[EN] TiAl intermetallic have demonstrated excellent behavior at high temperature, however, the processing for producing coatings is not easy due to its high melting point, otherwise the coaxial laser cladding process promise to be an excellent tool for obtaining extensive overlapping coatings, achieving complete fusion and deposition of alloys with high melting point on surfaces with complex shape. In this work we study the parameters of coaxial laser process and preheating the substrate to achieve Ti48Al2Cr2Nb intermetallic coatings on Ti6Al4V sheet 3 mm thick, in order to improve the tribological, oxidation and corrosion behavior of the Ti6Al4V alloy. The geometrical and chemical dilution analysis of the single tracks obtained at different levels in the laser processing variables were able to identify combinations that minimize defects such as cracks, high dilution and inadequate aspect ratio. It found a direct relation between the cooling rate and the coaxial laser process parameters such as the powder feeding rate and scanning velocity. Thus the process was optimized by minimizing the cooling rate with decreasing the velocity. After this was selected as appropriate preheating temperature 350 ºC and were obtained coatings with 40% overlap, using process parameters which generate laser specific energy of 70, 80, 90 and 180 J/mm2, then they have been evaluated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers micro-hardness (HV) and nanoindentation. The microstructure of the coatings consists gamma-TiAl phase and alfa2-Ti3Al. Preheating the substrate has allowed obtaining coatings with good metallurgical bond, although cracks and pores are observed for some conditions. It is noted that the expected variation in chemical composition from coating surface to the substrate was found, with low dilution of vanadium. The hardness of the TiAl laser coatings is higher than the substrate and the bending tests results shown that the coatings have good adhesion but with limited ductility. The tribological properties of the coatings shows that in the wear tests at room temperature a lower wear rate is obtained compared to the substrate. In the case of high temperature, the coatings have a lower coefficient of friction; however, a higher wear rate is obtained when compared with the substrate. The coatings have good resistance to oxidation evaluated by isothermal oxidation tests in air at 800 ºC, when compared with the substrate, the thermal growth oxide up to 12 microns thick for 150 hours were obtained. The structure of the oxide layers is complex and comprises the growth of successive layers from the outer surface of the coating. We also studied the electrochemical corrosion behavior of the coatings obtained. The results indicate that the coaxial laser cladding can be a good alternative to obtain extensive TiAl intermetallic coatings, dense coatings with good substrate bonding and minimal defects were obtained, that improve the oxidation and wear behavior of Ti6Al4V alloy. / [ES] Los intermetálicos TiAl han demostrado tener un excelente comportamiento a alta temperatura, sin embargo, su procesado para la obtención de recubrimientos no es sencillo debido a su alto punto de fusión, por otra parte el plaqueado láser coaxial promete ser una excelente herramienta para la obtención de recubrimientos por solape de cordones, logrando la completa fusión y deposición de aleaciones con elevado punto de fusión sobre superficies con forma complejas. En esta tesis se ha estudiado los parámetros de procesado láser coaxial y el precalentamiento del sustrato para lograr recubrimientos con intermetálico Ti48Al2Cr2Nb sobre láminas de Ti6Al4V de 3 mm de espesor, con la finalidad de mejorar el comportamiento tribológico, de oxidación y de corrosión de la aleación Ti6Al4V. Del análisis geométrico y de dilución química de los cordones obtenidos con diversos niveles en las variables de procesado láser se logró identificar combinaciones que minimizan defectos como grietas, alta dilución y relación de aspecto inadecuadas. Se ha encontrado una relación directa entre la velocidad de enfriamiento y los parámetros del proceso láser coaxial, tal como la cantidad de polvo aportado y la velocidad de pasada. De esta manera el proceso ha sido optimizado minimizando la velocidad de enfriamiento con la disminución de la velocidad de pasada. De este análisis se ha seleccionado como temperatura adecuada de precalentamiento 350ºC y se han obtenido recubrimientos con un 40% de solape, utilizando parámetros de proceso que generan energías especificas aportadas por el láser de 70, 80, 90 y 180 J/mm2, los cuales han sido evaluados mediante microscopia óptica (MO), microscopia electrónica de barrido (MEB), difracción de rayos X (DRX), microdureza Vickers (HV) y nanoindentación. La microestructura de los recubrimientos se compone de fases gamma-TiAl y alfa2-Ti3Al. El precalentamiento del sustrato ha permitido la obtención de recubrimientos con buena unión metalúrgica, aunque se observan para algunas condiciones grietas y poros. Se observa que la variación en la composición química de la superficie del recubrimiento al sustrato es la esperada, con baja dilución del vanadio. La dureza de los recubrimientos obtenidos es más alta que la del sustrato, y en los ensayos de flexión se observó que los recubrimientos tienen buena adherencia pero limitada ductilidad. El comportamiento tribológico de los recubrimientos muestra que en los ensayos de desgaste a temperatura ambiente se obtiene una tasa de desgaste menor por parte de los recubrimientos comparados con el sustrato. Para el caso de alta temperatura los recubrimientos presentan un menor coeficiente de fricción, sin embargo, se obtiene una mayor tasa de desgaste cuando se compara con el sustrato. De los ensayos de oxidación isotérmica se observó que los recubrimientos tienen buena resistencia a la oxidación en aire a 800ºC, al compararlos con el sustrato, llegando a obtener capas de óxidos de hasta 12 µm de espesor a 150 horas de oxidación. La estructura de las capas de óxidos es compleja y comprende el crecimiento de capas sucesivas a partir de la superficie externa del recubrimiento. También se ha estudiado el comportamiento a corrosión electroquímica de los recubrimientos obtenidos. Los resultados indican que el plaqueado láser coaxial puede ser una buena alternativa para la obtención de recubrimientos con intermetálicos TiAl, obteniendo recubrimientos densos, con buena unión al sustrato y mínimos defectos, que mejoran el comportamiento ante la oxidación y el desgaste de la aleación Ti6Al4V. / [CAT] Els intermetàl·lics TiAl han demostrat tindre un excel·lent comportament a alta temperatura, però, el seu processat per a l'obtenció de recobriments no és senzill degut al seu alt punt de fusió, d'altra banda el plaquejat làser coaxial promet ser una excel·lent eina per a l'obtenció de recobriments per solapament de cordons, aconseguint la completa fusió i deposició de aliatges amb elevat punt de fusió sobre superfícies amb forma complexes. En aquesta tesi s'ha estudiat els paràmetres de processament làser coaxial i el preescalfament del substrat per aconseguir recobriments amb intermetàl·lic Ti48Al2Cr2Nb sobre làmines de Ti6Al4V de 3 mm de espessor, amb la finalitat de millorar el comportament tribològic, d'oxidació i de corrosió de l'aliatge Ti6Al4V. De l'anàlisi geomètric i de dilució química dels cordons obtinguts amb diversos nivells en les variables de processat làser es va aconseguir identificar combinacions que minimitzen defectes com esquerdes, alta dilució i relació d'aspecte inadequades. S'ha trobat una relació directa entre la velocitat de refredament i els paràmetres del procés làser coaxial, tal com la quantitat de pols aportat i la velocitat de passada. D'aquesta manera el procés ha estat optimitzat minimitzant la velocitat de refredament amb la disminució de la velocitat de passada. D'aquesta anàlisi s'ha seleccionat com a temperatura adequada de preescalfament 350 ºC i s'han obtingut recobriments amb un 40% de solapament, utilitzant paràmetres de procés que generen energies especifiques aportades pel làser de 70, 80, 90 i 180 J/mm2, els quals han estat avaluats mitjançant microscòpia òptica (MO), microscòpia electrònica de rastreig (MER), difracció de raigs X (DRX), microduresa Vickers (HV) i nanoindentació. La microestructura dels recobriments es compon de fases gamma-TiAl i alfa2-Ti3Al. El preescalfament del substrat ha permès l'obtenció de recobriments amb bona unió metal·lúrgica, tot i que s'observen per a algunes condicions esquerdes i porus. S'observa que la variació en la composició química de la superfície del recobriment al substrat és l'esperada, amb baixa dilució del vanadi. La duresa dels recobriments obtinguts és més alta que la del substrat, i en els assajos de flexió es va observar que els recobriments tenen bona adherència però limitada ductilitat. El comportament tribològic dels recobriments mostra que en els assajos de desgast a temperatura ambient s'obté una taxa de desgast menor per part dels recobriments comparats amb el substrat. Per al cas d'alta temperatura, els recobriments presenten un menor coeficient de fricció, però, s'obté una major taxa de desgast quan es compara amb el substrat. Dels assajos d'oxidació isotèrmica es va observar que els recobriments tenen bona resistència a l'oxidació en aire a 800ºC, al comparar-los amb el substrat, arribant a obtenir capes d'òxids de fins a 12 micres de gruix a 150 hores d'oxidació. L'estructura de les capes d'òxids és complexa i comprèn el creixement de capes successives a partir de la superfície externa del recobriment. També s'ha estudiat el comportament a corrosió electroquímica dels recobriments obtinguts. Els resultats indiquen que el plaquejat làser coaxial pot ser una bona alternativa per a l'obtenció de recobriments amb intermetàl·lic TiAl, obtenint recobriments densos, amb bona unió al substrat i mínims defectes, que milloren el comportament davant l'oxidació i el desgast de l'aliatge Ti6Al4V. / Zambrano Carrullo, JC. (2015). Desarrollo y caracterización de recubrimientos TiAl mediante procesado láser coaxial sobre Ti6Al4V [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/56148 / TESIS

This report covers the investigation of the next generation of sensors to be used in the sensor based tube system known as SentusysTM. One essential feature of the next generation of sensors is high-temperature endurance. The sensors (strain gauges and thermocouples) have been produced by means of thermal spraying techniques, short-pulse laser ablation and laser cladding. It has been found that the sensors seem to work in general, however, much research and development remain.

The diploma thesis deals with study of laser cladding technology and possibilities of its use in renovation of casting molds made of hot-work tool steel. The theoretical part describes methods of laser cladding, testing methods and characteristics of the base material and its heat treatment. In the experimental part the test clads, and the metallographic samples were made. The samples were evaluated in terms of macrostructure and microstructure, especially clad geometry, dilution, and defects like pores and cracks. Microhardness was also measured. In conclusion a technical and economic evaluation was performed.

The research is focused on cladding of inconel 625 using the MAG - CMT method. It was found that welding without an oscillation does not create the necessary geometry to establish additional layers. When welding with an oscillation, it was researched that the current between 150 and 200 A appears most appropriate in the synergistic mode for welding inconel 625. The resulting weld bead was made at a current of 190 A with pulse dynamics correction set to -4 and correction of arc length to +10 and welding speed of 315 mm per minute.The weld bead was not ideal mainly due to insufficient height. The improvement of results could be achieved by set oscilation with fluent change in acceleration. Because of the time options and difficulty of programming it was used only constant speed for all experiments.

No description available.

This thesis addresses the study and preparation of documentation for the new building firehouse. The building is considered the location of the fire brigade units. The building is part three storey and part two storey. The building has a steel skeletal support system to ensure stability. The ceiling structure is a composite concrete and steel. Roofed building's flat roof with a classic sequence of layers. Circuit structures are formed with Z and C profiles. Filled with mineral wool. The facade is ventilated. The ground plan is rectangular object, the maximum dimensions are 55,15x27,30 m. The building is basement, covered only with flat roofs.

The diploma thesis described the basic principles and characters of the long period fiber gratings (LPFGs). Our concern was to describe basic mathematical description of these gratings needed to their modelation and simulation. Consequently some exact models leading to changes in the shape of the spectrum LPFGs were suggested, these methods were the chirping, apodization and changes in the average refractive index navg. In the Matlab environment, programes for counting the important parametres LPFGs were created and meanwhile each model leading to the change in the shape of the spectrum was simulated.

Les superalliages à base de nickel durcis par précipitation γ' et notamment l'Inconel 738 LC (IN738LC), sont des matériaux largement utilisés dans les parties chaudes de turbomoteurs d'avions et d'hélicoptères. Ces matériaux disposent d'excellentes propriétés mécaniques à haute température. Toutefois, des défauts ou des fissures peuvent apparaitre sur ces pièces, lors de leur élaboration par fonderie ou bien pendant leur durée en service, ce qui nécessite leur réparation. Cependant, les pièces constituées en IN738LC sont sujettes à de la fissuration au cours des procédés de réparation de type soudage. Il s'avère que le rechargement laser est une technique de fabrication additive prometteuse permettant de réparer des pièces abimées. Le présent travail consiste en l'étude de la réparabilité par projection de poudre de l'alliage IN738LC réputé non soudable. Cette étude comporte deux volets expérimentaux et numériques du rechargement de pièces en Inconel 738 LC au moyen du procédé CLAD. Pour cela, nous avons réalisé des essais de rechargement suivant plusieurs configurations illustrant les cas de réparations rencontrés industriellement. Deux mécanismes de fissuration distincts sont mis en évidence respectivement dans la zone affectée thermiquement du substrat et dans le dépôt. Une simulation multi-physique est également développée pour rendre compte des phénomènes thermiques, mécaniques et métallurgiques observés lors du rechargement laser. Ces simulations sont comparées à des mesures expérimentales pour validation. Enfin, ces outils de simulation sont utilisés afin de définir des critères numériques de risque de fissuration. En résumé, un préchauffage à haute température permet d'éliminer le risque de liquation et donc de fissures dans la ZAT ainsi que dans les dépôts, ce qui démontre qu'il est possible d'envisager une réparation sur cet alliage réputé non soudable. / Y' hardened nickel-based superalloys, such as Inconel 738 LC (IN738LC), are materials which are extensively used in hot sections parts of helicopter and aircraft engines. Those materials exhibit enhanced mechanical properties at high temperature. Nevertheless, cracking and several defects can occur on these parts during casting or during their service life. However, welding type repairing processes can lead to considerable cracking of IN738LC superalloy. It appears that laser cladding is a promising additive manufacturing technology which allows the repair of damaged parts. The present work main objective is aimed at investigating Inconel 738 LC repair by laser cladding. Both experimental and numerical aspects are studied for the repair of IN738LC by means of the CLAD process. Experimental laser clad deposits are produced under several configurations following industrial cases. Two distinct cracking mechanisms are identified in the heat-affected zone and within the deposit, respectively. A multi-physics simulation of laser cladding is developed in order to take into account thermal, mechanical and metallurgical phenomena. Simulation is compared to experimental measurements for validation. Finally, these numerical tools are used to define cracking risk criteria. In summary, a high preheating of the samples allows to suppress liquation and HAZ cracking, but also to obtain un-cracked deposit, which indicates that the repair of non-weldable alloys is possible.

The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald nuclear power plant representing the first generation of Russian-type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs of 4 units represent different material conditions as follows: • Irradiated (Unit 4), • irradiated and recovery annealed (Units 2 and 3), and • irradiated, recovery annealed and re-irradiated (Unit1). The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam. Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall. This report presents test results measured on the trepans from the beltline welding seam No. SN0.1.4. and forged base metal ring No. 0.3.1. of the Units 1 2 and 4 RPVs. The key part of the testing is focussed on the determination of the reference temperature T0 of the Master Curve (MC) approach following the ASTM standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined: • The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed. • KJc values of the weld metals generally followed the course of the MC though with a large scatter. • There was a large variation in the T0 values evaluated across the thickness of the multilayered welding seams. • The T0 measured on T-S oriented SE(B) specimens from different thickness locations of the welding seams strongly depended on the intrinsic structure along the crack front. • The reference temperature RT0 determined according to the “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs - VERLIFE” and the fracture toughness lower bound curve based thereon are applicable on the investigated weld metals. • A strong scatter of the fracture toughness KJc values of the recovery annealed and re-irradiated and the irradiated base metal of Unit 1 and 4, respectively is observed with clearly more than 2% of the values below the MC for 2% fracture probability. The application of the multimodal MC-based approach was more suitable and described the temperature dependence of the KJc values in a satisfactory manner. • It was demonstrated that T0 evaluated according to the SINTAP MC extension represented the brittle fraction of the data sets and is therefore suitable for the nonhomogeneous base metal. • The efficiency of the large-scale thermal annealing of the Greifswald WWER 440/V230 Unit 1 and 2 RPVs could be confirmed.

No description available.