J.P. Rivière

Characterisation of Ti1−xSixNy nanocomposite films

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.

Structural transitions in hard Si-based TiN coatings: the effect of bias voltage and temperature

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 .

Preparation of magnetron sputtered TiNxOy thin films

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.

Structural, electrical, optical, and mechanical characterizations of decorative ZrOxNy thin films

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...

Residual stress states in sputtered Ti1−xSixNy films

Abstract The present paper reports on the influence of Si addition on the properties, namely stresses and thermoelastic behaviour, of r.f. reactive magnetron sputtered TiN coatings, in order to reach a further increase of coating performance in industrial application. Residual stresses were determined by two distinct methods, one of them being the so-called mechanical method. In this method, the deflection of the substrates, before and after deposition, is measured using a high precision co-ordinate measuring unit as well as an interference optical microscope (deflection method). The second method used is X-ray diffraction using the sin 2 ψ method. By heating the samples and in situ observation of substrate deflection evolution with temperature, the analysis of thermally-induced stresses was also carried out. Regarding the results, compressive residual stresses up to approximately 11 GPa were observed. The stress magnitude was found to depend on the total amount of Si addition to TiN matrix; for large Si additions (>12 at.%) a significant reduction was observed. Furthermore, the analysis of thermally-induced stress allowed the determination of the real effective deposition temperature, which led to a value of approximately 200 °C for the conditions employed within this work.

High current density nitrogen implantation of an austenitic stainless steel

Abstract Surface modification of AISI 304L austenitic stainless steel under high flux and low energy nitrogen ion implantation has been carried out at moderate temperatures in the range 270–400 °C with 1.2 keV ions and current densities between 0.5 and 1 mA/cm2. The influence of temperature, current density and fluence on the nitrogen transport and the microstructure of the nitrided layer have been investigated. The nitrogen depth profiles have been determined by nuclear reaction analysis, the microstructure of the modified layers has been analysed by X-ray diffraction and transmission electron microscopy. It is shown that the processing temperature and the ion flux have a major influence on both the profile shapes and the unusually deep penetration depth of nitrogen. The results suggest that above a critical temperature the nitrogen transport increases rapidly giving rise to a flat depth profile. The formation of the well known expanded austenite γN has been observed and its structure identified to a f.c.c. lattice containing a high density of stacking faults induced by the high level of internal stresses. The X-ray photoelectron spectroscopy study of the Cr2p3/2, Fe2p3/2 and N1s binding states demonstrates clearly the preferential bonding of chromium with nitrogen. The atomic transport of nitrogen and the profile shapes are discussed in relation with both the specific role of Cr and additional processes such as the formation of surface vacancies and adatoms.

Pvd grown (Ti, Si, Al)N nanocomposite coatings and (Ti, Al)N/(Ti, Si)N multilayers: structural and mechanical properties

Abstract In the last few years a considerable effort has been undertaken in order to optimise the production techniques of thin films and improve their quality. In this work, nanocomposite films resulting from Si additions to a (Ti,Al)N matrix have been prepared by RF and/or DC magnetron sputtering, with deposition rates varying from 0.21 μm/h to 4.6 μm/h. Rutherford Backscattering (RBS) and Electron Microprobe Analysis (EMPA) were used in order to access the chemical composition as well as the density of the films. For samples prepared with low deposition rates (deposited by a combination of RF and DC reactive magnetron sputtering) both symmetric and asymmetric XRD scans showed the development of crystalline phases whose structure is very similar to that of bulk TiN. The peak positions revealed changes of the lattice parameter from 0.420 to 0.428 nm with an increase of Si content dependent on the deposition rate. The lowest lattice parameter corresponds to a Ti–Si–Al–N phase where some of the Si and Al atoms are occupying Ti positions in the f.c.c. TiN lattice, while the highest lattice parameter corresponds to a system where at least a partial Si segregation can be enough to nucleate and develop the Si 3 N 4 phase that forms a layer on the growth surface, covering the (Ti,Al)N nanocrystallites and limiting their growth. As for the (Ti,Al,Si)N crystalline texture evolution, a (111) preferential growth for (Ti,Al)N and for low Si content was observed, while at intermediate Si content the texture changed to (200). With the increase of the Si content there is a corresponding decrease in the size of the diffracting grains. For samples prepared with high deposition rates (DC sputtered samples) High-Resolution Transmission Electron Microscopy (HRTEM) micrographs revealed a columnar growth associated with the f.c.c.-type structure of both phases. Small crystallites with sizes between ±7 and ±10 nm were observed. The use of (Ti,Al) and (Ti,Si) targets, relatively high deposition rates and an alternate deposition resulted in a multilayer of (Ti,Si)N/(Ti,Al)N. This system was produced with modulation periods between 5 and 10 nm, as shown by HR-TEM results, when the samples were grown with a deposition rate between 2 and 4.6 μm/h, respectively. Their average ultramicrohardness can be as high as 50 GPa. The residual stress values for the multilayer system are significantly lower than that of (Ti,Si,Al)N nanocomposite coatings.

Chemical bonding of nitrogen in low energy high flux implanted austenitic stainless steel

AISI 304L austenitic stainless steel was implanted at 400 °C with 1.2 keV nitrogen ions using a high beam current density of 1 mA/cm2. The nitrogen depth profile, structure, and chemical composition in the modified surface layer were determined by nuclear reaction analysis (NRA) and x-ray diffraction (XRD). The chemical bonding of Fe, Cr atoms with nitrogen was investigated by x-ray photoelectron spectroscopy (XPS). For a treatment time of 1 h, the formation of a thick nitrided layer of about 3.5 μm with a high nitrogen content (∼20 at. %) is observed by NRA. The nitrogen depth profile is characterized by a nearly flat shape over a thickness of 2.5 μm followed by an abrupt decrease. XRD spectra show the formation in the nitrided layer of a phase usually called expanded austenite γN, which corresponds fairly well with a nitrogen solid solution of the fcc structure containing a high density of stacking faults. The XPS study of the Cr 2p3/2, Fe 2p3/2, and N 1s binding states indicate clearly the preferential...

On the mechanism of ion nitriding of an austenitic stainless steel

Abstract The mechanism of nitrogen transport has been investigated in an austenitic stainless steel (AISI 304) under high flux and low energy nitrogen ion beam irradiation at moderate temperatures in the range 270–550°C. The profiles of the distribution of nitrogen have been analyzed with nuclear reaction analysis (NRA) and glow discharge optical spectroscopy (GDOS), and the surface roughness with scanning AFM. The modeling is based on the study of the stochastic mixing of atoms ‘ballistically’ displaced by incident ions. The development of surface roughness and the formation of an altered layer highly enriched by nitrogen are analyzed, and it is concluded that the transport of nitrogen into the bulk results from a flux of matrix atoms driven by mobile vacancies at temperatures above 350°C. This behavior is consistent with an altered layer ‘growth’ that is controlled by the ion-beam-induced displacements of surface atoms.

Mechanical characterization of reactively magnetron-sputtered TiN films

Abstract TiN hard coatings with thickness ranging from 1.2 to 3.5 μm were prepared by r.f. reactive magnetron-sputtering in an Ar/N 2 gas mixture. Texture, residual stresses, hardness and adhesion as a function of the r.f. power and bias voltage were investigated. X-ray diffraction experiments showed a unique δ-TiN phase for all the samples. All coatings revealed residual compressive stresses, whose amplitude increased with the r.f. power up to 800 W, followed by a slight decrease. The increase in adatom mobility is the main parameter that explains this behaviour up to 800 W, whereas the decrease observed for r.f. powers above 800 W can be explained from the stress relaxation that occurs due to internal cracks resulting from the large amount of accumulated elastic stresses. Defect annihilation effect is the main parameter, which can explain the stress behaviour at higher bias voltages. The effect of ion bombardment and the defect creation at the lower negative voltages are the main parameters that explain the increase observed in stress state. Residual stresses together with the reduced grain size are the main factors that seem to control the hardness and adhesion behaviour. Differences in failure mechanisms were detected with the variation in the deposition conditions, indicating a clear influence in coating performance.