Mechanical properties, bonding characteristics, and oxidation behaviors of Nb-Si-N coatings

Nb-Si-N coatings with Si contents of 0-30 at% were fabricated through reactive direct current magnetron cosputtering. The processing parameters were various sputtering powers, substrate holder rotation speeds, and nitrogen flow ratio (N2/(N2 + Ar)). Three phase regions, namely face-centered cubic (f.c.c.) NaCl structure, X-ray amorphous, and nanocrystalline phases, were identified and related to the chemical compositions of the coatings. Low-Si-content (0-13 at%) and middle-N-content (39-45 at%) Nb-Si-N coatings exhibited an f.c.c. structure, high-Si-content (17-30 at%) and high-N-content (45-53 at%) Nb-Si-N coatings exhibited an X-ray amorphous structure, and low-Si-content (6 at%) and low-N-content (26-30 at%) Nb-Si-N coatings exhibited a nanocrystalline structure. Examining the bonding characteristics of the Nb-Si-N coatings by using X-ray photoelectron spectroscopy indicated that NbN tended to form preferentially and was followed by Si3N4, which is consistent with the laws of thermodynamics. The correlations between the mechanical properties, residual stresses, and structures of the Nb-Si-N coatings were investigated using nanoindentation, a curvature method, and X-ray diffraction. The oxidation behaviors of the Nb-Si-N coatings annealed in air at 400-600 °C were also examined.