Structure–property relations of arc-evaporated Al–Cr–Si–N coatings

The addition of silicon to the widely used aluminum-containing transition metal nitrides is promising for the synthesis of hard and thermally stable films with good oxidation resistance. For that reason, Al–Cr–Si–N coatings were deposited by reactive cathodic arc-evaporation under industrial conditions from Al70Cr30 − xSix (x = 0, 1, 2, 5 at.%) targets at substrate bias voltages ranging from − 40 V to − 150 V. The structure of the well adherent coatings was investigated by X-ray diffraction and Raman spectroscopy, which indicated at higher Al/Cr ratio > 1.9 an increased tendency of the metastable face-centered cubic solid solution of AlN in CrN to separate into a cubic–hexagonal phase mixture. At higher bias voltages, this effect is gradually inverted and the single cubic phase can be retained. X-ray photoelectron spectroscopy revealed dominant Si–N bonds suggesting either a substitutional solid solution or a separate Si–N phase. Mechanical properties, i.e. hardness and elastic modulus, measured by indentation together with stress evolution demonstrate the beneficial effect of the conservation of the metastable cubic phase.