L. Rebouta
University of Minho
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Featured researches published by L. Rebouta.
Surface & Coatings Technology | 2000
F. Vaz; L. Rebouta; P. Goudeau; J. Pacaud; H Garem; J.P. Rivière; A. Cavaleiro; E. Alves
Abstract Ti 1− x Si x N y films were synthesised by RF reactive sputtering from Ti and Si elemental targets, in an Ar/N 2 gas mixture. XRD results revealed the development of a two-phase system, composed of a nanocrystalline f.c.c. TiN (phase 1: B1 NaCl type) and a second one (phase 2), where Si atoms replaced some of the Ti ones, inducing a structure that we may call a solid solution. An amorphous phase, supposed to be of silicon nitride, within grain boundaries seems to be also present, especially for high Si contents. TEM experiments confirmed the f.c.c.-type structure for phase 2, which is the only phase that develops without ion bombardment. The higher lattice parameter of phase 1 (∼0.429 nm compared to 0.424 nm for bulk TiN) may be explained by the residual stress effect on peak position. The Ti replacement by Si would explain the low value of the lattice parameter for phase 2 (∼0.418 nm). All samples showed good results for hardness (Hv≥30 GPa), and Ti 0.85 Si 0.15 N 1.03 at a deposition temperature of 300°C showed a value of approximately 47 Gpa, which is approximately double that of pure TiN. For higher deposition temperatures, an increase in hardness is observed, as demonstrated by this same sample, which at 400°C reveals a value of approximately 54 GPa. Similar behaviour was observed in adhesion, where this same sample revealed a critical load for adhesive failure of approximately 90 N. In terms of oxidation resistance, a significant increase has also been observed in comparison with TiN. At 600°C, the oxidation resistance of Ti 0.70 Si 0.30 N 1.10 is already 100 times higher than that of TiN. For higher temperatures this behaviour tends to be even better when compared with other nitrides.
Surface & Coatings Technology | 2000
L. Rebouta; C.J. Tavares; R. Aimo; Z. Wang; K. Pischow; E. Alves; T.C. Rojas; J.A. Odriozola
Abstract Films resulting from Si additions to TiN matrix were prepared with Si contents in the range 0–19 at.%, using a closed field unbalanced DC magnetron sputtering system. Transmission Electron Microscopy (TEM) analyses revealed the nanocrystalline nature of these coatings, confirming the results of grain size evaluation from X-ray diffraction (XRD) patterns. Nanoindentation tests and scratch tests were carried out for the mechanical characterisation. Regarding the results, the samples show hardness values as high as 45 GPa. Best hardness values were found for Si content in the range 4–10 at.%. Almost all samples showed high critical loads for total adhesion failure, generally higher than 80 N, although the critical load for the first adhesion failure was found to be lower than 20 N for several samples. XRD patterns revealed the presence of only one phase that can be assigned to a cubic B1 NaCl structure, typical for TiN, with a lattice parameter of approximately 0.430 nm. The preferential growth, as a function of Si content, changes from a strong (111) orientation at the lowest Si additions to a weak (200) orientation at the highest Si content. Density values in the range 3.0–3.7 g/cm3 were obtained for most of the samples prepared with deposition rates between 0.5 and 1.1 μm/h, although higher density values were obtained for higher Ti deposition rates, with maximum of approximately 4.7 g/cm3 for the case of samples with low Si content.
Thin Solid Films | 2001
S. Carvalho; L. Rebouta; A. Cavaleiro; L.A. Rocha; J Gomes; E. Alves
c ˆ´ ˜ ITN, Departamento de Fisica, E.N. 10, 2686-953 Sacavem, Portugal d ´´ Abstract In this work (Ti,Si,Al)N films were deposited using only rf or a combination of rf and d.c. reactive magnetron sputtering. Chemical composition, thickness, film structure and mechanical properties of the films were investigated by means of Rutherford backscattering (RBS), electron microprobe analysis (EPMA), ball-cratering, X-ray diffraction (XRD) and ultramicroindentation, respectively. All samples showed high hardness values, exceeding, in some cases, 50 GPa. XRD results revealed the formation of a mixture of two phases whose structure is similar to TiN. One phase is noted as being TiN bulk with a lattice parameter of 0.428 nm and develops only in conditions of high surface mobility. This behaviour can be associated with the segregation of the SiN phase, though the formation of an amorphous AlN phase cannot be excluded. Another phase, which is noted as Ti-Si-Al-N x
Surface & Coatings Technology | 1999
L. Cunha; M. Andritschky; L. Rebouta; K. Pischow
Abstract Chromium and titanium–aluminium nitrides were deposited, by physical vapour deposition techniques, on stainless steel substrates and their corrosion behaviour was studied in two different environments: a gaseous environment containing HCl at a temperature of 350°C and a 1 M HCl aqueous solution environment, at room temperature. X-ray photoelectron spectroscopy was used to study the mechanism of the reactions that occurred in the gaseous environment. This analysis shows an oxidation of the surface caused by the substitution of nitrogen by oxygen. Open circuit potential and potentiodynamic polarisation measurements were performed in the aqueous solution environment. The aqueous corrosion behaviour of the nitride coatings is strongly dependent on the microdefect density of the coating.
Journal of The European Ceramic Society | 1997
F. Vaz; L. Rebouta; M. Andritschky; M.F. da Silva; J. C. Soares
Abstract (Ti,Al)N coatings prepared by combined DC and RF magnetron sputtering were annealed in air at temperatures between 500 and 900 °C, in order to obtain information regarding the oxidation behaviour. The depth concentration profile of the oxidized layers was measured by Rutherford Backscattering Spectrometry (RBS). During the heat treatment at 500 °C, the Ti 0.35 Al 0.65 N coating forms a Ti and Al mixed oxide with about 10 at% of nitrogen. After the annealing at 600 °C of Ti 0.62 Al 0.38 and Ti 0.35 Al 0.65 N coatings, the nitrogen amount disappears and the oxide layer is still homogeneous. At temperatures between 750 and 900 °C, a two-layer structure is formed, consisting generally in a protective superficial layer of Al 2 O 3 with traces of Ti, followed by a titanium-rich zone. The Ti 0.35 Al 0.65 N system showed a slightly higher oxidation resistance than the Ti 0.62 Al 0.38 N one. On the other hand, the Al-rich coating, Ti 0.19 Al 0.81 N, revealed the worst oxidation resistance, similar to the AlN coating, and the oxide layer is always homogeneous.
Surface & Coatings Technology | 2001
F. Vaz; L. Rebouta; Ph. Goudeau; T. Girardeau; J. Pacaud; J.P. Rivière; A Traverse
Abstract (Ti,Si)N films were grown by reactive magnetron sputtering. X-Ray diffraction experiments (XRD) showed the development of a mixture of two crystalline phases with lattice parameters higher ( a =0.429 nm: phase 1 — indexed with TiN) and lower ( a =0.418 nm: phase 2 — indexed to a Ti–Si–N phase) than that of bulk TiN ( a =0.424 nm). Transmission electron microscopy revealed nanocrystalline grains of an fcc structure in both crystalline phases. X-Ray absorption spectroscopy results indicated that in these films there are Si atoms bonded to Ti. This means that in phase 2 there must be some Si atoms occupying Ti positions within the TiN lattice, which explains the lower lattice parameter for that phase. Phase 2 was the only phase observed for low surface mobility conditions of the deposited material (low temperature =300°C and absence of ion bombardment of the growing film). This low surface mobility conditions of the deposited material might explain the claimed substitution of Ti with Si in TiN. When present, the lattice parameter of phase 2 is approximately the same for all Si contents, which ranged from 2.5 up to nearly 20 at.%. The enhancement of the surface mobility, either by a temperature increase or by ion bombardment during film growth, induces higher phase segregation, and therefore the XRD diffraction peaks from phase 2 disappear. For deposition temperatures near ∼ 500°C, and/or biased substrates, the complete segregation of phases was observed (no traces of phase 2), thus forming a nanocomposite structure composed of nanocrystalline grains of TiN embedded in an amorphous silicon nitride phase-nc-TiN/a-Si 3 N 4 .
Surface & Coatings Technology | 2002
E. Ribeiro; A. Malczyk; S. Carvalho; L. Rebouta; J.V. Fernandes; E. Alves; A.S. Miranda
d ´˜ Abstract A d.c. reactive magnetron sputtering technique was used to deposit (Ti, Si, Al)N films. The ion current density in the substrate was varied by the superimposition of an axially symmetric external magnetic field between the substrate and target. It was found that the variation of the magnetic field strength induced changes in the ion current density in the substrate with a consequent change in film properties. XRD patterns of sputtered films revealed changes of the lattice parameter (from 0.418 nm to approx. 0.429 nm) with the increase of the ion yatom arrival rate ratio. As already reported for samples prepared by r.f. sputtering, both can be assigned to a cubic B1 NaCl structure, typical for TiN. The lowest lattice parameter corresponds to a metastable phase where Si and Al atoms occupy Ti positions, while the highest lattice parameter corresponds to a system where at least a partial segregation of TiN and SiN phases already occurred, leading to the formation of a nanocomposite film of the type nc-TiAlNya- x Si N. The mixture of the metastable phase with nanocomposite coating phases in some samples indicates that, in general, the 34 segregation of TiN and SiN phases is not complete. Hardness values as high as 45 GPa were measured. Small Si additions to x (Ti, Al)N coatings induce a reduction in the pin-on-disk sliding wear rate. � 2002 Elsevier Science B.V. All rights reserved.
Surface & Coatings Technology | 1995
F. Vaz; L. Rebouta; M. Andritschky; M.F. da Silva; J.C. Soares
We prepared TiN-based multicomponent hard coatings by combined d.c. and r.f. magnetron sputtering with different contents of Ti, Al, Zr and Si on high speed steel substrates at 300°C. These coatings, with thicknesses ranging from 1 to 3 μm, were annealed in air at temperatures between 500 and 850°C in order to obtain information on their oxidation behaviour. The composition-depth profiles of heat-treated coatings were then measured by Rutherford backscattering spectrometry (RBS). The results show that the introduction of aluminium improves the oxidation resistance in all cases. During the heat treatment of Ti0.62Al0.38N at 600°C, a mixed oxide of Ti and Al is formed. At temperatures between 700 and 850°C, a protective superficial layer of Al2O3 with traces of Ti is formed, which is followed by an aluminium-depleted zone. However, for Ti0.57Al0.38Zr0.05N coatings, no protective Al2O3 layer was found on the surface after heat treatment. At 600°C, the oxidation resistance of Ti0.57Al0.38Zr0.05N is similar to that of (TiAl)N, but is about 30 times poorer at 700°C due to the absence of the protective Al2O3 layer. The Ti0.62Al0.26Si0.12N system shows a slightly lower oxidation resistance than (TiAl)N (Kp = 9.0 × 10−12 kg2 m−4 s−1 and Kp = 6.4 × 10−12 kg2 m−4 s−1 at 800°C respectively). It also forms a two-phase scale as in (TiAl)N, but the amount of Ti in the Al-rich outer layer is about 10 at.%, instead of 4at.% found in the (TiAl)N system. In the temperature range 700–850°C, oxidation is thermally activated with activation energies of 187 kJ mol−1 and 296 kJ mor−1 for (TiAl)N and (TiAlSi)N coatings respectively.
Surface & Coatings Technology | 2003
F. Vaz; Paulo Monteiro Cerqueira; L. Rebouta; Sérgio M. C. Nascimento; E. Alves; Ph. Goudeau; J.P. Rivière
Within the frame of this work, r.f. reactive magnetron sputtered TiNxOy films were deposited on steel, silicon and glass substrates at a constant temperature of 300 °C. The depositions were carried out from a pure Ti target, under the variation of process parameters such as the substrate bias voltage and flow rate of reactive gases (a mixture of N2/O2). Film colours varied from the glossy golden type for low oxygen content (characteristic of TiN films) to dark blue for higher oxygen contents. X-ray diffraction (XRD) results revealed the development of a face-centred cubic phase with 〈111〉 orientation (TiN type; lattice parameter of approx. 0.429 nm), and traces of some oxide phases. Scanning electron microscopy (SEM) revealed a mixture of very dense and columnar type structures. All these results have been analysed, and are presented as a function of both the deposition parameters and the particular composition, and crystalline phases present in the films.
Journal of Applied Physics | 2005
P. Carvalho; F. Vaz; L. Rebouta; L. Cunha; C.J. Tavares; C. Moura; E. Alves; A. Cavaleiro; Ph. Goudeau; E. Le Bourhis; J.P. Rivière; J. F. Pierson; O. Banakh
The main objective of this work is the preparation of decorative zirconium oxynitride, ZrOxNy, thin films by dc reactive magnetron sputtering. Film properties were analyzed as a function of the reactive gas flow and were correlated with the observed structural changes. Measurements showed a systematic decrease in the deposition rate with the increase of the reactive gas flow and revealed three distinct modes: (i) a metallic mode, (ii) a transition mode (subdivided into three zones), and (iii) an oxide mode. The measurements of target potential were also consistent with these changes, revealing a systematic increase from 314to337V. Structural characterization uncovered different behaviors within each of the different zones, with a strong dependence of film texture on the oxygen content. These structural changes were also confirmed by resistivity measurements, whose values ranged from 250to400μΩcm for low gas flows and up to 106μΩcm for the highest flow rates. Color measurements in the films revealed a chan...