TAGS: Industrial Coatings
Lukas Gröner from Fraunhofer IWM, MicroTribology Center µTC, develops a robust coating that effectively protects steel from the ingress of hydrogen. The barrier effect of this so-called MAX phase layer is 3500 times greater than that of untreated steel.
Hydrogen Barrier Combines the Strength of Ceramic and Metal
In his doctoral thesis at the Fraunhofer Institute for Mechanics of Materials IWM, MicroTribology Center µTC, and at the Institute for Microsystems Technology at the University of Freiburg im Breisgau, physicist Lukas Gröner developed and tested special coatings for steel components that prevent the penetration of atomic hydrogen.
These are so-called MAX phase materials that have been researched internationally for more than ten years. "
MAX phases have amazing properties because they combine the characteristics of ceramics and metals," says Lukas Gröner, a scientist in the Tribological and Functional Layer Systems group. Like ceramics, MAX phases are insensitive to attack by oxygen and very heat-resistant.
In his doctoral thesis, Lukas Gröner also examined how the MAX phase coating behaves when it is heated to a high level - as could be the case in gas turbines or fuel cells in the future. In order to simulate normal operating stresses, he heated the material to 700 degrees and left it in the oven for up to 1000 hours. A thin layer of a special aluminum oxide - the α-Al
2 - was created on the top of the coating O
3. As it became apparent in the further course of the investigations, this thin aluminum oxide coating significantly strengthens the barrier effect of the protective layer against hydrogen.
New Test Bench Measures Barrier Effect Against Hydrogen
To test how well the MAX phase layer prevents hydrogen from penetrating into the metal, Lukas Gröner first developed a test stand for sheet-metal samples. In this trainer, he compared uncoated steels with MAX phase-coated steels. This made it possible for the first time at the Fraunhofer IWM to precisely quantify the penetration of hydrogen and to determine the so-called permeation reduction factor (PRF) as a measure of the barrier effect.
The results make one sit up and take notice: steels with a MAX phase layer that were not heated kept the hydrogen 50 times (PRF 50) better than untreated steels. However, the results were particularly impressive for the coated steels that had been heated and an α-Al
2 O
3 Layer had formed. These held back the hydrogen around 3500 times more than the untreated steel. "
These are values that absolutely meet the requirements of industry," emphasizes Lukas Gröner.
Gröner says
, "The MAX phase coatings are ideal for such applications because they protect the metallic components from heat and at the same time can dissipate the electrical current that is generated inside the fuel cell."
The coating is also suitable for gas turbines.
Lukas Gröner cannot yet say whether the new coating process will be offered by the industry as a service in future or whether it will find its way onto the market in another form. The individual PVD coating process steps also must be optimized. However, Lukas Gröner has proven in every case that MAX phase layers can provide excellent protection against hydrogen.
Source: Fraunhofer IWM