Fraunhofer Institute for Surface Engineering and Thin Films IST
Complex tool geometries coated with an intermediate layer.
CVD diamond coatings for machining
Research into diamond-based coating technologies and applications
CVD diamond-coated tools are used in particular for machining high-strength and highly abrasive materials. The adhesive strength of the diamond coating on the tool, which is usually made of WC-Co carbide, is decisive for the service life of the tools. For cobalt-containing carbides, intermediate layers represent a promising approach to meeting current challenges.
Interlayers as an alternative to etching pretreatment
CVD diamond coating of cobalt-containing WC-Co carbides is challenging due to diffusion processes, among other things. Etching the tool edge zone reduces the cobalt content, but can also weaken it. An alternative is provided by intermediate layers, which act as a diffusion barrier and can be deposited without pretreatment.
Development of adhesive coating systems
One focus of current work at Fraunhofer IST is the development and optimization of coordinated and therefore adhesive coating systems consisting of an intermediate layer and a CVD diamond layer. In a completed joint project, extensive coating system screenings were carried out on test specimens with different cobalt contents. Based on these investigations, promising coating systems were identified and transferred to tools with complex geometries.
Testing in machining trials
In addition to standardized sandblasting tests, machining trials were also carried out to evaluate the coating adhesion of the newly developed coating systems. The coated tools were used both for drilling in an aluminum-silicon alloy and for milling carbon fiber reinforced plastic (CFRP). The developed coating systems showed very good results after defined tool life, in many cases already reaching the level of the etched reference tools. The wear behavior is particularly noteworthy: the coated tools showed continuous wear; there was no large-area coating failure.
Outlook: Application to hard metals with high cobalt content
An exciting next step is to transfer the findings to WC-Co hard metals with higher cobalt contents (>12%). Previous studies show that etching preparation can be avoided and that CVD diamond coatings can be applied with good adhesion. Future studies of tools with cobalt contents >12% could further shift the application limits and reveal the potential for applications beyond machining.
Insight into the project
Tool coated with an intermediate layer and a CVD diamond layer.
Tool coated with an intermediate layer and a CVD diamond layer.
REM image of a CVD diamond-coated intermediate layer.