A. Cavaleiro

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.

Ultra-microhardness testing procedure with Vickers indenter

Abstract Depth-sensing indentation equipment is widely used for evaluation of the hardness and Youngs modulus of materials. The depth resolution of this technique allows the use of ultra-low loads. However, aspects related to the determination of the contact area under indentation should be cautiously considered when using this equipment. These are related to the geometrical imperfections of the tip, the diamond pyramidal punch and the formation of pileup or the presence of sink-in, which alter the shape and size of the indent. These and other aspects, such as the thermal drift of the equipment and the scattering at the zero indentation depth position related to surface finishing, are discussed in this work. A study concerning the hardness and the Youngs modulus results determined by Vickers indentation on different materials was performed. Samples of fused silica, BK7 glass, aluminium, copper and mild steel (for which the values of Youngs modulus were previously known) were tested using indentation loads in the range 10–1000 mN. Moreover, two methods are proposed for performing the indentation geometrical calibration of the contact area; these are compared with a former method proposed by Oliver and Pharr (OP). The present methods are based on: (i) analysis of the punch profile using atomic force microscopy (AFM); and (ii) a linear penetration-depth function correction (LM), based on knowledge of the values of the Youngs modulus of several materials. By applying these methods to the indentation load/indentation depth results, it was possible to draw some conclusions about the benefit of the AFM and LM methods now under proposal.

Microstructure and mechanical properties of nanocomposite (Ti, Si, Al)N coatings

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

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...

Tuning of the surface plasmon resonance in TiO2/Au thin films grown by magnetron sputtering: The effect of thermal annealing

Nanocomposites consisting of a dielectric matrix, such as TiO2, with embedded noble metal nanoparticles (NPs) possess specific optical properties due to the surface plasmon resonance (SPR) effect, interesting for several applications. The aim of this work is to demonstrate that these properties are sensitive to the nanostructure of magnetron-sputtered TiO2/Au thin films, which can be tuned by annealing. We study the role of the shape and size distribution of the NPs, as well as the influence of the crystallinity and phase composition of the host matrix on the optical response of the films. All these characteristics can be modified by vacuum annealing treatments of the deposited films. A theoretical interpretation and modeling of the experimental results obtained is presented. The model involves a modified Maxwell-Garnett approach for the effective dielectric function of the composite (describing the SPR effect) and the transfer matrix formalism for multilayer optics. Input data are based on the experiment...

The influence of the addition of C and N on the wear behaviour of W–S–C/N coatings

WSx can be used as an alternative to MoSx as a solid self-lubricant material for applications at temperatures greater than room temperature, owing to its greater thermal stability. Moreover, good mechanical properties have been obtained when W-based sputtered coatings are alloyed with C and/or N. The aim of this study was to produce coatings of a W–S–C/N system combining good hardness with a low friction coefficient. The coatings show columnar cross-section morphology becoming featureless with increasing C/N content. The introduction of C/N into the W–S film leads to the deposition of amorphous structures. The W–S–C/N coatings are deficient in sulfur. The hardness of the coatings containing C/N reaches 5.5 GPa vs. 0.5 GPa for the W–S film. The wear coefficient calculated during reciprocal ball-on-disk testing, decreases significantly with the addition of C/N and, in some cases, the friction coefficient is also lower (<0.1) than for W–S films. However, on pin-on-disk testing W–S films behave better than W–S–C/N films. The analysis of the worn tracks showed that this behaviour can be attributed to a lack of adhesion and cohesion of the coatings, as is confirmed by the low critical loads (5–6 N) obtained by scratch-testing.

Hardness versus structure in W-Si-N sputtered coatings

In this research work the influence of the addition of Si on the structure, morphology and hardness of W‐(N ) coatings was studied. The films were deposited by reactive sputtering from a W target superimposed with increasing number of Si small plates. The partial pressure ratio between nitrogen and argon was varied in the range 0‐2. Thus, nitrogen content was in the range 0‐60 at.%, and the silicon-to-tungsten contents ratio reached, for the greatest number of silicon plates, 0.5. Depending on the nitrogen content, the structure of the films varies from the single b.c.c. tungsten phase to the f.c.c. NaCltype W 2 N. The synergistic action of both Si and N can originate the formation of amorphous structures. The hardness of the films was determined by ultramicroindentation technique by using either low loads (70 mN ) and/or an empirical model which allows to eliminate the influence of the substrate on the measured values. Hardness values as high as 50 GPa was obtained. Generally, the films containing amorphous phases present lower hardness values than crystalline ones.

Mechanical behaviour of W–S–N and W–S–C sputtered coatings deposited with a Ti interlayer

Abstract In this research work, W–S films doped with increasing contents of nitrogen and carbon were studied. The films were deposited with a Ti interlayer to promote the adhesion to the substrate. For low N or C contents the film presents the WS 2 phase, whereas for higher content they are amorphous. Doping W–S films with N or C leads to significant improvements in the hardness (from 0.6 to 6 GPa). C-containing W–S films had better tribological behaviour than N-doped ones. In relation to undoped W–S films, more than one order of magnitude reduction in the wear coefficients was reached for W–S–C films, particularly for higher applied loads in the sliding contact (10 N).

Influence of Ti addition on the properties of W–Ti–C/N sputtered films

Thin films of W–Ti–CyN were deposited by d.c. reactive magnetron sputtering from W–Ti targets with 0, 10, 20 and 30 wt.%Ti. The influence of titanium and interstitial element (carbon and nitrogen) contents on the structure, hardness and adhesion of the coatings was evaluated by X-ray diffraction analysis, ultramicroindentation and scratch-testing, respectively. The results show different compositional dependencies of the structure and grain size of the films. Hardness was related with the structure of the films, including lattice distortion and grain size. The higher hardness values (f50 GPa) were obtained for W–Ti–N films with 40–45 at.%N deposited from the W–20 wt.%Ti target in a reactive N atmosphere. However, these films present relatively 2 low adhesion to the substrates with critical loads of 30 N. The best compromise between hardness and adhesion was reached for W–Ti–N films with low nitrogen and titanium contents. 2003 Elsevier Science B.V. All rights reserved.

Elastic properties of Ti,Al,Si N nanocomposite films

Ž. Ti,Al,Si N films have been prepared by d.c. and rf reactive magnetron sputtering, with Si contents in the range 211 at.% and Ž. Al contents between 4 and 19 at.%. Samples prepared in rotation mode three magnetrons presented densities between 4.0 and 3 Ž. 4.6 gcm , while samples prepared in static mode magnetron with Ti target with small pieces of Si and Al displayed densities mainly in the range 3.03.9 gcm 3 . For comparison purposes, the evaluation of Youngs modulus was performed by both Ž. depth-sensing indentation and surface acoustic wave SAW techniques. Indentation results revealed systematically higher values than those obtained by SAW. These discrepancies might be related with the relatively low density of the films. Hardness values of approximately 60 GPa were obtained with samples with a composition of approximately 28.5 at.% titanium, 12 at.% aluminium, 9.5 at.% silicon and 50 at.% nitrogen. XRD patterns showed the presence of two different crystalline phases, as in the case of Ž.