S. B. Fisher

On the temperature rise in electron irradiated foils

Abstract The temperature rise in thin metallic foils under intense electron irradiation has been computed as a function of beam conditions, electron energy, and the physical properties of the foil. The model due to Gale and Hale was used in conjunction with the corrected Bethe electron energy loss formula for relativistic electrons. Although the nature of the assumptions made renders the results generally unapplicable to low thermal conductivity materials, a set of beam conditions etc. are specific for the particular case of a small temperature rise in a ceramic foil (UO2).

Dislocation loop growth in pure iron under electron irradiation

Abstract In common with all ferritic metals, pure iron is resistant to irradiation induced void swelling, although the reasons for this are not well understood. This paper describes a number of high energy electron irradiations of iron foils, to examine their behaviour in the early stages of damage. The nucleation and growth of dislocation loops has been observed and compared with existing theoretical models. In previous similar experiments only one type of loop has been reported, but in the present study a second set of loop was formed, which grew alongside the first and eventually interacted with them. Although electron irradiations do not necessarily reproduce precisely the effects of neutrons in a reactor, there are nevertheless some wider implications of these results, and in particular the role of interstitial solutes in the swelling resistance of ferritic materials is discussed.

The void swelling of a γ′-hardened alloy

Abstract The swelling behaviour of a γ′-hardened alloy has been studied by High Voltage Electron Microscopy. The rate of void swelling has been found highly dependent on damage rate, temperature and γ′-particle size. Significant swelling was only achieved at damage rates approaching 10−2 d/a/sec, and at specific γ′-particle sizes. At small (≃ 30 A), and large (>700 A) particle diameters the swelling rate was high. In the fully aged condition with particle diameters of the order 200 A, the swelling rate was minimized. The mechanism of void swelling has been attributed to the nonconservative climb of irradiation induced dislocations.

ELECTRON RADIATION DAMAGE IN COPPER IN THE HIGH VOLTAGE ELECTRON MICROSCOPE.

Abstract The various factors influencing the nucleation of radiation damage in the HVEM are reviewed. A method for obtaining quantitative information from observations is given. The effect of reirradiation at room temperature on the damage formed at elevated temperatures is shown. This effect may give experimental information concerning the strain fields surrounding large dislocation loops.

The effect of stress on the incubation and growth of voids

Abstract The influence of stress on void growth at high temperatures through its effect on the thermal emission of vacancies from internal sources has been included in numerical solutions of swelling for several years. In this paper we formulate this stress effect into an analytical expression which describes both the incubation and subsequent growth of cavities in an irradiated material under stress.

The effect of mutual recombination on dislocation point defect sink strengths

Abstract The diffusion equations which describe the distribution of point defects around a line dislocation have been solved by a computer iterative technique for the case of dislocations in copper. The sink strengths have been calculated in a manner consistent with the requirements of the rate theory continuum model [RTC]. When mutual recombination is negligible the appropriate analytic results are reproduced exactly. An increase in mutual recombination leads to an increase in both sink strengths and the bias parameter. An empirical relation is derived for the variation of sink strength with mutual recombination.

The dose dependence of swelling in irradiated metals

Abstract The dose and dose rate dependences of swelling are determined theoretically for metals under different types of irradiation. The simple theory assumes that it is the preferential absorption of interstitials by climbing dislocations that is directly responsible for the swelling. In particular, the different dose dependences observed under ion, electron, and neutron irradiation are explained in terms of the dislocation configurations operative in each case.

The effect of foil surfaces on the loss of point defects from electron irradiated metal foils

Abstract The diffusion equations which describe the point defect distributions in electron irradiated metal foils have been solved by a computer iterative technique.

The quantitative analysis of loop-growth and void-swelling in nickel

Abstract Dislocation loop and void growth experiments at several temperatures in the HVEM have been used to investigate point defect behaviour in nickel. It has been found that the dislocation bias is about 5% for interstitials and that voids also have a preference for interstitial defects. The value of the void bias is much less than the dislocation bias, being about 0.5%, so that swelling still occurs. The vacancy migration energy, E v m , has been confirmed to be 1.1 ± 0.1 eV .

High voltage electron microscopy observations of the growth of interstitial loops in an iron-nitrogen alloy

Abstract Precipitation of interstitial loops and iron nitride in an iron nitrogen alloy, has been examined in the temperature range 30 °C to 300 °C using a High Voltage Electron Microscope. The use of thick foils has enabled the direct observation of iron nitride precipitation. Observations confirm both theoretical and indirect experimental studies of the hardening behaviour of α-iron alloys following neutron irradiation. Many of the interstitial loops are of {100} type. In certain cases, the unfaulted ½{110} type are observed. The precipitation of iron nitride at the edge of the loop, effectively prevents further growth thus inhibiting void swelling.