Results 1 - 10 of 4811
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[en] In this paper, the evolution of the microstructural and performance of IN783 hightemperature bolts in service was studied. The results showed that under high-temperature service environment, with the increase of service time, the superalloy of IN783 bolt and the precipitation quantity of second phase increased. The second phase mainly existed in the form of particles and rods, which were distributed in an obvious oriented way. With the extension of service time, the strength of the alloy increased, but the hardness decreased, the plasticity and toughness decreased significantly, so it is difficult for the IN783 high-temperature bolts to reach the normal level of safe service. Therefore, the IN783 high-temperature bolts that have been in service for a long time should be strictly supervised and replaced appropriately to reduce losses.
[de]Die vorliegende Arbeit untersucht die Entwicklung des Gefüges und der Leistungsfähigkeit von Bolzen aus IN783 während des Hochtemperaturbetriebs. Die Ergebnisse zeigten, dass beim Einsatz in Hochtemperaturanwendungen mit fortschreitender Betriebszeit die Menge an ausgeschiedener Sekundärphase in dem aus der Superlegierung IN783 bestehenden Bolzen zunahm. Die Sekundärphase trat hauptsächlich in Form von Partikeln und Stäben auf, die eindeutig gerichtet verteilt waren.
[en] In the additive manufacturing of polycrystalline nickel-base superalloy Inconel-738LC (IN738LC) by laser-powder bed fusion (L-PBF), the critical issue is the formation of micro-cracks during the process. These are solidification cracks that occur at the last stage of solidification. The first part of the thesis is an extensive chemical composition analysis at high-angle and low-angle grain boundaries with solidification cracks and on those that are devoid of cracks. The second part of the thesis consists of a multi-scale residual stress study. These results are used to rationalize the contribution of solute enrichment and tensile stresses at interfaces to the solidification cracking mechanism during the L-PBF process.
[en] The sintering behaviour of two aluminium alloys, Alumix 321 and 6061, was studied in this paper. Both have a similar Mg, Cu and Si contents, but have been obtained by different methods. the Alumix 321 alloy is produced by mixing the initial elements as powders and the 6061 is obtained by water atomization. The work carried out includes the study of the green properties, the determination of the compressibility and green strength curves as well as the microstructural characterization of the powders. Thermal analyses (DTAs and Dilatometries) were performed in order to study the behaviour of both alloys with temperature. furthermore, different sintering temperatures were studied by characterizing the mechanical properties of the sintered materials. It can be concluded that the 6061 alloys has better properties than the Alumix 321, when both were sintered at 600 degree centigree. (Author) 27 refs
[en] A multi-component mean field model has been applied to predict the particle evolution of the γ′ particles in the nickel based superalloy IN738LC, capturing the transition from an initial multimodal particle distribution towards a unimodal distribution. Experiments have been performed to measure the coarsening behaviour during isothermal heat treatments using quantitative analysis of micrographs. The three dimensional size of the γ′ particles has been approximated for use in simulation. A coupled thermodynamic/mean field modelling framework is presented and applied to describe the particle size evolution. A robust numerical implementation of the model is detailed that makes use of surrogate models to capture the thermodynamics. Different descriptions of the particle growth rate of non-dilute particle systems have been explored. A numerical investigation of the influence of scatter in chemical composition upon the particle size distribution evolution has been carried out. It is shown how the tolerance in chemical composition of a given alloy can impact particle coarsening behaviour. Such predictive capability is of interest in understanding variation in component performance and the refinement of chemical composition tolerances. It has been found that the inclusion of misfit strain within the current model formulation does not have a significant affect upon predicted long term particle coarsening behaviour. Model predictions show good agreement with experimental data. In particular, the model predicts a reduced growth rate of the mean particle size during the transition from bimodal to unimodal distributions.