Since hard coatings used in metal cutting applications are exposed to temperatures up to 1000 °C, their oxidation stability is a crucial parameter for the tool lifetime. Thus, within this work, the detailed oxidation mechanisms of chemical vapor deposited TiN, Ti(C,N) and TiC coatings were studied. Coating powders were subjected to a heat treatment between 420 and 940 °C in ambient atmosphere and their phase composition was monitored in-situ by X-ray diffraction. Rietveld refinement allowed to quantify the phase fractions of TiN, Ti(C,N), TiC, TiO 2 rutile and TiO 2 anatase at every measurement temperature. Combining this method with differential scanning calorimetry and thermo-gravimetric analysis allowed to precisely track the progress of the involved reactions during oxidation. TiN exhibits the highest oxidation onset temperature of 640 °C. This fact is attributed to the higher Gibbs free energy of the oxidation reaction compared to TiC and the large domain size of the nitride. The latter observation also explains the single-step reaction to rutile without anatase formation. In case of Ti(C,N) and TiC, rutile and anatase form in the course of the oxidation. Ternary Ti(C,N) displays the highest oxidation end temperature and is only entirely consumed at 880 °C. Owing to the lower Gibbs free energy of the oxidation and the lower domain size in comparison to the nitride, TiC exhibits the lowest oxidation onset and end temperature.
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