Thermal behavior of carbon nitride and TiN/NbN superlattice films

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Abstract
Hard coatings are commonly used today to enhance the life of numerous tools and wear parts. As carbon nitride and TiN/NbN superlattice films prepared by reactive sputtering were being evaluated for such tribological applications, it appeared necessary to test their thermal behavior to determine their stability at high temperatures. The coatings were reactively sputtered on silicon, M1 steel, or cemented carbide substrates. Two deposition conditions were used for the carbon nitride films producing either soft or hard films. The effect of a metal interlayer, either chromium or titanium, has also been studied. Two modulation periods were used for the TiN/NbN films with the same deposition conditions. Thermal annealings were performed up to 700 °C under vacuum in the 10−6 Torr range. Several properties of the coatings before and after these annealings were evaluated and compared, including hardness (nano-indentation), adhesion/cohesion (scratch test), structure x-ray diffraction, and composition Auger electron spectroscopy. The carbon nitride coatings lost part of their nitrogen, and both the hardness and the critical load dropped as the annealing temperature was increased. Carbon nitride films deposited on silicon wafers peeled off after treatment at 400 °C, while films deposited on an M1 steel remained adhered. A critical temperature for both chemical and physical properties around 600 °C was observed. For the TiN/NbN superlattice films, annealing up to 700 °C caused almost no intermixing, while the nitrogen content, the hardness, the adhesion/cohesion, and the structure remained unaffected.

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