Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 26 MONDAY AFTERNOON
RIVA-TF-MoA-OR.9 INFLUENCE OF PRESSURE ON THE STRUCTURAL ME-
CHANICAL AND DECORATIVE PROPERTIES OF TiN THIN FILMS DEPOSITED BY
CATHODIC ARC EVAPORATION. A. Lousa, J. Esteve. Departamento de Física Aplicada y
Óptica, Universidad de Barcelona, Avda. Diagonal 647, E-08028 Barcelona, Catalunya, Spain. J.P.
Mejia, A. Devia. Laboratorio de Física del Plasma, Universidad Nacional de Colombia Sede Manizales,
Campus La Nubia, Manizales, Colombia.
Titanium nitride TiN is one of the hard materials most widely studied and commonly used as decorative
coatings, wear-resistant coatings, diffusion barriers and electrodes in industrial applications. TiN
coatings are deposited by different PVD and CVD deposition techniques. The typical gold color of
TiN makes it an attractive candidate for decorative applications. TiN can be obtained in a relatively
wide range of compositions around stoichiometry. Changing the stoichiometry around the 1:1 composition
broadens the spectrum of colors and can modify the mechanical properties compared with
those of stoichiometric TiN.
Cathodic Arc Evaporation (CAE) is a especially attractive PVD deposition technique both for its
unique abilities (highly ionized vapor which allows ion energy control through substrate bias voltage,
high deposition rates, excellent adhesion), and for been widely use in industrial applications. It
is well known that composition, structure and properties of the deposited films depend on the process
parameters such us growth temperature, substrate bias voltage, gas pressure in the vacuum chamber.
The purpose of this work is to study the feasibility of depositing TiN coatings of different gold tones
with good mechanical properties by using a metallic Ti cathode and varying the nitrogen partial pressure
in a CAE reactive process. This pressure was varied between 5x10 -4 and 3x10 -2 mbar. The other
technological parameters were kept fixed for all the samples at the following values: cathodic current,
60 A, substrate temperature 400 ºC, substrate bias voltage, -300 V. The coatings were deposited
on polished steel substrates.
The resulting film thickness varied between 1-2 microns, with high deposition rates which ranged
from 8 μm/h for the samples deposited at low pressure, to 4 μm/h for the samples deposited at high
pressure. The composition of the coatings studied by XPS indicates an increasing nitrogen content as
the nitrogen partial pressure is increased. SIMS analysis shows that this composition is uniform
throughout the coatings thickness. The crystalline structure was studied by XRD which shows typical
diffraction patterns corresponding to polycrystalline TiN. The evolution of the crystalline structure
with pressure is discussed in terms of grain size and preferred orientation. The color characteristics
of the samples were analyzed by spectral reflectometry in the visible range. The reflectivity
spectra show a gold-like shape with significant shifts that correlates to the nitrogen content in the
samples. The mechanical properties of the coatings were characterized by dynamical nanoindentation
(NanoTest 550, Micro Materials Ltd.) with a Berkovich diamond tip. The hardness and Young’s
modulus values were obtained by the Oliver and Pharr analysis method. The Young modulus values
resulted close to the bulk TiN value (310 GPa). The hardness of the coatings increases with nitrogen
pressure until reaching a maximum of 24.5 GPa at 1.3x10 -2 mbar, in the intermediate zone of the
studied range, and decreasing for higher pressures.
In summary, we have shown that the control of the nitrogen pressure is useful to obtain TiN coatings
with a wide palette of gold colors and good mechanical properties.
41