Neutron damage in α-titanium

Abstract

The neutron damage structure in annealed and cold-worked Marz grade titanium has been analysed following high dose irradiation of between 10 25 and 10 26 n/m 2 (E > 0.1 MeV) over a temperature range of 589 to 778 K. The damage consists mainly of (i) 〈a〉 type dislocation loops aligned in bands parallel with (0001) and (ii) network dislocations. In most cases the majority of loops have vacancy character, especially at the lower temperatures. This is explained in terms of the larger interstitial loops forming a network in annealed samples and interstitials being absorbed at network dislocations in cold-worked samples. Faceted cavities are observed in the 64% cold-worked material irradiated at temperatures < 650 K. They are observed mainly within grains of ≲ 3 μm diameter and are concentrated in regions of high network dislocation density and coexisting with large planar basal defects having b =1/n(20 2 ̄ 3) . They are also found close to some grain boundaries and triple points. In larger grains of ≳ 5 μm diameter the majority of loops exhibit displacement fringe contrast and have b = 1/n 〈1 2 ̄ 10〉 . The difference in microstructure from grain to grain is explained in terms of an increased concentration of impurities at grain boundaries during recrystallisation and irradiation, and variations in internal stress.