Performance of V–4Cr–4Ti alloy exposed to the JFT-2M tokamak environment

A long-term test has been conducted in the JFT-2M tokamak fusion device to determine the effects of environmental exposure on the mechanical and chemical behavior of a V–4Cr–4Ti alloy. Test specimens of the alloy were exposed in the outward lower divertor chamber of JFT-2M in a region away from direct contact with the plasma and were preheated to 300°C just prior to and during selected plasma discharges. During their nine-month residence time in JFT-2M, the specimens experienced approximately 200 lower-single-null divertor shots at 300°C, during which high energy particle fluxes to the preheated test specimens were significant, and approximately 2010 upper-single-null divertor shots and non-divertor shots at room temperature, for which high energy particle fluxes to and expected particle retention in the test specimens were very low. Data from post-exposure tests have indicated that the performance of the V–4Cr–4Ti alloy would not be significantly affected by environmental exposure to gaseous species at partial pressures typical for tokamak operation. Deuterium retention in the exposed alloy was also low (<2 ppm). Absorption of interstitials by the alloy was limited to the very near surface, and neither the strength nor the Charpy impact properties of the alloy appeared to be significantly changed from the exposure to the JFT-2M tokamak environment.