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Yannick Champion – One of the best experts on this subject based on the ideXlab platform.

  • Activation Volume and energy of bulk metallic glasses determined by nanoindentation
    Materials & Design, 2018
    Co-Authors: Lisa Krämer, Yannick Champion, Verena Maier-kiener, Baran Sarac, Reinhard Pippan
    Abstract:

    Abstract Nanoindentation strain-rate jump testing was used to determine Activation Volumes and energies of various metallic glasses and composites. Three different single phase metallic glasses and three composites (two with amorphous/crystalline Cu and one with an amorphous/amorphous structure) were investigated. The state of the materials was additionally changed by varying the testing temperature between room temperature and 430 °C, by performing high pressure torsion and by thermal cycling. The results show that testing temperature is the main parameter controlling Activation Volume and energy, whereas material modifications by high pressure torsion and thermal cycling do not significantly affect them.

  • Activation Volume in heterogeneous deformation of Mg65Cu12.5Ni12.5(Ce75La25)10 metallic glass
    Journal of Applied Physics, 2015
    Co-Authors: Nicolas Thurieau, Loïc Perrière, Mathilde Laurent-brocq, Yannick Champion
    Abstract:

    Depth variation at constant load in instrumented nano-indentation was used to measure Activation Volume controlling shear band formation in the Mg65Cu12.5Ni12.5(Ce75La25)10 metallic glass. A series of measurements revealed a large scattering of the data spanning from 100 A3 to 800 A3. The distribution of values, which is not following a normal one, may be attributed to the atomic structure of metallic glasses with the absence of long range order, leading to different Volume fraction of shear bands for independent experiments. Activation Volume is analyzed considering the variation of shear band Volume fraction leading to a unique value of a true Activation Volume. An interpretation for the distribution of values is proposed.

  • Activation Volume and deviation from cottrell stokes law at small grain size
    International Journal of Plasticity, 2010
    Co-Authors: Cecilie Duhamel, Yves Bréchet, Yannick Champion
    Abstract:

    Abstract Dependence of Activation Volume with flow stress is examined for metals with grain size lower than 0.3 μm and larger than few tens of nanometers, where plastic deformation is most likely to be governed by a combination of grain boundary sliding and dislocations activity. The experimentally observed deviation from the classic linear behavior given by Cottrell–Stokes law [Basinski, Z.S., 1974. Forest hardening in face centered cubic metals. Scripta Metallurgica 8, 1301–1308] is analyzed, thanks to a modified Orowan equation taking into account of the grain boundaries sliding coupled to dislocations activity. These results are compared to experimental measurements of the Activation Volume, between room temperature and 120 °C, for a copper nanostructure with a grain size of 100 nm. A constant Activation Volume is observed at low stress (or high temperature) followed by an increase of Activation Volume with stress (inverse Cottrell–Stokes behavior). This analysis follows our initial experiments on this fine grained metal prepared by powder metallurgy, which exhibits ductility at near constant stress and strain rate [Champion, Y., Langlois, C., Guerin-Mailly, S., Langlois, P., Bonnentien, J.-L., Hytch, M.J., 2003. Near-perfect elastoplasticity in pure nanocrystalline copper. Science 300, 310–311].

Cecilie Duhamel – One of the best experts on this subject based on the ideXlab platform.

  • Activation Volume and deviation from cottrell stokes law at small grain size
    International Journal of Plasticity, 2010
    Co-Authors: Cecilie Duhamel, Yves Bréchet, Yannick Champion
    Abstract:

    Abstract Dependence of Activation Volume with flow stress is examined for metals with grain size lower than 0.3 μm and larger than few tens of nanometers, where plastic deformation is most likely to be governed by a combination of grain boundary sliding and dislocations activity. The experimentally observed deviation from the classic linear behavior given by Cottrell–Stokes law [Basinski, Z.S., 1974. Forest hardening in face centered cubic metals. Scripta Metallurgica 8, 1301–1308] is analyzed, thanks to a modified Orowan equation taking into account of the grain boundaries sliding coupled to dislocations activity. These results are compared to experimental measurements of the Activation Volume, between room temperature and 120 °C, for a copper nanostructure with a grain size of 100 nm. A constant Activation Volume is observed at low stress (or high temperature) followed by an increase of Activation Volume with stress (inverse Cottrell–Stokes behavior). This analysis follows our initial experiments on this fine grained metal prepared by powder metallurgy, which exhibits ductility at near constant stress and strain rate [Champion, Y., Langlois, C., Guerin-Mailly, S., Langlois, P., Bonnentien, J.-L., Hytch, M.J., 2003. Near-perfect elastoplasticity in pure nanocrystalline copper. Science 300, 310–311].

  • Activation Volume and deviation from Cottrell-Stokes law at small grain size
    International Journal of Plasticity, 2010
    Co-Authors: Cecilie Duhamel, Yves Bréchet, Yannick Champion
    Abstract:

    Dependence of Activation Volume with flow stress is examined for metals with grain size lower than 0.31 mu m and larger than few tens of nanometers, where plastic deformation is most likely to be governed by a combination of grain boundary sliding and dislocations activity. The experimentally observed deviation from the classic linear behavior given by Cottrell-Stokes law [Basinski, Z.S., 1974. Forest hardening in face centered cubic metals. Scripts Metallurgica 8, 1301-1308] is analyzed, thanks to a modified Orowan equation taking into account of the grain boundaries sliding coupled to dislocations activity. These results are compared to experimental measurements of the Activation Volume, between room temperature and 120 degrees C, for a copper nanostructure with a grain size of 100 nm. A constant Activation Volume is observed at low stress (or high temperature) followed by an increase of Activation Volume with stress (inverse Cottrell-Stokes behavior). This analysis follows our initial experiments on this fine grained metal prepared by powder metallurgy, which exhibits ductility at near constant stress and strain rate

  • Activation Volume and deviation from Cottrell–Stokes law at small grain size
    International Journal of Plasticity, 2010
    Co-Authors: Cecilie Duhamel, Yves Bréchet, Yannick Champion
    Abstract:

    Abstract Dependence of Activation Volume with flow stress is examined for metals with grain size lower than 0.3 μm and larger than few tens of nanometers, where plastic deformation is most likely to be governed by a combination of grain boundary sliding and dislocations activity. The experimentally observed deviation from the classic linear behavior given by Cottrell–Stokes law [Basinski, Z.S., 1974. Forest hardening in face centered cubic metals. Scripta Metallurgica 8, 1301–1308] is analyzed, thanks to a modified Orowan equation taking into account of the grain boundaries sliding coupled to dislocations activity. These results are compared to experimental measurements of the Activation Volume, between room temperature and 120 °C, for a copper nanostructure with a grain size of 100 nm. A constant Activation Volume is observed at low stress (or high temperature) followed by an increase of Activation Volume with stress (inverse Cottrell–Stokes behavior). This analysis follows our initial experiments on this fine grained metal prepared by powder metallurgy, which exhibits ductility at near constant stress and strain rate [Champion, Y., Langlois, C., Guerin-Mailly, S., Langlois, P., Bonnentien, J.-L., Hytch, M.J., 2003. Near-perfect elastoplasticity in pure nanocrystalline copper. Science 300, 310–311].

Robert C. Liebermann – One of the best experts on this subject based on the ideXlab platform.

  • Activation Volume of Si diffusion in San Carlos olivine: Implications for upper mantle rheology
    Journal of Geophysical Research: Solid Earth, 1999
    Co-Authors: F. Béjina, O. Jaoul, Robert C. Liebermann
    Abstract:

    The effect of pressure on silicon diffusion in San Carlos olivine has been determined using a uniaxial split-sphere apparatus (USSA-2000) and the nuclear reaction analysis technique (NRA) on the 30Si isotope. Experiments were performed at high temperature, T = 1763 K, and pressures between 4 and 9 GPa. The specimens were inserted into a pure Fe capsule, which is very effective in maintaining the oxygen fugacity within the stability field of olivine, as well as providing a soft medium to mechanically protect the crystals. Diffusion profiles along the b→ crystallographic axis and of characteristic length of the order of 50 nm were obtained after annealing the olivine samples between 1 and 4 hours. We find the Activation Volume for silicon diffusion in San Carlos olivine to be VSi = +(0.7±2.3) × 10−6 m3/mol after a correction for oxygen fugacity which is pressure-dependent. This result demonstrates that pressure has practically no effect upon silicon diffusion under our temperature and pressure conditions. Extrapolation of our high-pressure measurements to 1 atm gives a Si diffusion coefficient, log(DSi) = −18.9±1.0 (with DSi in m2/s). Finally, our experiments show that according to the point-defect model of Jaoul [1990], the Activation Volume for creep of olivine at high temperature is dominated by the effect of pressure on the Mg defect concentration and has an Activation Volume close to 6 × 10−6 m3/mol.

  • Activation Volume of silicon diffusion in San Carlos olivine
    Geophysical Research Letters, 1997
    Co-Authors: F. Béjina, Paul Raterron, Jianzhong Zhang, O. Jaoul, Robert C. Liebermann
    Abstract:

    The Activation Volume of silicon diffusion (Vsi) in olivine is reported for the first time. Specimens of San Carlos olivine single crystal were annealed at 1763 K and at pressures to 9 GPa in an uniaxial split-sphere apparatus. 30Si was used as tracer and the diffusion profiles were analyzed using the resonant nuclear reaction 30Si(p,γ). We obtain Vsi = (−1.9 ± 2.4)×10−6 m³/mol with a more probable value close to zero.