Capabilities of Nanostructured Tungsten for Plasma Facing Material

One of the bottle necks for fusion to become a reality is the lack of materials able to withstand the harsh conditions taken place in a reactor environment. In particular, plasma facing materials (PFM) have to resist large radiation fluxes and thermal loads. Nowadays, tungsten is one of the most attractive materials proposed for PFM. However, it is known that the irradiation of tungsten with H leads to surface blistering and subsequent cracking and exfoliation which is unacceptable. In particular, these effects have been observed to be more severe when W is subjected to pulse irradiation

Continuum mesoscale modelling of nanocrystalline fcc metals under shock-loading using an spectral formulation fed by molecular dynamics results

In this paper we present a micromechanical approach based on Fast Fourier Transforms to study the role played by dislocation glide and grain boundary (GB) accommodation in the determination of the yield strength of nanostructured materials under shock. For this, we construct unit cells representing self-similar polycrystals with different grain sizes in the nanometer range and use local constitutive equations for slip and grain boundary accommodation. We study the effect of grain size and shock pressure on the local and effective behavior of nanostructured fcc materials with parameters obtained from experiments and atomistic simulations. Predictions of a previous pressure-sensitive model for the effective yield strength behind a shock front are improved by considering strain partition between slip and GB activity

Shock compression of [001] single crystal silicon

Silicon is ubiquitous in our advanced technological society, yet our current understanding of change to its mechanical response at extreme pressures and strain-rates is far from complete. This is due to its brittleness, making recovery experiments difficult. High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon (using impedance-matched momentum traps) unveiled remarkable structural changes observed by transmission electron microscopy. As laser energy increases, corresponding to an increase in peak shock pressure, the following plastic responses are are observed: surface cleavage along {111} planes, dislocations and stacking faults; bands of amorphized material initially forming on crystallographic orientations consistent with dislocation slip; and coarse regions of amorphized material. Molecular dynamics simulations approach equivalent length and time scales to laser experiments and reveal the evolution of shock-induced partial dislocations and their crucial role in the preliminary stages of amorphization. Application of coupled hydrostatic and shear stresses produce amorphization below the hydrostatically determined critical melting pressure under dynamic shock compression

A numerical study of energy transfer mechanisms in materials following irradiation by swift heavy ions

61.80.Az Theory and models of radiation effects, 63.20.kd Phonon-electron interactions,

Deformation of nanocrystalline materials at ultrahigh strain rates – microstructure perspective in nanocrystalline nickel

Nanocrystalline materials with grain sizes smaller than 100 nm have attracted extensive research in the past decade. Due to their high strength, these materials are good candidates for high pressure shock loading experiments. In this paper, we investigated the microstructural evolutions of nanocrystalline nickel with grain sizes of 10-50 nm, shock-loaded in a range of pressures (20-70 GPa). A laser-driven isentropic compression process was applied to achieve high shock-pressures in a timescale of nanoseconds and thus the high-strain-rate deformation of nanocrystalline nickel. Postmortem transmission electron microscopy (TEM) examinations reveal that the nanocrystalline structures survive the shock deformation and that dislocation activity is the prevalent deformation mechanism when the grain sizes are larger than 30 nm, without any twinning activity at twice the stress threshold for twin formation in micrometer-sized polycrystals. However, deformation twinning becomes an important deformation mode for 10-20 nm grain-sized samples

Laser compression and fragmentation of metals

Using the Janus LLNL and Omega facilities, we are using laser energy to generate shock and quasi-isentropic compression of monocrystalline, polycrystalline, and nanocrystalline FCC and BCC metallic specimens(Cu, Ni, V). We have investigated the internal defects generated by experimental and computational (MD) means. By comparing experimentally observed and computationally predicted structures we can obtain new insights into the fundamental deformation mechanisms. We have also investigated the mechanisms of spall initiation, propagation, and fragmentation