Using carbon and nitrogen to combat the eggshell effect

A supplement or replacement for DLC coatings is offered by a Danish company with its process for surface hardening of stainless steel and titanium. In addition to technical and economic advantages, the sustainability of process solutions is playing an increasing role among customers.

Diamond-Like Carbon or DLC coatings for short are used in many areas where very good friction properties and wear resistance are required. The DLC coatings applied by time-consuming and cost-intensive PVD or PACVD processes are usually only a few micrometers thick. However, if the component must also be corrosion-resistant, making the use of stainless steels essential, the DLC system has some weak points. The soft stainless steel as a carrier medium and the correspondingly high hardness gradient to the DLC layer promote the eggshell effect. If this or other causes lead to a defect in the coating, this is often the starting point for the detachment of the layer.

Hardening instead of coating

The surface hardening of Expanite, which uses a gas-based diffusion process to embed carbon and nitrogen deep into the component surface, improves the load-bearing capacity and thus counteracts the eggshell effect. If defects occur in the hardening layer, this does not lead to further flaking because, unlike the applied DLC layer, it is a diffusion hardening layer that is coherent with the base material. In addition, the gas-based diffusion process is significantly more energy-efficient and environmentally friendly than comparable wear protection processes. Another positive effect on the life cycle assessment is that the vacuum treatment does not require any time-consuming cleaning of the parts after hardening, for example with aggressive chemicals.

Application examples show suitability in practice

"We have already replaced the classic DLC coating in various applications, from the classics such as running and sealing surfaces in bearings to pump components or knife edges to applications in medical technology," explains Dr. Holger Selg, application expert and Expanite Sales Director DACH. He goes on to say, "In some cases, the two technologies have also been combined and a DLC coating applied in addition to our Expanite hardcoat, thus creating a very resilient system."

The Expanite process, developed specifically for corrosion-resistant materials, is suitable for austenitic, martensitic, ferritic and duplex stainless steels, as well as nickel-based alloys such as Inconel and Hastelloy. For titanium materials, the company has developed the new ExpaniteHard- Ti special process to market maturity in recent years.

Expanite GmbH
www.expanite.com