Evaluation of surface modifications for oxidation protection of vanadium-base alloys in helium-cooled blanket designs

Abstract

Vanadium-base alloys are currently being considered for application to high-temperature helium-cooled fusion reactor blanket designs. A major drawback is their known sensitivity to low levels of oxidizing impurities that would normally be present as water vapor in the helium coolant gas. Although baseline data on the oxidation resistance of vanadium alloys are lacking, protection of vanadium alloy surfaces exposed to the helium coolant will probably be necessary for contiuous blanket operation at temperatures above 875 K. Surface alloying of vanadium-base alloys appears to be a feasible method of creating an oxidation-resistant surface. To examine this approach, a series of V-15Cr-5Ti alloy sheet specimens was surface alloyed with chromium. Oxidation tests were then conducted in flowing helium containing up to 100 vppm H 2O. Temperatures up to 925 K and times up to 1000 h were utilized. Control samples of unmodified V-15Cr-5Ti and a Type 316 stainless steel were also included. Significant reductions in oxygen pickup were observed with surface-alloyed specimens. These results suggest that surface alloying techniques offer great promise for protecting vanadium alloy surfaces against oxidation at blanket operating temperatures.