Z. Budinská1, R. Novák1,
T. Kubart1, T.Polcar1, D. Nováková2
1CTU, Faculty of
Mechanical Engineering, Dept. of Physics
Technická 4, 16601 Praha 6
2CTU, Faculty of Transportation
Sciences, Depth. of Applied Mathematics
Na Florenci 25, 110 00 Praha 1
Superlattice coatings are multilayered coatings with layer thickness
in nanometer range, consist of two materials with large shear modulus mismatch. They total thickness of
coatings is usually about 1-2 micrometer. The value of microhardness of
superlattice coatings is higher than microhardness for each single layer film
of these materials. It was also found; that the change of microhardness was
related to the modulation periods or modulation ratios in metal or ceramic
modulated multilayer films. Hardness anomalies come from the elastic modulus
difference between the superlattice layers. Due to this structure these films
exhibit better mechanical, electronic, magnetic and optical properties. [1]
One of the component generally used is titanium nitride, the other one is nitride of niobium, vanadium, tantalum or chromium. For coatings working at higher temperature it is suitable to use combination of titanium nitride and aluminium nitride. Maximum of working temperature is then about 930° C, and it is much more than 790° C for TiN.
X-ray diffraction analysis allows the study of layers for single materials (measurement of lattice constants) and for multilayers too. Also we can study the change of texture, internal stress etc.
Our laboratory has been interested in coatings prepared by reactive
magnetron sputtering. In order to prepare superlattice coatings we rearranged
one of our equipment. It has been equipped with three unbalanced magnetrons and the sample
holder was driven by a stepper motor. Therefore it was possible to
change thickness of each sublayer by changing the speed of substrate
rotation. In this paper the results of
TiN/CrN and TiN/Ti coatings (substrate steel or Si) study are presented.
The XRD measurements were made using the X-ray
diffractometer with standard Bragg-Brentano geometry and CrKa radiation. Other parameters of coatings (thickness, microhardness)
were measured using the standard methods.
Our next aim is to adapt the adjustment of our apparatus for sputtering of other types of multilayers (superlattice coatings). We are interested in a multilayered system consisting of pure titanium as a bonding layer, followed by hard superlattice TiN/CrN or TiN/VN and the outer layer of selflubricated coating (as MoS2) for the reduction of friction coefficient.
This combination seems to be very promising. In the meantime the structure of TiN/CrN coatings is studied in details in order to verify technology of sputtering. Another aim is to manage determination the superlattice period and structure of multilayers using high - angle X-ray diffraction .
[1] Yashar, P.C., Sproul W.D., Vacuum , 55 (1999) 179-190