M. Clin

Performances tribologiques de l’acier inoxydable, du TMA et du Cu-NiTi recouverts de DLC

Resume L’amelioration de la friction et la resistance a l’usure font partie des proprietes des couches de carbone amorphe. L’objectif de notre travail est d’etudier les performances tribologiques des couches de carbone amorphe (DLC : Diamond-Like Carbon) deposees sur des fils orthodontiques : Cu-NiTi, acier et TMA. Les substrats etudies (acier inoxydable, TiMo, Cu-NiTi) sont des alliages frequemment utilises en orthodontie. Des tiges .019 x .025 inch de 5 cm ont ete fixees sur un support metallique en acier inoxydable. Les depots de DLC ont ete realises selon la technique “plasma enhanced chemical vapor deposition”. Un tribometre muni d’une balance, d’un moteur et d’un capteur electronique a ete utilise pour calculer le coefficient de frottement. Pour verifier la reproductibilite, chaque test a ete repris 10 fois. L’ensemble des donnees a ete recueilli a l’aide du logiciel WinDataq Lite pour calculer le coefficient de frottement et representer son evolution en fonction du temps. Le coefficient de frottement du couple acier inoxydable recouvert de DLC/acier non recouvert a subi une augmentation par rapport au couple d’acier non recouvert, alors que pour les deux autres couples (acier/Cu-NiTi et acier/TMA), le coefficient de frottement a diminue de 20 % a 30 %.

Infrared and Raman Spectroscopic Study of Carbon-Cobalt Composites

Analysis of carbon-cobalt thin films using infrared spectroscopy has shown existence of carbon-cobalt stretching mode and great porosity. The Raman spectroscopy and high-resolution transmission electron microscopy have been used in order to investigate the microstructure of the films. These films exhibit complex Raman spectra suggesting the presence of amorphous and crystallized phases. The different fractions of phases and the correlation between the atomic bond structures and the Raman features depend on the cobalt content.

Discommensuration patterns in the BiSrCaCuO high Tc superconductors

Abstract We present a transmission electron microscopy study of the discommensuration (DC) walls in the superconducting bismuth-cuprates. High resolution evidence for the translation slip across a wall is obtained for the first time in these materials. A consistent relationship is established between the observed characteristics of the walls in several phases of this structural family: number of walls merging at a node, average distance between DCs, and value of the modulation wavenumber. We show that a wide range of ‘latent’ commensurate periods, between 4 b and 9 b , determine the characteristics of the walls.

Incommensurate multisoliton regimes in the bismuth—type high Tc superconductors

Abstract A systematic investigation by transmission electron microscopy on bismuth oxide superconductors, has established existence of discommensurations. This investigation on the (2201), (2212) and (2223) phases of this material shows that discommensurations exist with various “latent” lock—in wave—vectors between b*/4 and b*/10.

HREM and Simulation Study in the Bi–Sr–Ca–Cu–O System

We have studied the Bi-Sr-Ca-Cu-O family by high resolution electron microscopy (HREM). We have simulated the HREM images using a phenomenological model. The experimental and calculated results agree quite well.

TEM investigation of discommensurations in the bismuth-type high Tc superconductors

Abstract The existence of discommensurations in the superconducting bismuth-cuprates is established on the basis of several consistent features: translation-shift across a wall, characteristics of the nodes where several discommensurations merge, correspondence between the average distance of the lines in real space and the modulation wavelength deduced from microdiffraction. We have observed a variety of “latent” lock-in wavevectors between b∗/4 and b∗/10 depending either on the investigated phases or on the amount of substitution of lead to bismuth.