Since their discovery in 1991 carbon nanotubes (CNTs) have attracted much interest due to their remarkable mechanical, thermal, electrical, chemical and optical properties. In connection with their mechanical properties, CNTs have been studied in various forms for tribological applications including their use as lubricant additives for oil and water. In this work, the tribological properties of functionalized nanotubes (single and multi-walled) modified with carboxylic acid when used as lubricant additives at different concentrations (0.01, 0.05%) were studied under rolling-sliding conditions in a twin-disk testing machine. The tests were performed using 5% of creepage and pressures of 0.8GPa and 1.1GPa. The results indicated that the presence of carbon nanotubes leads to a decrease in both friction coefficient and wear rate for both systems studied (oil and water)

The use of surface texturization to reduce friction in sliding interfaces has proved successful in some tribological applications. However, it is still difficult to achieve robust surface texturing with controlled designer-functionalities. This is because the current existing gap between enabling texturization technologies and surface design paradigms. Surface engineering, however, is advanced in natural surface constructs especially within legless reptiles. Many intriguing features facilitate the tribology of such animals so that it is feasible to discover the essence of their surface construction. In this work, we report on the tribological behavior of a novel class of surfaces of which the spatial dimensions of the textural patterns originate from micro-scale features present within the ventral scales of pre-selected snake species. Mask lithography was used to produce implement elliptical texturizing patterns on the surface of titanium alloy (Ti6Al4V) pins. To study the tribological behavior of the texturized pins, pin-on-disc tests were carried out with the pins sliding against ultra-high molecular weight polyethylene discs with no lubrication. For comparison, two non-texturized samples were also tested under the same conditions. The results show the feasibility of the texturization technique based on the coefficient of friction of the textured surfaces to be consistently lower than that of the non-texturized samples.

Se estudiaron las propiedades reológicas de un aceite lubricante base polialfaolefina (PAO) al que se agregaron nanotubos de carbono (NTC) monocapa y multicapa como aditivos. Los ensayos reológicos realizados apuntaron a estudiar la variación de la viscosidad en función de la temperatura, la carga y la tasa de cizallamiento para mezclas con contenidos de nanotubos de carbono de 0.01% y 0.05% en peso. Adicionalmente, se evaluó la mojabilidad del PAO con y sin la adición de los nanotubos de carbono. Los resultados mostraron que la adición de los nanotubos de carbono a las concentraciones ensayadas lleva a una variación de la viscosidad con respecto a las temperaturas probadas. Fue observado un incremento significativo del esfuerzo de corte con respecto a la tasa de deformación, y tanto para el caso de monocapa como de multicapa dicho esfuerzo presentó tendencia a aumentar cuando la concentración de NTC fue de 0.05%.

The tribological behavior of wheel and rail material twin-disc samples prepared under laboratory-controlled grinding operations was studied. A laboratory grinding device was designed and validated to produce similar results to those found in the field in terms of surface quality and presence of white etching layer (WEL). The test samples were evaluated in a twin-disc machine under dry and lubricated conditions. The results showed that the surface finishing parameters and the microstructure change greatly depending on the surface preparation procedure, and that such changes affect the tribological response of the samples. The wear rates of the tribological tests for the different rail surface qualities showed a reduction of 47.4% for the lubricated tests and 7.3% for the dry tests when the surfaces of the rail specimens were finished by grinding. This is only applied when the WEL thickness was less than 4 μm.