Resistance to hydride formation in zirconium: An emerging possibility

Fully recrystallized Zircaloy 2 was subjected to hydride formation through gaseous hydrogen charging. Primarily grain boundary hydrides were observed. To describe the relative preference, if any, a hydride preference index (HPI) was proposed: HPIQ = fh,Q/fr,Q, where fh,Q and fr,Q are the respective fractions of Q-type boundary present among hydrided boundaries and present in the total sample. HPIQ values were estimated from 1200 distinctly hydrided boundaries and showed a clear preference for hydride formation and grain boundary nature. Coincident site lattice boundaries were, in general, resistant to hydride formation. Elastically harder grains or orientations also arrested the formation of hydrides. The study indicates a clear possibility: a previously unknown/uncharted possibility of suitably ‘tailored’ zirconium microstructures, microstructures with reduced potential for ‘hydride embrittlement’ and delayed hydrogen cracking.