Several workers have previously investigated the magnetic properties of copper and aluminium, but in most cases too small regard has been paid to the changes in magnetic susceptibility brought about by mechanical and thermal treatments previous to measurements. In the present work I have attempted to correlate changes in the magnetic susceptibilities of copper and aluminium with metallurgical changes in the metal lattices. A somewhat tentative theory is outlined covering this correlation. Previous investigations by Kussmann and Seeman led to the conclusion that iron impurity in the pure copper was the sole cause of the various magnetic changes recorded. This it is hoped to disapprove. To get some insight into the changes caused by such ferromagnetic impurity a series of magnetic measurements were carried out on low iron content iron-copper alloys, very kindly supplied by Imperial Chemical Industries Ltd., “Metals Division”. The thesis falls naturally into four main parts, and appendices are added at the end to avoid interpolation of the work with definitions etc. Throughout the thesis (Parts III and IV) only a few experimental values, typical of the many results obtained, are quoted.

The equation for the conservation of momentum in the mushy zone during solidification is derived using the volume averaging technique. The conditions under which the momentum equation reduces to Darcy's law are elucidated. Permeabilities for flow of interdendritic liquid in Al-Cu alloys with equiaxial structures are measured using a simple, cost-effective permeameter. Center-to-center distance between grains (180 μm to 450 μm), specific surface (3.21 x 10⁻² μm⁻¹ to 3.095 x 10⁻¹ μm⁻¹), and volume fraction liquid (0.166 to 0.434) are the structural parameters studied in this investigation. Permeability in Al-Cu alloys with equiaxial grains is structure sensitive. For example, permeabilities for globular structures (nondendritic) are approximately one order of magnitude greater than permeabilities for the dendritic-globular structures, when the volume fraction liquid is approximately 0.3. To better understand the dependence of permeability on structure morphology, structure evolution during the permeability testing was studied in isothermal coarsening experiments. Dimensionless permeabilities based on specific surface, and center-to-center distance between grains are presented along with the theoretical results for flow through different arrays (simple cubic, body-centered cubic and face-centered cubic) of uniform spheres. With dimensionless permeability defined as KSᵥ², where Sᵥ is the specific surface of the solid, the empirical data compare reasonably well with theoretical curves for flow through arrays of uniform spheres. Numerical experiments are performed to obtain permeabilities for flow parallel to primary dendrites in columnar structures with high volume-fraction liquid where physical experiments may fail. The results of numerical experiments are presented along with the analytical results for flow parallel to cylinders arranged in square and triangular packing, analytical results for flow through periodically constricted tubes and the available empirical data. The results indicate that there is a transition in the behavior of permeability in the neighborhood of volume fraction liquid equal to 0.65.

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No description available.

Les conditions thermodynamiques et cinétiques dans les moteurs cryogéniques sont sévères, en particulier pour la mince paroi interne de la chambre de combustion. Bien que peu résistant mécaniquement, un alliage de cuivre est utilisé pour maximiser les transferts thermiques à travers cette paroi et ainsi améliorer l’efficacité du moteur. Cependant, les fluctuations de concentration et de pression des propergols (tels que l’oxygène ou l’hydrogène liquide) à la surface de la paroi favorisent l’endommagement de l’alliage, en particulier si la paroi n’est pas en permanence couverte d’une pellicule d’hydrogène (barrière contre l’oxydation). Ce phénomène est connu sous le nom de « blanching », qui est la succession de courts cycles d’oxydation et de réduction dues à l’exposition de la paroi de la chambre de combustion aux atmosphères oxydants et réducteurs. Le blanching mène à la diminution de l’épaisseur de la paroi de la chambre, pouvant même conduire à la rupture de la paroi.Les alliages de cuivre peuvent, en fonction de leur composition, apporter une protection à l’oxydation et à la réduction. Comme le cuivre est indispensable grâce à sa conductivité thermique élevée, des éléments d’addition sont souvent ajoutés à l’alliage pour augmenter ses résistances mécaniques et chimiques. Cette étude met en avant les différences de comportement aux cycles d’oxydoréduction de trois matériaux (Cuivre OFHC, et deux alliages Cuivre-Chrome) à des hautes températures. Elle permet de cibler l’endommagement thermochimique qui se produit dans les « vraies » chambres de combustion.Les essais réalisés consistent en l’oxydation et la réduction d’échantillons pendant 40 cycles successifs dans des atmosphères contrôlées à 600, 750 ou 900°C. L’oxydation est obtenue par l’air artificiel (O2+N2) et la réduction est obtenue par l’introduction de monoxyde de carbone. Les différences obtenues entre les échantillons des différents essais peuvent être due à la croissance d’oxydes secondaires, qui ne sont pas réduits pendant la phase de réduction, alors que le cuivre et ses oxydes simples le sont. Les couches d’oxydes doivent être identifies, car leur exploitation pourrait renseigner sur le comportement à l’oxydoréduction des matériaux pendant le blanching. Les analyses RAMAN et MEB confirment bien la présence d’oxydes secondaires sous la couche principale d’oxyde de cuivre, montrant que ce type d’endommagement est probablement lié à la composition des matériaux et de leur comportement à haute température. / Conditions in combustion chambers of liquid rocket engines are severe, especially for the inner liner of the chamber wall. The copper alloys used in the thin inner liner of the chamber wall ensure an efficient cooling. However, concentration fluctuations of the propellants such as H2 and O2 on the surface of the inner liner of the chamber wall can lead to a damage of the alloys, especially if the wall is not permanently protected by H2. This phenomenon is known as Blanching, which is a quick redox cyclic, leading to a physical-chemical reduction of the width of the wall, even up to fracture. Copper alloys can - depending on their composition - provide a protection to oxidation and reduction. As copper is mandatory because of its high thermal conductivity, some addition elements are usually used in order to optimize the mechanical and chemical resistance of the alloy. This study shows the differences of the behavior between three copper alloys (OFHC copper and two Copper-Chromium alloys) under oxidation-reduction cycles at 750°C. The experimental investigations aim at assessing blanching in the range of real liquid rocket engines combustion chambers conditions.The performed tests consisted in oxidizing and reducing of samples 40 cycles under controlled atmospheres at 600°C, 750°C or 900°C. Oxidation is obtained by industrial quality air (O2+N2), and reduction by CO as low safety risk replacements for the O2+H2 atmosphere in the engine. The differences between the different conditions may be caused by the growth of secondary copper oxides, which are not reduced during the reduction phases.Oxide layers have to be identified, as their exploitation may lead to a principal understanding of the behavior of the chamber wall material during blanching, and may help to determine oxidation and reduction law parameters. RAMAN and SEM analyses confirm the presence of secondary copper oxide layers below the reduced copper on the surface of the sample.

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Enhancing the effective peel resistance of plastically deforming adhesive joints through laser-based surface micro-machining Edwin Hernandez Diaz Inspired by adhesion examples commonly found in nature, we reached out to examine the effect of different kinds of heterogeneous surface properties that may replicate this behavior and the mechanisms at work. In order to do this, we used pulsed laser ablation on copper substrates (CuZn40) aiming to increase adhesion for bonding. A Yb-fiber laser was used for surface preparation of the substrates, which were probed with a Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS). Heterogeneous surface properties were devised through the use of simplified laser micromachined patterns which may induce sequential events of crack arrest propagation, thereby having a leveraging effect on dissipation. The me- chanical performance of copper/epoxy joints with homogeneous and heterogeneous laser micromachined interfaces was then analyzed using the T-peel test. Fractured surfaces were analyzed using SEM to resolve the mechanism of failure and adhesive penetration within induced surface asperities from the treatment. Results confirm positive modifications of the surface morphology and chemistry from laser ablation that enable mechanical interlocking and cohesive failure within the adhesive layer. Remarkable improvements of apparent peel energy, bond toughness, and effective peel force were appreciated with respect to sanded substrates as control samples.

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No description available.

No description available.