Titanium nitride

TiN is currently the dominant hard coating for improving the wear resistance of cutting tools and engineering components. Figure 1 represents examples of laser-acoustic measurements for TiN films with thickness of d = 1.3 and 1.6 µm deposited by ion plating on steels. The tests were performed to study the effect of pre-sputtering the steel surface on the film adhesion [1].

example 9
Figure 1: Dispersion curves of the surface acoustic wave propagation, measured for a TiN coated steel with different film thickness d and pre-sputtering time tS, and for the pure steel substrate as well

Comparing the curves of the coated samples with those of the non-coated sample reveals the way that the TiN films influence the surface wave dispersion. For the non-coated sample, the phase velocity c is nearly constant. Not so for the coated samples, for which the dispersion curves increase with frequency, due to the higher Young’s modulus of the films compared to the substrate. The slope of the dispersion curve increases with increasing film thickness. However, for the same film thickness the slope reduces with reducing pre-sputtering time tS. This indicates that films with lower pre-sputtering time tS have a lower stiffness, due to micro-defects in the film and at the interface. The effect of varying film stoichiometry was excluded by analyzing the films with Auger spectroscopy.
The Young’s moduli of the TiN films were calculated by fitting the theoretical dispersion curve. The results in Table 1 reveal the reduction of the film modulus with reducing pre-sputtering time tS.

Table 1: Young’s moduli of TiN films of different thickness and pre-sputtering time tS deduced from the dispersion curves in Figure 1

example 10

The film adhesion of the samples was tested by several techniques [1].
Figure 2 shows the correlation of the film modulus with the acoustic activity in the scratch test. These results were obtained for a large number of test samples ensuring a sufficient statistic significance. They suggest a lower Young’s modulus of a TiN film to indicate a reduced mechanical protection by this film.

example 11

Figure 2: Correlation of Young’s modulus E of the TiN films with the total number of acoustic emission events NAE in the scratch test

[1] H. Ollendorf and D. Schneider: Surface & Coatings Technology 113 (1999) 86

Back