Processing effects on the tribological characteristics of reactively sputtered chromium oxide (Cr₂O₃) overcoat films

Abstract

The mechanical and tribological characteristics of thin chromium oxide films are investigated by controlling the process parameters in reactive deposition and subsequent annealing. From this, the correlation between the deposition process, film structure, and properties is established. Substrate heating and oxygen partial pressure are found to be the critical parameters that alter the oxygen concentration and crystallization of the films which, in turn, affect their stress, hardness, and wear resistance. The chromium oxide film deposited at 150 °C in pure argon and annealed at 300 °C shows a hardness of 25 GPa, which is near the bulk hardness of Cr2O 3, and exhibits a good wear resistance with adhesive wear being the dominant wear mechanism. Reactive deposition at 25 °C or with excessive oxygen leads to films with nonstoichiometric composition, which hinders their crystallization upon low-temperature annealing. As a result, the hardness is reduced, and the wear resistance deteriorates several orders of magnitude with a concomitant transition of the wear mechanism from adhesive into an abrasive regime.