Gas-induced swelling in helium-implanted copper during annealing

Abstract

A detailed transmission electron microscopy (TEM) investigation of the gas porosity (GP) in pure copper homogeneously implanted with helium at 323 K to a concentration of c He ⋍ 300 appm as a result of postimplantation annealing for up to 0.5 h at temperatures between 838 and 1193 K has been carried out. General features of the GP development in the bulk and near vacancy sources (primary and secondary GP, correspondingly) are similar to those for nickel reported previously in detail. First, sizes of small overpressurized (primary) gas bubbles formed in Cu at T > T HeV D ⋍ 785 K (dissociation temperature of HeV complexes) were determined and He density therein estimated: ρ He ⋍ 105 nm −3 . Large, near-equilibrium (secondary) bubbles arise not only near the outer surface and some grain boundaries but also locally in the vicinity of very small — less than 100 to 150 nm in size — inclusions. Under conditions of vacancy deficit they act as vacancy “point” sources in the course of their formation and/or due to phase transformation therein. By means of X-ray microanalysis, microdiffraction and CBED these inclusions were identified as copper sulphide precipitates. A supposition was made why in fcc metals (Ni, Cu) implanted with helium up to a certain concentration dislocations fail to supply vacancies into the surroundings up to temperatures of about 0.75 T m ( T m — the melting point).