Two aerospace superalloys, Inconel 718 and IMI 318, were machined with different grades of PVD (KC730 and KC732) and CVD (KC950) coated tools in order to evaluate their performance under various cutting conditions and to further investigate the effect of the machining conditions on surface finish and surface integrity of the work materials. A self-propelled rotary tool was also developed and used for machining under the finishing conditions. Tool wear, component forces and surface roughness were recorded and analysed during the machining trials. Study of the surface integrity involved physical as well as metallographic examination and analysis of the machined surfaces. The results of the machining trials show that the multi-layer (TiN/TiCN/TiN) PVD coated KC732 tools gave the best overall performance when machining both Inconel 718 and IMI 318, especially at lower feed conditions. Flank wear, excessive chipping, flaking of tool materials close to the cutting edge or on the rake face were the dominant failure modes when machining with the PVD coated tools while flank wear and notching were dominant when cutting with the CVD coated tools. These failure modes are associated with attrition, abrasion, diffusion and plastic deformation wear mechanisms acting individually or in combination during machining. The statistical regression analysis of the tool life data shows that wear of the PVD and CVD coated tools used for machining Inconel 718 was mainly affected by cutting speeds employed while cutting speed and feed rate exhibited similar influence on tool performance when machining IMI 318 with PVD coated tools. Tool life equations for each of the three coated grades when machining both superalloys under the cutting conditions investigated were derived. Severe plastic deformation and hardening of the machined surfaces occurred after machining both materials due to a combined action of increased component forces, thus increased stresses, and high temperature. Softening of the top surface layer when machining IMI 318 can be attributed to overaging of the titanium as a result of highly localised surface heating during machining. Tearing of the machined surfaces occurred when machining IMI 318 with the PVD coated tools, particularly with KC732 tools as a result of irregular flank wear and excessive chipping of KC732 tools. The self-propelled rotary tool (SPRT) incorporating K68 straight grade carbide exhibited superior wear-resistance when machining IMI 318 due to the absence of thermally related wear mechanisms caused by reduced temperature and the use of the entire edge of a round insert during rotary cutting. The minimal subsurface alterations (such as plastic deformation and hardness) when machining Inconel 718 and IMI 318 with the SPRT can also be attributed to lower cutting temperature with rotary action.

The thesis work discuss about how the materials mechanical properties are influenced by the microstructure. The most common way of altering the microstructure of the material is by heat treatment.The mechanical properties that are of interest are strength, toughness, ductility, creep and fatigue. The material under consideration iswidely used superalloy In718. Two different sets of specimens areheat treated at different temperatures and influence of heat treatmenton the grain size is analyzed. In order to get better understanding ofthe grain size on mechanical properties, microstructural investigation was done using SEM. Efforts are made to understand the influence of different elements on the overall characteristic of the material. The tensile, creep and stress relaxation tests were conducted and the results were discussed. / Master Thesis

L’Inconel 718 est un superalliage base nickel, élaboré dans les années 60, utilisé dans la fabrication de pièces pour les parties chaudes des moteurs d’avion. Il acquiert ses propriétés mécaniques et sa microstructure finale au cours du procédé de mise en forme appelé forgeage à chaud. La maîtrise de ce procédé nécessite de comprendre l’interaction entre les phénomènes d’écrouissage et de recristallisation dynamique tout en intégrant l’influence de diverses conditions thermomécaniques. Cette étude s’est focalisée, expérimentalement, sur les phénomènes liés au forgeage à chaud en mise en forme unipasses et multipasses super-δ-solvus (1050 °C). Afin de les caractériser, des essais de compression ont été réalisés à l’échelle de pions. Des trempes à l’hélium, après déformation, ont permis de figer les microstructures dans le but de comprendre leur évolution en fonction des paramètres thermomécaniques (ε, et T). Des observations ont ensuite été réalisées expérimentalement : microscopie optique et à balayage, EBSD et diffraction des neutrons. Une attention particulière a été portée sur l’évolution de la phase δ, influençant indirectement les propriétés mécaniques de l’alliage, au cours de traitements thermiques puis thermomécaniques. La quantification ainsi que la détermination des cinétiques d’évolution statiques et dynamiques de cette phase a permis de mieux comprendre son influence au cours du forgeage sub-δ-solvus (980 °C). Un chaînage séquentiel a été développé entre deux modèles, l’un de plasticité cristalline implémenté dans un code éléments finis (CPFEM) et l’autre de recristallisation, implémenté dans un code automates cellulaires. Ce chaînage séquentiel permet de décrire les évolutions de champs mécaniques et de microstructures au cours du forgeage à chaud et a été validé par une comparaison avec les résultats expérimentaux. MOTS CLÉS : forgeage à chaud, Inconel 718, recristallisation dynamique, mise en forme multipasses, phase δ, plasticité cristalline (CPFEM), automates cellulaires, chaînage séquentiel, agrégats polycristallins 3D. / Developed in the 60’s, the nickel-base superalloy, Inconel 718, is widely used for hot parts of aircraft engines. The hot forging process confers to the alloy its final microstructure and its mechanical properties. The control of the process requires a deep knowledge of the interactions between the hardening phenomena and the dynamic recrystallization for the various thermomechanical conditions which are used. The present study mainly focuses on the experimental characterization of the phenomena linked to hot forging in the super-δ-solvus domain (1050 °C), as well for a single pass process as for a multipass one. Hot compression tests are used to simulate forging. After deformation, samples are helium quenched in order to freeze the microstructure that allows understanding its evolution as a function of the thermomechanical parameters (ε, and T). Microstructure analyses have then been performed using optical and scanning microscopy, EBSD, and neutron diffraction. A specific attention is paid on the study of the -phase evolution as it has a direct influence on the mechanical properties of the alloy. Its evolution is followed along thermal and thermomechanical treatments. The measure of the static and dynamic precipitation kinetics has led to a better understanding of the -phase role during hot forging at temperatures below solvus (980 °C). A sequential coupling is developed, based on two models; the first one is a crystal plasticity model implemented in a finite element code (CPFEM), the second one being a modeling of recrystallization using a cellular automata approach. The coupling allows the evolutions of the mechanical fields and the microstructure to be simulated during hot forging. The numerical results fit correctly most of the experimental data, mechanical and structural.

No description available.

This diploma thesis is focused on description of the properties of a layer of Inconel 718 applied on austenitic steel AISI 304 by the Cold Spray and subsequently remelted by electron beam. The first part presents the Cold Spray with its properties, advantages and disadvantages, and also describes the principle of electron beam remelting and other possible uses of electron beam, for example welding, drilling, heat treatment etc. The second part describes the material and the methods used for the preparation and evaluation of the samples. There are evaluated the porosity, microstructure and microhardness of the layers applied by the Cold Spray and these properties are further compared with the properties of the same layers remelted by electron beam. In conclusion, the results of the porosity of the layers applied by the Cold Spray are discussed with the literature and the results of electron beam remelting are only partially described here, because it was not possible to find literature about this topic. There are also suggestions for further research of the properties of this layers, which is necessary to know before implementing this method of producing layers for commercial production.

Increasing tool life is a significant objective in production. Achieving this objective in a machining process poses a significant challenge, especially during cutting hard-to-cut materials such as superalloys, due to the severe tool chipping/failure at the beginning of the cut. Although numerous attempts have been carried out to improve tool performance and prolong tool life during the machining of difficult-to-cut materials over the past several years, researchers have not obtained sufficient control over sudden tool failure/chipping. The focus of this study is to prolong tool life and control tool chipping by developing an ultra-soft deposited layer on the cutting tool that can protect it during the machining of difficult-to-cut materials such as Inconel 718. In the current study, an ultra-soft layer of material is deposited on the tool through two different techniques; a typical physical vapor deposition (PVD) technique and a novel developed method called “pre-machining”. In the PVD method, the soft layer is deposited under a high vacuum environment using a PVD coater. In the novel pre-machining method, the soft layer is deposited through a very short machining process involving Al-Si. It should be mentioned that soft coatings have never been used before for machining applications of difficult-to-cut materials including Inconel 718. This study shows that in contrast to what is expected, depositing an ultra-soft layer on the cutting tool significantly improves tool performance, by reducing chipping, and improving the machined surface integrity during cutting of Inconel 718. The obtained results show up to a 500% ± 10% improvement in tool life and around a 150% ± 10% reduction in cutting forces. Significant reductions in work hardening, residual stress, and surface roughness on the machined surface were other main achievements of the current study. / Thesis / Doctor of Philosophy (PhD) / Inconel 718 is considered to be a difficult-to-cut material due to its poor machinability. Significant tool failure at the early stage of cutting is the main challenge of machining this material and is the most significant contributing factor to its high manufacturing costs. Studies show that the common methods used to tackle this issue have not been completely successful. The goal of the present study is to tackle the machining challenges of Inconel 718 by developing tool coatings that meet the specific needs of the material to eliminate tool failure and thereby improve overall machining performance. For this purpose, a new tool coating material and a novel deposition technique that can be used as an alternative for commonly used coatings were developed in this study to improve the tool performance during the machining of Inconel 718. In addition, thorough studies have been carried out to gain a better understanding of the dominant wear phenomena and tool surface treatments that result in an improvement in the machinability of Inconel 718.

The aim of this thesis was to investigate if the robotized welding method FSW (Friction Stir Welding) could be applied for joining a rotating structure in an aero engine at Volvo Aero Corporation. FSW is expected to introduce less defects than today’s welding methods and could therefore be suitable for critical aero components. The material is the nickel based alloy Inconel 718, however a material experimentation is outside the scope of this report.The main goal of this study is to verify if the ESAB ROSIO robot based FSW-system has a suitable work space to be able to weld the rotating structure, and if the welding tool has accessibility to the joints. The FSW-process needs a rigid fixture, and a number of fix-ture concepts are presented based on a proposed weld sequence. A final fixture design is proposed, which requires a new design of the structure.The accessibility studies were performed in the robot simulations software Robot Stu-dio. This showed that the robot was unable to weld the proposed model in all areas in the original design. If the robot and the rotating structure can be redesigned the access will be achieved as shown in Robot Studio simulations.In order to be implemented in real production a number of further actions need to be taken and the result of this study can be a basis for these.

Ces travaux de thèse concernent l’étude du comportement thermo-physique de mélanges de polymères biosourcés chargés de poudre d’Inconel 718 mis en forme par Moulage par Injection de poudre Métallique. Des matériaux et procédés innovants pouvant permettre une amélioration du procédé ont été étudiés. L’utilisation de polyéthylène glycol (PEG), choisi pour ses propriétés de solubilité dans l’eau, et de polymères biosourcés, pour diminuer l’impact environnemental, ont été choisi. Les nuances de polymères biosourcés ont été choisies adaptées aux conditions du procédé de moulage par injection, il s’agit d’acide polylactique et de polyhydroalcanoates. De même, l’utilisation du CO2 à l’état supercritique comme solvant, a pour objectif de diminuer le temps de déliantage ainsi que d’augmenter la qualité des composants réalisés. Les résultats obtenus ont montré une dégradation du PEG et de l’acide stéarique lors des cycles de mélangeage de de moulage par injection dans les conditions d’utilisation des polymères biosourcés. L’utilisation des mélanges chargés composés de polymères biosourcés ont permis d’améliorer l’homogénéité des composants injectés, mais ont engendré des défauts lors de l’étape de déliantage. Ces défauts ont pu être éliminés par l’utilisation de CO2 à l’état supercritique comme solvant du PEG. Ce dernier procédé a permis une diminution importante du temps de déliantage ainsi qu’une amélioration de la qualité des composants finaux. Les composants densifiés possèdent les propriétés mécaniques correspondantes à l’Inconel 718. / The works done during this PhD focuses on the study of the thermo-physical behavior of bio sourced polymer blends loaded with Inconel 718 powder (feedstock) to be shaped by the Metal Injection Molding process (MIM). First, a review of the researches related to the MIM process was conducted to identify innovative materials and processes that can improve the MIM process. Thus, the use of polyethylene glycol (PEG), selected for its properties of solubility in water, and bio sourced polymers, in order to reduce the environmental impact, were selected. The bio sourced polymers have been selected in accordance with the conditions of the injection molding process, and the choice was made to use polylactic acid (PLA) and polyhydroalkanoates (PHA and PHBV). Similarly, the supercritical CO2 as solvent was chosen to reduce the time of binder removal as well as increasing the quality of components produced. Thermo-physical, mechanical and rheological characterizations were made to determine the behavior of the different feedstock formulations. The results showed a degradation of the PEG and of the stearic acid under the conditions of use of the biopolymers, during the mixing and the injection stages. The use of feedstock made of bio sourced polymers have improved the homogeneity of the injected components, but they have generated defects during the debinding step. These defects have been eliminated by the use of CO2 in the supercritical state as solvent of the PEG. This method has significantly decrease the time of binder removal and improved the quality of the final components. Finally, densified components have the mechanical properties corresponding to Inconel 718.

L’Inconel 718 est utilisé dans les disques de turbine des moteurs d’avion, de par sa haute résistance à la corrosion, à l’oxydation, au fluage et sa haute résistance mécanique à très haute température. Le nombre total de cycles de ces composants mécaniques s’élève à 109~1010 durant sa vie. Ils subissent des chargements de grande amplitude à faible fréquence, comme les forces centrifuges ou les contraintes thermiques mais aussi des chargements de faibles amplitudes à très haute fréquence, du aux vibrations des pales. Dans ce travail, on se propose d’étudier la fatigue à très grand nombre de cycles (VHCF) de l’Inconel 718 en utilisant des machines de fatigue ultrasonique, fonctionnant à 20KHz. Le système d’acquisition utilise des cartes NI et le logiciel LabView pour superviser la fréquence, la température, les déplacements durant toute la durée des tests. Des capteurs laser Keyence utilisant deux sondes pour les faces supérieure et inférieure de l’éprouvette permettent de capturer la fréquence et les modes de vibration. La différence entre les valeurs moyennes mesurées permet d’accéder à l’allongement de l’éprouvette, dû à l’auto-échauffement.3 types de matériaux avec différents traitements thermiques, AR, DA et DAHQ de l’ONERA et SAFRAN sont comparés. La différence au niveau de la taille de grain, de la phase, des précipités, … est analysée par micrographie métallographique en utilisant un microscope optique (MO) et un microscope électronique à balayage (MEB). Le comportement en traction quasi-statique et sous chargement cyclique contrainte-déformation est aussi proposé. La transition entre durcissement et adoucissement cyclique apparait à l’issue du traitement thermique. Finalement, les surfaces de ruptures sont observées en utilisant des caméras optiques et un MEB afin d’identifier les mécanismes de ruptures de l’Inconel 718 dans le domaine de la fatigue à très grand nombre de cycles. / Inconel 718 is widely used in turbine disk of aeronautic engines, due to its high resistance to corrosion, oxidation, thermal creep deformation and high mechanical strength at elevated temperature. The total cycle of these mechanical components is up to 109~1010 during its whole lifetime. It endures high-amplitude low-frequency loading including centrifugal force or thermal stress, and also low-amplitude high-frequency loading came from vibration of blade.In this work, the very high cycle fatigue (VHCF) behaviour of Inconel 718 with self-heating phenomenon without any cooling is studied using ultrasonic fatigue system at 20KHz. Acquisition system is improved using NI capture card with LabView for monitoring the frequency, temperature, displacement and so on during all the tests. Keyence laser sensor with two probes at the top and bottom surfaces of the specimens is used to reveal the frequency and vibration mode. The difference of mean values between these two probes is the elongation of the specimen caused by self-heating phenomenon.Three sets of materials with different heat treatment, As-Received (AR), Directly Aged (DA) and Directly Aged High Quality (DAHQ) from ONERA and SAFRAN are compared. The difference of grain size, phase, precipitate particle, etc. is investigated by metallographic micrograph using optical microscope (OM) and scanning electron microscope (SEM). Quasi-static uniaxial tensile property and cyclic stress-strain response is also proposed. The transition from cyclic hardening to cyclic softening appears after aged heat treatment. Finally, fracture surfaces are observed using optical camera and scanning electron microscope in order to identify the mechanism of fracture of Inconel 718 in the VHCF domain.

L'Inconel 718 est un superalliage base nickel très utilisé pour produire les disques de turboréacteurs. Typiquement, une gamme de forgeage à chaud se compose de plusieurs étapes de déformation et de recuit. La présence des particules de seconde phase (particules de phase delta dans l'Inconel 718) permet en principe de limiter la croissance de grains pendant les étapes de recuit grâce au phénomène d'ancrage de Zener. Néanmoins, l'hétérogénéité microstructurale (distribution des particules, écrouissage, composition chimique) peut favoriser une croissance anormale des grains pendant le recuit. Ce phénomène est connu industriellement sous la terminologie d'"éclatement de grains". Les objectifs de la thèse étaient d'identifier les mécanismes responsables de l'éclatement des grains qui peut survenir durant les étapes de recuit sur les pièces forgées en Inconel 718, de les modéliser, et de simuler numériquement le phénomène. Les mécanismes physiques à l'origine du phénomène sont d'abord étudiés expérimentalement grâce à la caractérisation (par MEB et EBSD) des pièces forgées. L'influence des particules de seconde phase et de l'énergie stockée (estimée par des mesures de désorientations intragranulaires) est notamment étudiée. A partir des observations réalisées, une explication est proposée : le phénomène apparaît lorsque les forces motrices pour la migration des joints de grains dépassent la force de freinage de Zener ; ceci peut se produire lorsque la microstructure contient de l'énergie stockée, distribuée de manière hétérogène. Des essais de torsion à chaud sont mis en place pour reproduire, en laboratoire, le même phénomène, étudier la sensibilité aux paramètres thermomécaniques, et tester les hypothèses émises concernant les mécanismes. Les mécanismes ainsi identifiés comme responsables de l'éclatement de grains sont enfin simulés au moyen d'un modèle numérique en 2D. Le modèle numérique en champ complet est basé sur la méthode des éléments finis, et utilise le formalisme level-set pour décrire les joints de grains. La simulation de l'évolution microstructurale prend en compte à la fois les forces motrices des joints de grains liées à la capillarité et à l'énergie stockée, et l'interaction des joints de grains avec les particules de seconde phase. Ainsi, l'effet de la distribution de l'énergie stockée (estimée à partir de données expérimentales) a pu être étudié numériquement dans des microstructures avec particules. / Inconel 718 is a nickel base superalloy commonly used to manufacture the rotating disks of turbojet engines. Such disks are generally produced by hot forging, which involves a sequence of different deformation and annealing steps. The presence of second phase particles (delta phase in Inconel 718) is commonly exploited to limit grain growth during annealing via the Zener pinning phenomenon. Nonetheless, microstructure heterogeneity (with regards to second phase particles, hardening, texture and chemical composition) can lead to inhomogeneous grain growth during annealing. The objectives of this PhD work were to understand, model and simulate numerically the phenomenon of inhomogeneous grain growth that can occur in Inconel 718 turbine disks during the annealing steps of hot forging sequences. The physical mechanisms which may explain the occurrence of the phenomenon are investigated experimentally by performing SEM and EBSD analyses of Inconel 718 industrial pieces. The focus is placed on the influence of second phase particles and strain energy (estimated from intragranular misorientations) on the occurrence of the phenomenon. From those observations, it is inferred that the phenomenon occurs when the grain boundary driving forces overcome the Zener pinning forces; this is achieved when stored energy is present and heterogeneously distributed. Moreover, hot torsion tests are carried out to reproduce the phenomenon in laboratory, to evaluate its sensibility to thermomechanical parameters and to test the previously postulated mechanism. The validity of this mechanism is finally demonstrated by modelling numerically the phenomenon in 2D. The full field numerical model is based on a level set description of the grain boundaries in a finite element context. Microstructure evolution is simulated explicitly taking into account Zener pinning, capillarity and stored energy driven grain growth in a single framework. The effect of strain stored energy distributions (estimated from experimental data) in pinned microstructures is investigated focusing on the conditions leading to inhomogeneous grain growth.