Cavity formation in an austenitic alloy of similar composition to type 3(6 stainless steel has been explored with regard to various methods of gas implantation. Irradiations were conducted at 900 K to doses of 1, 10, and 70 dpa with helium injection levels of 20 appm/dpa. Highest swelling (18%) was exhibited by the unimpUnted reference material; a lesser amount by simultaneous helium injection (11%). Greatly reduced swelling due to profuse cavity nucleation was the result of the preinjection of 1400 appm He, either at room temperature (S-1%) or at 900 K (*%). The dirlocation density was not sensitive to helium injection technique. Simultaneous injection of SO appm H/dpa, along with the He, nay have caused a modest increase in the cavity and dislocation concentrations at higher doses. The observations are compared with a theory of void growth kinetics to estimate the relative influence of voids and dislocations as point defect sinks.

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In an annealed austeniiic alloy undergoing bombardment with k MeV Ni ions to doses between I and 70 dpa at 840, 900, 950, 1025 and 1100 K, the introduction of simultaneously-implanted helium at a rate of 20 appm He/dpa moves the swelling versus temperature curve up the temperature scale by ItO to 70 K. Co-implantation of hydrogen (deuterium) at a rate of 50 appm D/dpa simultaneously with the helium causes little or no additional syste ,atic effects. The major change in microstructure caused by the gases is an enhancement of cavity nucleation by factors of 2 to 5 at 8'iO to 950 K, increasing to factors of thousands at 1)00 K. Concurrently there is a reduction in the size of cavities and in swelling at all temperatures below 1025 K, and an increase in cavity size and in swelling at 1100 K, where the cavities are gas stabilized. At 1025 K the increase in nucleation of cavities outpaces the reduction in size and causes increased swelling. The primary effects of the gases are decided at low doses below 1 dpa where cavity nucleation is completed and where the conditions governing cavity growth are established; at higher doses swelling is determined by cavity growth, which is dependent on dose only. The gases cause copious formation of cavities on grain boundaries, boding ill for mechanical properties.

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