Size Effect in the Plasticity of Multiscale Nanofilamentary Cu/Nb Composite Wires During in-situ Tensile Tests Under Neu
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Size Effect in the Plasticity of Multiscale Nanofilamentary Cu/Nb Composite Wires During in-situ Tensile Tests Under Neutron Beam Vanessa Vidal1,2, Ludovic Thilly2, Steven Van Petegem3, Uwe Stuhr3, Florence Lecouturier1, Pierre-Olivier Renault2, and Helena Van Swygenhoven3 1 Laboratoire National des Champs Magnétiques Pulsés, CNRS-UPS-INSA, 143 avenue de Rangueil, Toulouse, 31400, France 2 Laboratoire de Métallurgie Physique, CNRS-University of Poitiers, SP2MI, Boulevard M. et P. Curie, Teleport 2, BP 30179, Futuroscope Chasseneuil, 86962, France 3 Paul Scherrer Institut, Villigen-PSI, CH-5232, Switzerland
ABSTRACT Copper-based high strength nanofilamentary wires reinforced by bcc nanofilaments (Nb or Ta) are prepared by severe plastic deformation for the winding of high pulsed magnets. In situ tensile tests under a neutron beam were performed on a Cu/Nb nanocomposite composed of a multiscale Cu matrix embedding 554 Nb filaments with a diameter of 267 nm and spacing of 45 nm. The evolution of elastic strains for individual lattice plane in each phase and peak profiles in the copper matrix versus applied stress is presented. Then, the co-deformation behavior with different elastic-plastic regimes and load sharing is evidenced: the Cu matrix exhibits size effect in the finest channels while the Nb nanowhiskers remain elastic up to the macroscopic failure. A strong load transfer from the copper matrix onto zones that are still in the elastic regime is also revealed. Taking into account results from residual lattice strains also determined by neutron diffraction, the yield stress in the finest Cu channels is in agreement with calculations based on a single dislocation regime. INTRODUCTION The design and construction of non-destructive high field magnets still represent a significant challenge for materials selection and development because the components have both structural (high elastic limit) and functional (high electrical conductivity) requirements that are usually contradictory [1-3]. In this context, reinforced materials such as nanofilamentary Cu/Nb wires were processed via severe plastic deformation. These nanocomposites belong to the nanostructured materials family that is generating a great interest because of their unusual properties compared to bulk materials. Nevertheless, the combination of different phases with different microstructure dimensions lead to complex co-deformation behaviour. Thus, a complete characterization of the nanofilamentary wires and the understanding of the co-deformation behaviour are needed to optimize their application; such goal requires the use of complementary techniques. The Laboratoire National des Champs Magnétiques Pulsés, Toulouse, France, devotes, for more than a decade, large efforts to the characterization of plasticity mechanisms in copperbased nanocomposites wires. Notably, for Cu/Nb nanofilamentary wires, different types of techniques, as Transmission Electron Microscopy (TEM) observations, classical tensile test, X-
ray diffraction, in-situ
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