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In this work, a self-lubricating composite was manufactured using a novel hybrid 3D printing/in situ spraying process that involved the printing of an acrylonitrile butadiene styrene (ABS) matrix using fused deposition modeling (FDM), along with the in situ spraying of alumina (Al2O3) and hexagonal boron nitride (hBN) reinforcements during 3D printing. The results revealed that the addition of the reinforcement induced an extensive formation of micropores throughout the ABS structure. Under tensile-loading conditions, the mechanical strength and cohesive interlayer bonding of the composites were diminished due to the presence of these micropores. However, under tribological conditions, the presence of the Al2O3 and hBN reinforcement improved the frictional resistance of ABS in extreme loading conditions. This improvement in frictional resistance was attributed to the ability of the Al2O3 reinforcement to support the external tribo-load and the shearing-like ability of hBN reinforcement during sliding. Collectively, this work provides novel insights into the possibility of designing tribologically robust ABS components through the addition of in situ-sprayed ceramic and solid-lubricant reinforcements. [ABSTRACT FROM AUTHOR]

The tribological behavior of electrical contacts, especially separable type electrical connectors at low contact loads, are considered. The reliability of these connectors has been a major concern due to the fretting phenomenon that can lead to an unacceptable increase in contact resistance. This study analyzes various aspects of the fretting mechanism from a tribological perspective where friction and wear are the primary cause of degradation in electrical components. With the use of precise tribological equipment (high data acquisition rate of 5000 Hz), the electrical contact resistance and coefficient of friction at the contact interface are measured. The measurements were made in-situ for a simulated fretting environment under various constant loading conditions. It was observed that low contact loads (1 N) and low fretting frequency (1 Hz) leads to a high degree of fluctuation in the coefficient of friction. However, for the same conditions, the lowest wear rate and electrical contact resistance were observed. The reason behind this could be due to the lack of continuous electrical contact and a high degree of fretting frequency under low contact loads, ultimately leading to extended periods of an open circuit. Experimental analysis indicates the existence of an optimum loading condition at which the fretting wear effect is at its minimum. Detailed analysis of post fretting surface roughness, coating wear, and wear debris is conducted, as well as transfer film formations to explain the mechanism of fretting observed. [ABSTRACT FROM AUTHOR]

To achieve superior tribological performance without continuous lubricant supply, a novel ceramic - phosphonium based ionic liquids (P-ILs) system is developed via vacuum impregnation. The P-ILs with different viscosity and density impregnated in ceramic pellets were tested at different temperatures and sliding velocities. The results suggest that at a low temperature of 5 °C, the phosphonium benzoate and phosphonium salicylate IL exhibited a low coefficient of friction (COF) than the phosphonium saccharinate IL under a sliding velocity of 100 mm/s. Whereas this trend reversed at a higher temperature of 50 and 100 °C. Similar observations were also made for the wear rate of this unique system. It was found that the tribological performance of the P-IL+ceramic system depends on the thermal response of these ILs which is further correlated with the density and viscosity of P-ILs that control the supply of lubricants at the sliding interface. [ABSTRACT FROM AUTHOR]

A novel set of Al 2 O 3 -B 2 O 3 -CaO composites were manufactured using a cold press-sintering. The B 2 O 3 content in the composites was varied from 5 to 20 wt% and 2 wt% CaO was added to the composites. Dry sliding tests were conducted against an alumina ball at 10–95% relative humidity. The presence of the in-situ formed aluminum borate in the composite enhanced the micro-hardness and wear resistance, whereas the humidity-sensitive alumina phase reduced friction. Furthermore, addition of CaO improved the relative density upto ~92% which also led to significant improvement in hardness and wear resistance. However, the friction was negatively affected. The mechanism for enhanced wear resistance is demonstrated by considering the crystal-chemical approach and polarization theory for the double oxide systems. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) represent a new class of green lubricants that exhibit superior lubrication performance compared to conventional lubricants. Further, solid particle additives, particularly lamellar solid particles to enhance the tribological properties of base oils, are well known. In the current investigation, various sizes, shapes, and types of lamellar solid particles and multi-walled carbon nanotubes were added in Phosphonium-based ILs. The tribological properties of these lubricant mixtures were evaluated using a pin-on-disk test. It was revealed that within ILs, particle size was independent of particle material, where the nano sized particles exhibited improved tribological properties. The influence of particulate additives was empirically modeled by a fractal function using a fractal dimensions based on the particle size and the surface roughness. Synopsis: Addition of nano and sub-micron sized particles to the room temperature ionic liquid provides a sustainable solution in tribology. [Display omitted] • [P 6,6,6,14 ]Salicylate ionic liquid with different solid additives are evaluated for tribological application. • [P 6,6,6,14 ]Salicylate with nanosized solid additives outperform the pure ionic liquid and other lubricant mixture. • The lubricant mixture with the 70 nm hBN reduced COF and wear volume by ~ 60% compared to pure ionic liquid. • A fractal analysis is performed to highlight the relationship between additive particle size with the COF and wear volume. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are composed of multiple elements with equimolar or near equimolar composition that have superior mechanical and tribological properties. In this article, we present a review on the tribological performance of HEAs. The tribological properties of different HEAs systems have been evaluated, and it has been found that the wear rate strongly depends on the crystal structure of the phases. The most common structures are face-centered cubic (FCC), body-centered cubic (BCC), and dual-phase (FCC + BCC) alloys due to the high entropy of mixing instead of forming intermetallic phases. In general, HEAs with a BCC structure showed superior hardness and wear properties compared to FCC and FCC + BCC alloys. The lesser wear rate of HEAs with a BCC structure is attributed to the reductions in ductility, resulting in strong but brittle alloys. In addition to the crystal structure, the effect of temperature on the tribological performance of the HEAs is also discussed, which highlights their potential applications for high temperatures. Moreover, various other factors such as grain size, formation of an oxide layer, and wear mechanisms are discussed. [ABSTRACT FROM AUTHOR]

High-temperature liquid lubricants are often composed of petroleum-based oils. Recently, the lubrication industry has begun to shift towards environmentally benign lubricants to reduce the use of toxic petroleum-based oils. As a result, there has been a resurgence in the use of bio-based lubricants. These "biolubricants" consist of vegetable oils, synthetic ethers, and polyalkyleneglycols (PAGs) for use as high-temperature lubricants. The largest drawbacks to biolubricants are neither their toxicity nor their lubricity, but rather their thermal instability. Room-temperature ionic liquids (RTIL) are emerging biolubricants that has the potential to replace conventional lubricants at high temperatures. In this investigation 1,3-diakylimidazolium and trihexyl(tetradecyl)phosphonium cations are combined with carboxylate anions to create eco-friendly lubricants for high-temperature applications. Here, these RTILs are compared with bio-based and petroleum-based oils to evaluate their tribological properties through pin-on-disk testing and thermal stability via thermogravimetric analysis (TGA). Additionally, the influence of differing alkyl chain imidazolium cations of the 1-decyl through 1-allyl equivalents and various shape and sized anions are studied. Results indicate that the eco-friendly RTILs exhibit the lowest friction and wear properties as well as superior thermal stability because of their lamellar-like liquid crystal structure, electrostatic potential dipolar, and molecular adsorption layer. • Imidazolium and phosphonium ionic liquids (ILs) are considered for high temperature application. • Aromatic carboxylic anions improves tribological performance of ILs. • Eco-friendly phosphonium-based ILs with carboxylate anion outperformed bio-based and petroleum-based oils. • Thermal stability of ILs evaluated by thermal gravimetric analysis. • Eco-friendly phosphonium-based ILs showed lower onsets of thermal degradation temperature. [ABSTRACT FROM AUTHOR]

Wear and friction properties of Al2O3 composite reinforced with in-situ formed aluminum borate (9Al2O3·2B2O3) and hexa-boron nitride (h-BN) have been investigated. The initial constituents for the composites were Al2O3, AlN, and H3BO3. The H3BO3 was used as a source of B2O3, where B2O3 reacted with AlN and Al2O3 to form in-situ h-BN and 9Al2O3·2B2O3. Based on the thermodynamic calculation and phase transformation, four different compositions were selected. First, the powders were mixed by ball milling followed by compaction at 10 MPa. The compacted pellets were sintered at 1400 °C in vacuum. The composites were characterized using X-ray diffraction followed by hardness measurement and reciprocating sliding test against alumina and steel balls. The X-ray diffraction results revealed the formation of in situ phases of 9Al2O3·2B2O3 and h-BN that improved the tribological properties. By comparing the tribological performance of different composites, it was found that the hard 9Al2O3·2B2O3 phase maintains the wear resistance of composites, whereas the coefficient of friction is highly dependent on the counter ball. Against alumina ball, the lowest coefficient of friction was observed for the composites with maximum h-BN concentration and minimum aluminum borate concentration, whereas the opposite trend was observed against the steel ball. [ABSTRACT FROM AUTHOR]