Tensile behaviour and acoustic emission in zirconium alloys after thermal aging and sodium exposure

Tubular specimens of Zircaloy-2 and Zr–2.5%Nb alloys were exposed to flowing sodium at 613 K for different durations. Similar tubular specimens of the two alloys were also given equivalent thermal treatment. Tensile testing of all the specimens was carried out at a nominal strain rate of 5 × 10−4 s−1 and ambient temperature (298 K) along with recording of acoustic emission (AE) signals. Microhardness values of the specimens were determined. The tensile and microhardness results indicated marginal changes in the properties consequent to sodium exposure and thermal treatment. Higher AE generated in the sodium exposed and thermally treated specimens as compared to non-exposed/heat-treated specimens is attributed to decohesion of hydride platelets during tensile testing. While the tensile properties could not show any difference between the untreated and treated specimens, the AE results could very well bring out higher amount of decohesion of hydrides in sodium exposed as compared to thermally aged specimens.