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The performance and durability of high-pressure fuel systems in combustion engines are critical for consistent operation under extreme conditions. High-pressure fuel systems are traditionally lubricated with fuel that is compressed and delivered to the combustion chamber. However, lubrication with fuel presents significant challenges in these systems when used with low-viscosity fuels, leading to increased wear rates, especially in reciprocating contacts. This study delved into the tribological performance of steels of varying alloy content (annealed and hardened variants of AISI-52100, CF2, and D2) against alumina and hard 52100 counterbody materials in ethanol and decane environments. Friction and wear behaviors were evaluated, highlighting the influence of material interactions and environmental factors. Elastohydrodynamic lubrication analysis of the tested systems indicated that ethanol and decane form lubricating films of nanometer-scale thickness, confirming the boundary lubrication regimes of the performed tests. In summary, the tribological behavior trends were similar for alumina and 52100 counterbodies. Even though soft 52100 steel demonstrated low friction, its wear was the largest for both tested environments and counterface materials. Among all the tested materials, hard D2 experienced the lowest wear. 52100 and D2 steels showed opposite friction change behavior when comparing hard and soft samples, with lower friction observed for softer 52100 steel and harder D2 steel. Meanwhile, the wear was lower for harder candidates than for softer ones independent of the environment and counterbody material. Raman spectroscopy analysis of the formed wear tracks indicated the formation of carbon films with larger intensities of characteristic carbon peaks observed for more wear-resistant materials. These results suggest the synergistic effect of hardness and tribochemical activity in reducing the wear of materials.

This study investigates the rheological properties, elastohydrodynamic (EHD) film-forming capability, and friction coefficients of low molecular mass poly-a-olefin (PAO) base stocks with varying contents of high molecular mass olefin copolymers (OCPs) to assess their shear stability and their potential for energy-efficient lubrication. Several PAO-OCP mixtures were blended in order to examine the relationship between their additive content and tribological performance. Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy were used to characterize the molecular masses and structures, respectively. Density, viscosity, EHD film thickness, and friction were measured at 303 K, 348 K, and 398 K. Film thickness and friction were studied at entrainment speeds relevant to the boundary, mixed, and full-film lubrication regimes. The PAO-OCP mixtures underwent temporary shear-thinning resulting in decreases in film thickness and hydrodynamic friction. These results demonstrate that the shear characteristics of PAO-OCP mixtures can be tuned with the OCP content and provide insight into the effects of additives on EHD characteristics. [ABSTRACT FROM AUTHOR]

Ultrafine particles are often used as lubricant additives because they are capable of entering tribological contacts to reduce friction and protect surfaces from wear. They tend to be more stable than molecular additives under high thermal and mechanical stresses during rubbing. It is highly desirable for these particles to remain well dispersed in oil without relying on molecular ligands. Borrowing from the analogy that pieces of paper that are crumpled do not readily stick to each other (unlike flat sheets),we expect that ultrafine particles resembling miniaturized crumpled paper balls should self-disperse in oil and could act like nanoscale ball bearings to reduce friction and wear. Here we report the use of crumpled graphene balls as a high-performance additive that can significantly improve the lubrication properties of polyalphaolefin base oil. The tribological performance of crumpled graphene balls is only weakly dependent on their concentration in oil and readily exceeds that of other carbon additives such as graphite, reduced graphene oxide, and carbon black. Notably, polyalphaolefin base oil with only 0.01-0.1 wt % of crumpled graphene balls outperforms a fully formulated commercial lubricant in terms of friction and wear reduction. [ABSTRACT FROM AUTHOR]

Siloxane-based polymers (polysiloxanes) are susceptible to temporary shear-thinning that manifests as a reduction of elastohydrodynamic film thickness with increasing entrainment speed or effective shear rate. The departure from Newtonian film thickness can be predicted with the power-law exponent ns, an indicator of the severity of shear-thinning in a polymeric fluid that is influenced by the macromolecular structure. In this paper, a combination of extant rheological and tribological models is applied to determine the power-law exponent of several polysiloxanes using film thickness measurements. Film thickness data at several temperatures and slide-to-roll ratios are used to validate the methodology for several siloxane-based polymers with alkyl and aryl branches. [ABSTRACT FROM AUTHOR]

Siloxane-based polymers (polysiloxanes) exhibit a range of volume, viscosity, and pressure-viscosity behaviors that are strongly influenced by the macromolecular structure. In this report, a combination of extant rheological models is applied to develop a molecular-rheological modeling formalism that predicts polysiloxane rheological properties, such as specific volume, which means density, viscosity, and pressure-viscosity index variations with macromolecular structure, pressure, and temperature. Polysiloxane molecular features are described in terms of alkyl branch length L, pendant type J, density of branch functional monomers Q, and degree of polymerization DP. Both new and published data are used for model parameter determination and validation. Several siloxane-based polymers with alkyl, aryl, alkylaryl, cycloalkyl, and halogenated branches were synthesized to examine the modeled relationship between their molecular structures and rheological behaviors. [ABSTRACT FROM AUTHOR]

This article reports an investigation of the effect of melting and microstructure on the microscale friction of several silver–bismuth alloys using a high-temperature nanoindentation-tribotesting system. These studies showed that friction increases with temperature before melting. We modeled these results as due to the softening of the alloys with increasing temperature, which appears to adequately explain the experimental trend. The friction behavior upon melting depends on the alloy composition. For some alloy composition, friction was observed to exhibit a sharp decrease upon melting, while for another alloy composition, friction was observed to keep increasing with temperature. This unusual behavior can be explained by the difference in microstructure and phase composition as a function of temperature among different Ag–Bi alloys. [ABSTRACT FROM AUTHOR]

Presents a study that examined the effects of sputter gas composition, target power, substrate bias, substrate tilt and rotation on film growth and properties. Experimental methods; Results and discussion.

The dissociation of molecular to atomic hydrogen on clean surfaces of Ni3Fe with either an ordered or disordered structure has been directly investigated by thermal desorption studies. Results show that when exposed to an ordered Ni3Fe surface, molecular hydrogen dissociates to produce atomic hydrogen, which desorbs from the surface around 350 K. On the other hand, hydrogen does not dissociate on a disordered Ni3Fe surface. These results indicate that atomic ordering has a marked effect on surface chemical reactivity. Furthermore, our study provides a mechanistic basis to explain the hydrogen-induced embrittlement in ordered Ni3Fe but not in disordered Ni3Fe. [ABSTRACT FROM AUTHOR]

Melting occurs at the armature-rail interface during electromagnetic launch due to resistive heating. The liquid metal film at the interface is thought to decrease the friction and contact electrical resistance. The liquid metal is quenched at the rail surface, leaving a solid transfer film with surface properties that may affect the efficiency of subsequent launches. Notably, the transfer film contains pores which increase the overall rail electrical resistance. The reduction of atmospheric water vapor by liquid aluminum to produce hydrogen is thought to be the main source of porosity. To further examine the pore formation mechanism, we performed launch experiments using steel armatures and copper rails lubricated with two silver-bismuth alloys. Spherical pores similar to those observed in aluminum films are also present in silver-bismuth transfer films. Neither liquid silver nor bismuth is capable of reducing water vapor to hydrogen. This strongly suggests that the porosity is not due to hydrogen in these films. Air entrainment occurs in forced wetting when the three-phase contact line velocity exceeds a critical value. The critical wetting velocity is a function of surface tension and viscosity and is estimated to be 4-40 m/s for liquid bismuth at 600 K and a comparable value for liquid aluminum. Armature velocities exceed these values nearly instantaneously during launch. These results indicate that air entrainment is likely the source of porosity in transfer films. [ABSTRACT FROM AUTHOR]

Observes surface melting on small particles using x-ray diffraction from lead crystallites. Dependence of melting temperature on particle size; Distinctions between melting and surface melting; Attainment of a sharp crystallite size distribution by melting the smaller particles.

Focuses on detection of elusive surface atoms with atomic force microscopy. Application of scanning tunneling microscope (STM) in detection of surface atoms; Complications associated with the use of STM; Suitability of atomic force microscope in detection of surface atoms; Superiority of atomic force microscopy in comparison to STM for detection of surface atoms.

The article discuses that the transmission of bacteria and viruses through touched surfaces which is an important public health concern, heightened recently by the COVID-19 pandemic. Topics discussed include Stainless steel has a pleasing appearance and is more corrosion-resistant than Cu; and demonstrated antimicrobial properties of copper, it is incumbent upon materials scientists to design potent antimicrobial copper-containing stainless steels as an economical option.