The temperature dependence of heavy-ion damage in iron: a microstructural transition at elevated temperatures

A transition is reported in the dislocation microstructure of pure Fe produced by heavy-ion irradiation of thin foils, which took place between irradiation temperatures (Tirr) of 300 C and 500 C. At Tirr (le) 400 C, the microstructure was dominated by round or irregular non-edge dislocation loops of interstitial nature and with Burgers vectors b = 1/2 111, although interstitial 100 loops were also present; at 500 C only rectilinear pure-edge 100 loops occurred. At intermediate temperatures there was a gradual transition between the two types of microstructure. At temperatures just below 500 C, mobile 111 loops were seen to be subsumed by sessile 100 loops. A possible explanation of these observations is given.