High fluence hydrogen implantation in copper: blistering and grain boundary movement

Annealed polycrystalline copper samples are implanted with 325 keV H+-ions at ambient temperature for total fluences of 2.2 to 8.4 x 1018 ions/cm2, and are examined using SEM and optical microscope. The critical fluence for blistering is about 5.2 x 1018 ions/cm2. The observations reported are (i) preferential decoration of grain boundaries with elongated blisters which have a tendency of interconnecting each other, (ii) irradiation induced grain boundary movement, (iii) onset of blistering only on few grains and tendency of coalescence, at the critical dose, (iv) spongy blister skins, and (v) simultaneous occurrence of blister exfoliation from the top and from the periphery. The observation (i) is attributed to preferential nucleation of gas bubbles along the grain boundaries and their successive coalescence; (ii) and (iii) are assigned to partial channeling; (iv) is understood to be a consequence of the growth and the coalescence of the bubbles within the skin; and (v) is considered to be the beam power effect. The D-t relationship predicted by the stress model is also examined. The measured skin thickness is within 18% of the calculated projected range. (author)