MICROSTRUCTURE AND MECHANICAL-BEHAVIOR OF TZM AND MO-5-PERCENT RE ALLOYS IRRADIATED WITH FISSION NEUTRONS

The response of microstructural and mechanical properties of TZM and Mo-5% Re alloys to neutron irradiation are reported. Irradiations were carried out at five temperatures between 323 and 723 K to a dose level of similar to 0.16 dpa. The resulting microstructures consisted of a high density of small loops in both alloys with the addition of characteristic loop rafting in TZM. There was a marked sensitivity of microstructure to temperature. Void formation was found in both TZM and Mo-5% Re after the 623 and 723 K irradiations. The irradiations induced a significant increase in Vickers hardness in all cases but with no obvious dependence on irradiation temperature. Even at the present low neutron dose, large increases in tensile strength and a drastic decrease in ductility were observed. These results are discussed in terms of source hardening of the matrix within grains rather than obstacle hardening. Although the fracture processes are concentrated at the grain boundaries, these are not due to grain boundary embrittlement.