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Rozprawy doktorskie na temat "Alliages nickel-titane – Fragilisation par l'hydrogène"
Puydebois, Simon. "Fragilisation par l'hydrogène en fatigue oligocyclique de l'Inconel 718 issu d’un procédé de fabrication additive (LBM)". Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI011.
Pełny tekst źródłaThis study focuses on the hydrogen embrittlement sensitivity (HE) under cyclic loading of a nickel based alloy, Inconel 718, manufactured by the additive manufacturing process (AM). This material is used in some components of Ariane cryogenic engines that are manufactured by ArianeGroup. Some of these components are solicited under "hydrogen atmosphere", and the risk of embrittlement is a major problem.The metallurgical states of the Inconel 718 AM alloy have been characterized at different structural scales in order to observe a possible impact of the manufacturing process on the microstructure and discuss the possible consequences on the mechanical behaviour of the alloy underhydrogen pressure. Moreover, a forged alloy has also been studied for comparison.To discuss the mechanisms of hydrogen embrittlement in the material, it is first necessary to study the hydrogen behaviour in the material. Electrochemical and gaseous permeation analyses as well as TDS were performed to provide insights into the mechanisms of hydrogen diffusion. Fromthese results, the involvement of grain boundaries in the diffusion mechanisms and the effect of microstructural heterogeneities on the trapping mechanisms in this material have been discussed.On the other hand, the influence of hydrogen on the mechanical behaviour has been investigated under monotonic and cyclic loading in terms of elasto-viscoplastic behaviour, crack initiation process, fatigue crack propagation and toughness. In a first part, the tensile behaviour of the Inconel 718 AMunder hydrogen pressure has been considered. The effects of the loading rate on the mechanisms of embrittlement have been addressed. Moreover, interrupted tensile tests have been carried out to identify the effect of hydrogen on the viscoplastic behaviour and allowing to discuss hydrogen /plasticity interactions.The fatigue behaviour of Inconel 718 AM in the presence of hydrogen gas was investigated by cyclic tests for a 0.1 load ratio (R) under a 300 bar H2 at room temperature. It has been shown that hydrogen leads to a clear decrease of the number of cycles to rupture and to a change in failure mode.The impact of hydrogen has been evaluated on the fatigue crack initiation and propagation stages as well as on the toughness of the material.Finally, all the obtained results allowed a discussion of the hydrogen embrittlement sensitivity of the material, taking into account the hydrogen / plasticity interactions
Mahloul, Noureddine. "Influence des impuretés soufre et phosphore sur les propriétés des alliages fer-nickel-carbone : conséquences vis-à-vis des mécanismes de fragilisation par l'hydrogène". Châtenay-Malabry, Ecole centrale de Paris, 1996. http://www.theses.fr/1996ECAP0443.
Pełny tekst źródłaEscobar, Claros Cesar Adolfo. "Etude de bioactivité, résistance à la corrosion et comportement en fatigue de l'alliage Ti-12Mo-6Zr-2Fe après différents traitements de surface". Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI051.
Pełny tekst źródłaDemand for new implants with improved bioactivity, corrosion resistance, and optimal mechanical properties has been increasing considerably. In this sense, different surface treatments are applied in titanium alloys to improve their osteointegration process. Nevertheless, the developments of new bioactive surfaces could cause a considerable reduction in fatigue and corrosion strength leading to catastrophic failures in clinical use. For these reasons, this work studied the biocompatibility, corrosion and fatigue performance of Ti-12Mo-6Zr-2Fe alloy treated with three different surface modifications, namely, chemical surface treatment (CST), nanotubes (Nt) and nanopores (NP). Samples were immersed in simulated body fluid (SBF) solution during different periods, 0, 1, 7, and 14 days. After 14 days immersed in SBF, samples with CST showed high hydroxyapatite (HAp) formation; Likewise, samples with Nt and NP exhibited lower and moderated HAP formation, respectively. In samples without surface treatment was not observed HAp formation. The electrochemical behavior was studied through polarization curves and electrochemical impedance spectroscopy (EIS). Samples with Nt and NP displayed higher corrosion resistance and lower passivation current (Ipass) compared with untreated samples, after 14 days of immersion in SBF; samples with CST showed the worst corrosion performance for all the surface conditions studied. Furthermore, within the framework of electrochemical investigations, EIS results of Nt and NP samples showed a characteristic behavior that could not be modeled by traditional equivalent circuits. Thus, it was proposed a two-channel transmission line model for analyzing this impedance results, leading to a successful fitting of the EIS data. Finally, was observed a reduction of the fatigue resistance in the samples treated with NP and CST, associated with hydrogen embrittlement processes, due to the pick-up of hydrogen during the respective surface treatments
Araujo, Paulo. "Etude par indentation interfaciale de l'adhérence du revêtement Ni-Cr projeté thermiquement : influence de l'hydrogène et effets thermiques". Lille 1, 2000. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2000/50376-2000-200.pdf.
Pełny tekst źródłaLachiguer, Amani. "Effet de la diffusion de l'hydrogène sur le comportement thermomécanique des alliages à mémoire de forme (AMF) à base nickel-titane : caractérisation, modélisation et simulation numérique". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0384/document.
Pełny tekst źródłaA degradation of the mechanical properties of NiTi-based shape memory alloys superelastic archs, used in orthodontic treatments, was observed after hydrogen absorption. The effect of hydrogen was first investigated on the global behaviour of archs using tensile tests and secondly on the local behaviour using nanoindentation tests. A first approach to model the behavior of AMFs after hydrogen absorption has been proposed, by introducing the dependence of martensitic transformation parameters on the average hydrogen concentration, observed in the stress-strain curves obtained, in an existing dedicated model to SMA. A second approach is to propose a coupled thermomechanical model. A new thermodynamic potential is defined by introducing the chemical strain due to the presence of hydrogen and the interaction of the latter with martensite variants. Thermodynamic forces are deduced from this potential and balanced by involving mechanical, thermal and chemical dissipative phenomena. The exploitation of the proposed model required the development of a special finite element adopting the hydrogen concentration as an additional degree of freedom that takes into account the thermomechanical coupling and the proposed formulation of the thermal and chemical equilibrium
Wen, Jing. "Effet de l'hydrogène sur la microstructure et la déformation en laminage à froid du titane de pureté commerciale et d'un alliage de titane β métastable". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0167/document.
Pełny tekst źródłaDue to an attractive combination of physical, chemical and mechanical properties, titanium and titanium alloys have become promising candidates in the field of chemical industry, aerospace and biomedical materials. During manufacturing procedures and applications, components are exposed to environments that can act as sources of hydrogen. Therefore, understanding their interaction with hydrogen upon various mechanical/thermal processing is important so that their properties and performance can be controlled and reliably predicted. With the aim of enhancing the properties and performance of titanium and reducing the cost of manufacturing products, the present work is primarily focusing on the effect of hydrogen on the cold rolling behavior and the subsequent annealing of titanium and titanium alloy characterized by different crystalline structure, i.e. hexagonal and body cubic centered (bcc) structure for the commercial pure titanium Ti50A and metastable β-titanium alloy β-21S, respectively. Since the microstructure of titanium and its alloys is the governing factor that determines their properties and performance, the microstructural evolution in the presence of hydrogen upon various procedures was analyzed by combination of XRD, SEM-EBSD and TEM. The introduction of hydrogen in Ti50A by electrolytic method induced the precipitation of two types of hydrides (δ-TiHx, ε-TiH2) in the phase matrix, and it was found that the volume fraction of these hydrides increased as the charging time increased. Five orientation relationships (ORs), three of them being new orientation relationships ever reported, between the -phase and the hydride δ-TiHx were determined. Moreover, the correlation between the rolling texture and the hydride precipitation was also established. It was found that the existence of the rolling texture facilitated the precipitation of δ-hydride following the OR2-type orientation relationship. X-ray analyses revealed a broadening of the diffraction peaks corresponding to the phase, indicating a increase of the dislocation density, these dislocations being necessary to accommodate the lattice misfit between hydrides and the matrix. Under compression loading, the observation of slip traces and tension twin {10 2}< 011> TT1 in the -grains containing hydrides, suggested that the hydrides had a certain ability to accommodate the imposed shear strain, depending on the orientation relationships between the matrix and the hydrides as well as on their thickness. Although no correlation between the nucleation of twinning and the hydride could be established in this study, the hydrides seemed to play an important role on the development of twinning deformation. The effects of hydrogen on the cold rolling behavior in Ti50A showed that, the formation of TT1tension twins can be facilitated due to the increase of the c/a ratio owing to the hydrogen addition and the existence of local stresses generated by the precipitation of hydrides. The refinement of the microstructure was also observed in the hydrogenated Ti50A-H suggesting that the presence of hydrides can enhance the generation of high angle boundaries (HABs). In addition, the formation of numerous geometrically necessary dislocations (GND) allowing the accommodation of the strain incompatibility between the hydride and matrix could be worked out by SEM-EBSD, which also confirmed analyses of the X-ray traces. In the case of β-21S alloy, with bcc structure that can accommodate a larger concentration of interstitial atoms, hydrogen was introduced by gas method. The effect of hydrogen on the microstructure was found to be closely related to the hydrogen concentration. In the range of hydrogen/metal ratio 0.052 < H/M < 0.300, the microstructure consisting of the single β-phase showed that the dissolved hydrogen atoms expanded the bcc β-lattice and suppressed the decomposition of the β phase upon cooling [...]
Ulff, Nicolas. "Analyse et prise en compte des effets de l’hydrogène sur le comportement thermomécanique des AMF à base NiTi". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0308.
Pełny tekst źródłaAdvances in the many fields that form medicine have many origins, one of them being the evolution of the materials used. In particular, the rise of the intelligent materials enables to consider new technical solutions, or to significantly improve existing devices. Shape memory alloys belong to this family of intelligent materials, due to their temperature dependent behavior. Their mechanical behavior is therefore more complex compared to more well-known materials such as steels. This allows, for example, to achieve a level of reversible deformation of the order of several percent. One of the first applications of these materials concerns the field of orthodontics, with the development of orthodontic wire in NiTi shape memory alloy. Its interest is to take advantage of the application of an almost constant force during the treatment. One problem with which dentists are confronted is due to the presence of hydrogen which leads to premature rupture and degradation of NiTi wires mechanical properties during orthodontic treatments. The brittle nature of the rupture is an indication of the multi-physical origin of this issue. This PhD proposal will focus on the analysis of these hydrogen effects on the thermomechanical behavior of Shape Memory Alloys (SMAs) in order to develop a finite element model. For that end, experimental characterizations will be carried out and analysis of obtained results will allow to formulate an adapted coupled chemo-thermo-mechanical constitutive model. This behavior model will be integrated in two special finite elements (2D and 3D) with coupled degrees of freedom (thermal, mechanical and chemical degrees of freedom). These elements will be implemented in the Abaqus code via the subroutine UEL. The obtained numerical tool will allow to analyze the effect of hydrogen diffusion on the performance of SMA-based orthodontic arches. These finite element predictions will be confronted with experimental observations
Poloni, Alexandre. "Étude de la sensibilité à la fragilisation par l’hydrogène de deux alliages de titane, le T40 et le TA6V ELI, sous polarisation cathodique en eau de mer par une approche locale de la rupture". Thesis, La Rochelle, 2020. http://www.theses.fr/2020LAROS003.
Pełny tekst źródłaThis study aims at understanding the hydrogen absorption mechanisms in titanium under cathodic polarization in seawater and then to provide risk assessments for engineers. The single-phase T40 and the two-phase TA6V ELI alloys were employed to study the influence of α and β phases as well as their distribution on the hydrogen embrittlement mechanisms. Hydrogen absorption kinetics were studied for several cathodic potentials in artificial seawater, while other electrolytes were used to validate some hypothesis. These kinetics are observed to be similar between the two alloys despite the differences in the absorption mechanisms and the hydrogen concentration at saturation. Then, this work investigates the role of the metallographic structure on the localisation of hydrides. The evolutions of the mechanical properties were studied by tensile tests on various orientations of solicitation, hydrogen concentrations and notches. As a result, these properties are observed to depend on the hydrogen concentration and the hydrides location. Models by finite elements were also used to determine local mechanical criterions of internal damage and fracture in term of hydrostatic stress and equivalent plastic strain. It allowed us to establish an abacus linking the evolutions of the mechanical properties to the hydrogen concentration. Moreover, this work also results in the determination of a maximum threshold of the cathodic potential at -1,1 V/SCE by comparing the laboratory results with those of on-site galvanic coupling by sacrificial anodes in natural seawater