Deformation and Fracture Characteristics for Irradiated Inconel X-750

Fast neutron irradiation to total fluences ranging from 7.7 × 10²¹ to 5.7 × 10²² n/cm² (3 to 16 dpa) resulted in a 65% increase in yield strength and a fourfold reduction in ductility. Intergranular fracture was the dominant failure mode for the irradiated material, whereas equal amounts of intergranular and trans-granular 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.