The reasons for strengthening of film materials

The mechanisms of strengthening of V-Cr-Cu-Ni-Co-Fe-Al high entropy alloy, (W, Ti)N, and TiN-Cu nanocomposite films deposited by DC magnetron sputtering (MS) and combined “vacuum arc evaporation - MS” have been investigated. Combined effect of compositional and structural changes occurring under the ion bombardment results in high (~ 14 GPa) hardness of HEA films. The microstructure of (W, Ti)N films depends on film-forming species arriving at the condensation surface (WN and TiN molecules, W, Ti, and N atoms). When the concentration of molecules is higher than that of atomic nitrogen, dispersed two-phase W2N+β-W material with maximal hardness (~ 55 GPa) forms. When the concentration of N atoms exceeds that of molecules, W2N single-phase film with coarse grains and lower hardness (~ 35 GPa) grows. The hardness of films deposited by simultaneous vacuum arc evaporation of titanium and MS of copper in Ar-N
₂
ambient depends on copper content in the film. With increasing the copper content from 0 to ~ 1.5 at % the hardness increases and reaches maximum (~ 42 GPa). Further increase in Cu content decreases the hardness. We discuss the results based on the idea that mechanical properties of a film are defined by the composition of film-forming species and the energy of particles bombarding the growth surface.