MICROSTRUCTURE OF RGT GRAPHITE BEFORE AND AFTER HELIUM IMPLANTATION

An investigation of the microstructure of RG-Ti-91 (RGT) graphite containing 7.5 wt% Ti, has been carried out, both before and after homogeneous implantation with He at 320 K up to about 0.08 at% causing a displacement damage of 0.1 dpa. Using TEM it can be shown that this material is textured and a relation has been found between its anisotropy and texture. The latter appears during synthesis when hot pressing of the furnace charge. At the same time grains of Ti powder transform into separated colonies of tiny TiC inclusions which provide for good strength and thermal conductivity across the laminated matrix structure. Helium implantation into specimens (0.6 mm in thickness) to a depth of 100 mum results in a partial loss of crystallinity in this layer, an increase of the c parameter by about 5%, swelling in excess of 10% and a remarkable strengthening of the matrix. High energy charged particle irradiation proved to be an adequate technique for the simulation of radiation effects due to fast neutrons. Inhomogeneous (in depth) swelling of anisotropic RGT results in internal stresses which may lead to crack formation and finally to rupture.