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Porous materials have recently attracted significant attention in the aerospace and biomedical fields for addressing issues related to friction and wear. Porous materials are beneficial in applications where continuous lubrication is not feasible or for components that operate under extreme conditions, such as high speeds, elevated temperatures, and heavy loads. The pores can serve as reservoirs for liquid lubricants, which are gradually released during the operation of the components. The tribological properties of these materials depend on their porosity, the lubricants used, and any additional additives incorporated into the porous materials. This review article provides insight into common fabrication techniques for porous materials and examines their tribological performance for all three classes of materials—polymers, metals, and ceramics. Additionally, it discusses design criteria for porous self-lubricating materials by highlighting the critical properties of both the substrate and lubricants. [ABSTRACT FROM AUTHOR]

The present work reports the utilization of laser treatment for the structuring of a B2O3 coating on ceramic substrates. The two ceramic substrates, pure Al2O3, and Al2O3-20wt% B2O3, were prepared in-house using cold pressing and sintering route. The coatings were prepared by applying the ethanol-B2O3 slurry on the ceramic substrate using a dip coater followed by drying at 100 °C. The dried coatings were subjected to the continuous laser at 22, 29, and 36 W of laser power to achieve the final coating. Coating characterization by X-ray diffraction (XRD) revealed the importance of laser power on controlling the phases of B2O3, which are H3BO3, HBO2, and amorphous B2O3. The crystallinity index (CI) of the coatings calculated using XRD spectrum decreased with an increase in laser power. The coating processed at 36 W showed the lowest CI that reveals higher amorphous B2O3 content. Sliding tests conducted in a controlled humid environment at three sliding velocities suggested a direct relationship between tribological performance and CI value—coating with lower CI value provided consistent lower COF. Additionally, a strong influence of the substrate on tribological performance was also observed—the coatings on the Al2O3-20wt%B2O3 substrate performed superior compared to the coating on the pure Al2O3. The effect of substrates is discussed in terms of thermal conductivity to achieve higher amorphous B2O3 content and the initial surface roughness of the substrates. [ABSTRACT FROM AUTHOR]

The eventual material degradation of steel components in bio-implant, marine, and hightemperature applications is a critical issue that can have widespread negative ramifications from a safety and economic point of view. Stemming from their tribological, corrosion, and erosionbased properties, there is an increasing need to address these issues effectively. As one solution, surface processing techniques have been proposed to improve these properties. However, common techniques tend to suffer from issues spanning from their practicality to their high costs and negative environmental impacts. To address these issues, friction-stir-processing (FSP) has been one technique that has been increasingly utilized due to its cost effective, non-polluting nature. By inducing large amounts of strain and plastic deformation, dynamic recrystallization occurs which can largely influence the tribological, corrosion, and erosion properties via surface hardening, grain refinement, and improvement to passive layer formation. This review aims to accumulate the current knowledge of steel FSP and to breakdown the key factors which enable its metallurgical improvement. Having this understanding, a thorough analysis of these processing variables in relation to their tribological, corrosion, and erosion properties is presented. We finally then prospect future directions for this research with suggestions on how this research can continue to expand. [ABSTRACT FROM AUTHOR]

In the present work, the effect of graphite nanoplatelets (GNPs) on tribological properties of the aluminum (Al), and Al/alumina (Al2O3) composite are studied. GNPs are multilayer graphene sheets which were used as a solid lubricant material. Two sets of composites, Al/GNPs and Al/GNPs/Al2O3 with varying amounts of reinforcements, were synthesized by powder metallurgy that involves cold compaction followed by hot compaction. The hardness of the composites increased with the addition of GNPs and Al2O3. The Al/GNPs composite with 1 wt.% of GNPs (Al/1GNPs) showed a 20% increase in hardness whereas Al/GNPs/ Al2O3 composite with 1 wt.% GNPs and 2 wt.% Al2O3 (Al/1GNPs/2Al2O3) showed 27% increases in hardness compared to the pure Al. The coefficient of friction measured at 20 N was observed to be 22% and 53% lesser for Al/1GNPs and Al/1GNPs/2Al2O3, respectively, compared to corresponding alloys without graphene Al. The X-ray diffraction and scanning electron microscopy analysis revealed the presence of GNPs at the worn surface after the tribology tests. The wear rate was also reduced significantly. In comparison with pure Al, the Al/1GNPs and Al/1GNPs/2Al2O3 composites resulted in 5- and 20-times lesser wear rate, respectively. The addition of Al2O3 caused reduction in wear rate due to higher hardness and load carrying ability, whereas composites with more than 1 wt.% GNPs showed higher wear rate due to lower hardness and higher porosity. The Al/1GNPs/2Al2O3 composite exhibited the least coefficient of friction (0.2–0.25) and wear rate (1 × 10−6–4 × 10−6 mm3/N.m) compared to other GNPs and Al2O3 reinforced Al composites. The worn surfaces were further analyzed to understand the wear mechanism by Raman spectroscopy, transmission electron microscopy, and x-ray diffraction to detect the Al4C3 phase formation, chemical bonding, and defect formation in graphene. [ABSTRACT FROM AUTHOR]

Lightweight high-strength metal matrix nano-composites (MMNCs) can be used in a wide variety of applications, e.g., aerospace, automotive, and biomedical engineering, owing to their sustainability, increased specific strength/stiffness, enhanced elevated temperature strength, improved wear, or corrosion resistance. A metallic matrix, commonly comprising of light aluminum or magnesium alloys, can be significantly strengthened even by very low weight fractions (~1 wt%) of well-dispersed nanoparticles. This review discusses the recent advancements in the fabrication of metal matrix nanocomposites starting with manufacturing routes and different nanoparticles, intricacies of the underlying physics, and the mechanisms of particle dispersion in a particle-metal composite system. Thereafter, the microstructural influences of the nanoparticles on the composite system are outlined and the theory of the strengthening mechanisms is also explained. Finally, microstructural, mechanical, and tribological properties of the selected MMNCs are discussed as well. [ABSTRACT FROM AUTHOR]

The application of tribology is not just limited to mechanical components of engineering systems. As a matter of fact, the understanding of friction and wear can be applied to everyday life. One of the important fields is skin tribology, as human skin interacts with various surfaces of different materials. This paper focuses on the friction behavior of the skin when in contact with the fabric and other materials in relative motion. The excessive friction at the fabric-skin interface may lead to discomfort, blistering, chafing, and pressure ulcers especially in athletes who experience higher friction due to rapid movement for an extended period. Other than understanding the fabric properties, it is equally important to understand the structure and properties of the skin to evaluate its function and interaction with the different fabric materials. The identification of the contributing factors of skin friction can help to design suitable fabric materials. An overview of skin functions and the factors that affect the friction on the skin-textile material interface are presented in this review article.