Lucas VAROTO – Microstructural Optimization of Cu-Cr alloys for Electrical Contacts in Vacuum Interrupters

Jury

Prof. Andreas Mortensen, EPFL, Lausanne (Suisse) - Rapporteur
DR. Eric Maire, INSA, CNRS, Lyon - Rapporteur
Prof. Thomas Pardoen, IMMC, UCLouvain - Examinateur
MC. Elodie Courtois, IRDL, Université Bretagne-Sud, Lorient - Examinatrice
Prof. Daniel Bellet, LMGP, Université Grenoble Alpes - Examinateur
DR. Jean-Jacques Blandin, SIMaP-GPM2, CNRS, G-INP - Directeur de thèse
MC. Guilhem Martin, SIMaP-GPM2, G-INP - Invité
Ing-Dr. Anthony Papillon, Schneider Electric, Grenoble - Invité
 

Abstract

Cu-Cr alloys with 25 to 50%pCr are widely used for electrical contacts in vacuum interrupters for medium-voltage applications, due to their excellent combination of mechanical, thermal and electrical properties. These properties result from the excellent conductivity of copper and a semi-refractory metal, chromium, which can withstand the constrains imposed by these applications. The properties of conventional Cu-Cr alloys (solid-state sintering-SSS and vacuum arc remelting-VAR) are of industrial interest to improve their performance, however the microstructure-properties relationship is not yet fully understood. Moreover, despite the interest in Cu-Cr composites, the design of new Cu-Cr composite microstructures has been limited by conventional manufacturing processes. In this thesis work, a multi-scale characterization of the microstructure of Cu-Cr SSS and VAR composites was carried out using techniques ranging from macro- to nanoscale, from X-ray tomography to transmission electron microscopy. Cr phase distribution and porosity population are characterized in 3D. The mechanical, electrical and thermal properties of these alloys have been characterized. By coupling numerical modeling to this multi-scale experimental study, the microstructure-properties relationships are rigorously established. The microstructural-property space of such alloys is unveiled. The design of new Cu-Cr alloy microstructures was investigated by means of rapid solidification. Microstructural evolutions were characterized. Their mechanical, electrical and thermal properties were improved compared to conventional Cu-Cr composites. We suggest that these new, improved microstructures may be of interest for medium-voltage applications of Cu-Cr electrical contacts, in particular to improve their current-breaking capability.