In-situ HVEM Investigations under the Influence of Ion Beams

A 200 kV ion accelerator was coupled to a 500 kV TEM for in-situ studies of the 80 keV He⁺ irradiation of 316 stainless steel. Dynamic and static observations of bubble growth, exfoliation and blistering show that slip bands, incoherent twin boundaries and grain boundaries are preferred sites for helium bubble formation. Bubble growth is enhanced by plastic deformation during irradiation. Exfoliation and blistering occur in samples thinner than the projected range of 80 keV He⁺ ions. Crack propagation during tensile tests proceeds through the bubbles enlarging them in diameter by a factor of two. Bubble enlargement also accompanies the formation of a blister cap. Brittle intergranular failure, even in samples with a large bubble population on the grain boundaries, occurred only when tensile tests were performed at elevated temperatures.