Harrison, Robert W., Greaves, Graeme, Hinks, J. A. and Donnelly, S. E. (2017) A study of the effect of helium concentration and displacement damage on the microstructure of helium ion irradiated tungsten. Journal of Nuclear Materials, 495. p. 492. ISSN 0022-3115

Transmission electron microscopy (TEM) with in situ He ion irradiation has been used to examine the damage microstructure of W when varying the helium concentration to displacement damage ratio, irradiation temperature and total dose. Irradiations employed 15, 60 or 85 keV He+ ions, at temperatures between 500 and 1000°C up to doses of ~3.0 DPA. Once nucleated and grown to an observable size in the TEM, bubble diameter as a function of irradiation dose did not measurably increase at irradiation temperatures of 500°C between 1.0 and 3.0 DPA; this is attributed to the low mobility of vacancies and He/vacancy complexes at these temperatures. Bubble diameter increased slightly for irradiation temperatures of 750°C and rapidly increased when irradiated at 1000°C. Dislocation loops were observed for at irradiation temperature of 500 and 750°C and no loops were observed at 1000°C. Burgers vectors of the dislocations were determined to be b = ±1/2<111> type only and both vacancy and interstitial loops were observed. The proportion of interstitial loops increased with He-appm/DPA ratio and this is attributed to the concomitant increase in bubble areal density, which reduces the vacancy flux for both the growth of vacancy-type loops and the annihilation of interstitial clusters.

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