PNNL

Abstract

Vanadium alloys are of interest to the Fusion program as potential first wall structural materials. The expected irradiation conditions for the first wall structural material include a range of temperatures where very high hardening caused by a high density of small, but shearable defect clusters results in a type of deformation called "localized deformation". At the onset of yield in a tensile test, a dislocation may move through a grain shearing the obstacles and clearing out a channel. Subsequent dislocations may easily pass through this channel. As the test progresses, more channels form. In the early stages of deformation, it is thought that the plastic deformation is confined to these channels. One important macroscopic result of this deformation behavior is rapid onset of necking in a tensile test and very low uniform elongation. As a means to help understand the range of stress states where localized deformation may adversely affect macroscopic ductility in vanadium alloys, compression test specimens fabricated from two heats of V-4Cr-4Ti are currently under irradiation in the High Flux Isotope Reactor (HFIR). The results of room temperature compression tests on the unirradiated control materials are presented here and compared with uniaxial tensile values from the literature.