The as-cast, two-phase, f.c.c. + B2, lamellar-structured, high-entropy alloy Fe<inf>28.2</inf>Ni<inf>18.8</inf>Mn<inf>32.9</inf>Al<inf>14.1</inf>Cr<inf>6</inf> was annealed in pure nitrogen at either 800 °C or 1000 °C for 100 h in order to harden the surface by nitridation. Similar nitriding treatments were performed on a comparably-structured, four-component alloy Fe<inf>30</inf>Ni<inf>20</inf>Mn<inf>35</inf>Al<inf>15</inf> for comparison. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyze the resulting microstructures and phase compositions. AlN formation near the surface completely depleted the matrix of Al resulting in a f.c.c. matrix containing AlN particles, while a two-phase lamellae structure remained in the center of the specimens. Nevertheless, the AlN-containing region exhibited a higher hardness than the AlN-free area. Interestingly, the presence of Cr led to much more rapid diffusion of nitrogen into the material.
Meng, F., & Baker, I. (2015). Nitriding of a high entropy FeNiMnAlCr alloy. Journal of Alloys and Compounds, 645, 376–381. https://doi.org/10.1016/j.jallcom.2015.05.021