Structural and mechanical property of Si incorporated (Ti,Cr,Al)N coatings deposited by arc ion plating process

(Ti,Cr,Al,Si)N coatings with different Al + Si fractions (0.6 and 0.65) were deposited by an arc ion plating (AIP) apparatus that is equipped with the plasma-enhanced type arc cathode. The (Ti,Cr,Al,Si)N coatings were deposited under different substrate bias voltages and effect of the deposition parameter on the composition, structure and mechanical properties was investigated. X-ray diffraction measurements of the (Ti,Cr,Al,Si)N coating deposited under different substrate bias voltages revealed that formation of the hexagonal phase (Wurzite structure) was only limited to a relatively low bias voltage range of 20 to 30 V. Above this bias voltage, the crystal structure of the coatings was single-phased cubic rock-salt structure (B1 phase) independent of the bias voltage. Grain size of the coating was calculated from the full width of half maximum (FWHM) of the X-ray diffraction peak and it was smaller than the one of conventional (Ti,Al)N or (Ti,Cr,Al)N coating with a comparable Al fraction. The grain size estimated from the cross-sectional TEM observation was less than 10 nm. From the TEM observation, the coating was compositionally homogeneous and there was no evidence that the film had a phase separation such as Si-rich and -poor region. Hardness of the (Ti,Cr,Al,Si)N coating with Al + Si = 0.6 was in the range of 26 to 27 GPa independent of the substrate bias. (Ti,Cr,Al,Si)N coating with Al + Si = 0.65 showed slight increase in hardness from 24 to 27 GPa when the substrate bias was increased to more than 100 V. To evaluate the oxidation resistance, annealing tests in the air at 1000 °C were conducted and surface SEM observations revealed that surface of the conventional (Ti,Al)N and (Ti,Cr,Al)N was covered with coarse oxide grains enriched with TiO2. Whereas only a dense but very thin protective oxide layer was observed in case of (Ti,Cr,Al,Si)N coating after the oxidation. These coatings were applied to the high-speed dry cutting tests against hardened D2 steel (HRC 60) and the result clearly indicated better performance of (Ti,Cr,Al,Si)N compared to the conventional coatings such as (Ti,Al)N and (Ti,Cr,Al)N.