Ensuring effective lubrication between sliding surfaces is one of the challenges in the field of tribology. In addition to the conventional parameters like speed, load, contact geometry and material parameters, the surface texture also influences the coefficient of friction. In the present investigation, the effect of surface texture on coefficient of friction under boundary lubricated condition was studied by sliding Al-4Mg alloy pins against EN8 steel discs of various surface textures using pin-on-disc machine. Both isotropic and directional textures were generated on the surfaces of the discs. Scanning Electron Microscopy and optical profilometer studies were carried out on the contact surfaces of both the pins and discs before and after the experiments. The result showed that the coefficient of friction varied considerably with surface textures. In addition, maximum value coefficient of friction was observed when pins slid perpendicular to the uni-directional texture and minimum when pins slid on random texture. Backscattered scanning electron micrographs revealed the transfer of iron from the disc to the pins and it was highest when pins slid perpendicular to the uni-directional texture and least for the random texture. However, no transfer layer of Al-Mg alloy was observed on the steel disc.
Surface texture of a tool plays an important role as it primarily controls the frictional behavior at the tribo interface. In the present investigation, pin-on-plate sliding tester was used to identify the effect of directionality of surface grinding marks on coefficient of friction and transfer layer formation. 080 M40 steel plates were ground to achieve different surface roughness with unidirectional grinding marks. Super purity aluminium pins were slid at a sliding velocity of 2 mm/s against the prepared steel plates. Grinding angle (i.e., the angle between direction of sliding and grinding marks) was varied between 0 o and 90 o in the tests. Normal load was varied from 0 to 120 N during the tests. Experiments were conducted under both dry and lubricated conditions in ambient environment. Scanning electron micrographs of the contact surfaces of pins and plates were used to study the surface features that included the morphology of the transfer layer. Surface roughness parameters of the steel plates were measured in the direction of the sliding using an optical profilometer. It was observed that the coefficient of friction and transfer layer formation depends primarily on the directionality of the grinding marks of the harder mating surface. Under lubricated conditions, stick-slip phenomena was observed, the amplitude of which depends on the plowing component of friction. The presence of stick-slip motion under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities. The grinding angle effect on coefficient of friction was attributed to the variation in plowing component of friction, which in turn depends on the mean slope of the profile of the harder mating surface.
In the present investigation, the tribological performance of aluminum micro (100 to 200 μm particle size) and nano (47 nm particle size) composites was studied using a three pin-on-disk tribometer under dry conditions. As a basis for comparison, the tribological performance of aluminum alloys was also studied. The pins made of these materials were then slid against a steel disk under ambient conditions. Tests were conducted at a sliding velocity of 1.58 m/s for a normal load of 30 N. The worn surfaces of the pins were analyzed using a scanning electron microscope. Based on the experiments, it was observed that the nano-composites significantly outperformed all of the other materials with respect to friction levels. It was also discovered that the nano-composites exhibited the best wear performance among the composites investigated. The size of the reinforcement particle trapped at the interface and the hardness ratio of the mating materials were specifically found to play an important role in determining the friction and wear performance of the materials investigated.
Stress corrosion cracking (SCC) is a critical failure mechanism that arises from the synergistic interaction between tensile stress and corrosive environments, leading to sudden and often catastrophic failures in structural components across various industries, including aerospace, nuclear energy, oil and gas, and marine engineering. This review synthesizes current understanding of SCC mechanisms, including film rupture and anodic dissolution, hydrogen embrittlement, and adsorption-induced cleavage, and evaluates material susceptibility across steels, aluminum alloys, nickel-based alloys, titanium, and emerging high-entropy alloys. Environmental factors such as aqueous chemistry, temperature, pressure, pH, and dissolved gases are examined for their roles in SCC initiation and propagation. Advanced testing methodologies, including slow strain rate testing, bent-beam configurations, electrochemical monitoring, and high-resolution microscopy, are discussed for characterizing SCC behavior. Engineering mitigation strategies are presented, encompassing material selection, stress reduction, surface treatments, and environmental control. Case studies illustrate real-world SCC failures and inform best practices. Emerging trends highlight the potential of machine learning for predictive maintenance and the development of SCC-resistant materials through additive manufacturing and microstructural engineering. This comprehensive review provides mechanical engineers with actionable insights for designing, maintaining, and safeguarding components against SCC in demanding service environments.
The wettability of ionic liquids (ILs) is relevant to their use in various applications. However, a mechanistic understanding of how the cation–anion pair affects wettability is still evolving. Here, focusing on phosphonium ILs, wettability was characterized in terms of contact angle using experiments and classical molecular dynamics simulations. Both experiments and simulations showed that the contact angle was affected by the anion and increased as benzoate < salicylate < saccharinate. Further, the simulations showed that the contact angle decreased with increasing cation alkyl chain length for these anions paired with five different tetra-alkyl-phosphonium cations. The trends were explained in terms of adhesive and cohesive energies in the simulations and then correlated to the atomic scale differences between the anions and the cations.
Cermet is an advanced class of material consisting of a hard ceramic phase along with a metallic binding phase with the combined advantages of both the ceramic and the metal phase. The superior properties of this class of materials are particularly useful in high-temperature, tribological, and machining applications. This review paper seeks to provide a comprehensive overview of the various cermet systems. More specifically, the most commonly used cermet systems based on tungsten carbide (WC), titanium carbide (TiC), titanium carbonitride (TiCN), and aluminum oxide (Al2O3) are discussed based on their development, properties, and applications. The effect of different metallic binders and their composition on the tribological and mechanical properties of these cermet systems is elaborated. The most common processing techniques for cermet systems, such as powder metallurgy (PM), reaction synthesis (RS), thermal spray (TS), cold spray (CS), and laser-based additive manufacturing techniques are discussed. The influence of the processing parameters in each case is evaluated. Finally, the applications and challenges of cermet systems are summarized.
