Influence of nitrogen on the structure and mechanical properties of r.f.-sputtered Cr–B–N thin films

Cr–B–N thin films were synthesized by r.f.-plasma assisted magnetron sputtering apparatus. The influence of nitrogen on the phase composition and mechanical properties of the Cr–B–N thin film is evaluated in this study. XRD results indicate that a phase transformation from CrB2 to h-BN and β-Cr2N occurred in the Cr–B–N films with increasing nitrogen partial pressures. The residual stress in the Cr–B–N films is compressive. Although it increases with increasing nitrogen partial pressure, the value is much smaller than that of the conventional sputtered films. The hardness of the films decreases due to the formation of soft h-BN phase in the Cr–B–N films. The anti-oxidation property becomes worse with increasing nitrogen partial pressure; however, it is noted that the lowest beginning temperature of oxidation is still approximately 860 °C, which is higher than the typical working temperature of contact area for high-speed cutting tools.