Experimental determination of the critical cavity radius in Fe-10% Cr for ion irradiation

A major problem associated with the design of fusion reactors is high energy neutron damage to structural materials. The combination of vacancies formed by atomic displacements with gases produced by transmutation reactions can cause the formation of cavities. An important parameter in the theory of cavity growth is the radius above which the cavity exhibits bias-driven growth. If the cavity radius is less than this “critical radius,” cavities lose as many vacancies due to thermal processes as are gained from the bias-induced influx of vacancies. When bias-driven growth occurs, large amounts of cavitational swelling can result, leading to severe dimensional instability. Cavities can attain the critical radius either by an abnormally high random influx of vacancies or by absorption of gas atoms. The addition of gas atoms to a cavity reduces the value for the critical radius. If the number of gas atoms exceeds a critical number of gas atoms, then the critical radius vanishes. There is then no barrier to bias-driven growth.