Hydrogen-free DLC coating on tools

Paul Boughton

In the development of PVD coatings, cross-fertilisation is of the utmost importance. One market can profit from the knowledge gained in another market. The tool market can hugely benefit from coatings developed for the automotive engine market. The Dutch PVD coating expert, Hauzer Techno Coating, has now transferred its tribological coating technology to the tool market.
In many tool applications, hardness of the coating is an important asset, as well as a good adhesion of the coating. But there are also other features of coatings that can become a huge advantage. Non-sticking for example is very important when machining soft materials such as aluminium or plastics. It enhances the lifespan of the tool and increases the productivity of the tooling equipment. Smoothness on the other hand can be a huge advantage for forming tools. This feature can eliminate the post-treatment step in the process. In automotive coating applications, these features have been extensively studied and coatings have been optimized with the results of this research.
Diamond Like Carbon (DLC) coatings are widely used in automotive applications for their excellent features for tribological purposes. The friction coefficient of DLC coatings is low and the material is non-sticking. Depending on the technology used to deposit the coating (sputtering, PACVD, arc evaporation), the features can be adapted to the application. DLC coating is very suitable for coating drills, inserts, end mills, saw blades, taps, punches, (plastic) moulds and dies. Apart from its use in machining aluminium, DLC coating can also be used on tools for machining other non-ferrous metals and plastics.
Another example of technology transferred from one market to another is hydrogen-free DLC (ta-C). During the European Nanocoat project, in which Hauzer participated, test were done with several different DLC coatings on automotive engine components (tappets). The tests, which were conducted at the FIAT Research Centre (CRF) in Turin, concluded that ta-C coatings were characterized by the highest hardness and showed the lowest friction coefficient. With the knowledge gained from the Nanocoat project, Hauzer has been able to solve the adhesion issues for ta-C. The result is a range of ta-C coatings with good adhesion and hardness values (40-70 Gpa with DB 1-2) which can be industrially applied.
During impact measurements by a large American engine manufacturer, it turned out that the ta-C coating was still intact with an impact load of 2 kN, just some small cracks were visible. A benchmark coating had already been removed with this impact load. The picture of the Rockwell indent shows good adhesion of the ta-C coating. The hydrogen-free ta-C coatings are produced by using arc technology, circular arc or laser arc, and have a diamond-like structure (mainly sp3). A typical hardness of 3000-7000 HV can be achieved with ta-C coatings. The typical friction coefficient is between 0.02 and 0.1. The advantageous features of ta-C together with the solution for the adhesion issues, make this coating a real promise for the future of precision tooling.

For more information, visit www.hauzer.nl

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