Experimental study of extruded powder metallurgy γ-TiAl based alloys

International audienceIn the context of research of lighter and/or stronger high temperature materials in order to improve aeroengines, the present work shows an example of a powder metallurgy (PM) manufacturing route for TiAl alloys that could be used for low pressure turbine (LPT) blades processing. In this frame, two different alloys, Ti-47Al-1Fe-1Zr-1Mo-0.2Si (at.%) FZM and Ti-43.5Al-4Nb-1Mo-0.1B (at.%) TNM-B1, were gas-atomized into powders, extruded, heat-treated and mechanically tested.Dans le contexte de la recherche de matériaux haute température plus légers et/ou plus résistants pour l'amélioration des performances des moteurs d'aéronefs, cet article présente un exemple de voie d'élaboration par métallurgie des poudres d'alliages base TiAl. Ces alliages sont potentiellement utilisables pour la fabrication d'aubes de turbine basse pression. Ainsi, l'alliage FZM de composition Ti-47Al-1Fe-1Zr-1Mo-0.2Si (% at.) et l'alliage TNM-B1 de composition Ti-43.5Al-4Nb-1Mo-0.1B (% at.) ont été atomisés par gaz, extrudés, traités thermiquement et testés mécaniquement

In-situ creep law determination for modeling Spark Plasma Sintering of TiAl 48-2-2 powder

Spark Plasma Sintering (SPS) is a process which allows powder densification, applying simultaneously a uniaxial external load and pulsed direct current of very high intensity through tools. This process is attracting significant attention, with a tremendous increase of studies in the metal powder densification field. Its growing popularity lies in the very fast heating rate and short cycle time driven by the Joule effect, which limits grain growth. However, this process implements different coupled electrical, thermal and mechanical phenomena. All this makes the process difficult to develop and to apply for routine industrial production, which has motivated the development of numerical simulation tools in order to understand and optimize the process. Up to now, very few models integrating the coupling between heat generation, electric transfer and mechanics have been proposed. In particular, a numerical predictive model for powder densification requires a good understanding of the mechanical behavior, in our case a viscoplastic compressive law (Abouaf mechanical model). In this article, we will discuss the characterization of the material during densification, focusing on the creep behaviors of dense and porous state materials used to simulate sintering in the Abouaf framework. Validations of the creep law parameters and also of the densification parameters will be presented and subsequently discussed

Spark plasma sintering of a commercial TiAl 48-2-2 powder: Densification and creep analysis

Commercial 48-2-2 TiAl powder was densified by spark plasma sintering. Fully dense materials with duplex and lamellar microstructures were obtained. An original protocol was developed to avoid carbide formation due to reactions between TiAl and graphite molds. TiAl materials with lamellar microstructures and high creep behavior were produced

Does social media usage matter? An analysis of online practices and digital media perceptions of communication practitioners in Europe

A key aspect for understanding and explaining online communication is the micro level of communication practitioners’ social media usage and their general attitudes towards digital platforms. This paper investigates how public relations practitioner's personal and professional use of social media is related to their perceptions of social media. A quantitative methodology was applied to perform this research. A population of 2710 professionals from 43 European countries working on different hierarchical levels both in communication departments and agencies across Europe were surveyed as part of a larger transnational online survey. Results show that practitioners with a high level of usage of social media give more importance to social media channels, influence of social media on internal and external stakeholders and relevance of key gatekeepers and stakeholders along with a better self-estimation of competences. Issues about diverse levels of overestimation of social media use, application and importance in the professional arena are also debated

Structural changes to resorbable calcium phosphate bioceramic aged <i>in vitro</i>

This work investigates the effect of mammalian cell culture conditions on 3D printed calcium phosphate scaffolds. The purpose of the studies presented was to characterise the changes in scaffold properties in physiologically relevant conditions. Differences in crystal morphologies were observed between foetal bovine serum-supplemented media and their unsupplemented analogues, but not for supplemented media containing tenocytes. Scaffold porosity was found to increase for all conditions studied, except for tenocyte-seeded scaffolds. The presence of tenocytes on the scaffold surface inhibited any increase in scaffold porosity in the presence of extracellular matrix secreted by the tenocytes. For acellular conditions the presence or absence of sera proteins strongly affected the rate of dissolution and the distribution of pore diameters within the scaffold. Exposure to high sera protein concentrations led to the development of significant numbers of sub-micron pores, which was otherwise not observed. The implication of these results for cell culture research employing calcium phosphate scaffolds is discussed

Modélisation de la durée de vie d'un revêtement aluminoformeur en conditions de sollicitations thermo-mécaniques

This study aims at modeling the life time of a NiAlPt coating used at high temperature and deposited on a single crystal nickel-based superalloy AM1. Usually, the life time of coatings is estimated through the evaluation of the mass of coated samples (Net Mass Gain curves), during thermal cycling tests. Existing models are very suitable to describe the evolution of coating in the case of poorly adherent oxide layer. Unfortunately, this is not the case of the studied NiAlPt coating. Moreover, it is impossible to obtain experimentally the Net Mass gain curve of a sample subjected to thermo-mechanical loading, experienced by engine components. Thus, the strategy adopted in this study is to correlate the microstructure of the coating with its life time, evaluated during thermal cycling.The experimental work included cyclic oxidation tests at different temperatures, cycling frequencies and in-phase, out-of-phase and complex thermo-mechanical loadings. For each of the tested condition, interrupted tests allowed the characterization of the microstructure evolution as a function of the loading parameters up to relatively long ageing time. Especially, the roughness of the coating surface has been investigated as well as the interdiffusion zone (IDZ) thickness evolution or the fraction of γ' phase transformed within the coating. These two last parameters where found to be correlated respectively to the time needed to reach the maximum of the Net Mass Gain curve and the time needed to reach the zero mass gain of the curve, under thermal cycling conditions.A model for the interdiffusion (IDZ) thickness evolution was proposed as a function of the loading parameters. The phase transformation in the coating was modeled using a mass balance condition for the aluminum in the coating, including roughness of the surface and oxide scale integrity considerations. This model based on original criteria allowed the estimation of the life time of a coated turbine blade under service conditions.Cette étude a pour objectif de modéliser la durée de vie d'un revêtement NiAlPt déposé sur un substrat monocristallin base Ni (AM1). De façon standard, la durée de vie des revêtements est évaluée en mesurant l'évolution de la masse d'un échantillon revêtu au cours d'un essai de cyclage thermique. Des modèles de durée de vie fondés sur ces mesures sont très bien adaptés aux revêtements pour lesquels la couche d'oxyde est peu adhérente, ce qui n'est pas le cas pour le revêtement NiAlPt objet de cette étude. D'autre part, il est impossible d'obtenir des courbes de gain de masse pour des conditions de chargement thermo-mécaniques complexes, tels que ceux supportés par une aube aéronautique en service. C'est pourquoi nous avons choisi d'étudier l'évolution de la microstructure du revêtement au cours du vieillissement et d'établir des liens entre cette évolution microstructurale et la durée de vie évaluée sur des essais de cyclage thermiques.La base d'essai réalisée regroupe des essais d'oxydation cycliques à différentes températures et fréquences de cyclage ainsi que des essais de fatigue mécano-thermique, en phase, hors-phase et complexes. Pour chaque condition testée, des essais interrompus ont permis d'estimer les évolutions microstructurales en fonction des conditions de chargement thermo-mécanique jusqu'à des temps relativement longs. Nous avons en particulier estimé les évolutions de rugosité de surface, d'épaisseur de la couche d'interdiffusion entre le revêtement et le superalliage, et la fraction de phase γ' transformée. Ces deux paramètres sont corrélés respectivement au maximum de la courbe de gain de masse et au nombre de cycle nécessaire pour atteindre un gain de masse nul, pour le système étudié en oxydation cyclique.Nous avons modélisé l'évolution de l'épaisseur de la couche d'interdiffusion en fonction des conditions de chargement thermo-mécaniques. La transformation de phase a été modélisée à l'aide d'un bilan de flux de matière dans le revêtement fonction de l'intégrité de la couche d'oxyde de croissance et de la rugosité de surface. Ces deux modèles ont permis d'estimer l'évolution microstructurale du revêtement en fonction des différents paramètres de chargement thermo-mécanique, et donc d'estimer une durée de vie basée sur ces critères

Lifetime modelling of turbine blade coatings under thermo-mechanical loadings

Cette étude a pour objectif de modéliser la durée de vie d'un revêtement NiAlPt déposé sur un substrat monocristallin base Ni (AM1). De façon standard, la durée de vie des revêtements est évaluée en mesurant l'évolution de la masse d'un échantillon revêtu au cours d'un essai de cyclage thermique. Des modèles de durée de vie fondés sur ces mesures sont très bien adaptés aux revêtements pour lesquels la couche d'oxyde est peu adhérente, ce qui n'est pas le cas pour le revêtement NiAlPt objet de cette étude. D'autre part, il est impossible d'obtenir des courbes de gain de masse pour des conditions de chargement thermo-mécaniques complexes, tels que ceux supportés par une aube aéronautique en service. C'est pourquoi nous avons choisi d'étudier l'évolution de la microstructure du revêtement au cours du vieillissement et d'établir des liens entre cette évolution microstructurale et la durée de vie évaluée sur des essais de cyclage thermiques.La base d'essai réalisée regroupe des essais d'oxydation cycliques à différentes températures et fréquences de cyclage ainsi que des essais de fatigue mécano-thermique, en phase, hors-phase et complexes. Pour chaque condition testée, des essais interrompus ont permis d'estimer les évolutions microstructurales en fonction des conditions de chargement thermo-mécanique jusqu'à des temps relativement longs. Nous avons en particulier estimé les évolutions de rugosité de surface, d'épaisseur de la couche d'interdiffusion entre le revêtement et le superalliage, et la fraction de phase γ' transformée. Ces deux paramètres sont corrélés respectivement au maximum de la courbe de gain de masse et au nombre de cycle nécessaire pour atteindre un gain de masse nul, pour le système étudié en oxydation cyclique.Nous avons modélisé l'évolution de l'épaisseur de la couche d'interdiffusion en fonction des conditions de chargement thermo-mécaniques. La transformation de phase a été modélisée à l'aide d'un bilan de flux de matière dans le revêtement fonction de l'intégrité de la couche d'oxyde de croissance et de la rugosité de surface. Ces deux modèles ont permis d'estimer l'évolution microstructurale du revêtement en fonction des différents paramètres de chargement thermo-mécanique, et donc d'estimer une durée de vie basée sur ces critères.This study aims at modeling the life time of a NiAlPt coating used at high temperature and deposited on a single crystal nickel-based superalloy AM1. Usually, the life time of coatings is estimated through the evaluation of the mass of coated samples (Net Mass Gain curves), during thermal cycling tests. Existing models are very suitable to describe the evolution of coating in the case of poorly adherent oxide layer. Unfortunately, this is not the case of the studied NiAlPt coating. Moreover, it is impossible to obtain experimentally the Net Mass gain curve of a sample subjected to thermo-mechanical loading, experienced by engine components. Thus, the strategy adopted in this study is to correlate the microstructure of the coating with its life time, evaluated during thermal cycling.The experimental work included cyclic oxidation tests at different temperatures, cycling frequencies and in-phase, out-of-phase and complex thermo-mechanical loadings. For each of the tested condition, interrupted tests allowed the characterization of the microstructure evolution as a function of the loading parameters up to relatively long ageing time. Especially, the roughness of the coating surface has been investigated as well as the interdiffusion zone (IDZ) thickness evolution or the fraction of γ' phase transformed within the coating. These two last parameters where found to be correlated respectively to the time needed to reach the maximum of the Net Mass Gain curve and the time needed to reach the zero mass gain of the curve, under thermal cycling conditions.A model for the interdiffusion (IDZ) thickness evolution was proposed as a function of the loading parameters. The phase transformation in the coating was modeled using a mass balance condition for the aluminum in the coating, including roughness of the surface and oxide scale integrity considerations. This model based on original criteria allowed the estimation of the life time of a coated turbine blade under service conditions

Company Spokesperson vs. Customer Testimonial: Investigating Quoted Spokesperson Credibility and Impact in Business-to-business Communication

Highlights: [•] Partial support for greater credibility of customer rather company spokesperson. [•] Quoting a customer adds credibility to business audience\u27s perception of an article. [•] Attitude toward product more positive when information quotes customer spokesperson. [•] Spokespersons trusted more by businesspeople with low expertise than high expertise