Effects of pulsed and/or dual ion irradiation on microstructural evolution in a Ti and Si modified austenitic alloy

The influence of pulsed 4 MeV Ni-ion bombardment, with and without simultaneous helium injection, at 958 K and damage levels from 1 to 50 dpa has been studied in a low swelling, Ti- and Si- modified austenitic stainless steel. Compared to continuous irradiation, pulsing caused an increase in the number density of interstitial loops formed during irradiation. Helium also increased the nucleation of interstitial loops. The main precipitates formed were a large number of small TiC particles uniformly distributed in the matrix, and a small number of relatively large eta and G precipitates. These course precipitates were somewhat larger in the pulsed specimens. Pulsing appeared to produce no significant change in swelling compared to continuous irradiation. However, for one specimen irradiated to 54 dpa, pulsing concurrent with substantial temperature fluctuations caused by beam heating may have been responsible for a larger swelling compared to continuous irradiation