Dissertationen zum Thema „Alliages réfractaires – Fissuration“
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Chassaigne, Jean-Christophe. „Fissuration à hautes températures du superalliage base nickel N18 élaboré par métallurgie des poudres : Etude du couplage mécanique-environnement en pointe de fissure“. Paris, ENMP, 1997. http://www.theses.fr/1997ENMPA001.
Der volle Inhalt der QuelleBennouna, Abdouh. „Etude de l'oxydation du superalliage réfractaire inconel 718 (NC19F eNb) : rôle des précipités de carbure de niobium et de phase delta (Ni 3Nb)“. Toulouse, INPT, 1986. http://www.theses.fr/1986INPT005G.
Der volle Inhalt der QuelleRézaï-Aria, Farhad. „Fatigue thermique et fatigue isotherme d'un superalliage à base de cobalt : étude métallurgique de l'endommagement et modélisation“. Paris 11, 1986. http://www.theses.fr/1986PA112377.
Der volle Inhalt der QuelleMolins, Régine. „Oxydation de superalliages à base de nickel : identification des mécanismes et conséquences sur le mode de propagation des fissures en fatigue à haute température“. Paris, ENMP, 1995. http://www.theses.fr/1995ENMP0526.
Der volle Inhalt der QuellePonnelle, Sylvain. „Propagation des fissures par fatigue a haute temperature dans l'Inconel 718 : effets de microstructure et de chargements complexes“. Paris, ENMP, 2001. http://www.theses.fr/2001ENMP1003.
Der volle Inhalt der QuelleDoghri, Anis. „Vers une maîtrise de la réparation par le procédé CLAD de pièces aéronautiques en Inconel 738 LC : compréhension des mécanismes de fissuration et modélisations associées“. Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0112.
Der volle Inhalt der QuelleY' 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
Branza, Traian. „Rechargement par soudage d'aciers réfractaires moulés : application à la réparation des matrices de formage superplastique“. Toulouse 3, 2005. http://www.theses.fr/2005TOU30246.
Der volle Inhalt der QuelleSuperplastic forming (SPF) of TA6V aeronautical sheets is performed at temperatures close to 900°C. Forming tools, manufactured with heat resistant cast steels, are exposed to highly severe thermomechanical stress likely to cause their damage. The purpose of this study is to develop weld repair techniques for SPF dies and to characterize the weld joints using microstructural investigations and mechanical testing. The parameters of welding and filling are optimized in order to guarantee the best quality of the welded zone. The influence that parameters related to the weld repair process and the materials used, have on the propensity of the cast steels to crack during welding, is investigated. These analyses are performed on the macrographs of the welded zone and also using image analysis technique. For the very deep groove, two weld repair techniques are developed, the surface remelting of the material and the buttering. The mechanical performances of the repaired structures are evaluated using low cycle fatigue tests. The mechanical behaviour of the weld repair joints is also investigated using numerical simulation
Govaere, Adèle. „Impact des carbures sur la variabilité des propriétés en fatigue de superalliages pour disques“. Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0020.
Der volle Inhalt der QuelleNowadays, original engine makers are challenged by the environmental requirements imposing drastic decrease of CO2 and NOx emissions. It leads to the development of γ/γ′ nickel-based superalloys to ensure good tensile and fatigue properties and a good oxidation behavior of turbine discs. AD730TM was elaborated for applications up to 700°C and the crack initiation and propagation mechanisms this alloy need to be investigated. Non-metallic inclusions are brittle elements that are sensitive to oxidation. They can act as stress concentration sites and can lead to crack initiation. Low cycle fatigue tests were performed at 450°C and 700°C to determine the tests conditions promoting a crack initiation from such inclusions. Fractographic analyzes revealed that inclusions lead to the specimen fracture when the environmental effects are limited and at high strain or stress ranges.In order to better understand the parameters promoting inclusions cracking, oxidation and in situ tensile tests in a SEM chamber were performed. They highlighted an important volume expansion and the cracking of niobium oxides. A stress threshold necessary to crack inclusions was also determined. To improve the fatigue tests understanding, crack propagation tests were carried out to estimate the crack initiation time according to the temperature and the stress range applied. This crack initiation time is shorter when the cracks initiate within inclusions
Doghri, Anis. „Vers une maîtrise de la réparation par le procédé CLAD de pièces aéronautiques en Inconel 738 LC : compréhension des mécanismes de fissuration et modélisations associées“. Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0112/document.
Der volle Inhalt der QuelleY' 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
Mataveli, Suave Lorena. „High Temperature Durability of DS200+Hf Alloy“. Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0032/document.
Der volle Inhalt der QuelleThe anisotropy in mechanical behavior of the directionally solidified DS200+Hf alloy and the damage mechanisms have been investigated between 650°C and1100°C. Single-crystalline specimens of the same alloy have also been used to get a better understanding of the anisotropy in mechanical properties and durability. Tension, creep, low-cycle fatigue (LCF), dwell-fatigue and crack propagation tests have been performed and analyzed by SEM observations to better understand the damage modes in this alloy. At 650°C, a considerable creep (and LCF) life anisotropy is observed while almost no anisotropy remains at 1100°C in creep. The γ rafting is mainly responsible for this decrease in creep anisotropy and for theincrease in creep rate in dwell-fatigue. An intergranular fracture mode has been observed for ail kind of solicitation along transverse direction, mainly due to the presence of grain boundary particles such as carbides. These carbides are also the main crack initiation sites in LCF at 650°C and at 900°C. At high temperature (900°C), oxidation not only controls the crack initiation mechanisms by inducing surface carbides cracking, but it also affects the crack propagation through a combined localized γ depletion and crack tip blunting, leading ove ra li to a higher crack propagation threshold. Such a behavior is not observed in high vacuum and surface carbides are no more the main crack initiation sites. lt is shown that at low temperature during transverse creep testing (750°C), highly misoriented grain boundaries, having one grain favorably oriented for single slip and lattice rotation, are the most critical ones
Mouelle, Loïc. „Caractérisation et modélisation d’assemblages de tôles en acier inoxydable austénitique brasées et soudées pour des applications d’échangeurs de chaleur“. Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0068.
Der volle Inhalt der QuelleThe aim of the study relies on an industrial context, in which, high pressure Plate Fin Heat Exchangers (PFHE) made of austenitic stainless steel 316L, are brazed with Ni-Cr-Fe-Si (BNi-5) alloy, then followed by dissimilar multipass TIG (Tungsten Inert Gas) welding process with nickel-based superalloy Inconel 625, used as filler metal. Due to their heterogeneous microstructure and chemical composition, fractures of brazed joints may appear during the welding of brazed assembly. Firstly, microstructural and chemical characterizations are made at the bonding interface between base metal, brazed joints and weld beads, to understand the fracture phenomena. Results show that a brazing cycle promoting the formation of γ-Ni single phase brazed joints, allows avoiding the fracture of brazed joints during welding. However, intergranular Si may involve the formation of hot cracks in brazed joints located in HAZ. The study of GOS (Grain Orientation Spread) through EBSD measurements, allows quantifying the magnitude and spatial distribution of plastic deformation in the HAZ after welding. A welding energy under 1100 J/mm limits the plastic deformation of brazed assemblies. Nanoindentation and tensile tests are also carried out at room temperature to determine the mechanical properties of brazed assembly. The results of tensile tests show that fracture occurs in the 316L, when brazed joints are formed by a γ-Ni single phase. Secondly, an original thermodynamically consistent modeling approach, dedicated to welding applications, is presented to describe the phenomenon of hardening recovery in metals during annealing heat treatment. The constitutive equations are based on a classical thermo-elasto-plastic formulation which is enhanced by a new recovery variable counterbalancing the effect of the hardening through a temperature-dependent evolution law. The model is implemented into the FE solver ABAQUS/Standard with the help of a User Material subroutine (UMAT). The identification of the model parameters is achieved through experimental compressive tests and heat treatments on 316L austenitic stainless steel. In addition, to evaluate the capabilities of the model, residual stress measurements are carried out on a welded plate and compared to values computed by numerical simulation. The obtained values match the experimental measurements. Finally, three-dimensional simulations of multipass welding are realized to estimate the stress and deformation fields during TIG welding process of a heat exchanger. The maximum stress in HAZ may reach 600 MPa during the cooling of the first welding pass. Thus, the results of numerical simulation are in agreements with the experimental observations, indicating that in case of fracture of brazed joints during welding, the fracture occurs from the cooling of the first passes
Larrouy, Baptiste. „Mécanismes de déformation et d'amorçage de fissures dans l'alliage Udimet™ 720Li en relation avec les paramètres microstructuraux“. Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2014. http://www.theses.fr/2014ESMA0019/document.
Der volle Inhalt der QuelleThis study contributes to the understanding of the deformation and damage mechanisms in a Nickelbasedsuperalloy (the Udimet 720Li) used for the manufacturing of aeroengines high pressure turbinedisks submitted to monotonic and cyclic loadings at temperatures below 500 °C under service conditions.Fatigue crack initiation at 20 °C and 465 °C was systematically observed at large crystallographic facetswhatever the microstructure. An extensive quantitative study of the slip activity at the surface showed thatcrack initiation results from a difficult slip transmission between neighbouring grains. In more details, alocalized crystallographic rotation confined in micro-volumes detected at the tip of slip bands interactingwith the grain boundary were identified to trigger crack initiation.The crystallographic configurations favouring such a process are closely related to the TWIST anglebetween active slip systems on each side of the grain boundary and to a dense and fine precipitationconfining the plasticity.Mots-clés
Lambourg, Aurélien. „Étude de la progression des fissures de fatigue à partir d’anomalie de surface dans une entaille“. Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2019. http://www.theses.fr/2019ESMA0023.
Der volle Inhalt der QuelleAircraft engine manufacturers have to meet with new certification requirements in damage tolerance. Thus they have to demonstrate that the presence of surface anomalies introduced during maintenance operations in critical areas does not lead to failure during service life. This study was undertaken in this framework to characterize the harmfulness of dent-type surface anomalies in a stress gradient with local plasticity, on the fatigue life of the Direct Aged Inconel 718Nickel based superalloy. A detailed experimental and numerical study have been conducted for a better control of the direct current potential drop (DCPD) technique used to monitor the crack initiation and the crack depth measurement in a stress gradient with plasticity. The method was improved in particular by taking into account the conductivity variation induced by plasticity and a new approach of the DCPD post-treatment, using two heats tints during propagation, was proposed. This method has a higher accuracy and reproducibility than without the use of heat tint on the crack measurement. Meanwhile different types of anomalies have been used to assess the respective influence of geometry and residual stress in relation with the presence of a macroscopic stress gradient on crack growth. It was thus shown that crack initiation is slow in the case of polished and FIB anomalies in comparison to EDM and indent anomalies, because of their geometry and residual stresses. Despite a fast crack initiation, the dent-type anomaly presents a reduced crack growth rate during the initial propagation stage because of the residual stresses. Furthermore, a singular crack shape was evidenced in that case by means of heat tinting, with a shape of mushroom. Different methods have been implemented to quantify service life and predict crack front shape. This study has shown that the shape factor is dependent, among others, of the applied maximal stress and of the stress ratio, and that crack growth rate can be slowed down near the anomaly edge by a stress concentrator effect. Finally, different simulation strategies provide some explanation about the origin of the mushroom shape of the crack front
Doremus, Luc. „Etude expérimentale et modélisaton de la micro-propagation à partir d'anomalies de surface dans l'Inconel 718DA“. Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2014. http://www.theses.fr/2014ESMA0003/document.
Der volle Inhalt der QuelleAircraft engine manufacturers have to meet with new certification requirements in damage tolerance. In particular they have to demonstrate that the presence of small surface anomalies introduced on engine parts during maintenance operations in critical areas do not lead to failure during service life. This study was undertaken to characterize the harmfulness of scratch and dent type surface anomalies on the fatigue life of the Nickel based superalloy Direct Aged Inconel 718.The influence of maximal stress, temperature, type and depth of surface anomalies was evaluated in a large series of experiments. An experimental and numerical in-depth study of the potential drop technique led to a good control of this tool and allowed to efficiently detect crack initiation and to measure the crack propagation. Indeed, the use of this technique has revealed that the crack initiation from scratches and dents is very rapid but that the first stages of crack growth are delayed.Specific tests were then performed to identify the physical origin of the observed phenomenon. A heat treatment was used to show that the compressive residual stresses created during the introduction process of surface anomalies have a great influence on the fatigue life. Different experimental and numerical techniques were used to quantify these residual stresses and some directions were identified to establish a new model able to predict the fatigue life of scratch and dent type surface anomalies
Gourdin, Stéphane. „Etude expérimentale et modélisation de la propagation de fissures à partir d'anomalies de surface dans le René 65“. Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2015. http://www.theses.fr/2015ESMA0015/document.
Der volle Inhalt der QuelleAnomalies, introduced during maintenance operations, are not critical for in-service life of a component. This study was undertaken to characterise the harmfulness of scratch and dent anomalies on the fatigue behaviour of the nickel based superalloy René 65.In order to separate the effects of the geometry and the residual stresses, scratches and dents have the same V-type profile. A 3 points DCPD method has been used to improve the detection of the initiation and also to have information about the crack front morphology. Experimental results showed that the initiation fatigue life is short and a slowdown of the fatigue crack growth in the first stages. We also observed, thanks to heat tints marking, aparticular crack front morphology for cracks initiating from scratches. Heat treatment has been used and showed that the heterogeneous mechanical field induced by the fabrication of the anomalies controls the fatigue life and that it constitutes one of the parameters to be taken into account in a future modelling. A modelling strategy of the crack propagation from dent anomalies has been developed. This model is based on the knowledge of the residual stress field by finite elements simulations, and the application of the calculated stress field in a numerical crackgrowth model. The results confirmed that the residual stresses were the physical source of the fatigue crack growth slow-down and also responsible for the evolution of the crack front morphology. They also allowed us to identify the parameters which have to be measured during non-destructive testing