A TEM study of the aging of Zr tritides

Abstract

Zr-tritides were investigated by TEM for aging times up to almost 3 y. After ∼ 3 weeks 3He bubbles of ∼1 nm in diameter were detected. The bubble density soon reached a value of ∼ 5 × 1023 m−3 and then apparently remained constant. Using strong diffraction contrast the interstitial loop and dislocation damage accompanying bubble formation could be imaged. Loops, network dislocations and internal boundaries were found to be heavily decorated with tiny bubbles. After ∼ 2 y an interconnected system of He filled channels evolved from these structures. The observed microstructural evolution is discussed in the light of bubble nucleation and growth models. From the bubble densities, energies of He diffusion or He dissociation from He clusters, respectively, of ∼ 1 eV are derived. Under the present conditions, bubbles can grow by loop punching or by the diffusional transfer of self-interstitials (SIA's) from the bubble surface to dislocations attached to them. Under high pressure, bubbles at dislocations could be unstable against elongation along the dislocations. The evolving system of channels presumably is responsible for 3He loss in the “state of accelerated 3 He release”.