Intrinsic martensite formation in neutron irradiated V-1.6%Y alloys with fine-grained structure of highly pure matrix

Effects of neutron irradiation were examined on microstructural evolution in powder metallurgically processed V-1.6Y (in wt%) alloys comprising essentially fine grains and very fine dispersoids of Y2O3 and YN. The alloys feature a highly pure matrix free from gaseous interstitials such as oxygen and nitrogen. Optical and transmission electron microscopy observations revealed that the martensite of a vanadium bct structure with a tetragonality (c/a) of 1.06 formed heterogeneously in some of the bcc grains of V-1.6Y irradiated at 290 and 600 °C to 0.25 and 0.6 displacement per atom, respectively, but not in unirradiated V-1.6Y. The martensite had {1 0 1)bct habit planes parallel to {1 1 0}bcc in the matrix and a high density of {1 0 1)bct microtwins as the lattice invariant shear strain. To the authors' knowledge, the emergence of martensite is the first to be observed for vanadium or its alloys in neutron irradiated states. The cause of the martensite formation is discussed.