THE BORDONI RELAXATION - THREE VALLEYS MODEL

Une méthode analytique du calcul du frottement intérieur dû à la formation des doubles décrochements est développée à partir de la théorie cinétique dans le cas de trois vallées de potentiel. Le modèle permet de décrire correctement les résultats expérimentaux, à condition que la dislocation ne franchisse pas de trop nombreuses vallées de potentiel.The analytical description of internal friction related to the double-kink relaxation is obtained applying the kinetic theory in the case of three potential valleys. This model can describe experimental curves in the case in which dislocations do not pass by many potential valleys

Analysis of Mechanical Loss Spectra in Zirconia Ceramics by Appying the Coupling Model

Mechanical loss spectra (two peaks) observed in ZrO2 doped with Y2O3 (2-10 mol%), are attributed to oxygen vacancy (V)-yttrium (Y) associates (V-Y pairs and V-2Y agglomerates). Both peaks were analysed numerically by applying the coupling model. It has been shown that : i) the activation enthalpy H for both peaks increases with Y2O3 content, ii) the values of coupling parameter n are about 0.6 - 0.7, iii) the activation enthalpy H0 corresponding to the noninteracting system (dilute case) is about 0.4 eV which is considerably smaller than the activation enthalpy for reorientation of isolated dipoles (0.8 - 0.9 eV

Application of the Coupling Model to Magnetic After Effects in the Fe72Co10Nb6B12Fe_{72}Co_{10}Nb_{6}B_{12} Amorphous Alloy

It was shown that magnetic reluctivity measured versus time after demagnetization for pre-annealed samples of the $Fe_{72}Co_{10}Nb_6B_{12}$ amorphous alloy exhibits highly non-exponential behavior which can be described by the coupling model. The relaxation intensity and the coupling parameter describing correlation effects in free volume diffusion decrease with increasing 1 h annealing temperature indicating annealing out of free volume and formation of iron clusters in amorphous matrix

INTERNAL FRICTION STUDIES ON STRUCTURAL RELAXATION AND CRYSTALLIZATION IN Co75Si10B15 METALLIC GLASS

On a étudié le frottement interne /FI/ et le module de torsion en fonction de température dans l'alliage amorphe CO75Si10B15. Sur la courbe FI on a trouvé les maximums liés à la cristallisation du cobalt et à la précipitation de ces composés intermétalliques avec le bore et le silicium. Sur la courbe G/T/ on a démontré l'existance d'un processus de relaxation structurale. On a évalué l'énergie de ce processus : 0,48eV.Internal friction /IF/ and shear modulus as functions of temperature were investigated for Co75Si10B15 metallic glass. On the IF curves were found maxima associated with the crystallisation of cobalt and also with the precipitation of intermetallic compounds of cobalt with boron and silicon. A structural relaxation process was ascertained on the G/T/ curve. The energy of this process was estimated and found to be 0.48 eV

Application of the Coupling Model to Magnetic After Effects in the Fe 72

It was shown that magnetic reluctivity measured versus time after demagnetization for pre-annealed samples of the $Fe_{72}Co_{10}Nb_6B_{12}$ amorphous alloy exhibits highly non-exponential behavior which can be described by the coupling model. The relaxation intensity and the coupling parameter describing correlation effects in free volume diffusion decrease with increasing 1 h annealing temperature indicating annealing out of free volume and formation of iron clusters in amorphous matrix

ANALYSE DE LA VARIATION DES PICS DE BORDONI AVEC LA LONGUEUR LIBRE DES SEGMENTS DE DISLOCATIONS DANS LE MAGNÉSIUM DE HAUTE PURETÉ

Durant bombardement électronique la longueur des segments libres de dislocations diminue et on a analysé la variation de l'amplitude et de la température des pics de Bordoni. Les résultats sont quantitativement interprétés dans le cadre de la théorie d'Esnouf de la relaxation de Bordoni.A quantitative analysis of the variations of amplitude and temperature of Bordoni peaks during electron irradiation is given in the framework of Esnouf's theory of Bordoni relaxation

PHÉNOMÈNES ANÉLASTIQUES DUS AUX DÉFAUTS CRÉÉS PAR BOMBARDEMENT ÉLECTRONIQUE ET À LEURS INTÉRACTIONS AVEC LES DISLOCATIONS DANS LE MAGNÉSIUM

Le spectre de frottement interne du Mg très pur écroui et/ou irradié est interprété en termes de migration des défauts ponctuels et de leurs interactions avec les dislocations.The internal friction spectrum of pure Mg after cold work and/or irradiation has been interpreted in terms of point defects migration and their interaction with dislocations

Mössbauer temperature study of the Fe80Nb6B14 amorphous alloy

Temperature studies in the range 300 800 K of amorphous Fe80Nb6B14 alloy using Mössbauer spectroscopy are presented. It is shown that at a temperature close to 700 K iron clusters with non-collinear magnetic structure are formed. The observed magnetic permeability enhancement effect in the annealed at elevated temperatures alloy, which takes place in amorphous phase, is due to the strong ferromagnetic exchange between Fe clusters via the amorphous matrix and reduction of internal stresses