Zirconium sees considerable use in the nuclear industry due to its low neutron cross-section but is susceptible to the formation of hydrides. These have a significant effect, despite their small volume fraction (<0.4%), since they form preferentially at regions of high stress concentrations. Thus, crack faces become surrounded by brittle hydrides which subsequently fracture and allow the crack to grow despite no change in the macro-stress state. The factors influencing hydride formation remain unclear as does our understanding of the micro-mechanics governing their response to applied stresses. As a preliminary analysis, in-situ tensile tests have been performed on Zircaloy-2 (Zr + 1.4%Sn) charged with hydrogen (600ppm) and the strain response of both matrix and hydrides determined. The results indicate that the hydrides experience elastic strains far beyond the expected elastic limit followed by a pseudo-plastic region – presumably due to the cracking of the hydrides.

Strain development during in-situ loading of the Zr matrix and hydride particles in hydrogen charged Zircaloy-2. The Zr follows the macroscopic strain while the hydrides show unexpectedly high strains.