In situ TEM observations of ion irradiation damage in boron carbide

This paper presents an in situ Transmission Electron Microscopy (TEM) study of the damage formation process in ion-irradiated boron carbide used as neutron absorber for fast nuclear reactors. We focused our experiment on the damage induced by 1 MeV gold ions irradiation performed on the JANNuS-Orsay in situ dual ion beam TEM facility. The effects of the crystallographic orientation and the temperature (RT, 500 degrees C and 800 degrees C) on the ion-irradiated boron carbide structure were studied. The different steps of damage formation leading to amorphization are described. At RT, material amorphization is observed at a damage dose threshold around 7.5 displacements per atom (dpa). It is also shown that no amorphization occurred when irradiation is performed at 500 degrees C or 800 degrees C up to the highest fluence studied (3 x 10(15) ions cm(-2), i.e. 7.6 dpa).