POSTIRRADIATION TENSILE AND CREEP-PROPERTIES OF HEAT-RESISTANT ALLOYS

The effect of neutron irradiation on high-temperature tensile and creep properties of austenitic heat-resistant alloys was studied. The effect, which appeared in the loss of ductility at elevated temperatures, was caused by helium produced by a nuclear transmutation reaction of thermal neutrons with boron and nickel in the alloy. The fracture mode was characterized by intergranular cracking. The tensile properties were determined at 700 to 1000 degree C after irradiation up to a maximum thermal neutron fluence of 1. 2 multiplied by 10**2**5 n/m**2. Creep tests were made at 900 degree C after irradiation to 6. 6 multiplied by 10**2**4 n/m**2. The tensile ductility was reduced with increasing deformation temperature, due primarily to the loss of necking elongation. In the postirradiation creep tests, significant reduction in rupture life also occurred. In both tensile and creep properties, the iron-base alloys were superior to the nickel-rich alloys, and, in particular, a heat of Incoloy alloy 800 showed exceptionally high resistance to irradiation.