Deformation and fracture characteristics for irradiated Inconel X-750

Fast neutron irradiation to total fluences ranging from 7.7 x 1021 to 5.7 x 1022 n/cm2 (3 to 16 dpa) resulted in a 65% increase in yield strength and a four-fold reduction in ductility. Intergranular fracture was the dominant failure mode for the irradiated material, whereas equal amounts of intergranular and transgranular cracking were found in the unirradiated condition. This fracture mechanism transition resulted from intense heterogeneous deformation in a matrix strengthened by an irradiation-produced dislocation substructure. Planar slip bands impinged on the grain boundaries causing very high local stresses. Intergranular cracking resulted because the hardened matrix prevented relaxation of the stress concentrations