AlCr-based coatings now even more resistant to wear

The Vienna University of Technology has published new findings on wear-protection coatings based on aluminum-chromium oxides: A small amount of iron makes the coating even more resistant to wear.

Ceramic coatings based on aluminum-chromium are particularly hard and resistant to oxidation and thus protect drills, milling tools, indexable cutting inserts and other tools from wear. In fulfilling this role, the coatings need to be able to withstand high temperatures and extreme mechanical loads. The addition of small quantities of iron improves the material properties of the aluminum-chromium oxide coatings. Coatings that have had iron added are deposited with a high fraction of wear-resistant phases, thus increasing the service life time and mechanical resilience of the tools.

 

The formation and effects of droplets

Hard coatings based on aluminum-chrome oxides are applied to the tools by means of arc evaporation. This involves an electric arc melting tiny quantities of the cathode material. Reacting with oxygen, the evaporated material is deposited on the substrate as a thin ceramic hard coating. Droplets are also incorporated in the hard coating during this process. These defects are partly made up of pure metal particles ranging from a few nanometers up to hundreds of nanometers in size. The droplets make the hard coating on the tools rougher, which in turn has a negative impact on the flow of chips during drilling, for instance. The tool can fail in deep drill holes and chips can clog the flutes.

The addition of iron results in a considerable improvement. Compared with pure AlCr oxide coatings, AlCrFe-based coatings form fewer and far smaller droplets, and these furthermore assist the formation of particularly wear-resistant phases.

Powder-metallurgical manufacturing technology makes it possible for Plansee to produce targets and cathodes using precisely defined material compositions such as AlCrFe. Plansee uses state-of-the-art technology such as SPS machines (SPS = spark plasma sintering) to manufacture prototypes quickly and economically efficient in a wide range of target dimensions and compositions.

Christian Koller's paper "Role of droplets and iron on the phase formation of arc evaporated Al–Cr-oxide coatings" was supported by Plansee and received the prestigious Acta Journals Student Award. You can download the complete paper here: http://www.sciencedirect.com/science/article/pii/S0257897215300062

 

For more information and for your personal contact at Plansee for aluminum-chromium targets and cathodes, click here.