Creep Deformation in V-4Cr-4Ti in a Low-Oxygen Lithium Environment

Abstract

Vanadium alloys, especially V-Cr-Ti alloys, are candidates for first wall and blanket structures of fusion reactors. However, a major vulnerability of this class of alloys is the affinity for oxygen and other interstitial solutes. Oxygen, nitrogen, carbon, and hydrogen can severely harden and embrittle vanadium alloys. Oxygen is particularly troublesome because of its prevalence and its relatively high diffusivity. In determining creep behavior, the effects of oxygen must be understood. In the present study, specimens, in the form of pressurized tubes, were exposed to liquid lithium, the coolant of choice for vanadium systems, at temperatures of 665, 765, and 800°C. Under these conditions, oxygen is removed from the vanadium alloy by the lithium. The data produced were compared with data from similar specimens tested in a high vacuum environment, where the oxygen level in the alloy is expected to slowly increase, at Pacific Northwest National Laboratory in order to evaluate the effect of oxygen. The Li-exposure resulted in higher creep rates and shorter rupture times. The effect was most clear at 800°C, where deformations 4–6 times higher were observed for the Li-exposed specimens.