Diffusion barrier with 30-fold improved performance using AlCrTaTiZrN high-entropy alloy

Abstract High-entropy alloys nitrides (HEA-N) have been proposed as diffusion barriers to prevent metal diffusion. Due to their lack of grain-boundaries and large lattice distortion, HEA-N have lower diffusion than binary nitrides. Despite the interest, very few quantitative studies have been performed to precisely measure metal diffusion in HEA-N. Here we report, for the first time, iron diffusion rates and activation energy in AlCrTaTiZrN HEA-N thin-films, and demonstrate that they are lower than reported values in TiN. AlCrTaTiZrN was deposited on steel from a metal alloy target using reactive radio frequency sputtering under various nitrogen flow rates. X-ray diffraction shows that as the nitrogen flow rate increases, microstructure of the films changes from amorphous to nanocrystalline. Thermal stability studies at 700–900 °C show that AlCrTaTiZrN remains chemically and structurally stable up to 800 °C. SIMS shows that the HEA-N films effectively block Fe diffusion up to 800 °C. At higher temperatures, the films are mechanically stable but not effective as barrier films, due to recrystallization in AlCrTaTiZrN. The measured diffusion coefficient is 7 × 10 − 22 m 2 s − 1 at 700 °C, 30 times lower than any polycrystalline nitride barrier reported in literature. The study not only conclusively demonstrates the effectiveness of AlCrTaTiZrN as diffusion barrier, it also provides quantitative data that can be used by engineers to precisely design barrier layers.