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High-velocity oxy-fuel deposition stages of titanium oxide coatings were analyzed and reported here. For the first stages of deposition, process maps were used to evaluate the influence of deposition parameters such as stand-off distance (SOD), powder feed rate (PFR) and fuel/oxygen ratio (F/O) on velocity and temperature of in-flight particles. These parameters were then combined with particle size distribution (PSD) to further optimize the deposition process considering the spray trace width and the area covered by splats and non-molten particles as responses. Furthermore, the structural, morphological and mechanical characteristics either of single splats, clusters of semi- and/or non-molten particles or coatings were obtained by, x-ray diffraction, Raman spectroscopy, scanning electron microscopy and nanoindentation. During coating build-up, lower PFR and F/O induce more splat particles and fewer clusters of semi- and/or non-molten particles, whereas the PSD affects the width of the spray trace. The combination of F/O and SOD upper levels was related to a high percentage of TiO2 splat deposition. Finally, the proposed methodology allowed to obtain dense TiO2 coatings with a higher content of rutile phase and an average thickness of 65 µm. [ABSTRACT FROM AUTHOR]

Abstract: Black corals (antipatharians) are colonial cnidarians whose branched tree-like skeleton is mostly constituted of chitin fibrils inside a lipoproteic matrix. The skeleton exhibits growth rings formed by chitin layers (micro-lamellae). In order to know the effect of the arrangement microlamellae of chitin of black corals and to improve the understanding of the role of chitin structure in the antipatharian skeleton, the mechanical properties of the skeleton of two black corals, Antipathes caribbeana and Antipathes pennacea, were examined using nanoindentation tests. Measurements of reduced elastic modulus, nanohardness and the viscoelastic behavior were measured with a spheroconical indenter. The results indicate variations in the values of the mechanical properties clearly associated with different structures present in the skeletons, the core being the one that invariably shows the maximum values. The solid multilamellar arrangement of black coral chitin, its viscoelastic behavior, and the anisotropic mechanical response, are relevant factors contributing to the successful adaptation of black coral colonies to shallow as well as to very deep waters. [Copyright &y& Elsevier]

Abstract: In this paper we have applied different methods based on nanoindentation techniques to measure the toughness of SiO2-poly methyl-methacrylate hybrid films on organic acrylic substrates. The hybrid films were deposited by the Sol–Gel method from precursor solutions containing tetraethyl-orthosilicate, methylmethacrylate and 3-trimethoxysilyl propyl methacrylate (TMSPM) as the coupling agent. The influence of TMSPM content in the hybrid precursor solution on the fracture behavior of the hybrid films was studied. The classical indentation crack length method was applied from nanoindentation tests to determine the stress intensity factor by direct measurement of crack length from atomic force microscopy images. A second method, based on the pop-in analysis allowed the separation of crack formation from film delamination from multiple pop-ins. Finally, a third method based on energy methods is also reported and discussed. The amount of TMSPM in the precursor solution showed a strong influence on the toughness of the hybrid films. [Copyright &y& Elsevier]

Poly(methyl methacrylate) (PMMA) is one of the most commonly plastics used as dentalbase material, due to its good biological compatibility and mechanical properties. Chitosan has wide application in chemical, biochemical and biomedical fields of research. In this work, chitosan (CTS) was functionalized with glycidyl methacrylate (GMA), to ease a further reaction with MMA. The resulting co-polymer was finally blended with PMMA and poly(butyl acrylate) PBA which works as a damper, the polymers were cured by UV to obtain the final resin. Characterization of UV-cured resins was carried out by thermal measurements, X-ray diffraction, atomic force microscopy (AFM), micro and nanoindentation, water absorption and elution in water. As a result a higher thermal stability of the final resin compared with the precursor co-polymer ((CTS-GMA)-g-PMMA) was obtained. The resin presented roughness in the nanometer scale and nanoparticles embedded in the acrylic matrix producing a tough material. However, XRD measurements show that all materials are in an amorphous state. Values of hardness and elastic modulus results were very near to those of the dentine. The results of elution in water of the tested resin samples show them as clinically acceptable as a dental base material. [ABSTRACT FROM AUTHOR]

Abstract: Optical and surface spectroscopies as well as nanoindentation techniques have been used to study ZrN coatings on 316L stainless steel obtained by DC-reactive magnetron sputtering. The deposit process was carried out using initial and working pressures of 10−6 Torr and 10−3 Torr, respectively. The experimental set-up for optical spectra acquisition was designed for the study in situ of the plasma in the deposition chamber. Auger spectroscopy, SEM and X-ray diffraction were used to characterize the coatings. Nanoindentation tests were carried out to measure the mechanical properties of the coating. Plasma characterization revealed the presence of CN molecules and Cr ions in the plasma. Surface spectroscopy results showed that ZrN, Zr3N4 and ZrC coexist in the coating. These results allowed the understanding of the mechanical behavior of the coatings, demonstrating the importance of the plasma characterization as a tool for tailoring the properties of hard coatings. [Copyright &y& Elsevier]

Abstract: Zirconium nitride was deposited by reactive unbalanced magnetron sputtering at different N2 partial pressures, on an AISI 316L stainless steel substrate. The mechanical properties of the coatings were evaluated by means of nanoindentation tests employing a Berkovich indenter and loads which varied between 120–9000 µN. The sliding wear behavior of the substrate-coating systems was studied under a normal load of 2 N using a ball-on-disc tribometer, with an AISI 52100 ball (6 mm diameter) as counterpart. It has been found that N2 partial pressure has a significant effect both on the hardness and corresponding Young''s modulus of the coatings. As the N2 partial pressure increases from 1×10−4 Torr to 10×10−4 Torr, the hardness and Young''s modulus of the coatings decrease from 26 to 20 GPa and 360 to 280 GPa, respectively. The nanoindentation tests revealed the presence of a third oxide layer (10 nm thick, approximately) on the surface of the coating. Scanning electron microscopy (SEM) analysis performed on the worn triboelements indicated that both abrasive and adhesive wear mechanisms could take place in addition to the substrate plastic deformation. The deposition conditions and coating mechanical integrity determine the predominant wear mechanism. [Copyright &y& Elsevier]

Abstract: The mechanical properties of thin amorphous tungsten–carbon films (WX CY) deposited on unheated substrates by non-reactive DC-cosputtering were characterized by nanoindentation as a function of the penetration depth of the Berkovich indenter. The results were analyzed using the work-of-indentation model. Films with Y in the range of 65–70at% show maximum hardness of about 22GPa, value comparable to the measured for a bulk WC reference sample. Chemical composition and structure were determined using other techniques such as X-ray diffraction, scanning electron microscopy as well as Raman and Auger electron spectroscopies. [Copyright &y& Elsevier]

Abstract: We report on a study of structure, composition and mechanical properties of (Ti,Al)(B,N) coatings, deposited by reactive DC magnetron sputtering on Corning glass and AISI D2 tool steel substrates and their dependence on variations of nitrogen/argon flux ratio. The Ti–Al–BN target used was fabricated from a mixture of powders of Ti (70wt%), Al (15wt%) and BN (15wt%). The samples were found in the centre of the ternary diagram of phases of the Ti(Al)–B–N system as a mixture of Ti1-xAlxN, BN and TiB2 phases. BN and TiB2 appear as amorphous materials, while Ti1-xAlxN is a nanocrystalline material with a structure of rock-salt- or wurtzite-type, depending on Al content. We found that the mechanical properties of the coatings are remarkably affected by the structure of the Ti1-xAlxN phase, which is a cubic phase (fcc) for x0.5 and a mixer of cubic and hexagonal (wurtzite-type) for x>0.5. [Copyright &y& Elsevier]

Measurement of mechanical properties in cermets is complex since they are formed by several phases. How to quantitatively determine the relationship between the performance and the complex microstructure of this particular group of materials, especially when analyzing the effect of the reinforcement phase, is still one of the top challenging problems yet to be solved. Hardness and elastic modulus of bimodal WC–Co HVOF thermal spray coatings doped with vanadium carbide (VC) additions were studied by performing a statistical analysis of nanoindentation results. A mathematical deconvolution procedure and a Weibull distribution analysis of hardness and elastic modulus results are proposed to identify the individual contribution of each phase to the mechanical properties of different WC–12Co coatings. Both analysis methods allowed to detect a reinforcing effect of vanadium on the hardness and elastic modulus of bimodal VC-doped coatings. The combination of VC additions and a bimodal WC particle size distribution in the WC–Co coatings proved successful in increasing their mechanical properties, as the coatings processed in this work showed better mechanical properties than that reported in the literature for coatings having exclusively a bimodal WC particle size distribution or those only doped with VC additions. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical behavior and microstructure of highly densified, spherically shaped, polycrystalline Al2O3–YSZ composites, processed from pseudoboehmite powders by sol–gel is reported here. Processing was carried out by combining nanometric sized α-Al2O3 (120nm) seeds and YSZ particles of tetragonal structure. The YSZ particles were homogeneously distributed in a coarse-grained matrix of alumina, both inside grains and along grain boundaries. Fracture surfaces, achieved by impact tests showed toughening effects of the zirconia particles. The tetragonality of the YSZ phase stability even after fracture events and fracture toughness measurements by Vickers indentation, where the crack tip interacts with YSZ particles, are all provided and discussed. The local mechanical properties, such as elastic modulus, indentation hardness and the onset of plastic deformation or fracture contact pressure of both YSZ particles and the Al2O3 matrix were quantified by nanoindentation. Evidence of coercive contact pressure was observed in YSZ from indentation stress–strain curves. [Copyright &y& Elsevier]

Abstract: Chromium aluminum nitride (Cr1−x Al x N) coatings were deposited onto AISI H13 steel and silicon substrates by r.f. reactive magnetron co-sputtering in (Ar/N2) gas mixture from chromium and aluminum targets. Properties of deposited Cr1−x Al x N coatings such as compositional, structural, morphological, electrochemical, mechanical and tribological, were investigated as functions of aluminum content. X-ray diffraction patterns of Cr1−x Al x N coatings with different atomic concentrations of aluminum (0.51< x <0.69) showed the presence and evolution of (111), (200), and (102) crystallographic orientations associated to the Cr1−x Al x N cubic and w-AlN phases, respectively. The rate of corrosion of the steel coated with Cr1−x Al x N varied with the applied power; however, always being clearly lower when compared to the uncoated substrate. The behavior of the protective effect of the Cr1−x Al x N coatings is based on the substitution of Cr for Al, when the power applied to the aluminum target increases. The mechanical properties were also sensitive to the power applied, leading to a maximum in hardness and a reduced elastic modulus of 30 and 303GPa at 350W and a monotonic decrease to 11 and 212GPa at 450W, respectively. Finally, the friction coefficient measured by pin-on disk revealed values between 0.45 and 0.70 in humid atmosphere. [Copyright &y& Elsevier]

Thin films type multilayer of Alúmina (Al2O3) and yttria stabilized zirconia (YSZ) were deposited on silicon (100) and stainless steel AISI 304 substrates by a multi-target system magnetron sputtering in r.f (13,56 MHz), with targets of 8mol.% Y2O3-ZrO2 and aluminium purity (99,95 %) under fixed atmosphere of Ar/O2 at temperature of 300 °C. The influence of the number of bilayers of [Al2O3/YSZ]n varying from 35, 70, 100 and 200 on the structure, mechanical and tribologic behavior of the prepared coatings was studied. Structural, mechanical and tribologic characterization was undertaken by X-ray diffracción (XRD), nanoindentation and pin-on-disc respectively. Evidence of the tetragonal phase of zirconia with preferential orientations (111)t and (200)t was observed. Increments of the number of bilayers lead to an increase in hardness and elastic modulus from 2.5 to 5 GPa and 70 to 112 GPa, respectively. Furthermore the friction coefficient diminished as a function of the number of bilayers from 0.8 and 0.3. These results show the possibility to apply this type of multilayer materials as coatings for wear protection and thermal insulation on metallic substrates. [ABSTRACT FROM AUTHOR]