[SY-B6] Symposium B-6

[SY-B6] Dose Effect on the Irradiation Induced Loop Density and Burgers Vector in Ion-Irradiated Ferritic/Martensitic Steel HT9 Through In-Situ TEM

Ce Zheng¹, Stuart Maloy², ^○Djamel Kaoumi¹ (1.North Carolina State University, United States of America, 2.Los Alamos National Laboratory, United States of America)

TEM samples of F/M steel HT9 were irradiated to 20 dpa at 420°C, 440°C and 470°C in a TEM with 1 MeV Kr ions so that the microstructure evolution could be followed in situ and characterized as a function of dose. Dynamic observations of irradiation induced defect formation and evolution were done at the different temperatures. The irradiation-induced loops were characterized in terms of their burgers vector, size and density as a function of dose and similar observations and trends were found at the three temperatures: (i) both a/2 <111> and a <100> loops are observed; (ii) in the early stage of irradiation, the density of irradiation induced loops increases with dose (0-4 dpa) and then decreases at higher doses (above 4 dpa), (iii) the dislocation line density shows an inverse trend to the loop density with increasing dose: in the early stages of irradiation the pre-existing dislocation lines are lost by climb to the surfaces while at higher doses (above 4 dpa), the build-up of new dislocation networks is observed along with the loss of the radiation-induced dislocation loops to dislocation networks; (iv) at higher doses, the decrease of number of loops affects more the a/2 <111> loop population; the possible loss mechanisms of the a/2 <111> loops are discussed. Also, the ratio of a <100> to a/2 <111> loops is found to be similar to cases of bulk irradiation of the same alloy using 5 MeV Fe²⁺ions to similar doses of 20 dpa at similar temperatures.