Internal friction studies of nanocomposite superhard nc-TiN/a-Si3N4 and nc-(Ti1−xAlx)N/a-Si3N4 films

Elastic and anelastic properties of TiN/a-Si3N4 and (Ti1−xAlx)N/a-Si3N4 superhard nanocomposite (nc) films prepared by plasma-induced chemical vapor deposition (PCVD), magnetron sputtering and vacuum arc deposition (physical vapor deposition, PVD) have been investigated by mechanical spectroscopy. One internal friction peak with relaxational nature was observed at temperatures around 230-280 °C and frequencies about 100 Hz for as-deposited films prepared by PVD, while no peak was detected in the films prepared by PCVD whose hardness was as high as 50 GPa. A comparison of a series of samples indicates that the peak is higher for films with lower hardness. The activation energy and the pre-exponential factor of the relaxation time are deduced as 0.7-1.0 eV and 10−10 to 10−12 s, respectively. The intensity of this peak decreases with increasing annealing temperature. After annealing at 600-750 °C, this peak disappears and Young's modulus increases, in agreement with the increase in the hardness upon the annealing reported earlier. This internal friction peak is suggested to be associated with a thermally activated relaxation process within the interfaces that were not fully developed during the PVD process.