Continuous observation of microstructural evolution in pure nickel and austenitic stainless steel specimens with and without external stress was conducted during electron irradiation in a high-voltage electron microscope. Irradiation was performed with 1-MeV electrons at damage rates ranging between 1 × 10-4 and 2 × 103 dpa/s (dpa = displacement damage per atom) at around 723 K for nickel and 823 K for austenitic stainless steel.
Loading and unloading of the specimen was repeated, and the response of the unfaulting of radiation-produced Frank loops to the load change was examined. The results indicated that the susceptibility of Frank loop to stress-induced unfaulting showed a maximum at a certain size.
Shrinkage of unfaulted small loops induced by the growth of adjacent large perfect loops was also found during irradation. The results are discussed in terms of the size dependence of the bias factor of dislocation loops and forces acting between dislocation segments in each loop.
The relationship between the growth rate of Frank loops and external stress was also examined. Growth rates of loops growing linearly in size with dose were measured along with the orientation of the loops and that of the external stress. A relative increase in the growth rate of those Frank loops with their Burgers vectors closely aligned to the tensile stress axis were noted.