CRTI Library

Effet d’un traitement de surface par projection thermique sur les propriétés structurales et mécaniques d’une fonte grise

La technique de projection thermique occupe aujourd’hui une place de plus en plus importante parmi les familles de traitements de surface qui joue un rôle incontournable dans de nombreux domaines industriels particulièrement dans la mécanique. Dans ce travail, nous allons montrer l’effet d’un revêtement de molybdène déposé par le procédé de projection à flamme-fil sur les propriétés microstructurales et mécaniques d’une fonte grise à graphite lamellaire.Les caractérisations par microscopie optique, électronique à balayage et par diffraction RX ont mis en évidence le rôle de la nouvelle microstructure obtenue après projection thermique à flamme-fil dans l’amélioration des propriétés mécaniques particulièrement la résistance à l’usure par abrasion de la fonte grise à graphite lamellaire. Les résultats ont montré que le taux d’usure obtenu pour la fonte revêtue en molybdène est faible que celui de la fonte nue. Cette évolution présente une bonne concordance avec la variation de la dureté. Voir les détails

Mots clés : traitement de surface, molybdène, fonte grise, microstructure, propriétés mécaniques.

ENHANCEMENT OF THE MECHANICAL PROPERTIES OF GRAYCAST IRON BY FERRITIC NITROCARBURIZING PROCESS

In this paper, we studies the mechanical properties of green cast iron ferritic nitrocarburizing after treatment in salt bath at 580°C at different holding time. The nitrocarburizing process has contributed changes in surface properties.After characterization and analysis the microstructure by scanning elctronic microscopy and X-ray diffraction, the obtained results show that the structure led to marked improvement in mechanicals properties particularly hardness and abrasive wear. Voir les détails

Mots clés : Gray cast irons, Salt bath nitrocarburizing, mechanical properties, Surface properties, abrasive wear.

Magnetic microwave and absorbing properties of Fe-Co alloy synthesisedby mechanical alloying process

In this paper, the structure and magnetic properties of nanocrystalline Fe(1–x)Coxmixtures are investigated. These structures are prepared using mechanical alloying based onplanetary ball mill under several milling conditions. The structural effects of mechanicalalloying of powders were investigated by scanning electron microscopy, X-ray diffractionanalysis and bench of microwaves. Consequently, alloy powder with an average grain size of10–13 nm was obtained. Maximum saturation magnetisation Ms was obtained at acomposition value of 65%Co. Microwave measurements were performed on the mechanicallymilled Fe(1–x)Cox powder Voir les détails

Mots clés : powder technology; mechanical alloying; microstructure; microwave.

Structural and magnetic studies of nanocrystalline Fe80Ni20 alloy prepared by high-energy ball milling

Mechanical alloying is a powder metallurgy processing technique involving the cold welding, fracturing and rewilding of powder particles in high energy. It has been used to obtain nanocrystalline alloys. Fe-20 wt. % Ni alloys were synthesised using a planetary ball mill (Retsch PM400). X-ray Diffraction (XRD) was used to identify and characterise various phases during the milling process. It is shown that the bcc Fe(Ni) solid solution was formed after 2 h of milling. The steady state grain size is about 12 nm. Many nanostructures' magnetic materials have exhibited excellent soft magnetic properties, which suit so many applications. We used electromagnetic methods (hysteresis) to characterise the variation of the residual magnetisation and the coercive field.r Voir les détails

Mots clés : nanostructure, nanocrystalline alloys, Magnetic Properties, microstructure, high-energy ball milling, mechanical alloying.

Monitoring of metal powder by eddy current

Nanocrystalline Fe(1−x)Cox, Fe, Fe80N120,Cu70Fe18Co12 mixtures have been prepared by mechanical alloying using a planetary ball mill under several milling conditions. Their structures and magnetic properties were investigated. Mechanical alloying is a non-balanced process for synthesis materials. The structural effects of mechanical alloying of powders were investigated by scanning X-ray diffraction analysis. In this report, we examine the applicability of eddy current techniques in-process for monitoring of powder density particle size and the time necessary to structure variation. An eddy current based monitoring system developed to measure metal powder density is expanded for monitoring metal powder diameter in metal compounds. Experimental sensor readings were gathered using four different metal powders with known particle sizes Fe(1−x)Cox, Fe, Fe80N120 and Cu70Fe18Co12. Analysis of the data showed that the sensor output was in relation with different parameter of powder (diameter, density and structure) that the sensitivity of the sensor differed with the type of metal powder. The merit of this technique is its reliance on a simple and inexpensive sensor probe. Voir les détails

Mots clés : metal powders, Mechanical Alloying, Magnetic Properties, Eddy Current, NDT, nondestructive testing, process monitoring, nanocrystalline materials, planetary ball milling, powder density, particle size, structure variation, sensors, sensor probes, nanostructures, nanotechnology.

The Non Destructive Testing Methods Applied to Detect Cracks in the Hot Section of a Turbojet

All aircraft whatever they are; are regularly audited. These controls are mainly visual and external; other controls such as "major inspection" or "general revisions” are more extensive and require the dismantling of certain parts of the aircraft. Some parts of the aircraft remain inaccessible and are therefore more difficult to inspect (compressor, combustion chamber, and turbine). The means of detection must ensure controls either during initial construction, or at the time of exploitation of all the parts. The Non destructive testing (NDT) gathers the most widespread methods for detecting defects of a part or review the integrity of a structure. The aim of this work is to present the different (NDT) techniques and to explore their limits, taking into account the difficulties presented at the level of the hot part of a turbojet, in order to propose one or more effective means, non subjective and less expensive for the detection and the control of cracks in the hot section of a turbojet. To achieve our goal, we followed the following steps: - Acquire technical, scientific and practical basis of magnetic fields, electrical and electromagnetic, related to industrial applications primarily to electromagnetic NDT techniques. - Apply a scientific approach integrating fundamental knowledge of synthetic and pragmatic manner so as to control the implementation of NDT techniques to establish a synthesis in order to comparing between the use of different methods. - To review recent developments concerning the standard techniques and their foreseeable development: eddy current, ultrasonic guided waves ..., and the possibility of the implication of new techniques. Voir les détails

Mots clés : Combustion Chamber, Crack, Hot Section, Nondestructive Testing (NDT), turbine

Modeling and Simulation for 3D Eddy Current Testing in Conducting Materials

The numerical simulation of electromagnetic interactions is still a challenging problem, especially in problems that result in fully three dimensional mathematical models. The goal of this work is to use mathematical modeling to characterize the reliability and capacity of eddy current technique to detect and characterize defects embedded in aeronautical in-service pieces. The finite element method is used for describing the eddy current technique in a mathematical model by the prediction of the eddy current interaction with defects. However, this model is an approximation of the full Maxwell equations. In this study, the analysis of the problem is based on a three dimensional finite element model that computes directly the electromagnetic field distortions due to defects. Voir les détails

Mots clés : Eddy Current, Finite Element Method, Non destructive testing, numerical simulations

Contribution à l’étude de la cohésion d’un multi-matériau obtenu par brasage 

L’exploitation des ressources fossiles reste une politique stratégique pour l’économie nationale. La valorisation optimale est tributaire d’une amélioration continuelle des performances de production. La résistance au terrain abrasif et l’efficacité hydraulique du système de refroidissement exigent l’adaptation d’outils de forage plus performants.Pour les formations géologiques tendres à mi-dures, les outils de forage monobloc en taillants PDC (Polycristalline Diamond Compact) sont les mieux adaptés. Le niveau de performance (mètre foré) repose essentiellement sur la réussite de la consolidation des poudres par infiltration et de la cohésion par brasage du couple matrice-taillant (PDC). Le contrôle des paramètres nécessaires à l’optimisation de la brasure du taillant PDC (WC-Co) sur le corps de l’outil de forage, nécessite la connaissance des propriétés physico-chimiques de l’alliage d’apport et des matériaux à assembler, ainsi que les interactions aux interfaces.Le succès des techniques de fabrication associées à la Métallurgie des Poudres, résidant particulièrement dans les taux de productivité à ce jour inégalés lors de la mise en forme des outils aux géométries complexes, est mis à l’épreuve par le développement récent de la technique combinant l’usinage du corps en acier (tour à 5 axes) et le rechargement de composite réfractaire. Cette alternative de qualité au procédé classique nous interpelle pour contribuer, à travers ce sujet de thèse, à contribuer à l’évaluation du degré d’adhérence du taillant PDC avec le corps en matrice infiltrée ou du corps en acier. Le comportement ultérieur de l’outil de forage repose sur la stabilité de l’interface substrat du PDC/Brasure/corps de l’outil (matrice ou acier). Voir les détails

Mots clés : multi-matériaux, interfaces, brasage, rechargement, outils en PDC, matrice infiltrée, acier faiblement allié