Effect of nitrogen flow on the properties of quaternary CrAlSiN coatings at elevated temperatures

CrAlSiN coatings were reactively fabricated on Si substrates from metallurgical Cr0.45Al0.45Si0.10 alloy target by r.f. magnetron sputtering. The thermal stability, oxidation resistance and decomposition behavior of CrAlSiN coatings were investigated after annealing at temperatures between 900 and 1100 °C for 1 h in air. The phase identification, chemical states, oxide content on the surface, and hardness of CrAlSiN coatings were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), and nanoindentation, respectively. The oxidation resistance of CrAlSiN coatings with a gas flow ratio (R=N2N2+Ar) over 0.25 was fairly good after heat treatment at 900 and 1000 °C. Especially for coatings with R = 0.25 to 0.33, the oxygen contents on the surface of CrAlSiN coatings were only 2.7 at.% to 6.5 at.%, respectively. Furthermore, the hardness of CrAlSiN coatings increased with R and reached a maximum value of 30.4 ± 1.4 GPa with R ranging from 0 to 0.5. The effect of Si addition on hardness and oxidation resistance of the CrAlSiN coatings was also evaluated.