Jean-Pierre Celis

Characterization of thin nickel electrocoatings by the low-incident-beam-angle diffraction method

The low-incident-beam-angle diffraction technique (LIBAD) has been developed as a powerful X-ray diffraction tool for the characterization of thin crystalline coatings. The technique can be implemented to determine the residual stress state in thin coatings, their crystallographic texture, by means of the orientation distribution function, and thickness, as well as the stress profile in a coating as a function of depth. As an example, electrodeposited nickel coatings on a copper substrate have been characterized with this technique for thicknesses varying from 0.6 to 3.8 μm. Crystallographic texture and mean residual stress appear to be correlated with the coating thickness. So, for example, the residual stress of the coatings evolves from a low to a high tensile stress with increasing coating thickness. The stress in the uppermost region of the substrate is influenced by the stress state in the coating. The stress profile in the coating was found to be linearly dependent on the information depth.

Tribological behaviour of different diamond-like carbon materials

Abstract This paper comparatively studies the tribological behaviour of different types of diamond-like carbon (DLC) coatings in a reciprocating sliding wear test. The results are interpreted in terms of structure and surface morphological characteristics. At the beginning of each reciprocating sliding wear test, the higher coefficient of friction of the DLC coatings reflects the original surface conditions of contacting counterfaces, whereas the low coefficient of friction achieved under the steady regime is linked to the presence of wear debris and an enlarged real contact area. sp2 carbon bonding has been related to the occurrence of a higher coefficient of friction and surface damage of DLC materials compared to bulk diamond. The a-C coatings and ta-C films have a lower coefficient of friction at the steady regime than the a-C:H coatings, possibly due to a significant amount of hydrogen in the a-C:H coatings.

Comparative measurement of residual stress in diamond coatings by low-incident-beam-angle-diffraction and micro-Raman spectroscopy

Two experimental techniques for the quantitative measurement of residual stress in thin polycrystalline diamond coatings have been developed. The x-ray low-incident-beam-angle-diffraction (LIBAD) allows one to measure the lattice strain with well-defined in-depth information, while micro-Raman spectroscopy permits one to accurately measure the frequencies of the zone-center optical phonons of diamond which are related to the lattice strain. The interpretation of the measured information in terms of residual stress is outlined for both techniques. The residual stress data obtained by either method in thin CVD diamond coatings were found to be in excellent agreement. The sign and magnitude of the balanced biaxial stress in the coating plane depend mainly on the substrate material used for the diamond deposition. Compressive stress was present in diamond coatings deposited on WC-Co substrates, whereas tensile stress was found in those on SiAlON substrates.

Residual stresses of diamond and diamondlike carbon films

This paper evaluated the internal stresses of different diamond and diamondlike carbon (DLC) coatings. For the diamond coatings, the stresses were determined using micro-Raman spectroscopy and x-ray diffraction (XRD), while the stresses of DLC films were determined with bent plate method. The internal stress was related to the structural properties of the coatings. Direct current plasma jet, combustion flame, and microwave chemical-vapor deposition processes were used to prepare the diamond coatings on the tungsten carbide or molybdenum substrates, while the DLC films were deposited on the silicon wafers with filtered cathodic vacuum arc process. From the Raman spectra of the diamond coatings, the compressive internal stresses were determined, which were related to the microstructure of the coatings. The results from XRD were comparable with those obtained from micro-Raman spectroscopy. Higher compressive residual stresses in the DLC films were noticed, which were also related to their chemical bonding na...

Fretting wear of metallic multilayer films

Fretting wear behaviour of electrodeposited Cu/Ni multilayer films with 10 and 5 nm thick sublayers has been investigated against a hardened steel ball as the counter body and compared with that of the constituents, Cu and Ni. The wear tests were carried out by using a ball-on-flat geometry at a translation frequency of 8 Hz and slip amplitude of 100 μm. Friction force was recorded on line during the tests. At the end of the tests, the wear scars were examined by laser surface profilometry, scanning electron microscopy and energy dispersive X-ray microanalysis. It has been observed that the frictional and wear mechanisms are very different for copper, nickel and Cu/Ni multilayers. Fretting of copper creates a relatively smooth wear scar mainly by mechanical ploughing of the asperities on steel counterbody (abrasive wear) and shows a very little third body interaction. Fretting of nickel involves adhesive wear resulting in a large transfer of steel to nickel, which is attributed to the strong chemical interaction between nickel and the steel counterbody. Fretting on multilayers involves a strong third body interaction resulting in ploughing mainly by debris (abrasive wear). The coefficient of friction is approximately 0.45 for copper, and approximately 0.8 for nickel as well as for multilayers. The values of the coefficient of friction for nickel and Cu/Ni multilayers found under the present fretting conditions are approximately double the corresponding values reported earlier for sliding wear conditions. It has been found that Cu/Ni multilayer is more resistance to fretting wear than the constituents, copper and nickel. Furthermore, the fretting wear resistance of Cu/Ni multilayers with 5 nm thick sublayer is better than that of the multilayers with 10 nm thick sublayers.

Integrated high-frequency inductors using amorphous electrodeposited Co-P core

We have made integrated inductive components with a cobalt-phosphorous core by electrodeposition and characterized them. Electrodeposited Co-P is considered an alternative to nickel-iron alloys, which have similar magnetic properties but lower electrical resistivity. The inductive components show a steady inductance up to 10 MHz.

Biotribocorrosion (tribo-electrochemical) characterization of anodized titanium biomaterial containing calcium and phosphorus before and after osteoblastic cell culture

The purpose of this study was to investigate the relationship between the osteoblastic cells behavior and biotribocorrosion phenomena on bioactive titanium (Ti). Ti substrates submitted to bioactive anodic oxidation and etching treatments were cultured up to 28 days with MG63 osteoblast-like cells. Important parameters of in vitro bone-like tissue formation were assessed. Although no major differences were observed between the surfaces topography (both rough) and wettability (both hydrophobic), a significant increase in cell attachment and differentiation was detected on the anodized substrates as product of favorable surface morphology and chemical composition. Alkaline phosphatase production has increased (≈20 nmol/min/mg of protein) on the anodized materials, while phosphate concentration has reached the double of the etched material and calcium production increased (over 20 µg/mL). The mechanical and biological stability of the anodic surfaces were also put to test through biotribocorrosion sliding solicitations, putting in evidence the resistance of the anodic layer and the cells capacity of regeneration after implant degradation. The Ti osteointegration abilities were also confirmed by the development of strong cell-biomaterial bonds at the interface, on both substrates. By combining the biological and mechanical results, the anodized Ti can be considered a viable option for dentistry.

Correlating in vitro scratch test with in vivo contact free occlusal area wear of contemporary dental composites

OBJECTIVES The aims of this study are to determine the extent to which the ranking order for clinical Contact-Free-Occlusal-Area (CFOA) wear performance of composites correlates with the ranking based on in vitro scratch hardness, and to analyze the extent to which the microstructure influences the overall trend. MATERIALS AND METHODS The patient data and CFOA wear measurements of 16 Tetric-C, 17 Tetric-EC, 16 Gradia-DP, 18 Filtek Supreme, 19 Z100 restorations in 31 subjects (8 males, 23 females) of two randomized clinical trials were fitted in a mixed-effect model. The in vivo performance of the restoratives was summarized by ranking the estimated material-related coefficients in the model. Scratch tests on two specimens per composite were run at a constant speed of 0.05 mm/s under indenter with normal loads of 15, 25, and 35 mN. Scratch width, depth and hardness calculated by imaging the scratch tracks were summarized in a model, the material-related coefficients were ranked and correlated with that of in vivo ranking order. RESULTS The best in vivo model included as significant factors (p<0.0001) the variables material, time/month, cavity type, and jaw type. The CFOA wear ranking order - Filtek Supreme, Z100>Tetric-C, Tetric-EC>Gradia-DP-correlated closely (R(2)=0.991) with the order of scratch hardness - Z100>Filtek Supreme>Tetric-C, Tetric-EC>Gradia-DP. SIGNIFICANCE Scratch tests could roughly categorize a new material as to whether it will probably exhibit a high or low in vitro scratch resistance and/or clinical CFOA wear rate.

Tribocorrosion: Material Behavior Under Combined Conditions of Corrosion and Mechanical Loading

Oxide particles, referred to as ‘debris”, are released from the contacting materials. Then, the debris can be removed from the contact zone or on the contrary trapped in it. In the case of removal, the debris dissolve chemically or are dragged out by a hydraulic flow along the material surface. In this case, the tribocorrosion mechanism is based on a repeated tearing off of the oxide after each contact and eventually a removal of some of the underlying material depending on the intensity of mechanical stress acting on the contacting materials. The major concern is then to quantify and eventually to model the kinetics of repassivation as accurately as possible. This type of tribocorrosion process can be classified as an oxidative wear mechanism as, for example, the ‘mild oxidative wear model’ (Quinn, 1992). In the case of debris trapping, one has to consider that under appropriate hydrodynamical, chemical, and thermal contact conditions and relative speed of the two contacting bodies, the debris will remain temporarily in the contact zone mainly as colloids with a diameter usually in the range of a few hundred nanometers. Two cases may then be distinguished: (a) the debris accelerates the wear in comparison to the case of debris-free contacts is accelerated by an abrasive effect, or (b) the debris slows down the wear compared to the case where the contact zone is free of any debris, resulting in a protective effect.

Electric and magnetic FEM modeling strategies for micro-inductors

Electroplated micromagnetic components, such as planar and toroidal inductors and transformers with ferromagnetic cores are promising devices. The characteristics of the materials used in these micro-scale components differ significantly from the properties of the common materials used in large-scale magnetics. The dimensional constraints due to the fabrication process form a main difference as well. For the design of such devices, two- and three-dimensional numerical field modeling techniques, such as FEM, are essential. This paper discusses modeling strategies combining two- and three-dimensional FEM methods, along with circuit equations, allowing investigation of the behaviour and design of new components.