Heat generated in a machining process is a common and critical obstacle faced in today's machining industries. The heat generated in the cutting zone has a direct negative influence on the tool life which, in turn contributes to increase the manufacturing costs. Especially, in machining of Heat Resistant Super Alloys, HRSA this is a very limiting factor. HRSA are capable of retaining their mechanical strength and hardness at elevated temperatures. This property is advantageous in the application in e.g. aero-engines but also a disadvantage, since it also lowers the machinability significantly. This work is an attempt to improve the heat transfer from the cutting zone, which would lead to an increase in the tool life. To achieve this goal, the cutting tool has been modified to create an improved interface between the coolant and tool in the high-temperature areas. Two generations of inserts have been designed and investigated. Firstly, an insert with surface texture features has been created with the purpose of increasing the available surface area for heat dissipation: First generation, Gen I. Secondly, a GenII was designed as a further improvement of Gen I. Here, several channel features on the rake face were added, reaching out from the contact zone to the near proximity of the cutting edge. This with the purpose of improving access of the coolant closer to the cutting edge. The experiments were conducted in facing operations of Alloy 718 with uncoated round carbide inserts. All experiments were carried out with high-pressure coolant assistance, with a pressure of 16 MPa on the rake face and 8 MPa on the flankface, respectively.The two generations of inserts, Gen I and Gen II, were experimentally evaluated by tool wear analysis in comparison with a regular insert. The results shows that the tool life increased significantly for the Gen I insert, compared to a catastrophic failure of the regular insert at the same conditions. Regarding the Gen II insert,an increase in tool life by approximately 30 to 40 percent compared to Gen I insert was observed.

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Manufacturing of aero engine components requires attention to residual stress and final shape of the product in order to meet high quality product standards.This sets very high demands on involved manufacturing steps to meet design requirements. Simulation of manufacturing processes can therefore be animportant tool to contribute to quality assurance.The focus in this work is on simulation of a manufacturing process chain comprising of sheet metal forming, welding and a stress relief heat treatment.Simulation of sheet metal forming can be used to design a forming tool design that accounts for the material behaviour, e.g. spring back, and avoid problems such as wrinkling, thinning and cracking. Moreover, the simulation can also show how the material is stretched and work hardened. The residual stresses after forming may be of local character or global depending on the shape that is formed. However, the heat affected zone due to welding is located near the weld.The weld also causes large residual stresses with the major component along the weld. It is found that the magnitude of the residual stresses after welding is affected by remaining stresses from the previous sheet metal forming. The final stress relieve treatment will relax these residual stresses caused by e.g. forming and welding. However, this causes additional deformations.The main focus of this study is on how a manufacturing process step affects the subsequent step when manufacturing a component of the nickel-based super alloy 718. The chosen route and geometry is a simplified leading edge of an exhaust case guide vane. The simulations were validated versus experiments. The computed deformations were compared with measurements after each manufacturing step. The overall agreement between experiments and measurement was good. However, not sufficiently accurate considering the required tolerance of the component. It was found from simulations that the residual stresses after each process affects the subsequent step. After a complete manufacturing process chain which ends with a stress relief heat treatment the residual stresses were not negligible. VIII Special experiments were performed for studying the stress relief in order to understand how the stresses evolve through the heat treatment cycle during relaxation. It was found that the stresses were reduced already during the beginning of the heating up sequence due to decreasing Young´s modulus and yield stress with increasing temperature. Relaxation due to creep starts when a certain temperature was reached which gave a permanent stress relief.

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Electron beam melting (EBM), a metal additive manufacturing (AM) process, has received considerable industrial attention for near net shape manufacture of complex geometries with traditionally difficult-to-machine materials. This has fuelled considerable academic interest in investigating EBM of Alloy 718, a nickel ironbased superalloy possessing an exciting combination of good mechanical behaviour and cost effectiveness. EBM production of Alloy 718 is particularly promising for aerospace and other sectors which value rapid production of components with large scope for design flexibility. The EBM builds are characterized by presence of inevitable defects and, anisotropy within a build is also a concern. Consequently, as-built Alloy 718 has to be subjected to post-build thermal-treatments (post-treatments) to ensure that the parts eventually meet the critical service requirements. Not withstanding the above, limited knowledge is available about optimal post-treatments for EBM-built Alloy 718. Therefore, the main focus of the work presented in this thesis was to systematically investigate the response of EBM-built material to post-treatments, which include hotisostatic pressing (HIPing), solution treatment (ST), and aging. HIPing of EBM-built Alloy 718 led to more than an order of magnitude reduction in defect content, which was reduced from as high as 17% to &lt; 0.2% in samples built with intentionally introduced porosity to investigate limits of defect closure achievable through HIPing. In addition, HIPing also caused complete dissolution of δ and γ" phases present in the as-built condition, with the latter causing dropin hardness of the material. HIPing had no effect on the carbides and inclusions such as TiN, Al2O3 present in the built material. The evolution of microstructure during ST and aging was systematically investigated. Growth of potentially beneficial grain boundary δ phase precipitates was found to cease after a certain duration of ST, with samples subjected to prior-HIPing exhibiting lesser precipitation of the δ phase during ST. While the specimen hardness increased onaging, it was observed to plateau after a duration significantly shorted than the specified ASTM 'standard' aging cycle. Therefore, prima facie there are promising prospects for shortening the overall heat treatment duration. A combination of HIPing, ST, and aging treatments in a single uninterrupted cycle was also explored. Future work involving incorporation of a shortened heat treatment schedule in a combined cycle can have significant industrial implications. / <p>Articles submitted to journals and unpublished manuscripts are not included in this registration</p>

<div>Defects are unavoidable, life-limiting and dominant sites of damage and subsequent failure in a material. Ni-based superalloys are commonly used in high temperature applications and inevitably found to have defects in the form of inclusions, voids and microscopic cracks which are below the resolution of standard inspection techniques. A mechanistic understanding of the role of defects in such industrially relevant bulk polycrystalline material is essential for philosophies of design and durability to follow and ensure structural integrity of components in the inevitable presence of such defects. The current understanding of defect-mediated damage, in bulk Ni superalloys, is limited by experimental techniques that can capture the local micromechanical state of the material surrounding the defect. In this work, we combine mechanical testing with in-situ, non-destructive 3-D X-ray characterization techniques to obtain rich multi-modal datasets at the microscale to interrogate complex defect-microstructure interactions and elucidate the mechanisms of failure around defects. The attenuated X-ray beam, after passage through the material, is utilized through computed micro-tomography to characterize the defects owing to its sensitivity to density differences in the material. The diffracted X-ray beam, after illuminating the material, is employed through high energy diffraction microscopy in various modes to interrogate the evolving micromechanical state around the discovered defects.</div><div>Three case studies are performed with specimens made of a Ni-based superalloy specially designed and fabricated to have internal defects in the form of: (i) an inclusion, (ii) a microscopic crack, and (iii) voids. In each case, the grain scale information is investigated to reveal heterogeneity in the local micromechanical state of the material as a precursor for the onset of failure. Models and simulations based on finite element or crystal plasticity are utilized, wherever necessary, to assess the factors essential to the underlying mechanism of failure. In the first case study, the detrimental effects of an inclusion in initiating a crack upon cyclic loading is interrogated and the state of bonding, residual stresses, and geometrical stress concentrations around the inclusion are demonstrated to be of utmost importance. In the second case study, the propagation of a short fatigue crack through the microstructure is examined to reveal the crystallographic nature of crack growth through the (i) alignment of the crack plane with the most active slip system, (ii) the correlation between the crack growth rate and the maximum resolved shear stresses, and (iii) the dependence of the crack growth direction on microplasticity within grains ahead of the crack front. In the third case study, the role of voids in ductile failure under tensile loading is explored to illuminate the activation and operation of distinct mechanisms of inter-void shear and necking under the control of the local state of stress triaxiality and the local plasticity within the grains at critical sites of fracture.</div><div>In summary, a grain scale description of the micromechanical state has been unambiguously determined through experiments to examine the heterogeneity around defects in the material. It has enabled us to identify and isolate the nature of factors essential to the activation of specific mechanisms at the onset failure. The grain scale thus provides an ideal physical basis to understand the fundamentals of defect mediated damage and failure instilling trust in the predictive capabilities of models that incorporate the response of the grain structure. The generated datasets can be used to instantiate and calibrate such models at the grain level for higher fidelity. </div>

Dès la loi impériale du 23 Prairial an XII (12 juin1804) qui impose l’obligation d’inhumation pour tous au cimetière, la sculpture se met au service du portrait du défunt, dans cet espace si particulier qui tient à la fois du cadre privé et du cadre public. Héritier d’une tradition jusqu’alors réservée aux nobles et au roi, le portrait funéraire s’affiche dans une iconographie qui oscille entre symbolique et réalisme des traits physiques; le militaire est honoré comme héros tandis que le curé est vénéré par les paroissiens. S’inscrivant dans la mode de la statuomanie galopante des années 1880, les cimetières lorrains rejoignent la volonté publique d’honorer ses Grands Hommes, à une époque où la « Petite Patrie », la Lorraine, rencontre la « Grande Patrie », la France, où des artistes connus et parfois moins connus mettent leur savoir-faire et leur notoriété au service de portraits de notables. Le portrait funéraire connaît alors son âge d’or. Alors que le cimetière moderne se construit peu à peu grâce à son organisation parcellaire, les familles éprouvent très rapidement le besoin impérieux de matérialiser, sur ces concessions familiales, le souvenir des traits de leur défunt et le portrait sculpté leur en offre la possibilité et le voilà qui quitte l’intimité des salons pour être installé soit sur la stèle de la tombe familiale. C’est ainsi que l’époux éploré se souvient du visage de sa chère épouse, que des parents effondrés peuvent se consoler d’avoir perdu un petit ange en lui substituant un autre visage, plutôt idéalisé, ou mieux la figure d’un autre ange, plus solide car en marbre et plus protecteur. Peu à peu, le cimetière se pare d’un peuple de statues que viennent compléter quelques motifs professionnels, rares toutefois. La personnalisation de la tombe reste toutefois très discrète, la douleur contenue. La sculpture funéraire, et le portrait en particulier, se mettent au service de l’expression de sentiments filiaux ou conjugaux, réservés jusqu’alors à l’intimité, mais traduisent un élitisme que la législation du 23 prairial an XII ne souhaitait pas. Pendant la période 1880-1930, les commanditaires des portraits funéraires bénéficient d’une offre élargie de produits notamment grâce à l’essor de la photographie et au procédé de vitrification. Sans concurrencer le portrait sculpté porté principalement par le médaillon de bronze et la ronde-bosse, le vitrail photographique permet de promouvoir le souvenir du défunt dans un écrin luxueux, où, pour la première fois, la présence de la couleur fait animer ces visages et les rend presque vivants. Mais, c’est un luxe que peu de familles peuvent s’offrir. Alors, le médaillon photographique sur plaque émaillée, plus modeste, permet à une clientèle moins fortunée d’accéder au portrait funéraire au cimetière. Après 1930, alors que chapelle et vitrail disparaissent des allées du cimetière, le médaillon peut définitivement prendre place sur les sépultures. Très vite, c’est un succès assuré qui ne se dément pas, aujourd’hui encore. La période de 1940 à nos jours est de loin la plus riche en portraits funéraires et ce grâce à des techniques bien maîtrisées, celle de la photographie sur médaillon de porcelaine et celle de la gravure mécanique ou artistique, grâce également à de nouveaux supports que sont les plaques funéraires, les urnes, les vases. Et il n’est pas rare qu’une famille ait recours à des techniques différentes pour chacun de ses défunts. La façon de présenter le défunt a également évolué ; le modèle de studio photographique cède la place à un modèle présenté « au naturel », c’est-à-dire issu de l’album photographique familial et de nouveaux symboles montrent le défunt sous des aspects plus personnels. Désormais, le portrait funéraire du défunt au cimetière n’est plus seulement un visage mais c’est aussi un sportif, un chasseur, un motard, un professionnel, un amoureux des bêtes, un amateur de pétanque / From the imperial law of 23 Prairial year XII (June 12, 1804) which imposes the burial obligation for all in the cemetery, the sculpture puts itself at the service of the portrait of the deceased, in this very special space which is at the same time of the private frame and the public setting. Heir to a tradition hitherto booked with noble and to the king, the funerary portrait is displayed in an iconography which oscillates between symbolic system and realism of the physical features; the soldier is honored as hero while the priest is venerated by the parishioners. Falling under the fashion of the “statuomanie galopante” years 1880, the Lorraine cemeteries join the public will to honour its Great men, at one time when the “Small Fatherland”, Lorraine, meets the “Great Fatherland”, France, where known artists and sometimes less known put their know-how and their notoriety at the service of portraits the notable ones. The funerary portrait knows its golden age then. Whereas the modern cemetery is built little by little thanks to its compartmental organization, the families test the imperative need very quickly to materialize, on these family concessions, the memory of the features of their late and the carved portrait give of it them the opportunity and here it is which leaves the intimacy of the living rooms to be installed either on the family stele of the tomb. Thus the tearful husband remembers the face his dear wife, that ploughed up parents can comfort themselves to have lost a little angel in him substituent another face, rather idealized, or best the figure of another angel, more solid because out of marble and more protective. Little by little, the cemetery is avoided of people of statues which some professional reasons come to supplement, rare however. The personalization of the tomb remains however very discrete, the pain contained. The funerary sculpture, and the portrait in particular, are put at the service of the expression of subsidiary or marital feelings, hitherto booked with the intimacy, but translate an elitism which the legislation 23 Prairial An XII did not wish. For the period 1880-1930, the silent partners of the funerary portraits profit from a widened offer of products in particular thanks to rise of the photography and with the process of vitrification. Without competing with the carved portrait carried mainly by the bronze medallion and the sculpture in the round, the photographic stained glass makes it possible to promote the memory of late in a luxurious house, where, for the first time, the presence of the color makes animate these faces and makes them almost alive. But, it is a luxury which few families can offer. Then, the photographic medallion on enamelled plate, more modest, makes it possible to less fortunate customers to reach the funerary portrait with the cemetery. After 1930, whereas vault and stained glass disappear from the alleys of the cemetery, the medallion can definitively take seat on the burials. Very quickly, these is a assured success which is not contradicted, still today. The period of 1940 to our days is by far richest in funerary portraits and this thanks to techniques controlled well, that of photography on porcelain medallion and that of mechanical or artistic engraving, grace also to new supports which are the funerary plates, the ballot boxes, vases. And it is not rare that a family resorts to different techniques for each one of her late. The way of presenting the late one also evolved; the photographic model of studio gives way to a model presented “to the naturalness”, i.e. resulting from the family photographic album and new symbols show the late one under more personal aspects. From now on, the funerary portrait of late with the cemetery is not only any more one face but it is also a sportsman, a hunter, a motorcyclist, a professional, in love with the animals, an amateur of game of bowls.