For nitride-HEAFs, Huang et al. prepared (AlCrNbSiTiV)N films and investigated the effect of nitrogen content on structure and mechanical properties. They found that both values of hardness (41 GPa) and elastic modulus (360 GPa) reached a maximum when R N = 28%. The (AlCrMoTaTiZr)N x film deposited at R N = 40% with the highest hardness of 40.2 GPa and elastic modulus of 420 GPa. Chang et al. fabricated (TiVCrAlZr)N on silicon substrates under different R N = 0 ~ 66.7%. At R N = 50%, the hardness and elastic modulus of the films reached maximum values of 11 and 151 GPa. Liu et al. studied the (FeCoNiCuVZrAl)N HEAFs and increased the R N ratio from 0 to 50%. They observed both values of hardness and elastic modulus exhibited maxima of 12 and 166 GPa with an amorphous structure at R N = 30%. Other related nitride-based HEAFs are summarized in Table 2. Compared to pure metallic HEAFs (Table 1), most nitride-based films have larger hardness and elastic muduls due to the formation of binary compound consisting of nitrogen. However, there are still some films possessing relatively low hardness, which are smaller than 20 GPa, The reason is the inclusion of non-nitride-forming elements.