ICMCTF 2012! - CD-Lab Application Oriented Coating Development

mm 3 /Nm to ~18 x 10 -5 mm 3 /Nm, indicating a mild wear regime, as
expected, was attributed to the increase of the coating hardness.
9:20am B4-2-6 Abrasive wear properties of AlCrN, AlTiN and CrN
coatings, J.L.M. Mo, M.H. Zhu, Southwest Jiaotong University, China, A.
Leyland, A. Matthews (A.Matthews@sheffield.ac.uk), University of
Sheffield, UK
Abrasive wear properties of AlCrN, AlTiN and CrN coatings deposited by a
multiple arc vapor deposition technique on cemented carbide substrates
were evaluated on a micro-scale abrasion tester under different normal loads
(Fn=0.2, 1 N) and different numbers of ball revolutions (N=10, 20, 50, 100,
200 rev) . A micro-blasted 25 mm diameter hardened steel sphere was used
as counterface ball and a suspension of SiC particles (mean size of 4-5 μm)
as the abrasive slurry. After the wear tests, the wear craters were studied by
stylus profilometer and Scanning Electron Microscopy (SEM) and the wear
behaviors were investigated. It was shown that the AlCrN coating had much
better anti-abrasive wear properties than the AlTiN coating, though the
latter had a lower Habrasive particles/Hsurface ratio. The CrN coating exhibited
much worse abrasive wear resistance as compared to the two ternary nitride
coatings. A three-body rolling wear mechanism was found to be dominant
under the relative lower normal load of 0.2 N. However, the three coatings
showed different abrasive wear degradation behaviors: the AlCrN coating
showed the best resistance to the impaction deformation and thus a great
potential in rolling wear resistance, the AlTiN coating showed relative
higher wear rate with the worn surface being characterized by a heavier
deformation, the CrN coating showed the worst abrasive wear resistance by
heavier plastic deformation and a dominant wear mechanism of cracking
and micro-spalling. The difference between the AlCrN and AlTiN coatings
were further studied under higher normal load of 1 N, in that case two-body
grooving wear was the relatively dominant mechanism, the AlTiN coating
exhibited much heavier grooving wear than the AlCrN coating.
9:40am B4-2-7 Annealing-induced structural and mechanical property
changes of CVD-(Si)-B-C coatings, C. Pallier, G. Chollon
(chollon@lcts.u-bordeaux1.fr), P. Weisbecker, F. Teyssandier, LCTS-
CNRS, France
Amorphous B-C and Si-B-C ceramics were deposited by CVD from BCl3-
CH4-H2 and BCl3-CH3SiCl3-H2 mixtures, respectively, at temperatures
around 1000°C and reduced pressure. All the as-deposited (Si)-B-C ceramic
coatings are nearly amorphous and consist of a common very disordered
boron carbide phase (BxC) and, in the Si-B-C coatings, sub-nanometric SiC
crystals. The proportions of the BxC and the SiC phases vary with the
deposition conditions. A SiC grain growth is observed after heat treatment
beyond 1200°C, while the amorphous B-C-rich phase is gradually
transformed into free aromatic carbon and B4C nanocrystals, in agreement
with the thermodynamic equilibrium. This particular crystallization process
is expected to lead to a significant time/temperature-dependent change of
the density and the mechanical properties. It has to be considered to better
understand and predict the behavior of the ceramic matrix composite parts
in future aeronautic engines.
The crystallization behavior in inert atmosphere of the (Si)-B-C ceramics is
investigated in situ, by differential scanning calorimetry analyses and X-ray
diffraction. Ex-situ analyses are also conducted by heat-treating the
specimens under high vacuum at different temperatures/durations, and by
characterizing the resulting microstructures at short and long range, by solid
MAS-NMR, Raman microspectroscopy, neutron diffraction, X-ray
absorption, X-ray diffraction and transmission electron microscopy.
Indentation tests are achieved at room temperature on the pristine and
annealed coatings, to evaluate their stiffness, hardness and toughness. High
temperature tensile tests are also performed on model 1D composites
consisting of (Si)-B-C coatings deposited on soft carbon monofilaments.
These micro tensile tests allow the evaluation of the changes of (i) the
volume (or density), (ii) the Young’s modulus, (iii) the creep rate and (iv)
the thermal expansion of the coatings. We expect the mechanical behavior
and the structural ordering of the (Si)-B-C ceramics to be strongly
interrelated. The results obtained on the various specimens will be discussed
on the basis of their elemental composition, initial structure and processing
conditions.
10:00am B4-2-8 Thermal evolution of thermal, electrical and optical
properties of Ti-Al-N coatings, R. Rachbauer
(richard.rachbauer@oerlikon.com) OC Oerlikon Balzers AG, Liechtenstein,
J.J. Gengler, Air Force Research Laboratory, Thermal Sciences and
Materials Branch, US, A. Voevodin, Air Force Research Laboratory, US, K.
Resch, Materials Science and Testing of Plastics, Montanuniversitaet
Leoben, Austria, P.H. Mayrhofer, Montanuniversität Leoben, Austria
Physically vapor deposited Ti1-xAlxN thin films are well acknowledged in
various industrial applications due to their beneficial effect on lifetime and
performance of e.g. cutting or milling tools. The excellent thermal stability
Wednesday Morning, April 25, 2012 52
of Ti1-xAlxN is determined by the incorporation of Al on Ti lattice sites in a
cubic (c) supersaturated metastable solid solution of Ti1-xAlxN after
deposition. Thermally activated diffusion processes lead however to a series
of decomposition phenomena, involving first recovery of deposition
induced defects and then the spinodal decomposition process which
accounts for a hardness increase with increasing isostructural
decomposition state into c-TiN- and c-AlN-enriched domains [1, 2]. The
subsequent recrystallisation and development of a dual phase structure
composed of cubic TiN and hexagonal AlN initiates deteriorating
mechanical properties. Earlier investigations [3] have proven the big
potential of the age hardening phenomenon for high temperature
applications in cutting applications, however the development of thermal,
electrical and optical properties has not yet been investigated as a function
of temperature. Hence, the present study focuses on the thermal evolution of
heat conductivity, electrical resistivity and optical reflectance from room
temperature up to 1400 °C and relates to decomposition induced structural
and chemical changes of Ti1-xAlxN. This contribution aims for a deeper
understanding of Ti1-xAlxN thin films under thermal load, which is
necessary for the development of e.g. state-of-the-art protective coatings for
cutting tools or thermal barrier coatings for electronic devices.
References:
[1] P. H. Mayrhofer, A. Hörling, L. Karlsson, J. Sjölen, T. Larsson, C.
Mitterer, L. Hultman, Self-organized nanostructures in the Ti-Al-N system,
Appl. Phys. Lett. 83 (2003) 2049-2051
[2] R. Rachbauer, S. Massl, E. Stergar, D. Holec, D. Kiener, J. Keckes, J.
Patscheider, M. Stiefel, H. Leitner, P. H. Mayrhofer, Decomposition
pathways in age hardening of Ti-Al-N thin films, J. Appl. Phys. 110 (2011)
023515
[3] A. Hörling, L. Hultman, M. Odén, J. Sjölen, L. Karlsson, Mechanical
properties and machining performance of Ti1-xAlxN-coated cutting tools,
Surf. Coat. Technol. 191 (20005) 384-392
10:20am B4-2-9 Pressure and Temperature Effects on the
Decomposition of Arc Evaporated Ti1-xAlxN Coatings During Metal
Machining, N. Norrby (nikno@ifm.liu.se), M. Johansson, Linköping
University, Sweden, R. M'Saoubi, Seco Tools AB., Sweden, M. Odén,
Linköping University, Sweden
This study focuses on the coherent and isostructural decomposition of cubic
c-(Ti,Al)N thin films during metal machining, i.e. under the influence of
large normal stress and elevated temperature typical for the selected cutting
application. It is well known that c-(Ti,Al)N decomposes in two steps at
elevated temperatures. In the first step, c-(Ti,Al)N decomposes spinodally
into coherent isostructural cubic TiN- and AlN-enriched domains and in the
second step a transformation from c-AlN to the stable wurtzite AlN occurs.
Associated with the first step is an increase in hardness due to a coherency
strain between the domains whereas the second step introduces large
incoherent precipitates, thus rapidly lowering the hardness. However, the
insight on the decomposition process during the application of variable
stresses and heat, as in the case of metal cutting is scarce.
Here we have deposited thin films of Ti0.6Al0.4N by cathodic arc evaporation
onto tungsten carbide (WC-Co) cutting tool inserts and studied the phase
and microstructure evolution after a continuous turning operation for 10
minutes in carbon steel (C45E). For comparison, reference samples have
been heat treated with a heating rate of 20 Kmin -1 followed by an isothermal
step of 10 minutes at 900 °C and 1000 °C respectively.
During turning at variable cutting speeds, vc , between 100 m/min and 400
m/min, the peak temperature at the cutting edge was between 750 °C and
950 °C as measured by an IR-CCD camera. The peak normal stress,
evaluated from measured contact forces during cutting, was about 2 GPa
and independent of the range of cutting speeds investigated. The deduced
stress distribution also shows that the normal stress along the rake face is
decreasing with an increasing distance from the cutting edge towards the
end of the tool-chip contact. Transmission electron microscopy (TEM),
including analytical scanning TEM (STEM) has been used for detailed
characterizations of the tool-chip interface along the cutting edge. The
progression of the spinodal decomposition is determined by the domain size
of the TiN and AlN enriched domains and is measured from STEM
micrographs. After heat treatments, the results show an increased domain
size from 2.8 to 5.0 nm with increasing annealing temperature from 900 to
1000 °C which is expected. After cutting tests however, an increase in
domain size from 3.2 to 5.6 nm is seen with the increasing normal stress
along the cutting edge. This implies that even relatively small pressures
promote coherent isostructural decomposition, which is in line with
theoretical studies but has previously not been shown experimentally.