S. Carvalho

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

Effects of ion bombardment on properties of d.c. sputtered superhard (Ti, Si, Al)N nanocomposite coatings

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.

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.

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.

Young's modulus of (Ti,Si)N films by surface acoustic waves and indentation techniques

c ¨ Abstract Ti Si N films with Si contents up to 17.5 at.% and N contents close to 50 at.% were prepared by r.f. reactive magnetron 1y xx y sputtering. Film densities are within the range 3.4-5.1 g ycm .X-Ray diffraction patterns indicated the formation of two crystalline 3 phases.In the case of low surface mobility, a metastable (Ti, Si)N phase was formed, where Si atoms occupied Ti positions. With increasing surface mobility, a crystalline TiN phase was observed.This behaviour may be explained by the occurrence of Si N segregation, leading to the formation of a nanocomposite film of the type nc-TiNync-(Ti,Si)Nya-Si N , although the 34 34 presence of Si N phase is difficult to prove.In some of the films, a mixture of the (Ti,Si)N metastable phase with the TiN phase 34 was observed, which indicates that the segregation of both TiN and Si N phases is not complete.The Youngs modulus, E ,o f 34 f each coating was evaluated using both indentation tests and the surface acoustic waves (SAW) method.For most samples, the results obtained by these two methods are in good agreement.Some differences were observed in films prepared with a bias voltage of y50 V and Si contents higher than 5.9 at.%. For these samples, indentation values of approximately 10-20% higher than those obtained from SAW were found.This discrepancy is related to the nanostructure of these coatings, and it should be pointed out that the SAW results are strongly correlated with the density of the material. 2002 Elsevier Science B.V. All rights reserved.

Ag+ release inhibition from ZrCN–Ag coatings by surface agglomeration mechanism : structural characterization

New multifunctional materials based on well-established materials to which functional properties are added, such as antibacterial performance, have become a relevant research topic, in order to meet the requirements of today’s technological advances. This paper reports the results of a detailed structural and chemical characterization study of ZrCN–Ag coatings produced by reactive magnetron sputtering, as well as the release of silver after immersion in a simulated body fluid (Hank’s balanced salt solution), which mimic the material behaviour within the human body. The chemical composition was evaluated by electron probe microanalysis, x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy, whereas the structure was assessed by Raman spectroscopy and x-ray diffraction. The material exhibits a homogeneous distribution of the elements throughout the films, with a (C + N)/Zr ratio of around 1.3 and 15 at% of silver. A mixture of amorphous (a-C and CNx) and crystalline phases (ZrCN) was identified. In addition, the silver was detected to be released in less than 0.7% of the total silver in the films, occurring during the first two hours of immersion; no further release was evidenced after this period of time. (Some figures may appear in colour only in the online journal)

Ag-Ti(C,N)-based coatings for biomedical applications : influence of silver content on the structural properties

Ag–TiCN coatings were deposited by dc reactive magnetron sputtering and their structural and morphological properties were evaluated. Compositional analysis showed the existence of Ag–TiCN coatings with different Ag/Ti atomic ratios (ranging from 0 to 1.49). The structural and morphological properties are well correlated with the evolution of Ag/Ti atomic ratio. For the samples with low Ag/Ti atomic ratio (below 0.20) the coatings crystallize in a B1-NaCl crystal structure typical of TiC0.3N0.7. The increase in Ag/Ti atomic ratio promoted the formation of Ag crystalline phases as well as amorphous CNx phases detected in both x-ray photoelectron spectroscopy and Raman spectroscopy analysis. Simultaneously to the formation of Ag crystalline phases and amorphous carbon-based phases, a decrease in TiC0.3N0.7 grain size was observed as well as the densification of coatings.

Influence of albumin on the tribological behavior of Ag-Ti (C, N) thin films for orthopedic implants

With the increase of elderly population and the health problems arising nowadays, such as cancer, knee and hip joint prostheses are widely used worldwide. It is estimated that 20% of hip replacement surgeries simply fail after 5years, due to wear loosening, instability and infection. In this paper it is reported the study of advanced materials with the ability to overcome some of these drawbacks. The development of ceramic coatings, based on carbonitrides of transition metals, such as TiCN, doped with silver, Ag, may represent an effective solution. Thin films of Ag-TiCN were produced by dc reactive magnetron sputtering with silver contents ranging from 4 to 8at.%. The physical, chemical, structural, morphological/topographical, mechanical and tribological properties were evaluated. The tribological tests were performed in a unidirectional wear simulator, pin on disk, being the antagonists of a ceramic Al2O3 ball, and using simulate body fluids as lubricant. Hanks Balanced Salt Solution (HBSS) and bovine serum albumin (BSA) in HBSS were chosen, in order to evaluate the lubrication ability of the solution containing the protein, albumin. The results revealed that the coatings with Ag content ranging from 4 to 8at.%, were the most promising, as the tribological properties were superior to the results reported by other authors, which also developed Ag-TiCN coatings containing similar Ag contents and using similar test conditions. The presence of albumin leads to a lower wear in all the test conditions, and this enhancement was higher in the hydrophobic surfaces.

Influence of surface features on the adhesion of Staphylococcus epidermidis to Ag–TiCN thin films

Abstract Staphylococcus epidermidis has emerged as one of the major nosocomial pathogens associated with infections of implanted medical devices. The initial adhesion of these organisms to the surface of biomaterials is assumed to be an important stage in their colonization. The main objective of this work is to assess the influence of surface features on the adhesion of S. epidermidis to Ag–TiCN coatings deposited by dc reactive magnetron sputtering. The structural results obtained by x-ray diffraction show that the coatings crystallize in a B1-NaCl crystal structure typical of TiC0.3N0.7. The increase of Ag content promoted the formation of Ag crystalline phases. According to the results obtained with atomic force microscopy, a decrease on the surface roughness of the films from 39 to 7 nm is observed as the Ag content increases from 0 to 15 at.%. Surface energy results show that the increase of Ag promotes an increase in hydrophobicity. Bacterial adhesion and biofilm formation on coatings were assessed by the enumeration of the number of viable cells. The results showed that the surface with lower roughness and higher hydrophobicity leads to greater bacterial adhesion and biofilm formation, highlighting that surface morphology and hydrophobicity rule the colonization of materials.

Effects of the morphology and structure on the elastic behavior of (Ti,Si,Al)N nanocomposites

(Ti,Si,Al)N nanocomposite coatings with different Ti, Si, Al contents, were deposited onto silicon and polished high-speed steel substrates, by r.f. and/or d.c. reactive magnetron sputtering. The stoichiometry of the films was investigated by electron probe microanalysis and Rutherford backscattering spectrometry (RBS). The density was derived by combination of RBS results and thickness measurements obtained by ball-cratering. For comparison purposes, the evaluation of the Youngs modulus was performed by depth-sensing indentation technique and with the laser-acoustic technique based on surface acoustic waves (SAW). Results showed in some cases differences in Youngs modulus measured by both techniques. The Youngs modulus obtained by SAW correlates with the density values from RBS, however, this behavior is not visible for the results measured with the ultramicroindentation technique. Both techniques indicate a small increase of Youngs modulus of (Ti,Al)N by incorporating Si into the matrix. However, this improvement only occurs for small Si content, whereas for high Si content the elastic parameter reduces until almost 300 GPa. The morphology of the coatings was investigated by scanning electron microscopy and correlated with the differences observed by both SAW and indentation techniques.