Characterization of surface Ag nanoparticles in nanocomposite a-C:Ag coatings by grazing incidence X-ray diffraction at sub-critical angles of incidence

Silver diffusion within nanocomposite films and/or toward the film surface is often observed during annealing of the silver-based nanocomposite films. In order to control and/or minimize this process, it is crucial to characterize the aggregated silver nanoparticles on the films surface. In this paper grazing incidence X-ray diffraction (GIXRD) with both sub-critical and supra-critical angles of incidence is used to characterize the Ag nanoparticles distribution, shape and structure both inside the matrix and on the nanocomposite film surface. The nanocomposite carbon coating containing Ag nanoparticles (a-C:Ag) was deposited by dc magnetron sputtering. The coatings were analyzed by GIXRD using fixed incident angles both below and above the critical angle for total reflection. By using sub-critical angles it was possible to eliminate diffraction from the bulk material allowing to estimate the size distribution of the nanoparticles sitting on the surface. The results obtained by GIXRD analysis were checked through comparison with the observations made by both TEM and SEM analysis. The proposed methodology can be used to characterized nanoparticles deposition on a surface and/or island formation during film growth as long an adequate substrate with high critical angle for total reflection is used.We gratefully acknowledge the financial support provided by the FCT—Fundação para a Ciência e Tecnologia and FSE for the grant SFRH/BD/82472/2011. This research is sponsored by the FEDER funds through the program COMPETE—Programa Operacional Factores de Competitividade and by the national funds through FCT—Fundação para a Ciência e Tecnologia in the framework of the Strategic Projects PEST C/EME/UIO0285/2011

Numerical and experimental study of the contact resistance for high copper alloys in force domain 1–100 N

High copper alloys were required by the industry to improve mechanical and electrical contact resistance for connecting device. This work addresses the electrical contact resistance law versus force in the range (1–100 N) for sphere/plan shapes. The designed samples are submitted to indentation (static contact) and insertion (sliding contact). Experimental power law of contact resistance versus forces was obtained where the law parameters are well related to electrical resistivity, Young modulus, yield stress... Previous analytical relationship Rc=f(Fc) in the literature and finite element simulation code are used to discuss the origin and the validity of such practical power law. Nevertheless the analytic expression are found unsatisfactory, the numerical model gives some agreement with this previous experimental law. However better convergence between numerical and experimental data was obtained in indentation when the surface topography is considered. The obtained results are a useful tool to evolve compromise between the electrical and mechanical aspects for a high loading contact. The main statement is that numerical model including the real topography and roughness is robust so it can be used in different contact shape and complex design for contact resistance evaluation. Finally, depending on the hardness and the resistivity, these uncoated materials were found to act on fretting apparitions and its level.

Plug-in connectors aging and in situ diagnostic tool force measurement implementation

International audienceThis paper concerns the study of plug-in connector used in low level (a few Amperes). In this case, the application fields are instrumentation and control (IandC) installations. The long service duration of these semi-permanent contacts throughout their lifetime relies on having a stable force. The objective of this study is to know the main mechanical parameters which impact on the connector’s lifetime. The main results are that insertion force and friction coefficient of contact change after thousands of insertion-extraction cycles. To avoid these parameters (insertion force and friction coefficient μ) that change during mating cycle, an innovative diagnostic tool has been investigated, to directly measure, in situ, the contact force of each spring of the connector. © 2016, Editura Cefin. All rights reserved

Fluctuation of contact voltage during fretting phases

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Fretting corrosion in power contacts: Electrical and thermal analysis

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Minimum fretting amplitude in medium force for connector coated material and pure metals

WOS:000287418800016International audienceFor automotive applications, the mechanical behaviour of the contact area under vibrations is one of the key factors for connector reliability. Such vibrations are typically in the range of 10-2000Hz and result in displacements of only a few microns, at the contact interface. In the present study, a bench test has been developed to control more representative motions down to 1 mu m. The objective is to determine the minimum amplitude for fretting-corrosion degradation based on the evolution of contact resistance and to study the effects of the material, the contact force, the coating for these low displacement amplitudes. To obtain the limit of the appearance of fretting, a sub-micrometer incrementing displacement amplitude methodology was applied on high stiffness bench test including a double PZT actuator. It was found that the fretting degradation starts to occur from 2 mu m to 6 mu m when the contact force is from 0.5N to 2.5N with a tin coated terminal. Moreover pure copper, tin and nickel have similar amplitude fretting limits while noble metals confirm the absence of fretting up t

Analysis of temporal and spatial contact voltage fluctuation during fretting in automotive connectors

International audienceOur study is focused on contact voltage fluctuations during fretting with small amplitudes of a few tens microns which generate damage of the contact of connectors. A contact composed by a pin and a curve female part are submitted to vibration cyclic of 25µm at 100Hz and supplied with current ramp from 0.1mA to 3A in two directions. With the help of fast devices, the voltage and position data acquisition are conjointly made with the common DC contact voltage dur-ing fretting. Some unexpected results state that voltage fluctuation occurs in the different stage of fretting and start at the beginning of test in the insertion direction and located at half of track. These small voltage fluctuations around few mV increased to few hundred millivolts and may reach few volt at ultimate phase of degradation with random distribu-tion along the track. When the motion is stopped the ohmic conduction of such fretting interface is ensured only when the subsequent voltage stay below a sutured value depending on the degradation and current level. It is found that the common three phases of degradation have a different saturation voltage which appears at higher and higher current and induce voltage breakdown. Regarding that symmetric characterises is obtained in two the directions current ramp the semiconducting behaviour effect of oxide layers on debris particle is negligible. As voltage-current experimental data was well fitted to similar equation of granular material conduction we have deduced the fitting parameters (V l and I 0) of interface

New contact material for reduction of arc duration for dc application

The phenomenon of arcing is the major cause of electrical contact degradation in electrical switches. Degradation involves contact erosion and/or welding. The use of special contact material and that of specific material processing may permit contact erosion to be reduced, in particular by shortening the arc duration. A short review of these approaches is presented in the first part of this paper. In the second part, the development of a new self-blowing contact material is described. This material has been tested under dc voltages from 14 V to 42 V. A reduction of the arc duration by a factor of 4 approximately was obtained as was a concomitant reduction of the extinction gap to less than 2 mm. This material will contribute to achieving better reliability in high current-high voltages breaking devices, and will aid in their miniaturization, e.g. in relays

Statistical Analysis of Voltage from Constriction to Micro-arc Values during Aging by Fretting

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