Radiation damage, annealing and thermal desorption in tungsten induced by low energy A+ion bombardment

Abstract

Abstract Prethinned foils of polycrystalline tungsten (over 70 per cent of transparent grains had (100) orientation or very near to it; other grains had (113) and (111) orientations) have been bombarded with 4 keV A+ ions. The ion doses varied from 2.1015 to 5.1017 ions/cm2. Electron microscope observations have shown that the intensity of damage in the form of large defect clusters, dislocations, complex dislocation tangles and networks increased with ion dose, but a 'saturation' effect was found at doses of 1 to 2.1017 ions/cm2. The concentration of damage depends on the crystallographic orientation of the grains. The maximum damage density was found in grains with (100) orientation at all bombardment doses. In (100) oriented grains a tendency for alignment of irradiation-induced dislocation loops was found. These row formations were parallel to the (110) direction. The development of such alignment depends on ion energy, flux and dose, and it is closely connected with surface and crystal structure. For annealing studies temperatures of 650°C, 900°C, 1200°C, 1500°C and 2000°C were used. These temperatures have been shown, by us and some other authors, to represent the desorption peak temperatures for tungsten, obtained under similar bombardment conditions as used in the present study. While the annealing of damage at 650°C (one hour in a vacuum better than 10−7 torr) produced some effect only at the highest doses, heating one hour at 900°C had a remarkable effect even for ion doses lower than 1.1017 ions/cm2. The main maximum in thermal desorption spectra at temperatures around 1200°C agrees very well with the most intense annealing of damage in tungsten. Correlation of the annealing process in ion bombardment tungsten with thermal desorption spectra helps to explain the processes occurring in tungsten connected with low energy ion bombardment, namely damage formation, thermal desorption and annealing of damage. Evidence of high damage density in tungsten at different ion doses and low ion energies suggests that the radiation damage model for desorption and the analysis of our results given earlier were correct. Our results agree with the annealing studies of damage in other bcc metals.