Page 322 - 00. Complete Version - Progress Report IPEN 2014-2016

322 Materials and Nanotechnology | Progress Report

of these materials causes phase transforma- and CrN peaks in the XRD patterns, while for
tion from alpha-alumina to gamma-alumina. the lower periodicity (≤10nm) coatings, just
Heat effects during femtosecond laser treat- one intermediate lattice (d-spacing) was de-
ment causes the grains to be in the nanome- tected. An almost linear increase of hardness
ter scale. Without heat effects, the grains are with decreasing bilayer period indicates that
in the micrometer scale. The use of femtosec- interfacial effects can dominate the harden-
ond laser permits control of the surface rough- ing mechanisms.
ness of the alumina specimens. The higher
the femtosecond laser energy, the higher is Rietveld´s method
the wettability of the specimen and the total
surface energy. Specimens with laser textured The aim of this study was to evaluate the ag-
surfaces upon immersion in 1.5 SBF for 6 and ing behavior of a dental Y-TZP submitted to an
15 days revealed apatite layers well bonded to accelerated hydrothermal aging (HA). Specifi-
the substrate and without detachment. The cally: a) determine the kinetic curve of tetrag-
adhesion of apatite to surfaces of specimens onal to monoclinic phase transformation (t-
that were not textured with femtosecond la- m); b) calculate the speed of the front of phase
ser was inadequate. transformation zone growth during the HA; c)
evaluate the relationship between percentage
The production of tribological nanoscale mul- of monoclinic phase and depth of phase trans-
tilayer CrN/NbN coatings up to 6 μm thick by formation with the biaxial flexural strength
Sputtering/HIPIMS has been reported in liter- (BF); d) evaluate the effect of the association of
ature. However, high demanding applications, HA and fatigue at the BF. Sintered discs of den-
such as internal combustion engine parts, need tal Y-TZP (YZ- Vita YZ, LP- Lava Plus) were sub-
thicker coatings (>30 μm). The production of mitted to HA at 120°C, 130°C and 150°C and
such parts by sputtering would be econom- analyzed by X-ray diffraction analysis (XRD).
ically restrictive due to low deposition rates. One specimen of each group was submitted to
In this work, nanoscale multilayer CrN/NbN scanning electron microscopy (SEM) and opti-
coatings were produced in a high-deposition cal coherence tomography (OCT) to calculate
rate, industrial-size, Cathodic Arc Physical Va- the phase transformation depth and the speed
por Deposition (ARC-PVD) chamber, contain- of the front transformation zone. Groups (YZ,
ing three cathodes in alternate positions (Cr/ LP and LA-Lava) were divided according to the
Nb/Cr). Four 30 μm thick NbN/CrN multilay- aging time (n=10): 0, 5, 25, 70 and 140 hours
er coatings with different periodicities (20, (150°C/3.01 bar). After the HA, the YZ group
10, 7.5 and 4 nm) were produced. The coat- was divided once again (n=10): with and with-
ings were characterized by X-Ray Diffraction out mechanical cycling, all ceramics were sub-
(XRD) and Transmission Electron Microsco- mitted to biaxial flexural strength test (ISO
py (TEM). The multilayer coating system was 6872) and one way analysis of variance (ANO-
composed of alternate cubic rock-salt CrN and VA) (ο=0.05) to compare the results. XRD re-
NbN layers, coherently strained due to lattice sults indicated that YTZP presented a sigmoidal
mismatch. The film grew with columnar mor- behavior due to the limited depth of XRD pen-
phology through the entire stratified struc- etration (~6.3 μm). SEM and OCT analysis con-
ture. The periodicities adopted were main- firmed a linear growth of the front as function
tained throughout the entire coating. The 20 of the time to all temperatures One way ANO-
nm periodicity coating showed separate NbN VA showed a decrease in mechanical strength

Instituto de Pesquisas Energéticas e Nucleares