Nanometer Scale Chemomechanical Characterization of Antiwear Films

We report the first nanometer scale chemical and mechanical (chemomechanical) characterization of selected features of a tribologically derived zinc dialkyl-dithiophosphate (ZDDP) antiwear film. AFM permits identification of the features responsible for preventing wear. These features are identified by nearby microscale fiducial marks, and their mechanical properties are determined by imaging nanoindentation. The same features are then studied by X-ray photoelectron emission microscopy (X-PEEM), which provides both elemental and chemical information at 200 nm spatial resolution. The mechanical properties are then determined for the same features, which are formed of a polyphosphate glass. This information provides new insights into the mechanisms by which ZDDP antiwears films are effective at inhibiting asperity contact between two metal surfaces     

Torsion Tribological Behavior of Polytetrafluoroethylene Composites under Dynamic Normal Load: Effect of Dynamic Normal Load Amplitude

The torsion tribological behavior of polytetrafluoroethylene (PTFE) composites was investigated under different dynamic normal loads. The difference between the shapes of T–θ curves under static and dynamic normal loads indicates that the torsion regime was affected by the dynamic normal loads. Dynamic loads not only produced new frequency components but also enhanced the amplitude of frequency components produced by the static load. The biaxial dynamic stress and transformation of the torsion regime under dynamic loads produce higher wear than that of a static load. The wear mechanisms under static and dynamic loads are abrasive wear and adhesive and fatigue wear, respectively.     

Modified falex testing: A tool for understanding the compound layer capabilities

The usefulness of Falex testing in assessing the scuffing resistance of nitrocarburized steel was established by carrying out tests on treated medium-carbon and hot-working steel specimens. Though the test could be employed as a quality control measure for the compound layer thickness, it was found inadequate in bringing out the subtle variations in the compound layer characteristics of specimens of different steels. By a modified form of Falex testing, the heat resisting ability of the compound layer of different steels could be distinctly brought out.     

Fractal characterization of wear-erosion surfaces

Wear erosion is a complex phenomenon resulting in highly distorted and deformed surface morphologies. Most wear surface features have been described only qualitatively. In this study wear surfaces features were quantified using fractal analysis. The ability to assign numerical values to wear-erosion surfaces makes possible mathematical expressions that will enable wear mechanisms to be predicted and understood. Surface characterization came from wear-erosion experiments that included varying the erosive materials, the impact velocity, and the impact angle. Seven fractal analytical techniques were applied to micrograph images of wear-erosion surfaces. Fourier analysis was the most promising. Fractal values obtained were consistent with visual observations and provided a unique wear-erosion parameter unrelated to wear rate.     

Effect of experimental parameters on the high-stress abrasive wear behavior of steels and a software package for its prediction

The effect of different experimental factors on the high-stress abrasive wear properties of steels has been studied. A correlation among the factors has been established by linear regression analysis. A computer software in Microsoft Basic language utilizing linear regression analysis has been developed with the capability of predicting the wear response of steels from the experimental factors.     

Advances in solid lubrication with MoS2 multilayered coatings

The general classification of solid lubricant types is reviewed, along with the reasons for choosing and methods of depositing solid lubricants, in particular MoS₂. The best‐performing and most flexible technique for making MoS₂ films is by physical vapour deposition (PVD), and the variants of that technology are considered. The intrinsically‐lubricating, lamellar structure of pure MoS₂ is described, along with a brief summary of the wear and failure modes. Present applications for lubrication by MoS₂ in spacecraft and dry machining are described. Anti‐adhesion uses in extruding and moulding are also mentioned. The current modification of MoS₂ films is by addition of dopants (co‐sputtering), by multilayering as a series of films each fulfilling a specific task, or by stacking repeating nanometre‐scale films. Composite films of MoS₂ islands in a hard film matrix are also being developed.     

Preparation and tribology of aerogel silica and alumina-silica as lubricant oil additives

Aerogel silica and an aerogel mixture of aluminium and silica were prepared using the ethanol supercritical fluid drying technique. Their physical properties were characterised using XRD, transmission electron microscopy, (TEM), and N₂ adsorption. The tribological properties of a 500 SN oil containing the aerogel and a dispersing agent were evaluated using a four-ball machine and a block-on-ring tribotester. Results indicated a greater wear resistance and load-carrying capacity and a lower friction coefficient than for the basic oil. In the oil, the aerogel worked by its deposition on the rubbing surface. Copper stearate was superior to dodecyl alcohol as a dispersing additive, and ultrasonic treatment helped promote the dispersion of the aerogel in oil. There existed an optimum ratio of aluminium isopropyl alcoholate to tetraethanol silicate. The corresponding aerogel mixture gave a maximum value of P_E.     

Friction and solid-solid adhesion on complex metallic alloys

The discovery in 1987 of stable quasicrystals in the Al–Cu–Fe system was soon exploited to patent specific coatings that showed reduced friction in ambient air against hard antagonists. Henceforth, it was possible to develop a number of applications, potential or commercially exploited to date, that will be alluded to in this topical review. A deeper understanding of the characteristics of complex metallic alloys (CMAs) may explain why material made of metals like Al, Cu and Fe offers reduced friction; low solid–solid adhesion came later. It is linked to the surface energy being significantly lower on those materials, in which translational symmetry has become a weak property, that is determined by the depth of the pseudo-gap at the Fermi energy. As a result, friction is anisotropic in CMAs that builds up according to the translation symmetry along one direction, but is aperiodic along the other two directions. A review is given in this article of the most salient data found along these lines during the past two decades or so.