Thermal stability of sputter deposited nanocrystalline W 2N/amorphous Si3N4 coatings

The thermal stability of nanocomposite W-Si-N coatings, which had been sputter deposited at increased silicon target currents, was studied by annealing at 800 or 900 °C in vacuum by using x-ray diffraction, x-ray photoelectron spectroscopy, electron probe microanalysis, scanning electron microscopy, atomic force microscopy, and microhardness testing. The crystalline W2 N coatings were decomposed to W with the loss of interstitial N atoms and the presence of microcracks at their surfaces after annealing at 900 °C. The coating consisting of nanocrystalline (nc-) W2 N imbedded in amorphous (a-) Si3 N4 matrices and the amorphous coatings underwent partial recrystallization, the loss of interstitial N atoms, and morphological changes upon annealing. The nc- W2 Na- Si3 N4 coating had the least N in grain boundaries and the lowest atomic ON ratio, and it had no failure after annealing at 900 °C, showing high thermal stability. The hardness of the coatings was decreased, but the nc- W2 Na- Si3 N4 coating maintained the highest hardness (46.6±3.7 GPa) after annealing at 900 °C. © 2006 American Vacuum Society.