitrogen-modified PVD–MoSsub.2 coatings in a vacuum. Short-running tests (1000 cycles) of coated steel discs paired with uncoated steel discs made from 100Cr6 (1.3505, AISI 52100) were conducted on a two-disc tribometer. The slide-to-roll ratio of 10.5% was kept constant, while the load was varied in two steps from 1.1 GPa to 1.6 GPa. Subsequently, a comparison was made between the worn and the pristine coatings by means of nanoindentation and an optical analysis of the wear track. The formation of a load-bearing solid lubrication was achieved for both MoSsub.2-variants. The main differences affected the material transfer and wear mechanisms. The worn coatings reached a similar wear coefficient of 4 × 10sup.−6 mmsup.3Nsup.−1msup.−1 and a possible compaction of the coatings was found, indicated through an increased indentation hardness (for MoSsub.2 1158% and MoSsub.2:N 96% at a 1.1 GPa load). The assumed tribological mechanism changed with nitrogen modification, but scales with increasing load. The nitrogen-modified MoSsub.2 coating showed less compaction than pure MoSsub.2, while the frictional behavior was improved by a 17% reduction of the coefficient of friction.
The wear resistance of epitaxial layers of alpha- and beta-polymorphs of gallium oxide grown on sapphire substrates has been considered. This is one of the first studies of the tribological ...properties of a promising wideband semiconductor crystal. As a result of tribotests conducted with the participation of a sapphire counterface in the process of dry friction in air, it has been shown that the layers of a metastable alpha-Ga.sub.2O.sub.3 are more resistant to abrasion than the layers of the thermostable beta-phase. At the same time, the obtained values of the wear coefficients allow us to attribute both polymorphs to wear-resistant materials and especially alpha-Ga.sub.2O.sub.3 with a corundum structure. In addition, alpha- and beta-Ga.sub.2O.sub.3 demonstrate extremely low values of friction coefficients: lower than those of sapphire.
The tribological performance of sputtered (Al,Cr,Nb,Ta,Ti)N, ▪ , and ▪ coatings on steel substrates was compared against TiN in dry ball-on-disk and scratch tests in ambient air at 20°C, 400°C and ...700°C. The (Al,Cr,Nb,Ta,Ti)N and TiN perform similar in all tests, with (Al,Cr,Nb,Ta,Ti)N showing higher oxidation and abrasion resistance. The adhesion of (Al,Cr,Nb,Ta,Ti)N is superior to TiN at 20°C, but worse at elevated temperature due to an earlier onset of recovery processes that increase the mismatch in coefficient of thermal expansion with the substrate. The ▪ is the most abrasion resistant coating at room temperature owing to its high hardness, but suffers from oxidation in hot air. Scratch tests yield a similar adhesion strength to TiN at 20°C, but the anisotropic lattice expansion and shrinkage of the hexagonal structure at elevated temperatures lead to early delamination in the scratch test. The ▪ also adheres poorly on the steel, resulting in quick delamination during all tests.
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•The tribological behavior of ceramic high-entropy coatings is compared.•(Al,Cr,Nb,Ta,Ti)N is more abrasion and oxidation resistant than TiN.•(Al,Cr,Nb,Ta,Ti)O fails prematurely due to poor adhesion.•(Hf,Ta,V,W,Zr)B2 is abrasion resistant, but suffers from oxidation and spallation.•TiN has overall the best adhesion at high temperatures.
The applications projected in the coatings are in implants with the lower extremities since they require a great load capacity and are essential for walking. Therefore, the use of devices or implants ...is necessary for recovery, osteosynthesis, and fixation. The tribocorrosive behavior of nanostructured compounds based on titanium oxide with an intermediate layer of gold deposited on titanium substrates was determined. These coatings were obtained using the reactive magnetron sputtering technique. Tribocorrosive properties were evaluated at sliding speeds of 3500 mm/min, 4500 mm/min, 6000 mm/min, 7500 mm/min, and 9000 mm/min with loads of 1 N, 2 N, 3 N, 4 N, and 5 N. The coatings were characterized by X-ray photoemission spectroscopy and X-ray diffraction, and the surface roughness was analyzed by atomic force microscopy. The dual mechanical and electrochemical wear tests were carried out with a potentiostat coupled to a pin on the disk system. The system was in contact with a hanks solution (37 °C), which acted as a lubricant. Structural characterization made it possible to identify the TiOsub.2 compound. In the morphological characterization, it was found that the substrate influenced the surface properties of the coatings. The tribological behavior estimated by the wear rates showed less wear at higher load and sliding speeds. It was shown that it is possible to obtain coatings with better electrochemical and tribological performance by controlling the applied load and slip speed variables. In this study, a significant decrease corresponding to 64% was obtained, specifically in the speed of deterioration, and especially for a load of 5 N, depending on the sliding speed that went from 0.2831 mpy (Mils penetration per year) to 3500 mm/min compared to 0.1045 mpy at 9000 mm/min, which is explained by the mechanical blockage induced by the coating.
Due to the excellent properties of Ti (C,N)-based ceramics, such as high hardness, excellent wear resistance, exceptional thermal deformation resistance, and sound chemical stability, they have been ...widely used in cutting tools or molds. Thus, revealing their tribological behavior against hard materials is of great significance. Some studies have reported the tribological behavior of Ti(C,N)-based cermets and hard cermets, but so far, the effects of Mosub.2C additions on the frictional properties of Ti(C,N)-based cermets are still unclear. In this study, Ti(C,N)-10WC-1Crsub.3Csub.2-5Co-10Ni-x Mosub.2C cermets (x = 4, 6, 8, 10 and 12 wt.%) were sintered using a vacuum hot-pressing furnace. Furthermore, the core–rim morphologies of the sintered samples were observed in SEM images. Then, the wear resistance of the cermets was studied against a Sisub.3Nsub.4 ball at a 50 N load using the fretting wear test. Finally, the wear mechanism was characterized using a combination of SEM, EDS and XPS. The experimental results indicated that the wear mechanisms of the cermets were mainly abrasive wear, adhesive wear, and the formation of an oxide film. As the content of Mosub.2C increased from 4 wt.% to 12 wt.%, the friction coefficient and wear volume had a variation law of first decreasing and then decreasing, and reached minimum values at 6 wt.% and 12 wt.%, and the lowest friction coefficient and wear rate were 0.49 and 0.9 × 10sup.−6 mmsup.3/Nm, respectively. The 6 wt.% Mosub.2C greatly improved the hardness and fracture toughness of the cermet, while the 12 wt.% Mosub.2C promoted the formation of an oxide film and protected the friction surface. The cermet with 6 wt.% Mosub.2C is recommended because it has comprehensive advantages in terms of its mechanical properties, tribological properties, and cost.
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