1,211 research outputs found
Atomic environment and interfacial structural order of TiAlN/Mo multilayers
Multilayered TiAlN/Mo coatings were deposited by dc reactive magnetron sputtering in a custom-made chamber. In order to assess the composition of these coatings, a combined study of Extended X-ray Absorption Fine Structure (EXAFS) and Rutherford Backscattering Spectrometry (RBS) experiments were performed. Through the simulation of the EXAFS spectra, giving the local environment of the titanium atoms inside the nitride (TiAlN), a cubic phase has been evidenced with aluminium atoms occupying titanium sites. For modulation
periods in the range of 3.6–11.8 nm, RBS simulations on these multilayers also enabled the determination of the level of intermixing that occurs at the interfaces as a function of the negative bias voltage and number of layers. It was observed that the intermixing width could be as high as 2.1 nm for the roughest samples (larger periods) or as low as 0.4 nm for those with the sharpest interfaces (smaller periods).Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER) -Ministério da Ciência e Tecnologia.Cooperação CientÃfica e Tecnológica Internacional (ICCTI) - Ambassade de France in Portugal - Project no. 543 B3/2001.Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional “Ciência, Tecnologia, Inovação - POCTI/32670/CTM/2000
Structural analysis of Ti1−xSixNy nanocomposite films prepared by reactive magnetron sputtering
Nanocomposite thin films consisting of both nanosized solid solutions or nanosized polycrystalline materials embedded in various amorphous matrix materials thus provide a grate potential for future mechanical devices. In this paper we report on the preparation of films resulting from additions of Si to TiN matrix by r.f. reactive magnetron sputtering. Structural properties such as growing characteristics (type of matrix, texture and grain size) will be analysed in some detail. Conventional transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM), together with both symmetric and asymmetric mode X-ray diffraction (XRD) experiments were used for this characterisation. The atomic composition of the samples was obtained by Rutherford Backscattering Spectrometry (RBS).
The analysis will be carried out as a function of the Si content in the Ti1-xSixNy matrix and several relations will be made regarding important parameters such as texture evolution, grain sizes, but most specially by the type of matrix developed. Regarding the results, all samples develop a double fcc phase with lattice parameters of 4.30 Ã… and 4.17 Ã…, corresponding to cubic TiN and most likely to a cubic lattice of SiNx, respectively.
Although no significant changes in texture were observed till Si compositions up to 10.6 at. %, the arrangement in atoms planes seem to vary. Results show that an asymmetric arrangement is developed in samples of small Si additions. This arrangement becomes more isotropic with the increase of Si contents, which we attribute to the increase in the SiNx content. In fact this increase leads also to the development of a small amorphous tissue of Si3N4 for large Si additions.The authors gratefully acknowledge the financial support of the ‘Fundação para a Ciência e Tecnologia’ (FCT) during the course of this research under project n PBICT/P/CTM/1962/95 and also the French CNRS Institution and the Portugese ICCTI Institution through CNRS/ICCTI Programs (N: 5522-1998 and 7087-1999)
Optimization and thermal stability of TiAlN-Mo multilayers
In this work we focus on the optimization and thermal stability of nanocomposite TiAlN/Mo multilayers that were produced by reactive
magnetron sputtering on high-speed steel substrates, with modulation periods below 5 nm. These multilayers were annealed between 600–
900 ºC for 1 h in a vacuum furnace. Preliminary X-ray diffraction results reveal that these coatings are very stable up to 900 ºC, since the multilayer
chemical modulation is not severely affected. At intermediate annealing temperatures the modulation period decreases due to interdiffusion at
the interface, resulting in a thicker interface between metal/nitride and hence decreasing the thickness of those layers.Portuguese FCT/MCES scientific program
Delocalization of slowly damped eigenmodes on Anosov manifolds
We look at the properties of high frequency eigenmodes for the damped wave
equation on a compact manifold with an Anosov geodesic flow. We study
eigenmodes with spectral parameters which are asymptotically close enough to
the real axis. We prove that such modes cannot be completely localized on
subsets satisfying a condition of negative topological pressure. As an
application, one can deduce the existence of a "strip" of logarithmic size
without eigenvalues below the real axis under this dynamical assumption on the
set of undamped trajectories.Comment: 28 pages; compared with version 1, minor modifications, add two
reference
Structural evolution of Ti-Al-Si-N nanocomposite coating
Ti–Si–Al–N films were prepared by rf reactive magnetron sputtering, in static and rotation modes, using
a wide range of different deposition conditions, which created conditions to obtain Ti–Al–Si–N coatings
with different structural arrangements.
Films prepared below a critical nitrogen flow, under conditions out of thermodynamic equilibrium,
revealed a preferential growth of an fcc (Ti,Al,Si)Nx compound with a small N deficiency. With nitrogen
flow above that critical value, the reduction of the lattice parameter was no longer detected. However,
a thermal annealing showed that a complete thermodynamically driven segregation of the TiN and Si3N4
phases was not yet obtained. The segregation upon annealing induced a self-hardening and showed
a multiphase system, where the crystalline TiN, (Ti,Al)N and (Ti,Al,Si)Nx phases were identified by X-ray
diffraction. This behavior is due to the de-mixing of the solid solution associated to a small N deficiency
Theory of monolayers with boundaries: Exact results and Perturbative analysis
Domains and bubbles in tilted phases of Langmuir monolayers contain a class
of textures knows as boojums. The boundaries of such domains and bubbles may
display either cusp-like features or indentations. We derive analytic
expressions for the textures within domains and surrounding bubbles, and for
the shapes of the boundaries of these regions. The derivation is perturbative
in the deviation of the bounding curve from a circle. This method is not
expected to be accurate when the boundary suffers large distortions, but it
does provide important clues with regard to the influence of various energetic
terms on the order-parameter texture and the shape of the domain or bubble
bounding curve. We also look into the effects of thermal fluctuations, which
include a sample-size-dependent effective line tension.Comment: replaced with published version, 21 pages, 16 figures include
Effect of the microstructure on the cutting performance of superhard (Ti, Si, Al)N nanocomposite films
A d.c. reactive magnetron sputtering technique was used to deposit (Ti,Si,Al)N coatings onto WC–Co
cutting tools. The microstructure of the coatings was analysed using X-ray diffraction (XRD) and highresolution
transmission electron microscopy (HRTEM) measurement. Before the cutting experiments, the
XRD results revealed a structure indexed to an fcc TiN. The results obtained by the XRD tests, with
detector variation in asymmetric mode (rocking curves) showed a decrease in the quality of the fiber
texture in the (111) grains with the change on deposition chamber geometry (two magnetrons in place of
four magnetrons). Cross-sectional HRTEM images of the (Ti,Al)N sample showed grains with a diameter
between 16 and 30 nm, while for the (Ti,Si,Al)N samples grains with a diameter between 6 and 10 nm
were observed. Furthermore, through the visualization of bright field images it was possible to discern
a columnar structure. For samples prepared at high deposition rates (2 mm/h), HRTEM micrographs
revealed the formation of the multilayer stacking of (Ti,Si)N/(Ti,Al)N
Ti–Si–C thin films produced by magnetron sputtering : correlation between physical properties, mechanical properties and tribological behavior
Ti–Si–C thin films were deposited onto silicon, stainless steel and high-speed steel substrates by magnetron sputtering, using different chamber configurations. The composition of the produced films was obtained by Electron Probe Micro-Analysis (EPMA) and the structure by X-ray diffraction
(XRD). The hardness and residual stresses were obtained by depth-sensing indentation and substrate deflection measurements (using Stoney’s equation), respectively. The tribological behavior of the produced films was studied by pin-on-disc. The increase of the concentration of non-metallic elements (carbon and silicon) caused significant changes in their properties. Structural analysis
revealed the possibility of the coexistence of different phases in the prepared films, namely Ti metallic phase ( alpha-Ti or beta-Ti) in the films with higher Ti content. The coatings with highest carbon contents, exhibited mainly a sub-stoichiometric fcc NaCl TiC-type structure. These structural changes were
also confirmed by resistivity measurements, whose values ranged from 10E3 Ohm/sq for low non-metal concentration, up to 10E6 Ohm /sq for the highest metalloid concentration. Astrong increase of hardness
and residual stresses was observed with the increase of the non-metal concentration in the films. The hardness (H) values ranged between 11 and 27 GPa, with a clear dependence on both crystalline structure and composition features. Following the mechanical behavior, the tribological results
showed similar trends, with both friction coefficients and wear revealing also a straight correlation with the composition and crystalline structure of the coatings
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