Stress and Hardness of CrN x films

Chromium nitride films CrN x with x ranging form 0 to 1 were deposited by reactive PVD. Both stress and hardness in the films are a function of the composition. The growth stress and hardness for the majority of the films can be related through the Hall Petch relation. It is shown that the hardest films fall outside this relation. It is also shown that the hardest films are nanocrystalline. It is argued that the hardness of these films is a consequence of the nanocrystallinity of these films.