On the Microstructural Development in Platinum-Modified Nickel-Aluminide Bond Coats

A numerical procedure for simulating the distortions exhibited by a thermally grown oxide (TGO) upon temperature cycling has been adapted to incorporate the microstructure of the bond coat. The focus is on the dual phase β/γ′ microstructure that develops upon oxidation of a system with a Pt-aluminide bond coat. The results reveal that the presence of the γ′-phase next to the TGO reduces its distortion locally, because of the superior high-temperature strength of γ′, relative to β. Conversely, in regions where the β-phase exists adjacent to the TGO, it distorts and the TGO propagates downward, while simultaneously lengthening. These results from the simulations are in direct correspondence with experimental observations

On the Microstructural Development in Platinum-Modified Nickel-Aluminide Bond Coats

A numerical procedure for simulating the distortions exhibited by a thermally grown oxide (TGO) upon temperature cycling has been adapted to incorporate the microstructure of the bond coat. The focus is on the dual phase β/γ′ microstructure that develops upon oxidation of a system with a Pt-aluminide bond coat. The results reveal that the presence of the γ′-phase next to the TGO reduces its distortion locally, because of the superior high-temperature strength of γ′, relative to β. Conversely, in regions where the β-phase exists adjacent to the TGO, it distorts and the TGO propagates downward, while simultaneously lengthening. These results from the simulations are in direct correspondence with experimental observations

Aspects of the Morphological Evolution in Thermal Barrier Coatings and the Intrinsic Thermal Mismatch Therein

The evolution of interfacial deformations and stresses in thermal barrier coatings due to the formation of the thermally grown oxide and the intrinsic thermal mismatch is investigated. The study focuses on systems that are prone to displacement instabilities of the thermally grown oxide and numerical models spanning a range of properties are investigated. Material changes in the Pt-modified aluminide bond-coat, such as martensitic transformation and the change from β- to γ′-grains, are considered. The numerical simulations show that when the mismatch is large enough to cause overall yielding in the bond-coat, the thermal expansion of the substrate (the superalloy) will rule the system response. Furthermore, the results suggest that the stresses and the interfacial deformation—thus the coating’s lifetime—may be optimized if the martensitic transition temperature can be controlled for bond-coats undergoing such transformations. However, we show that due to the sensitivity of the system, this is unlikely to be successful for a real material system

Aspects of the Morphological Evolution in Thermal Barrier Coatings and the Intrinsic Thermal Mismatch Therein

The evolution of interfacial deformations and stresses in thermal barrier coatings due to the formation of the thermally grown oxide and the intrinsic thermal mismatch is investigated. The study focuses on systems that are prone to displacement instabilities of the thermally grown oxide and numerical models spanning a range of properties are investigated. Material changes in the Pt-modified aluminide bond-coat, such as martensitic transformation and the change from β- to γ′-grains, are considered. The numerical simulations show that when the mismatch is large enough to cause overall yielding in the bond-coat, the thermal expansion of the substrate (the superalloy) will rule the system response. Furthermore, the results suggest that the stresses and the interfacial deformation—thus the coating’s lifetime—may be optimized if the martensitic transition temperature can be controlled for bond-coats undergoing such transformations. However, we show that due to the sensitivity of the system, this is unlikely to be successful for a real material system

Adolescents souffrant d’anorexie mentale Le rôle des parents, une approche baséesur l’évidence : bilan en 2018 [Adolescents suffering from anorexia nervosa: an evidence-based approach of the parent's role in 2018]

A new paradigm in the management of adolescents with eating disorders promotes different treatment orientations aiming at increasing therapeutic effectiveness as well as offering a more integrated and coherent care for families. Particular attention is given to the process of refeeding to avoid the severe somatic sequelae of eating disorder and the risk of a chronic course for a disorder which is well known for its « addictive » power and influence. The parents and the need for a strong alliance with the healthcare team stand at the centre of this new paradigm. This type of management requires professionals who are trained in these specific approaches and in multidisciplinary work

Microstructure and morphology of SiC

This paper deals with the study of a new generation of ceramic matrix composites, SiCf-SiBC, which consists of a 2.5D perform of SiC fibers and of a self sealing multilayered matrix. Three different batches of these CMCs have been investigated in a morphological point of view thanks to the observations performed at the mesoscopic scale by scanning electron microscopy and automatic image analysis, and also at a microscopic scale by transmission electron microscopy. Through this study, a lot of care was taken about the description of the pyrocarbon interphase and of the different matrix interfaces, which play a key role in the damage features, and more specially in the deflection of the matrix microcracks developed through tested mechanical composites

The Effect of Thermal Mismatch on Stresses, Morphology and Failures in Thermal Barrier Coatings

Platinum modified aluminide bond coat used for oxidation protection in thermal barrier coatings are prone to develop morphological instabilities in the interface to the ceramic top coat. Previous work has shown that there are a range of factors influencing this development, where key factors are the lateral growth strain in the thermally grown oxide, the relatively low yield strength of the Pt‐modified bond coat at high temperature, and cyclic loading. In this study we show that the development of the instabilities can be greatly enhanced due to the thermal mismatch between the substrate and the bond coat

Advantages of SiC Hi-Nicalon or NLM 202 fibers in SiCf-SiBC composites

International audienceSiCf-SiBC composites were produced using NLM 202 and Hi-Nicalon SiCf fibers. Tensile creep tests were performed under a reduced pressure of argon. These composites show a good creep resistance at 1473 K with a strain rate ranging from 10(-9) to 10(-7) s(-1), depending on the stress level. The creep strength was improved by using Hi-Nicalon instead of NLM 202 SiCf fibers, to the extent of increasing the loadability by 50 MPa at the same operating temperature or increasing the temperature by 50 K for the same load. The damage observed in SEM micrographs and the use of the damage mechanics provide evidence that creep is governed by a damage-creep mechanism in two steps

Understanding of the creep behavior of SiCf-SiBC composites

International audienceThis paper deals with some creep results on a new generation of a ceramic matrix composite with a self-healing matrix. This investigation is based on the creep curves, the observation of damages and their quantification by image analysis, and the application of the damage mechanics approach. The results obtained herein illustrate the concept of the damage-creep mechanism. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved

Insulator-Metal Crossover near Optimal Doping in Pr22xCexCuO4: Anomalous Normal-State Low Temperature Resistivity

Normal-state resistivity measurements at high fields and low temperatures in electron-doped Pr2-xCexCuO4 thin films reveal an insulator-metal crossover near a doping level x≈0.15, similar to a previous report on hole-doped La2-xSrxCuO4. The temperature dependence of the resistivity of insulatinglike samples is sublogarithmic, while for metallic samples (with x = 0.17) the resistivity is linear from 40 mK to 40 K. This surprising latter observation suggests an unusual contribution to the scattering processes at low temperature in these materials. We conclude that the ground state at x = 0.15, corresponding to the maximum transition temperature, is equivalent for hole- and electron-doped cuprates