Polished Diamond Coatings Show Potential in Dry Forming of Aluminum

Ecological and economic concerns have led to an increased interest in the realization of a lubricant-free forming technology. Some applications, such as the manufacture of overseas cables where lubricant residues lead to a risk of short circuits, require dry forming.

Seeking such technology, a group of researchers has tested the suitability of surface coatings for dry forming of aluminum. Testing at the Bremen Institute for Applied Beam Technology in Bremen, Germany, has revealed that polished polycrystalline CVD diamond coatings are extremely promising for dry forming of aluminum workpieces.

The researchers carried out oscillating-ball-on-plate tribometer tests in lubricant-free contact with a 5083 aluminum-alloy ball. With polished steel as the reference plate, the researchers compared results with those of carbonaceous coatings, namely a hydrogenated amorphous carbon coating and a polycrystalline CVD diamond coating (as deposited and polished). To provoke coating wear in the tribometer tests, the researchers employed 700-Mpa pressure and speeds of 50 mm/sec. across 99,900 cycles, with the reference uncoated tool steel tested under both lubricated and dry conditions.

Results showed that both the coefficient of friction and the wear rate of the plate and the aluminum ball were reduced significantly through the use of lubricant, with the polished CVD diamond coating leading to the lowest wear rate for both the plate and the aluminum ball. Furthermore, no aluminum adhesions could be detected on the polished diamond coating.

Further testing details and results can be found under the title Friction and Wear Performance of Different Carbon Coatings for Use in Dry Aluminium Forming Processes, which can be found in the publication Surface and Coatings Technology, and is described at www.doi.org/10.1016/j.surfcoat.2018.10.103.

Technologies: Finishing, Materials

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