Thermal stability of arc evaporated Al-Cr-O-N coatings

Abstract (Al x Cr 1−x ) δ (O 1−y N y ) ξ coatings were arc evaporated using Al 0.70 Cr 0.30 cathodes and different nitrogen-to-oxygen gas flow ratios and investigated with respect to their phase evolution and thermal stability. The utilization of specific nitrogen-to-oxygen ratios underlies elaborated cross-sectional transmission electron microscopy and selected area electron diffraction studies carried out on (Al,Cr)N–(Al,Cr) 2 O 3 –(Al,Cr)N gradient coatings. Based on dynamical differential scanning calorimetry and thermogravimetric analysis up to 1500 °C, in combination with subsequent X-ray powder diffraction, we can conclude, that the thermal stability of (Al x Cr 1−x ) δ (O 1−y N y ) ξ oxynitrides increase with increasing O content, up to ~81 at.% of the non-metallic sublattice. Especially, the high O-containing coatings are prone for the formation of volatile Cr-oxides. However, the typically observed two-step dissociation process of Cr–N bonds towards Cr (via the formation of Cr 2 N and N 2 -release), is delayed to a one-step process (up to 1500 °C) for N-contents below 10 at.% of the non-metallic sublattice. Consequently, by knowledge-driven fine-tuning of the nitrogen-to-oxygen ratio, the thermal stability of (Al x Cr 1−x ) δ (O 1−y N y ) ξ oxynitrides can be designed for their application-based specific needs.