Evaluating zirconium–zirconium hydride interfacial strains by nano-beam electron diffraction

Hydride reorientation in Zircaloy-4 examined by in situ synchrotron X-ray diffraction

“…This will cause a decrease in peak width (a) and increase in lattice parameter, d δ-{111} (b). The observed changes in associated strain are quite large; 0.015Å corresponds to a strain of ∆d/d 0.5% and a stress of ∼0.76 GPa but similarly large strains have been seen by both Colas [17] and Barrow [27]. It should also be recalled that these values correspond to local strains in the vicinity of nanoscale precipitates and so stresses in excess of macroscopic yield are possible.…”

“…This, along with the associated reduction in strain, can be rationalised by appealing to the {111} δ-ZrH habit plane, with its normal parallel to the α-Zr c-axis. A larger misfit strain along the [0001] α-Zr when compared to the [1120] α-Zr has been determined by both Carpenter [26] and Barrow [27]. This gives rise to the characteristic lenticular morphology of the zirconium hydride platelets, with the precipitates' short axis parallel to c, minimising the overall strain energy.…”

In situ observation of γ-ZrH formation by X-ray diffraction

“…Compared to commonly observed hydrogen rich BCT ε-ZrH 2 hydride, in which (nearly) all eight tetrahedral positions are fully (without loss of generality, we refer to it now as ε-ZrH 2 ) occupied by hydrogen, and non-stoichiometric FCC d-Zr hydride, which has the same sites partially and randomly filled, the g-ZrH has an ordered tetragonal unit cell with four hydrogen atoms on the tetrahedral sites of the (110) plane. According to some studies [19,20] the volume expansions caused by phase transformation of a / g and a / d can reach as high as 12.3% and 17.2%, respectively. Hence, the precipitation of hydrides will introduce significant amount of misfit strain on the Zr matrix and reduces its ductility.…”

In situ micropillar deformation of hydrides in Zircaloy-4

“…We have been able to attribute the subsidiary maxima to the presence of the hydrides in the packet and to rotation of the orientation of the matrix above/below the hydride packet. Since the precipitation of a hydride involves biaxial straining of the Zr matrix at the hydride-matrix interface [35,36] (with interfacial strains of 7.2% along [0001] α and 4.6% along [1120] α being predicted [36]), there is likely to be accompanying plastic deformation of the matrix. Due to constraint of the matrix, a consequence of the associated volume expansion, this deformation may result in local lattice reorientation due to an excess of dislocations resulting in broader matrix diffraction spots.…”