Étude de l'état mécanique des conducteurs en Nb3Sn durant le traitement thermique pour les futurs électro-aimants d'accélérateurs

The Nb3Sn phase is a superconducting material used in the fabrication of high-field electro-magnet conductors, and is essential for future particle accelerators. Several methods exist for shaping these conductors, but all require a heat treatment at temperatures above 600°C in order to forme the Nb3Sn. During this heat treatment, different intermediate phases appear, resulting an evolution of conductors deformations. It is necessary to quantify these deformations to ensure the integrity of the electro-magnet and the generated magnetic field. However, the underlying mechanisms behind these deformations are not yet fully understood, and currently, there is no model available to estimate the thermo-mechanical state of the conductor during the heat treatment.The present work focuses on studying the mechanical phenomena occuring during the heat treatment of Nb3Sn conductors. A microscopic analysis of the phenomena was conducted at the sub-element level, allowing the identification and quantification of phase change dynamics. An experimental measurement in situ of cable and strand deformations using digital image correlation was performed. The longitudinal dimensional changes confirmed behaviors reported in the literature for similar conductors and provided, for the first time, values for transverse dimensional changes. A thermo-chemo-elastic modeling of the strand was proposed, taking into account the phase change phenomena at the sub-element scale, as well as the thermomechanical state at the strand scale. These models provide, for the first time, an estimation of the mechanical state of a conductor during thermal processing. Further enrichment of the models is necessary to better align with experimental observations.