Success Story

Without DLC, the engine will pay the fee!

Even for extremely wear-resistant DLC coatings (diamond like carbon), there are critical conditions of use.

Diamond is the hardest material and can only be ground and polished with diamond dust. For this reason, coatings with diamond characteristics are used today to protect machine elements and sensitive surfaces from wear and traces of use. Such coatings are especially employed when lubrication or lubricants are no longer sufficient to prevent critical wear. Nevertheless, there are always traces of wear on such diamond or diamond-like coatings. Under which circumstances can these high-strength coatings wear at all?

These artificially produced diamond coatings usually contain a certain amount of graphite and are referred to as DLC coatings (Diamond Like Carbon). The graphite content is deliberately adjusted and enables – in addition to extreme wear resistance – surfaces with low friction. The coatings are usually only a few micrometres thick (i.e. about 1/10 of a hair diameter), but are intended to protect the component through-out its lifetime. The prerequisite for coated machine components is that the coatings adhere firmly to the base (a suitable substrate) and do not wear off. Normal wear processes of these coated components occur in the nanometre range (almost at the atomic level). AC²T was able to make these wear processes measurable in a practical way and thus it is possible to investigate the critical influences on these processes.

(Foto: iStock)

Measurement method

The method of measuring wear with radioactive isotopes is state of the art. However, it requires favourable boundary conditions and consistent research work to be able to implement this for real machine components. The RIC method (Radioactive Isotope Concentration), as designed by AC²T and used together with project partners, makes use of special precautions in the activation of the component surfaces as well as in the measurement itself. The activity of the samples is lower than that of natural radiation exposure, still the wear (progress) of the components can be determined precisely.

Moreover, the measurement of wear with radioactive isotopes is the only method, which allows to record wear continuously in nanometre resolution (in the adequate order of magnitude).

Impact and effects

The joint cooperation made it possible to investigate component groups of the drive train with regard to possible wear-critical influences. It was shown that the wear behaviour in the nanometre range can be critically changed by the chemical properties of the lubricant and the lubricating fuel alone. Moreover, the smallest dust particles (in the sub-micrometre range – i.e. significantly smaller than the thickness of the wear protection layer) can cause the DLC coating to flake off and thus lead to failure of this wear protection measure.

For DLC coatings, a sensitive balance of influencing parameters must be maintained. AC²T has succeeded in differentiating the effect of influencing parameters using a new measuring method. As a result, DLC wear protection coatings can be designed more efficiently, and the service life of sensitive surfaces can be significantly extended.

Left: section through a DLC-coated steel sample shown under a scanning electron microscope (image: CEST); right: schematic representation of DLC wear (image: AC²T).

Project coordination (Story)

Dipl.-Ing. Dr. Martin Jech
Project leader
AC2T research GmbH