Characterization of oxide layers made on aluminium alloy 7075 by different methods

Aluminium and aluminium alloys are now widely used as materials for structural applications due to a number of valuable properties. Improvement in functional and decorative properties of aluminium can be obtained by forming an oxide layer on its surface. The aim of the present study was to produce and compare the properties of oxide layers on the surface of aluminium alloy 7075 and compare their properties. Methods which were used during the study were as follows: phosphating, micro-arc oxidation, and a chemical method involving the formation of the passive layer. Layers were subjected to corrosion tests. SEM and EDS methods were used for characterization of received results. Also some tests on optical ptofilometer were done. It was proven that the micro-arc oxidation method allows for obtaining a layer with the greatest thickness and highest  corrosion resistance.  

The Microstructure, Mechanical and Friction-Wear Properties of (TiBx/TiSiyCz)x3 Multilayer Deposited by PLD on Steel

The microstructure, mechanical properties, and friction-wear performance of (TiBx/TiSiyCz)x3 multilayer coatings deposited on the M2 steel by the pulsed laser deposition are investigated in detail in as-deposited state and after annealing at 500 °C for 5 min in air. Scanning and transmission electron microscopies are used to reveal microstructural changes caused by annealing. The influence of post-deposition annealing on hardness and Young modulus is studied in nanoindentation test. A scratch-test is applied to reveal changes in adhesion and the coefficient of friction (CoF) of coated samples with diamond before and after annealing. Friction-wear properties are also analyzed in dry sliding with Al2O3 and 100Cr6 steel in ball-on-disc tests. Our analysis shows that the post-deposition annealing leads to partial devitrification of the TiBx layers, where nanocrystalline TiB2 phase is identified, while the TiSiyCz layers retain amorphous. Annealing significantly increases mechanical properties of coated samples and adhesion of the (TiBx/TiSiyCz)x3 multilayer to steel substrates. Friction-wear properties of coated samples are also notably improved. The values of CoF for coated samples tested with diamond (in the scratch-test), alumina, and 100Cr6 steel (ball-on-disc tests) are in the range of 0.05–0.23, while for M2 steel the CoF values are 0.8, 0.45, and 0.8, respectively

Étude expérimentale et modélisation de la réactivité chimique au sein de matériaux multiphasés ferrite - supraconducteurs

Des systèmes composites granulaires ferrite - supraconducteurs O4/Bi2Sr2Ca2Cu3Ox, en abrégé F/S) ont été élaborés et caractérisés en jouant sur trois paramètres: la fraction volumique en additifs de ferrite NiFe2O4, la température de traitement thermique, le temps de traitement thermique. Nous avons essayé de maîtriser la dégradation du solide composite en déterminant l'évolution de chaque phase au moyen de diverses techniques que nous avons essayé de corréler : diffraction de rayons X, mesures magnétiques à basse température, mesures de résistance électrique à basse température, mesure par specîroscopie d'impédance complexe électrique à haute température (T>25C). Dans une première étape, la thèse développe l'étude expérimentale de la dégradation du système par diffraction de rayons X et propose une première modélisation. Deux types de réactions sont mises en évidence, l'une entre constituants, l'autre d'auto-dégradation de la phase supraconductrice. L'analyse de la diffusion chimique des éléments aux interfaces ferrite/supraconducteur a été réalisée à partir de microscopie électronique à balayage. Elle a permis de compléter l'étude de dégradation en définissant des coefficients de diffusion apparents. Dans une deuxième étape, une étude cinétique à haute température par spectroscopie d'impédance complexe électrique a permis de compléter la description des mécanismes de réaction-diffusion au sein de ces systèmes multiphasés complexes. L'étude révèle encore la présence de deux types de réactions. Dans une troisième étape, nous analysons les résistances électriques à basse température (10 à 300 K) et sous champ magnétique modéré. Des effets magnétorésïstifs géants sont ainsi caractérisés en fonction des paramètres de traitement et de composition.Granular composite systems made of ferrite NiFejO^ and superconducting phase Bi2Sr2Ca2Cu3Ox. (noted as F/S composites) have been elaborated and characterized. These multiphase systems depend on three parameters: the ferrite volume fractions (<£), the temperature (T) and the time (t) of thermal treatment- The chemical degradation of the solid composite was controlled by determining the evolution of each phase using various techniques: X-ray diffraction analyses, scanning electron microscopy including X-ray local analyses, magnetic susceptibility and electrical resistance measurements at low temperature. High temperature electrical impedance spectroscopy analyses has been performed to better understand the chemical evolution of the system during a thermal treatment. Using the X-ray diffraction analyses, a kinetics study led to a modeling of the reaction kinetics in this composite system. Two types of reactions were considered: a S/F inter-grain reaction and a S/S self-degradation reaction. Using scanning electron microscopy and ED AX equipment, the concentration profiles of the elements of each phase S and F have been determined: diffusion coefficients have been defined using a simplified Pick law. High temperature electrical impedance spectroscopy analyses have delivered new kinetics data: two types of evolutions forthe resistance of the composite system are evidenced. New kinetics parameters are proposed through a mode! of evolution describing the degradation of a system. Finally the electrical resistances at low temperature of specific composites have been analyzed as a function of variable applied magnetic fields. Giant magnet oresi stive effects have been observed: they strongly depend on the thermal treatment parameters (temperature and time for a fixed composition).LYON1-BU.Sciences (692662101) / SudocTOULON-BU Centrale (830622101) / SudocSudocFranceF

The Influence of Electrophoretic Deposition Parameters and Heat Treatment on the Microstructure and Tribological Properties of Nanocomposite Si3N4/PEEK 708 Coatings on Titanium Alloy

Nanocomposite Si3N4/PEEK 708 coatings were successfully fabricated on the Ti-6Al-4V alloy substrate by electrophoretic deposition (EPD) and post-EPD heat treatment. The addition of chitosan polyelectrolyte into ethanolic-based suspensions enabled the cathodic co-deposition of ceramic and polymeric particles. Zeta potential measurements allowed the elaboration of stable suspensions. The selection of the optimal EPD voltage and time enabled uniform coatings to be obtained. Heating above the PEEK melting point and cooling with a furnace or in water resulted in the formation of dense coatings with semi-crystalline or amorphous polymer structures, respectively. Both coatings with a thickness in the range of 90&ndash;105 &micro;m had good adhesion and scratch resistance to the substrates, despite the presence of relatively high degrees of open porosity. The coatings improved the tribological properties of the titanium alloy. However, a strong relationship between the polymeric matrix structure and wear resistance was observed. Semi-crystalline coatings proved to be significantly more wear resistant than amorphous ones

Corrosion Resistance of Inconel 625 CMT-Cladded Layers after Long-Term Exposure to Biomass and Waste Ashes in High-Temperature Conversion Processes

The present study investigated the effect of corrosion on an Inconel 625-cladded layer using the cold metal transfer (CMT) method. The corrosion was caused by various ashes and high process temperatures. The ashes were obtained from the biomasses of mixed wood and oat straw, as well as from sewage sludge, by ashing. Long-term corrosion tests were carried out at 650 &deg;C over a period of 1000 h. The chemical composition, mineral phases, and corrosion effects were studied by X-ray fluorescence (XRF), scanning electron microscopy equipped with energy-dispersive X-rays (SEM&ndash;EDX), and X-ray diffraction (XRD) from the surface and on the cross-section of the samples. The chemical composition of the ashes was quite different, but representative of their particular fuel. Together with the effects of the operating temperature and mass transfer, significant differences in the degree of the corrosion depth were detected for the various ashes. For the investigated samples, the corrosion mechanisms were inferred based on the identified corrosion products

Nanostructured LaFeO

The orthorhombic LaFeO3 thin films grown by pulsed laser deposition on silicon showed nano-structuration of their surface and preferential crystallographic exposed facets, depending on the deposition temperature. The LaFeO3 film deposited at 850 °C has two types of grain termination, flat or tip-like, corresponding to two different growth directions, respectively [110] and [200]. However, due to the shape of the termination, the two types of grains expose the same {110} facets. The prepared lanthanum iron oxide films are iron deficient and consequently contains oxygen vacancies, the exact chemical formula being LaFe0.82O3-δ

Structural characterization of LaCoO3 thin films grown by Pulsed Laser Deposition

International audienc

Influence of W Addition on Microstructure and Resistance to Brittle Cracking of TiB2 Coatings Deposited by DCMS

The aim of this work was to determine the influence of the tungsten addition to TiB2 coatings on their microstructure and brittle cracking resistance. Four coatings of different compositions (0, 7, 15, and 20 at.% of W) were deposited by magnetron sputtering from TiB2 and W targets. The coatings were investigated by the following methods: X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). All coatings had a homogeneous columnar structure with decreasing column width as the tungsten content increased. XRD and XPS analysis showed the presence of TiB2 and nonstoichiometric TiBx phases with an excess or deficiency of boron depending on composition. The crystalline size decreased from 27 nm to 10 nm with increasing W content. The brittle cracking resistance improved with increasing content of TiBx phase with deficiency of B and decreasing crystalline size

The Effect of Strontium Doping on LaFeO3 Thin Films Deposited by the PLD Method

The aim of the presented investigations was to deposit the thin films La1&minus;xSrxFeO3 (x = 0, 0.1, 0.2) on (100) Si substrate by using the Pulsed Laser Deposition (PLD) method. Structure was exanimated by using XRD, SEM, AFM, TEM and XPS methods. The catalytic properties were analyzed in 4 ppm acetone atmosphere. The doping of Sr thin films La1&minus;xSrxFeO3 (x = 0, 0.1, 0.2) resulted in a decrease in the size of the crystallites, the volume of the elemental cell and change in the grain morphology. In the LaFeO3 and La0.9Sr0.1FeO3, clusters around which small grains grow are visible in the structure, while in the layer La0.8Sr0.2FeO3, the visible grains are elongated. The TEM analysis has shown that the obtained thin films had a thickness in the range 150&ndash;170 nm with triangular or flat column ends. The experiment performed in the presence of gases allowed us to conclude that the surfaces (101/020) in the triangle-shaped columns and the plane (121/200) faces in flat columns were exposed to gases. The best properties in the presence of CH3COCH3 gas were noted for LaFeO3 thin film with triangle columns ending with orientation (101/020)