Ion bombardment-induced nanocrystallization of magnetron-sputtered chromium carbide thin films

Nearly stoichiometric chromium carbide thin films (Cr3C2) were deposited by unbalanced r.f. magnetron sputtering of a chromium carbide target in a pure argon discharge. Their microstructure and hardness are shown to be strongly influenced by the working pressure and substrate bias during deposition. Further correlation with the plasma parameters, i.e. the energy and flux of argon ions as well as the flux of film-forming particles, is illustrated, which indicates the momentum transferred by bombarding ions per film-forming particle Pdens which creates a densification and simultaneously does not cause a mobility enhancement to be dominant for the film structure. Below a threshold value of Pdens of about 0.91 u0.5eV0.5, the resulting films exhibited an amorphous structure with a relatively low hardness of 1200 HV0.02. A nanocrystalline structure emerged only for larger values of Pdens, and was responsible for a hardness enhancement to 3500 HV0.02.