Transmutation-induced embrittlement of vanadium and several vanadium alloys in HFIR

Vanadium, V1Ni, V10Ti and V10Ti1Ni (at%) were irradiated in HFIR to doses ranging from 18 to 30 dpa and temperatures between 300 and 600°C. Since the irradiation was conducted in a highly thermalized neutron spectrum without shielding against thermal neutrons, significant levels of chromium (15–22%) were formed by transmutation. The addition of such large chromium levels caused strong embrittlement. At higher irradiation temperatures radiation-induced segregation of transmutant Cr and solute Ti at specimen surfaces caused strong increases in the density of the alloy. The resultant shrinkage, possibly compounded by thermal cycling, led to cracks developing at all intersections of grain boundaries with the specimen surface. This caused specimens irradiated at 500°C or below to often fail during retrieval from the reactor, as well as during electropolishing and other handling operations. At 600°C, the cracking and embrittlement processes are so severe that only a fine dust, composed mostly of individual grains or chunks of grains, was found in the irradiation capsule.