Atomistic study of helium bubbles in Fe: Equilibrium state

In the fusion irradiation environment, helium created by transmutation will play an important role in the response of structural materials to neutron radiation damage. Recently we have developed a new 3-body potential to describe the Fe-He interaction in an Fe matrix. We have used this potential to investigate the equilibrium state of He bubbles embedded into the bcc Fe matrix. We have investigated bubble size, He content and temperature effects. It was found that the equilibrium He content is rather low and at a room temperature it is -0.38 to 0.5 He per vacancy for bubble diameters from I to 6 nm. At constant bubble size, the equilibrium He/vacancy ratio decreases with temperature increase. For bubbles of 6 nm diameter it goes down as low as -0.25 at 900K. The results are compared with the capillarity model often used for estimating the equilibrium pressure of He bubbles.