J.A. Spitznagel

Ion beam modification of 6H/15R SiC crystals☆

Abstract Large single crystals of silicon carbide consisting predominantly of 6H polytype have been implanted with hydrogen, nitrogen, or aluminum ions at 300 K. Rutherford backscattering-channeling techniques have been used to characterize atomic displacement effects resulting from implantation and postimplantation annealing at 573 K. Amorphization fluences for all three ions correspond to deposition of a critical damage energy of 2 × 1021 keV cm 3 . Annealing of N+ or Al+ implanted crystals for 0.5 h at 573 K produces appreciable recovery in damaged but crystalline regions. Defect annealing is inhibited in amorphous and heavily doped areas of the crystals.

Mechanical response of single crystal Si to very high fluence H+ implantation☆

Abstract Single crystals of Si are doped at room temperature with hydrogen from 2 × 1016 H/cm2 to 1.6 × 1018 H/cm2 in a range of energy from 20 keV to 1 MeV. Experiments using RBS/channeling, profilometry and cross-section TEM are reported.

Implanted hydrogen effects at high concentrations in model low Z shielding materials

Abstract Shielding of near-plasma structural components has long been recognized as an important consideration in Tokamak operation. Various low Z materials have been proposed and tested to determine sputtering characteristics, hydrogen retention and isotope exchange kinetics. The mechanical response of these materials to high fluence atomic displacement damage and accumulation of hydrogen and helium is receiving extensive attention at the present time. We report on detailed mechanistic studies of a model shielding material. More extensive treatments are given elsewhere. 1,2

Simulation of Radiation Damage in Solids

A combined theoretical and experimental study of primary recoil spectra effects or radiation damage in silicon is presented. Calculations determined how the damage energy is partitioned into free defects and cascades by fast collisions. The theory also showed that on a time scale ~10-14 sec. a very weak mass dependence of the lattice damage is to be expected. Channeling experiments were then performed on <111> single crystal silicon implanted with 1.0 MeV 20Ne, 0.5 MeV 4He and 75 keV 1H. Energies and fluences of the ions were matched such that over the first 0.3 ¿m the damage energy deposited and the rate of energy deposition were the same for all species. The experimental data were analyzed assuming that equivalent primary damage states will evolve into statistically equivalent final damage states at high fluences. They confirm that the final damage is essentially independent of the mass of the bombarding ion.

Ion irradiation effects on high strength, high conductivity copper alloys

Abstract Microstructural effects in a solid solution cold work strengthened copper alloy (Cu−0.15 wt.% Zr), a precipitation strengthened alloy (beryllium copper) and a dispersion hardened alloy (Cu−0.6 wt.% Al as Al2O3 particles) after high energy ion irradiation at fluences from 1 dpa to 20 dpa at temperatures from 523 K to 773 K have been characterized by detailed TEM investigation. Atomic displacement processes result in texture-dependent accelerated recovery by dislocation climb and glide in the Cu−0.15 wt.% Zr alloy. Coarsening (or disappearance) of GP zones and accelerated growth of CuBe precipitates are observed in the beryllium copper alloy. Microstructural evolution in the oxide dispersion strengthened alloy entails progressive amorphization and dissolution of the Al2O3 particles.

Primary recoil spectra and subcascade effects in ion bombardment experiments

Abstract The motivation of this work is to compare atomic damage configurations associated with neutron and fast-ion damage. The question we set out to answer was: Which choice of ion mass and kinetic energy provides the best simulation of fast neutron damage? The answer which emerges is that the primary damage state, i.e. the statistical distribution of free defects, and subcascade regions before annealing, is remarkably independent of the ion species and its PKA spectrum. This conclusion is sufficiently surprising to warrant careful examination, and is presented together with a variety of qualifications.

Critical cavity sizes in dual-ion bombarded 304 SS part I: Experiment

Abstract A multikey computer file system and several algorithms relating measured cavity size distributions, point defect sink strengths and an equation of state for helium atoms in gas bubbles have been used to determine lower bound critical cavity sizes from dual-ion bombardment data for 304 SS. The results are discussed within the framework of the critical cavity size concept for a transition from gas-driven to bias-driven cavity growth.

Correlation Between Microhardness, Tensile Properties, and Notch Ductility of Irradiated Ferritic Steels

The work demonstrates that changes in Charpy V-notch impact properties can be monitored by microhardness measurements for radiation-embrittled ferritic steels in the transition region. A qualitative basis for understanding this relationship is developed from extension of existing models for lower-shelf fracture toughness and analysis of the shifts in the ductile-to-brittle transition temperature with changes in the yield strength. Microhardness is shown to correlate with the yield stress of the irradiated ferritic materials described in this report. A comparison of Charpy energy and yield stress data suggests that, for the purposes of this analysis, the fracture stress is insensitive to both irradiation and annealing in the transition region.

Deuterium and helium trapping at TiC particles in ferritic steel

Abstract First wall and blanket materials in Tokamak machines must accommodate increasing concentrations of helium and hydrogen isotopes. Alloy design principles point to the efficacy of trapping He and hydrogen at finely dispersed precipitates to minimize their impact on mechanical properties. Titanium carbide particles are known to trap He effectively in austenitic stainless steel. Less is known about TiC as a trap for helium and hydrogen isotopes in ferritic steels. This paper demonstrates the feasibility of directly measuring the trapping of helium and deuterium at TiC-ferrite interfaces using atom probe field ion microscopy.

Evolution of cavity size distributions in dual-ion irradiated austenitic stainless steel and Fe-Cr-Ni ternary alloys☆

Abstract The first four moments of experimentally measured cavity size distributions in dual-ion irradiated 304SS, Fe-12Ni-15Cr and Fe-30Ni-15Cr alloys have been calculated for a range of fluences, helium injection rates, and irradiation temperatures. The moments are shown to correctly describe the effects of alloy composition, fluence, helium and temperature on the evolution of the cavity size distributions. Experimentally determined moments are compared with those calculated from cavity nucleation and growth theories. The moments reflect the competition between nucleation and growth processes and provide insight into the details of the transient low swelling regime.