Performance of V–4Cr–4Ti material exposed to the DIII-D tokamak environment

As a first step to demonstrate the viability of using vanadium-base alloys for structural applications in fusion devices, six welded upper radiative divertor baffle support brackets made from a V–4Cr–4Ti alloy were installed in the DIII-D tokamak. To determine the effects of exposure to the tokamak environment, lead tests are being conducted on parent metal and weldment specimens. One of the issues to be addressed is whether excessive hydrogen uptake may occur to cause material embrittlement. Some of the lead tests have been completed. Data from samples exposed to up to four DIII-D operating cycles (≈4 years) indicate that the performance of the V–4Cr–4Ti alloy would not be significantly affected by the exposure. Brittle cleavage fractures are noted near the surface of some of the impact specimens, but only at very low (<−150 °C) test temperatures. Above −150 °C, all fractures are ductile.