Browsing by Author "Sauvage, Xavier"

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    Influence of strain rate and Sn in solid solution on the grain refinement and crystalline defect density in severely deformed Cu
    (Elsevier Ltd., 2021-03) Zaher, Ghenwa; Lomakin, Ivan; Enikeev, Nariman; Jouen, Samuel; Saiter-Fourcin, Allisson; Sauvage, Xavier; Department of Applied Physics; Complex Systems and Materials; Université de Rouen; St. Petersburg State University
    A commercially pure Cu and a Cu-8 wt.%Sn alloy were subjected to high pressure torsion (HPT) to study the effect of Sn as solute element and deformation rate on the grain refinement mechanism and the defect accumulation in Cu. The microstructure and hardness of produced ultrafine grained (UFG) states of both materials were carefully characterized. We show that addition of Sn in Cu leads to significant decrease in grain size, accumulation of higher stored energy and increase in hardness accompanied with the delay of hardness saturation with shear strain. Increasing HPT deformation rate induces significant heat dissipation in the processed materials markedly pronounced in CuSn8 as compared to Cu. Surprisingly, deformation rate has the opposite effect on the microhardness of UFG Cu and CuSn8, which decreases with the deformation rate for the case of Cu, while exhibits faster saturation to higher values for CuSn8. We also show that despite higher self-heating at higher deformation rates, higher HPT rotation speed provides reduction in grain size and increase in the defect density for CuSn8 alloy. This effect is assumed to be related to strong interactions between Sn solute atoms and strain-induced defects so that mechanically driven effects prevail over dynamic annihilation of dislocations. Finally, we present a qualitative model based on the phenomena of production and annihilation of dislocations. This model was able to reproduce the evolution of grain size, concentrations defects and hardness with different deformation parameters and after the addition of solute element in material.
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    Mechanism of large strain accommodation assisted by shear localization in a precipitation-hardened Cu–Be alloy
    (Elsevier Science, 2021-08-17) Lomakin, Ivan; Nigmatullina, Alfiia; Sauvage, Xavier; Department of Applied Physics; St. Petersburg State University; Université de Rouen
    The influence of the structural state on deformation mechanisms under large strains was investigated in a Cu – 2 wt.% Be alloy. Torque evolutions during straining exhibit serrations typical of structural relaxations in the precipitation-hardened alloy, but not in the solid solution state. Microstructure characterization revealed that homogeneous deformation of the solid solution led to strong grain size reduction (20 nm), while localization occurred in the precipitated state with numerous shear bands. The role of CuBe precipitates on hindering dislocation glide and the resulting shear localization under large strain is discussed.
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    Nanostructuring of beryllium bronze : Contribution of grain boundaries segregation and solid solution
    (Elsevier Science B.V., 2024-02-15) Lomakin, Ivan; Nigmatullina, Alfiia; Sauvage, Xavier; Department of Applied Physics; Complex Systems and Materials; St. Petersburg State University; Université de Rouen
    The impact of composition on grain refinement in solutionized Cu-Be alloys was investigated. High-pressure torsion resulted in grain sizes of 10–110 nm for Cu–1 wt.% Be and 10–20 nm for Cu-2 wt.%Be. Our findings indicate that Be stabilizes the nanoscale grain size, which is influenced by the balance between defect creation and annihilation. Consequently, Be concentration serves as a key parameter for directing microstructure and property changes during severe plastic deformation.