Crystallographic anisotropy change in nuclear grade graphite induced by compressive stress at high-temperatures

A nuclear grade graphite, H327, was deformed by the application of 22.6 MPa compressive stress at temperatures of 20, 800, 1000 and 12000C. Plastic deformation became larger with the stressing temperature, and the bulk density increase was mainly due to the longitudinal residual strain which was caused by the rupture and deformation of pores. The deformation within graphite crystallites was not detected by conventional X-ray method, however, appreciable increase in crystallographic anisotropy was observed for samples stressed at above 10000C. Moreover, these anisotropy changes were not recovered by the heat-treatments up to 20000C. These results suggest that large local distortions must occur at the crystallite boundaries and some of these strains might be accommodated by the increase in crystallite preferred orientation. (author)