[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. / [CA] 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]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/56148

This thesis reveals the tribological mechanisms behind the intrinsic low friction potential of the Co-based family of alloys called Stellites. Although being an established and important group of materials, a satisfactory explanation to why they exhibit low-friction properties under severe sliding conditions has not previously been found in the literature. The main part of this thesis is dedicated to the clarification of the tribological performance of Stellites in highly loaded sliding contact. The results should assist the development of Co-free alternatives, suitable for replacing Stellites in nuclear applications. Owing to their beneficial properties they are today the most commonly used material in the sealing surfaces on gate valves in the primary circuits of boiling water reactors (BWR). The underlying reason for the replacement in the nuclear applications is an undesired contribution to the background radiation level, originating from the Co in the Stellite surfaces. The Stellites mainly consist of Cr-rich carbides in a solid solution dominated by Co. The commonly used Stellite 6 and Stellite 21 were chosen as primary test materials and applied by laser cladding, providing a metallically bonded clad layer with a fine dendritic microstructure. By combining information from a series of dedicated tribological tests and modern high-resolution analysis instruments (e.g. SEM, XRD and TEM) available at the Ångström Laboratory at Uppsala University, the following conclusions can be made regarding the tribological performance of Stellites under high load sliding. Mechanisms. The (tested) Stellites form a thick deformation hardened layer, topped with a superficial easily sheared layer of hcp basal planes aligned parallel to the worn surface. The easy-shear layer is continually regenerated, replacing worn off material. Technical benefits. The Stellites offer low-friction properties thanks to their easily sheared surface layers. The risk of severe galling is also avoided by restricting shear and adhesive transfer to very thin superficial layers. In closed sliding contacts, self-generated protective layers formed by re-deposition of wear fragments are also offered.

Mechanical components operating at elevated temperatures can be identified in the aerospace industry as well as in metal forming. Hot stamping is a metal forming technique utilized for manufacturing high strength lightweight components for the automotive industry. Three types of Ni-based hardfacings doped with solid lubricants were manufactured using laser cladding. An additional hardfacing was also manufactured using the Ni-based alloy only as a reference. Solid lubricants added were Ag+WS2, WS2 and Cu+MoS2. These hardfacings were manufactured and tribologically evaluated for potential application in hot stamping tooling. Direct diode laser was used for the cladding process. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for characterization of the microstructure after deposition. Tribological testing was done using a reciprocating pin-on-disk tribometer under dry sliding conditions at temperatures in the range between RT and 600°C. Bearing steel ball and a flat pin made of the same material were used as counterbodies. Wear volume loss was measured using a 3D optical interferometer. For identification of the wear mechanisms SEM/EDS techniqueswere used. Formation of a lubricious CrxSy phase was detected after deposition, additionally encapsulation of silver particles by CrxSy was also observed. Reduction of friction coefficient was observed for every self-lubricating hardfacing compared to the reference. Lowest friction coefficient (0.23-0.3) was observed when the testing temperature was set to 400°C using a pin-on-flat configuration. Lowest wear rate was observed at 400°C, with the coating containing Ag and WS2 having a specific wear rate of 3.04 · 10−5mm3/Nm. The lubricity of the self-lubricating hardfacings was attributed to the CrxSy phase observed on the worn surface. At low to moderate temperatures abrasive wear is the main wear mechanism. At the highest testing temperature, oxidative wear was dominant.

Diploma thesis studies the layers created by laser cladding and method of testing abrasion resistance of these layers using the method of dynamic shock impactor. In the theoretical part describes laser technologies and their applications, hardness testing and methods of testing of coatings. Proposed by the mechanical testing of the selected materials were carried out and evaluated in the experimental part. The conclusion summarizes final results of the experiment.

The aim of my thesis is the analysis of properties of laser cladding. The theoretical part is focus on conventional methods of laser cladding, types and properties of lasers and its applications in industry. Then there is the description of preparing metallographic samples and its assessment, also there are types of wear enclosed. In the experimental part the nickel laser cladding were made by using semiconductor laser, in which the structure, the dilution, the EDS analysis and the hardness with respect to input parameters are assessed.

Ground engaging tools are very important components of machinery for agricultural applications, such as soil tillage. Ploughshare points serve as the first point of contact between ploughs and the hard minerals in the soil. One of the biggest problems that these tools encounter is abrasive wear, which decreases tillage quality, causes frequent tillage stops, increases fuel consumption of the tractor, and results in soil erosion. During this investigation, wear measurement, surface profiling and microscopic analysis were performed on three share point samples running in silica and granite sand – two points were commercial ones made of steel EN 22MnB5 and hardened. They served as commercial references. A third share point was also a commercial EN 22MnB5 one, but not hardened and laser cladded by a Ni-base + 50% carbide powder mix (Höganäs 1559–40 + 50% 4590). The abrasive wear testing was performed in an especially designed carousel tribometer. The laser cladded sample suffered only 30% of the wear shown in the EN 22MnB5 reference sample running under the same conditions. / Jordbearbetningsverktyg är väldigt viktiga komponenter i maskiner för jordbruksapplikationer, såsom jordbearbetning. Det är skärbladet på plogen, den så kallade plogbillen, som står för kontakten mellan plogen och de hårda mineralerna i jorden. Ett av de största problemen som dessa verktyg möter är abrasivnötning, som gör att verktygen efter en tid blir ineffektiva och bland annat orsakar frekventa stopp, erosion av marken och låg jordkvalité på grund av den försämrade jordbearbetningen samt ökar traktorns bränsleförbrukning. I denna undersökning testades provbitar av två olika slags stål runt i kvarts- respektive granitsand, och därefter utfördes mätningar på den nötning som skett samt även ytprofilering och mikroskopi gjordes. Testerna utfördes i kvartsand och i granitsand. Provbitar var två kommerciellt tillverkad härdade skärblad gjorda i stål EN 22MnB5. Ett tredje skärblad var också en komerciellt gjord i EN 22MnB5 stål men ohärdad och laserpåsvetsad med Ni-bas + 50% karbid pulverblandning (Höganäs 1559-40 +50% 4590). Provkörningarna utfördes i en speciellt utvecklad karusell-tribometer. Resultatet från provningarna visade att i fallet med laserpåsvetsade bitarna så var nötningen endast 30% relativt nötningen som EN 22MnB5-provet uppvisade under samma förutsättningar.

Orientador: Juno Gallego / Resumo: O desgaste abrasivo é uma das causas de falhas em equipamentos e responsável por prejuízos nos processos industriais. Uma técnica capaz de minimizar os efeitos deste fenômeno é a aplicação de revestimentos duros nas superfícies críticas. Recentemente foram desenvolvidos revestimentos contendo carbonetos de titânio formados pela fusão de misturas contendo cavacos das ligas ASTM F67 e ASTM F136 sobre peças de aço-carbono ASTM A-36. Após a aplicação do processo de soldagem GTAW obteve-se significativa fração volumétrica de TiC grosseiro com elevada dureza. No presente trabalho foi investigada a refusão dessas soldas pelo processo de soldagem a Laser Nd:YAG pulsado. A microestrutura das amostras foi analisada por difração de raios-X (DRX), microscopia eletrônica de varredura (MEV) e microdureza Vickers. A caracterização microestrutural mostrou que houve refinamento dos carbonetos de titânio (TiC) na matriz ferrítica refundida com o Laser, cujo principal efeito foi um endurecimento do metal de solda. A caracterização mecânica demonstrou um aumento na microdureza da superfície do material. Este comportamento favorece o uso da refusão a Laser para a melhoria da qualidade das superfícies que demandam maior resistência ao desgaste abrasivo. / Mestre

Le remplacement des alliages durs à base cobalt par des alliages à base fer suscite un intérêt croissant pour la protection anti-usure des pièces métalliques fonctionnant dans le circuit primaire d’une centrale nucléaire. Dans le cadre de cette thèse, une étude métallurgique détaillée a été effectuée sur des dépôts épais en Norem 02™ élaborés par le procédé de projection laser.Un affinement significatif de la microstructure du Norem 02™ a été obtenu après optimisation des paramètres du procédé (puissance laser, vitesse de balayage et débit de poudre), par rapport à un procédé concurrent par Plasma à Arc Transféré. Les essais tribologiques montrent que l’amélioration de la microstructure n’empêche cependant pas l’apparition du grippage à 300°C.La deuxième partie de cette étude a été consacrée à l’amélioration du Norem 02™ avec ajout de différents éléments chimiques. Le choix de ces ajouts adéquats a été validé grâce aux tests de frottement réalisés sur des échantillons en Norem 02™ modifié, sous haute contrainte mécanique (1 GPa) et à haute température (300°C). Parmi une dizaine d’éléments d’ajouts testés, l’ajout de titane a permis une transformation complète de la microstructure du Norem 02™. Cette transformation métallurgique a amélioré son comportement tribologique avec un faible coefficient de frottement (<0.3) à 300°C.L’origine de cette amélioration du comportement mécanique du Norem 02-Ti a été étudiée et expliquée par différentes analyses microstructurales (MO, MEB, EDS, EBSD) ainsi que des essais de traction sur des éprouvettes extraites des revêtements épais. / This study aims to substitute the cobalt-based hardfacing alloys with iron-based hardfacing alloys to protect mechanical parts operating in the primary circuit of a pressurized water reactor (PWR)Firstly, a detailed metallurgical study was carried out to characterize a thick deposit on Norem 02™ produced by the laser process (Direct Metal Deposition - DMD). Compared with a classical PTA process, a microstructure refinement was achieved after an optimization of process parameters (laser power, scanning speed and powder flow-rate). However, wear tests show that the improvement of the microstructure does not prevent the occurrence of galling at 300 ° C.The second part of this study is dedicated to Norem 02™ improvement with the addition of various chemical elements. The appropriate additions to this application have been validated by wear tests under high mechanical stress (1 GPa) and at high temperature (300°C). Among a dozen samples of modified Norem 02 ™, the addition of titanium was shown to provide a complete transformation of the initial Norem 02™’s microstructure. This metallurgical transformation improved its tribological behavior with a low friction coefficient (<0.3) obtained at 300 °C.Last, the origin of the mechanical behavior improvement of Norem 02-Ti was studied and explained by microstructural analysis (MO, MEB, EDS, EBSD) and tensile tests on specimens extracted from thick coatings.

Submitted by GABRIEL INÁCIO PONTIN null (gabrielguaira@hotmail.com) on 2017-08-15T18:00:10Z No. of bitstreams: 1 Dissertação Final - Gabriel Inacio Pontin.pdf: 2725651 bytes, checksum: f1433687bb33e3c16dd042c87cb686db (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-08-22T17:44:39Z (GMT) No. of bitstreams: 1 pontin_gi_me_ilha.pdf: 2725651 bytes, checksum: f1433687bb33e3c16dd042c87cb686db (MD5) / Made available in DSpace on 2017-08-22T17:44:39Z (GMT). No. of bitstreams: 1 pontin_gi_me_ilha.pdf: 2725651 bytes, checksum: f1433687bb33e3c16dd042c87cb686db (MD5) Previous issue date: 2017-07-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O desgaste abrasivo é uma das causas de falhas em equipamentos e responsável por prejuízos nos processos industriais. Uma técnica capaz de minimizar os efeitos deste fenômeno é a aplicação de revestimentos duros nas superfícies críticas. Recentemente foram desenvolvidos revestimentos contendo carbonetos de titânio formados pela fusão de misturas contendo cavacos das ligas ASTM F67 e ASTM F136 sobre peças de aço-carbono ASTM A-36. Após a aplicação do processo de soldagem GTAW obteve-se significativa fração volumétrica de TiC grosseiro com elevada dureza. No presente trabalho foi investigada a refusão dessas soldas pelo processo de soldagem a Laser Nd:YAG pulsado. A microestrutura das amostras foi analisada por difração de raios-X (DRX), microscopia eletrônica de varredura (MEV) e microdureza Vickers. A caracterização microestrutural mostrou que houve refinamento dos carbonetos de titânio (TiC) na matriz ferrítica refundida com o Laser, cujo principal efeito foi um endurecimento do metal de solda. A caracterização mecânica demonstrou um aumento na microdureza da superfície do material. Este comportamento favorece o uso da refusão a Laser para a melhoria da qualidade das superfícies que demandam maior resistência ao desgaste abrasivo. / The abrasive wear is one of the causes of failures in equipment and responsible for damages in industrial processes. A technique capable of minimizing the effects of this phenomenon is the application of hard coatings on critical surfaces. Recently, coatings containing titanium carbides produced by melting mixtures containing ASTM F67 and ASTM F136 chip blends on ASTM A-36 carbon steel parts have been developed. After an application of the GTAW get process, an important volumetric fraction of coarse TiC with high hardness was obtained. In the present work the remelts is investigated for welds by the pulsed Nd: YAG Laser process. A microstructure of the samples was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers microhardness. The microstructural characterization showed that there was a refinement of the titanium carbides (TiC) in the ferritic matrix remelt with the Laser, whose main effect was a hardening of the weld metal. The mechanical characterization showed an increase in the microhardness of the material surface. This behavior favors the use of laser cladding to improve the quality of surfaces that require high abrasive wear resistance.

The purpose of the project work was to build knowledge of the tribological behaviour of self-lubricating laser cladding, with and without external solid lubricant during conditions relevant for hot metal forming of aluminium. The materials used during the project were plates coated with a Ni-based self-lubricating clad and a reference sample of work tool steel. The self-lubricating laser clad was applied using a high power direct diode laser. The external solid lubricant used was a graphite dispersion. The external solid lubricant was applied on the samples using a spraying technique, leaving a dry layer of solid graphite on the plates. To test the tribological behaviour of the plates, linear reciprocating friction and wear tests were performed both under lubricated and dry conditions. During the dry tests, different surface roughness of the plates where investigated. The pins for the tribological test were made of AA7075. Parameters chosen for the tribological tests were based on conditions during hot forming of aluminium. After having taken images of the plates using scanning electron microscopy, and using a 3D optical profiler, the wear volume and material transfer was evaluated, and wear mechanism analysis was performed.   The tribological behaviour of polished Ni-based laser clad under dry conditions is comparable to that of the reference sample at its best performance. Using a mirror polished Ni-based laser clad under dry condition can be an option to not using external solid lubricant during hot forming of aluminium. Also, the surface roughness of the self-lubricating clad under dry conditions does not affect the coefficient of friction.