Alternative to Hard Chrome Plating with Hexavalent Chromium

The use of corrosion- and wear-inhibiting coatings based on hexavalent chromium will be severely restricted in the EU from September 2017. The EHLA (extreme high-speed laser material disposition) process from the Fraunhofer Institute for Laser Technology ILT presents an eco-friendly alternative to hard chrome plating.

In view of the impending approval restrictions on hexavalent chromium coatings, hydraulic-cylinder manufacturer IHC Vremac Cylinders has now changed over to the eco-friendly EHLA process from the Fraunhofer ILT in Aachen, Germany. In this process, a laser melts the powder particles above the melt pool. This allows the process speed to be increased from 0.5 to 3.0 metres per minute to up to 500 metres per minute according to Fraunhofer ILT. This process can reduce the coating thickness as well: whereas the minimum coating thickness was previously 500 micrometres, coatings as thin as 25 to 250 micrometres can now be applied economically. Furthermore, the coating roughness decreases to a tenth of the typical value with laser material deposition.

"The advantage of using EHLA to coat rotationally symmetric parts is that the necessary components can be integrated into a lathe", explains Thomas Schopphoven, head of the Productivity and System Technology team in the Laser Material Deposition group at Fraunhofer ILT. It took the plant manufacturer Hornet Laser Cladding less than six months to convert a lathe into a roughly 14-metre-long EHLA system.

Faster than thermal spraying

"For a hydraulic cylinder, we currently apply a protective layer of Inconel 625 some 400 micrometres thick, which then requires some grinding rework. The final layer thickness is around 200 micrometres," says Andres Veldman, Engineering Manager at IHC Vremac Cylinders. He also said that the process is significantly faster than thermal spraying and entails less post-processing than do other technologies.

The Dutch manufacturer has already begun series production. The EHLA process still costs around the same as thermal spraying, but Veldman assumes that the costs will decrease once the rework processes have been optimised. In order to convince the critical end customers in the offshore sector, the company had Lloyds certify EHLA in accordance with the DIN EN ISO 15614-7 standard.