Influence of Fe impurities on structure and properties of arc-evaporated AlCrN coatings

The influence of up to 5 at.% Fe in AlCr targets on microstructure and properties of arc-evaporated AlCr(Fe)N coatings is investigated. Analyses of the coatings by electron microscopy and X-ray diffraction reveal no significant changes in their microstructure. The incorporated Fe atoms are homogeneously distributed and mainly substitute Cr and Al atoms in the crystal lattice as suggested by elemental mappings, X-ray photoelectron spectroscopy and X-ray diffraction. There is no pronounced modification of the mechanical properties due to the Fe addition. However, thermogravimetric analysis in oxygen containing atmosphere reveals a reduction of the oxidation onset temperature due to the addition of Fe reaching 700–800 °C for the maximum Fe content studied. Raman spectra recorded from oxidised coatings indicate that the presence of Fe in the coatings promotes the formation of Cr2O3 at lower temperatures than for the reference AlCrN. This lower oxidation onset results in a reduced wear resistance at temperatures up to 700 °C. Nevertheless, the presence of Fe retards the ongoing oxidation reaction at temperatures exceeding 1000 °C, indicating the formation of a dense oxide scale.