✍ Scribed by S. Hofmann; H. A. Jehn
No coin nor oath required. For personal study only.
Reactively magnetron‐sputtered CrN~x~ and (Cr,Al)N~x~ hard costings were oxidized in air at temperatures between 500°C and 900°C for periods up to 16 h. The original and the oxidized samples were characterized by scanning electron microscopy, X‐ray diffraction and scanning Auger electron spectroscopy. The results show that CrN~x~ coatings oxidize by growth of chromium oxide layer on top of the coating governed by outward diffusion of Cr. Below the oxide layer, a Cr‐depleted and N‐enriched intermediate nitride layer is left. The ternary (Cr,Al)N~x~ nitride coating is about five times more oxidation resistant than CrN~x~ at all temperatures between 500°C and 900°C. The oxide layer on (Cr,Al)N~x~ shows a strong variation in composition with depth, which can be interpreted as a main oxide layer of a Cr‐rich (Cr,Al) oxide followed by an Al‐enriched (Cr,Al) oxynitride. In contrast to CrN~x~, a wide interdiffusion zone of N and O is found. In both cases the oxidation process is mainly controlled by Cr diffusion.
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