Mécanismes de déformation et d'amorçage de fissures dans l'alliage Udimet™ 720Li en relation avec les paramètres microstructuraux

Abstract : This study contributes to the understanding of the deformation and damage mechanisms in a Nickelbasedsuperalloy (the Udimet 720Li) used for the manufacturing of aeroengines high pressure turbinedisks submitted to monotonic and cyclic loadings at temperatures below 500 °C under service conditions.Fatigue crack initiation at 20 °C and 465 °C was systematically observed at large crystallographic facetswhatever the microstructure. An extensive quantitative study of the slip activity at the surface showed thatcrack initiation results from a difficult slip transmission between neighbouring grains. In more details, alocalized crystallographic rotation confined in micro-volumes detected at the tip of slip bands interactingwith the grain boundary were identified to trigger crack initiation.The crystallographic configurations favouring such a process are closely related to the TWIST anglebetween active slip systems on each side of the grain boundary and to a dense and fine precipitationconfining the plasticity.Mots-clés
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Baptiste Larrouy. Mécanismes de déformation et d'amorçage de fissures dans l'alliage Udimet™ 720Li en relation avec les paramètres microstructuraux. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2014. Français. ⟨NNT : 2014ESMA0019⟩. ⟨tel-01129092⟩

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