Jill Sundberg

Tribochemically Active Ti–C–S Nanocomposite Coatings

We demonstrate a new concept of self-adaptive materials, where sulphur is incorporated into TiC/a-C coatings and may be released in, for example, a tribological contact. By reactive sputtering with H2S, sulphur goes into the carbide to form a TiC x S y phase in an amorphous carbon matrix. The addition of sulphur lowers the friction against steel. Significantly lower friction is obtained against a tungsten counter-surface, as WS2 is generated in the contact. Annealing experiments and formation energy calculations confirm that sulphur can be released from TiC x S y . Ti–C–S coatings are thus chemically active in tribological contacts, creating possibilities of new low-friction systems.

Solution-based synthesis of AgI coatings for low-friction applications

Thin films of AgI have been synthesized from Ag surfaces and elemental I2 using a rapid and simple solution-based method. The effect of using ultrasound during the synthesis was studied, as well as the influence of the nature of the solvent, the I2 concentration, the time, the temperature, and the sonication power. The films were characterized using X-ray diffraction, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy, and found to consist of β-AgI, possibly along with some γ-AgI. It was found that sonication increases the film thickness and grain size. The nature of the solvent has a profound effect on the film growth, with mixtures of water and ethanol leading to thicker coatings than films synthesized using either component in its pure form. Selected coatings were tribologically tested, and the AgI coating was seen to lower the friction coefficient significantly compared to a reference Ag surface under otherwise identical conditions. Long lifetimes (over 30000 cycles) were seen against a Ag counter surface. Tracks and wear scars were studied using SEM and Raman spectroscopy, and it was found that the friction level remains low as long as there is AgI in the points of contact. This method is found to be a simple and fast way to deposit AgI on Ag with large possibilities of tuning the thickness and grains sizes of the resulting films, thereby optimizing it for the desired use.