Strain evolution in Zr-2.5 wt% Nb observed with synchrotron X-ray diffraction

Abstract The mechanical behaviour of hydrides in Zr alloy at low hydrogen concentrations continues to be the subject of research due to wide engineering application and highly complex behaviour of the Zr-H system. Significant structural differences between hydrides and α-Zr cause large dilatational strains associated with formation of the hydride precipitates in zirconium. Two hydride populations were observed to form under different strain states in the α-Zr matrix. The hysteresis of the hydrogen solubility is detected both in intensity and in strain curves for measured δ(111), α(00.2) and α{10.0} peaks. A two-dimensional analysis of α-strain was performed for the axial-hoop, hoop-radial, and axial-radial planes of Zr-2.5 wt% Nb pressure tube material. Variations in the hydrostatic and deviatoric strain components of the α-Zr with temperature were examined. In addition, a change in phase strain during a thermal excursion was considered as a sum of three cooperating components: phase thermal expansion (e T ), strains associated with other phase presenting in material (e [H] or e matrix ), and inter-granular strain within the phase caused by Type II stresses (e other ). The present study broadens our understanding of strain evolution in a Zr-H system undergoing hydride dissolution and precipitation. An X-ray synchrotron diffraction technique enables the in-situ following of strain variations in differently oriented grain families during the thermal cycle. In contrast to widely reported the average strain value within the α-phase, the diffraction patterns generated with this technique allow the evaluation of the anisotropic directionality of strains in different phases in Zr-H system generated during phase transformation.