Eutectic high entropy alloys (EHEAs) possess a natural duplex phase lamellar structure, which is usually viewed as in situ composites, achieving an excellent combination of strength and ductility owing to the scarce casting flaws and the synergetic effect from the composite structure. In this work we propose further enhancement of their properties by nitriding their surface. Unfortunately, nitriding of multiphase systems, especially EHEAs is challenging. The mechanism of nitrided layer formation and its phase composition are much easier to be studied separately on single phase alloys. Multiphase structure of a nitride layer can negatively affect its performance in application in which corrosion and/or friction occurs. The differences in electrochemical potential between phases can accelerate local corrosion of the layer, even though both phases can separately demonstrate good corrosion resistance. Moreover, uneven mechanical properties can increase the overall wear rate of the layers.
In this work we present the results of successful plasma nitriding of AlCoCrFeNix alloy systems. We  obtained increased hardness and corrosion resistance. Furthermore, reduction of friction and wear rate has also been observed.
It should be noted that to study the mechanical properties of nitrided layers we have used advanced techniques such as in-situ SEM nanoindentation and micropillars compression. For tribological properties not only classical approach with ball-on-disk tribometer is applied but also AFM measurements are performed. The complex multiscale approach provides us much better insight into the complicated mechanisms of nitrided EHEAs.