P. Jung

Atomic displacement functions of cubic metals

Abstract Atomic displacement functions for various cubic transition metals are derived from electron, ion and neutron damage rate data. Damage rates under electron and light ion irradiation as well as the total number of defects produced during α-implantation are calculated over a wide range of energies from these displacement functions. General relations for displacement functions and displacement energies are given which may be used for other metals or alloys for which no experimental data are available. The results are suggested to find practical use for correlating material behaviour from simulation experiments to a fusion environment.

Recommendation of miniaturized techniques for mechanical testing of fusion materials in an intense neutron source

Abstract Plans for the construction of an intense high energy neutron source for materials development for future fusion reactors call for miniaturized testing techniques which are indispensable for an effective use of the target area. A limited number of techniques is selected and recommendations for their standardization are given. It is the opinion of the authors that international efforts should concentrate on further development of these techniques, especially on a detailed correlation between miniature and bulk behavior.

The formation of helium bubbles near the surface and in the bulk in nickel during post-implantation annealing

Abstract A systematic TEM study on nickel specimens homogeneously implanted with about 1000 appm helium at room temperature and annealed for about 1 h between 873 and 1273 K is reported and interpreted. During annealing the observed bubble structure coarsens substantially. The coarsening rate is, however, much faster close to the surface than in the bulk. The apparent activation energies of the average bubble radius in these regions are 1.1 and 0.23 eV, respectively. Results from other investigations confirm and complete these findings. The enhanced coarsening near the surface is attributed to the relaxation of initially overpressurized bubbles by vacancies supplied by the nearby surface. The coarsening mechanism in this region is identified as Ostwald ripening. In the bulk, the latter is suppressed due to a reduction of the vacancy concentration by the overpressure in the bubbles. In this region bubble coarsening is attributed to coalescence via bubble migration controlled by surface diffusion.

Stress and stress transient effects on irradiation creep of 20% cold worked stainless steels and nickel alloys

Abstract Creep enhancement during 6.2 MeV proton irradiation was examined at 300°C for 20% cold worked specimens of pure nickel, Ni-1.2at%W, FeCrNi- and FeCrNiMo-alloys of AISI 316 composition and of commercial type 316 stainless steel. All materials showed a transition from linear to quadratic stress dependence. Stress transients during irradiation caused transient strains which were proportional to the stress change and about 10% of the elastic strain change. The results are compared to recent data from other light ion and reactor neutron experiments and are discussed with reference to theoretical models.

Helium production and long-term activation by protons and deuterons in metals for fusion reactor application

Abstract Cross sections for the production of helium and long-living radioactive isotopes by protons of 8, 16 and 24 MeV and by deuterons of 9 and 14 MeV were measured in foils of high purity Al, Ti, V, Fe, Ni, Cu and an AISI-316 type stainless steel. Ratios of helium production to displacement damage were derived which are commonly used as a quantity to characterize different irradiation environments. Release of the helium gas was measured during heating the specimens up to the melting temperature.

Irradiation creep in deuteron bombarded stainless steel

Abstract A high purity and a commercial version of cold worked type 316 stainless steel were irradiated with 10 MeV deuterons and 7 MeV protons at tensile stresses between 100 and 350 MPa and temperatures between 300°C and 400°C to investigate irradiation induced creep. The creep rate depends quadratically on stress and shows a slight increase with temperature. Comparison with other light-ion creep experiments and to in-pile creep data from fast reactors shows reasonable agreement if dose rates are properly converted to dpa rates. The results are compared with current theoretical models of a climb and glide creep mechanism.

Effects of irradiation and implantation on permeation and diffusion of hydrogen isotopes in iron and martensitic stainless steel

Abstract Permeation and diffusion of hydrogen were measured on virgin and preirradiated iron and martensitic stainless steel with thickness of 210 and 810 μm at temperatures from 100° to 400°C. A slight dependence of permeability on thickness and pressure was tentatively ascribed to surface effects. Pressure dependence of diffusivity and deviation from Arrhenius behaviour at low temperatures and/or small thickness was consistently described by a model of hydrogen trapping at saturable traps. Preirradiation at room temperature to displacement doses up to 1.5 × 10 −3 dpa had no influence on permeation but reduced the diffusivity in the steel. Diffusion coefficients were also derived from the time dependence of hydrogen release during implantation. The results show significant differences to the results from permeation measurements. Permeation was strongly increased under penetrative light ion irradiation, probably due to ionization and dissociation of the hydrogen gas on the upstream side.

Diffusion and agglomeration of helium in FCC metals

Abstract Foils of pure fcc metals (Al, Ni, Cu, Ag, Au) of thicknesses from about 1 to 150 μm were homogeneously implanted with 4He at room temperature to atomic concentrations from 10−9 to 10−4. A subsequent thermal desorption experiment allowed to discriminate between different diffusion mechanisms by which the helium migrates to the surfaces. Diffusion coefficients similar to self-diffusion data indicate that in Al, Ag and Au helium migrates predominantly by a vacancy mechanism, while relatively sharp release peaks indicate a dissociative mechanism in Ni and Cu. With increasing helium content and specimen thickness an increasing amount of helium is retained in the specimens. Comparison to computer models of helium agglomeration allows to derive the minimum size of stable agglomerates.

Void swelling and irradiation creep in stainless steel under compressive and tensile stress

Abstract Void swelling at 500°C and irradiation creep at 300°C in a pure Fe-Cr-Ni-Mo alloy of Type 316 stainless steel composition were measured at doses up to 0.4 dpa under uniaxial compressive or tensile stress up to 100 MPa. The irradiation creep rate under compression was nearly equal in its absolute value to that under tension. Neither the mean diameter nor the total number density of voids showed, within the experimental error, any noticeable dependence on the stress direction. This indicates an effect of the deviatoric stress component rather than the hydrostatic stress on void nucleation. Implications of this finding on the various proposed mechanisms of stress-effects on swelling are discussed.

A correlation between irradiation creep strength and yield stress of FCC metals and alloys

Abstract Transient and stationary creep under 6.2 MeV proton irradiation was investigated at temperatures between 100 and 400°C in pure metals (Ag, Cu, Pt, Ni) and in solution-hardened alloys (Ni-1.2 at% W, Ni-8.5 at% Al, Fe-18Cr-14Ni, Fe-19Cr-20 Ni-3Mo and AISI type 316 stainless steel). The creep rates of all materials depend linearly on dose rate and show below a stress σ lin also a linear dependence on stress. An empirical correlation of the stationary irradiation creep rate and of σ lin with the yield stress of the unirradiated material is established. Inferences from this correlation on current irradiation creep theories are discussed.