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Les objectifs de cette thèse sont d’établir les corrélations entre l’histoire thermomécanique, la microstructure et la perméabilité aux ultrasons de l’Udimet 720.La première approche est expérimentale et concerne l’étude de l’influence des paramètres thermomécaniques de mise en forme (température, vitesse de déformation et taux de déformation) sur l’évolution microstructurale, et l’identification des mécanismes de recristallisation associés. En parallèle, une modélisation mésoscopique du forgeage a été développée en couplant un modèle cristallin de déformation de type éléments finis et un modèle de recristallisation basé sur la méthode des automates cellulaires, afin de prévoir l’évolution microstructurale en fonction de la microstructure initiale et des conditions thermomécaniques.Une dernière partie traite de l’identification des paramètres microstructuraux néfastes à la perméabilité aux ultrasons, et de la modélisation de la propagation des ultrasons dans un matériau polycristallin pour quantifier l’influence des désorientations et de la taille des grains. / This works deals with the correlations between the thermomechanical process, the microstructure and the permeability to ultrasonic waves of the Udimet 720 superalloy. The first approach is experimental and concerns the influence of the thermomechanical parameters (temperature, strain rate and deformation ratio) on the microstructure evolution. In particular, this study focuses on the identification of recrystallization mechanisms. In parallel, a mesoscopic crystalline modelling of deformation implemented in a finite element code coupled to a recrystallization Cellular Automaton code has been developed and applied to forging processes. The model predicts the evolution of different experimental microstructures as a function of thermomechanical parameters.The last part deals with the identification of unfavorable parameters of the microstructure on the ultrasonic permeation. Moreover a modeling of the ultrasounds propagation in a polycrystalline material is proposed to quantify the effects of the average grain size and the grain misorientation distribution.

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O objetivo do presente trabalho é avaliar a microestrutura e as propriedades da superliga MAR-M247 modificada com nióbio (composição nominal: 10,2% em peso Co; 10,2W; 8,5Cr; 5,6Al; 1,6Nb; 1,4Hf; 1,1Ti; 0,7Mo; 0,15C; 0,06Zr; 0,015B; Ni balanço) submetida a diferentes rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica). O material foi produzido por fusão por indução a vácuo na empresa Açotécnica S.A. (Jandira/SP). As amostras no estado bruto de fusão e tratadas termicamente (solubilização e envelhecimento em uma e duas etapas por diferentes temperaturas e tempos) foram analisadas por MEV e MEV-FEG com EDS. Também foram realizadas medidas de análise térmica diferencial (DTA), dureza, difração de raios X e simulações em Thermo-Calc, JMatPro e PandaT. Em outra parte desta tese, realizada no Instituto Superior Técnico em Lisboa/Portugal, as amostras da superliga MAR-M247(Nb) foram fundidas pela técnica de laser melting e caracterizadas por MEV-FEG, EDS, dureza e EBSD, além de diversos cálculos envolvendo os parâmetros de processo utilizados. Além disso, os experimentos de deposição de pós de NiCr, NiCrAl e NiCrAlY no substrato da superliga MAR-M247(Nb) utilizando a técnica de laser cladding permitiram calcular alguns parâmetros geométricos e analisar a microestrutura dos depósitos (MEV-FEG, EDS e medidas de dureza) após o processamento e os tratamentos térmicos. Na última parte desta tese, foram realizados ensaios de oxidação isotérmica a 1000°C por até 216 horas (ar estático) na superliga MAR-M247(Nb). As amostras oxidadas (superfície e seção transversal) foram analisadas por MEV, medidas por EDS (pontual, line scan e mapeamento) e difração de raios X, além de cálculos das constantes kp e n. Os resultados desta tese permitem comparar as temperturas solvus de ?\' (1210oC), solidus (1310oC) e liquidus (1360oC) obtidas por Thermo-Calc com as temperaturas solvus de ?\' (1238oC), de fusão incipiente (1281oC) e liquidus (1370oC) obtidas por experimentos de análise térmica diferencial para a superliga MAR-M247(Nb). A microestrutura da superliga MARM247(Nb) no estado bruto de fusão é dendrítica com carbetos de W, Ti, Nb e Hf nas regiões interdendríticas. O tratamento de solubilização a 1260°C por 8 horas foi escolhido como condição ideal, enquanto que o tratamento de envelhecimento a 980°C por 80 horas apresentou o maior tamanho de partícula de ?\'. O material fundido pela técnica de laser melting apresentou trincas devido à formação de regiões eutéticas ?/?\' de baixo ponto de fusão. A microestrutura dos depósitos de NiCr, NiCrAl e NiCrAlY as clad é dendrítica com a fase solução sólida ?-Ni(Cr), além de poros e óxidos/carbetos. O depósito de NiCrAlY possui fases ricas em ítrio. A amostra de NiCr tratada 1150oC por 50 horas não apresentou evidências de segregação enquanto que as amostras de NiCrAl e NiCrAlY apresentaram a fase ?\' precipitada fina e uniformemente após tratamento térmico a 1100 e 1150°C por 10 e 50 horas. A estrutura da camada óxida da superliga MAR-M247(Nb) submetida a ensaios de oxidação isotérmica a 1000°C por até 216 horas consiste de NiO na camada externa, Cr2O3, TiO2, CoO, espinélios de (Ni,Co)Cr2O4 e partículas de W20O58 e HfO2 na camada intermediária e Al2O3 na camada interna. Finalmente, conclui-se que a microestrutura e as propriedades da superliga MAR-M247(Nb) são alteradas quando as rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica) mudam. / The aim of this work is to evaluate the microstructure and the properties of the niobiummodified MAR-M247 superalloy (nominal composition: 10.2 weight percent of Co; 10.2W; 8.5Cr; 5.6Al; 1.6Nb; 1.4Hf; 1.1Ti; 0.7Mo; 0.15C; 0.06Zr; 0.015B; Ni balance) submitted to different processing routes (heat-treatment, laser cladding and isothermal oxidation). The material was produced by vacuum induction melting at Açotécnica Company (Jandira/SP). The as-cast and heat-treated samples (solution and aging in one and two steps at different temperatures and times) were analyzed in SEM and FEG-SEM with EDX. Differential thermal analysis (DTA), hardness, X-ray diffraction and simulations with Thermo-Calc, JMatPro and PandaT were performed as well. In another part of this thesis, performed at Instituto Superior Técnico in Lisbon/Portugal, the samples of the MAR-M247(Nb) superalloy were produced by laser melting technique and characterized by FEG-SEM, EDX, hardness, and EBSD, besides some calculations involving the process parameters utilized. Furthermore, the experiments of NiCr, NiCrAl and NiCrAlY powder deposition on the substrate of MAR-M247(Nb) superalloy utilizing the laser cladding technique allowed the calculation of some geometric parameters, as well as the analysis of the microstructure of the deposits (FEG-SEM, EDX and hardness) after the processing and the heat-treatments. In the last part of this work, experiments of isothermal oxidation at 1000°C for up to 216 hours (static air) were performed in the MAR-M247(Nb) superalloy. The oxidized samples (surface and cross-section) were analyzed by SEM, EDX (punctual, line scan and mapping) and X-ray diffraction, besides some calculations of kp and n constants. The results of this thesis allow comparing the ?\' solvus (1210oC), solidus (1310oC) and liquidus (1360oC) temperatures obtained by Thermo-Calc with the ?\' solvus (1238oC), incipient melting (1281oC) and liquidus (1370oC) temperatures obtained by differential thermal analysis experiments of the MARM247(Nb) superalloy. The microstructure of the as-cast MAR-M247(Nb) superalloy is dendritic with W, Ti, Nb and Hf carbides in the interdendritic regions. The solution heattreatment at 1260°C for 8 hours was chosen as the ideal condition, whilst the aging heattreatment at 980°C for 80 hours presented the highest ?\' particle size. The material processed by laser melting technique showed cracks due to formation of low melting point ?/?\' eutectic regions. The microstructure of the NiCr, NiCrAl and NiCrAlY as clad deposits is dendritic with the ?-Ni(Cr) solid solution phase, besides pores and oxides/carbides. The NiCrAlY deposit has yttrium-rich phases. The NiCr sample heattreated at 1150oC for 50 hours didn\'t present evidences of segregation whilst the NiCrAl and NiCrAlY samples presented fine and uniform ?\' phase precipitated after the heattreatment at 1100 and 1150°C for 10 and 50 hours. The structure of the oxide layer of the MAR-M247(Nb) superalloy submitted to isothermal oxidation experiments at 1000°C for up to 216 hours has NiO in the outer layer, Cr2O3, TiO2, CoO, (Ni,Co)Cr2O4 spinels and W20O58 and HfO2 particles in the intermediate layer, and Al2O3 in the inner layer. Finally, it is possible to conclude that the microstructure and the properties of the MAR-M247(Nb) superalloy are modified when the processing routes (heat-treatment, laser cladding and isothermal oxidation) are changed.

Additive manufacturing (AM) is a general name used for manufacturing methods which have the capabilities of producing components directly from 3D computeraided design (CAD) data by adding material layer-by-layer until a final componentis achieved. Included here are powder bed technologies, laminated object manufacturing and deposition technologies. The latter technology is used in this study. Laser Metal Powder Deposition (LMPD) is an AM method which builds components by fusing metallic powder together with a metallic substrate, using a laser as energy source. The powder is supplied to the melt-pool, which is created by the laser, through a powder nozzle which can be lateral or coaxial. Both the powder nozzle and laser are mounted on a guiding system, normally a computer numerical control (CNC) machine or a robot. LMPD has lately gained attentionas a manufacturing method which can add features to semi-finished components or as a repair method. LMPD introduce a low heat input compared to conventional arc welding methods and is therefore well suited in, for instance, repair of sensitive parts where too much heating compromises the integrity of the part. The main part of this study has been focused on correlating the main process parameters to effects found in the material which in this project is the superalloy Alloy 718. It has been found that the most influential process parameters are the laser power, scanning speed, powder feeding rate and powder standoff distance.These process parameters have a significant effect on the temperature history ofthe material which, among others, affects the grain structure, phase transformation, and cracking susceptibility of the material. To further understand the effects found in the material, temperature measurements has been conducted using a temperature measurement method developed and evaluated in this project. This method utilizes a thin stainless steel sheet to shield the thermocouple from the laser light. This has proved to reduce the influence of the laser energy absorbed by the thermocouples.

The master`s thesis deal with analysis of machining technology of the bolt from the superalloy Ni80TiAl for the company Sanborn a.s. The aim of the thesis is the project of new technology by usage of new tool, indexable inserts and cutting conditions. The results are speedup of the roughing operation, reduction of the manufacturing cost and the product price.

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.

This thesis describes innovative methods used to predict high-stress amplitude, low cycle fatigue (LCF) behavior of a material commonly used in gas turbine blade design with the absence of such data. A combination of extrapolation and estimation techniques from both prior and current studies has been explored with the goal of developing a method to accurately characterize such high-temperature fatigue of IN738LC, a dual-phase Ni-base superalloy. A method capable of predicting high-stress (or strain) amplitude fatigue from incessantly available low-stress amplitude, high cycle fatigue (HCF) would lower the costs of inspection, repair, and replacement on certain turbine components. Three sets of experimental data at different temperatures are used to evaluate and examine the validity of extrapolation methods such as anchor points and hysteresis energy trends. Stemming from extrapolation techniques developed earlier by Coffin, Manson, and Basquin, the techniques exercised in this study purely implement tensile test and HCF data with limited plastic strain during the estimation processes. A standard practice in engineering design necessitates mechanical testing closely resembling planned service conditions; for design against fatigue failure, HCF and tensile data are the experiments of choice. High stress amplitude data points approaching the ultimate strength of the material were added to the pre-existing HCF base data to achieve a full-range data set that could be used to test the legitimacy of the different prediction methods. While some methods proved to be useful for bounding estimates, others provided for superior estimation.

Additive manufacturing (AM) is a general name used for production methodswhich have the capabilities of producing components directly from 3D computeraided design (CAD) data by adding material layer-by-layer until a final component is achieved. Included here are powder bed technologies, laminated object manufacturing and deposition technologies. The latter technology is used in this study.Laser metal deposition using powder as an additive (LMD-p) is an AM processwhich uses a multi-axis computer numerical control (CNC) machine or robot toguide the laser beam and powder nozzle over the deposition surface. Thecomponent is built by depositing adjacent beads layer by layer until thecomponent is completed. LMD-p has lately gained attention as a manufacturing method which can add features to semi-finished components or as a repair method. LMD-p introduce a low heat input compared to arc welding methods and is therefore well suited in applications where a low heat input is of an essence. For instance, in repair of sensitive parts where too much heating compromises the integrity of the part.The main part of this study has been focused on correlating the main processparameters to effects found in the material which in this project is the superalloy Alloy 718. It has been found that the most influential process parameters are the laser power, scanning speed, powder feeding rate and powder standoff distance and that these parameters has a significant effect on the dimensionalcharacteristics of the material such as height and width of a single deposit as wellas the straightness of the top surface and the penetration depth.To further understand the effects found in the material, temperaturemeasurements has been conducted using a temperature measurement methoddeveloped and evaluated in this project. This method utilizes a thin stainless steel sheet to shield the thermocouple from the laser light. This has proved to reduce the influence of the emitted laser light on the thermocouples.

No description available.