Microstructure et comportement mécanique du cuivre et d'un alliage Cu-Sn nanostructurés par déformation plastique intense et implantés à l'azote

Abstract : Copper is the most used material in electrical field applications. For electrical contacts, its oxidation behavior, thermal stability and hardness is essential. In this work, we attempted to find the key to make strong, but also conductive metal with a high corrosion resistance by finding an appropriate copper microstructure and surface treatment. It is well known that material properties are determined by their microstructure. Also, it was seen that nitride films enhance the oxidation resistance and the surface hardness. Therefore, to achieve our goal, pure copper and a bronze alloy Cu-8wt. %Sn have been subjected to high pressure torsion to make ultra-fine-grains and the surface was then implanted with nitrogen ions. We have investigated the effect of deformation on the hardness and the thermal stability by Vickers microhardness and DSC measurements. It is shown that tin in solid solution delay the recrystallization of the UFG produced by HPT. Tin also promotes the grain refinement and limit the dynamic annihilation during HPT deformation. Furthermore, a correlation between the properties and the microstructure was done by SEM and TEM analyses. A qualitative model taking into account the production and annihilation of dislocations has been developed to predict the influence of process parameters on the evolution of microstructure and hardness. Recrystallized and UFG Cu and CuSn8 were implanted with nitrogen. It has been shown by nanoindentation that their surface hardness increase significantly after implantation. TEM analyses (SAED, STEM HAADF and EELS) demonstrated the formation of copper nitrides which cause superficial hardening. Copper nitrides were also formed in CuSn8 whereas no tin nitride was detected. Moreover, it is interesting to note that the defects (in particular deformation twins) seem to be preferential nucleation sites for copper nitrides.
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Submitted on : Tuesday, September 24, 2019 - 9:35:13 AM
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Ghenwa Zaher. Microstructure et comportement mécanique du cuivre et d'un alliage Cu-Sn nanostructurés par déformation plastique intense et implantés à l'azote. Science des matériaux [cond-mat.mtrl-sci]. Normandie Université, 2019. Français. ⟨NNT : 2019NORMR031⟩. ⟨tel-02295197⟩

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