Hydrogen permeation testing parameter exploration for high-entropy alloys

Hydrogen permeation testing standards for metallic materials, such as ASTM G148 and ISO 17081, refer to the use of Devanathan-Stachursky cell-like electrochemical setups. This type of setup consists of two electrochemical cells separated by the testing specimen, that acts as a membrane. One of the cells is aimed to load one side of the specimen with a constant surface hydrogen concentration. The second cell is aimed to oxidize the hydrogen at the other side and monitor the rate at which the hydrogen effuses across the membrane. Both the working parameters at each cell and the membrane thickness are highly material and electrolyte dependent.

The standards and scientific literature guide the effective permeation testing conditions according to the membrane material and the electrolyte. Thorough studies may be found on common industrial alloys, such as iron, stainless steels, or nickel alloys. However, the development of high-entropy alloys (HEAs) offers a wide range of alloying options whose conditions for testing are not always covered by literature. These alloys are composed of several major elements and may show unexpected properties. Behavior of equiatomic and non-equiatomic CoCrFeMnNi alloy in hydrogen environments has been explored in recent years with promising results. This suggests that HEAs could be used as hydrogen barriers, but each new alloy combination is a new experimental challenge.

To contribute to the study of hydrogen permeation across different HEA families, a consortium composed of two universities, three research institutes, two metallic product manufacturers and an industry-oriented cluster is developing a research project (more information available at ). As stated above, one of the problems that are being faced is the determination of an effective set of permeation testing parameters for the alloys under study in the project. The aim of this contribution is sharing with the rest of the scientific community the advances achieved up to now by the consortium, covering:

• Microstructural and X-Ray diffraction analysis of the manufactured materials.
• Electrochemical study of the alloys to explore the permeation test conditions.
• Hydrogen permeation test results under the testing parameters defined.