A synchrotron x-ray diffraction study of strain and microstrain distributions in α-Zr caused by hydride precipitation (original) (raw)
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Quantification of dislocations densities in zirconium hydride by X-ray line profile analysis
Acta Materialia, 2016
Zirconium-based components in nuclear power plants are embrittled by precipitates of zirconium hydride, which involves a martensitic-type transformation of the hexagonal -Zr lattice into the face-centered cubic Zr sublattice of the hydride. As a result, the hydride precipitates have a complex and heavily distorted internal structure that manifests as broad peaks in X-ray diffraction experiments. By a detailed analysis of the peak widths measured for different crystal planes we have found that most of this broadening is the result of dislocations. The analysis also showed that -hydride has very anisotropic mechanical elastic properties, in agreement with ab-initio simulations presented in the literature. Provided with this peak-broadening model, we have quantified dislocation densities within -hydrides precipitated in several Zr alloys, by analyzing previously published X-ray diffraction experiments performed at three synchrotron X-ray sources. The specimens investigated correspond to components affected by different hydride embrittling processes, namely: (i) samples from various components, charged in the laboratory with H contents in the 250 wt ppm range, (ii) laboratory-produced hydride blisters in Zr2.5%Nb pressure
Strain evolution in Zr-2.5 wt% Nb observed with synchrotron X-ray diffraction
Materials Characterization, 2018
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 (ε T), strains associated with other phase presenting in material (ε [H] or ε matrix), and inter-granular strain within the phase caused by Type II stresses (ε 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.
Strain evolution of zirconium hydride embedded in a Zircaloy-2 matrix
Journal of Nuclear Materials, 2008
In situ synchrotron X-ray diffraction has been used to determine strain evolution in a minority phase, zirconium hydride, embedded in Zircaloy-2 (<100 wt ppm average hydrogen content). The elastic modulus of the hydride is similar to that of Zircaloy-2. Three regimes are observed: I -elastic, II -post-yield load transfer from Zircaloy-2 to hydride, and III -strain saturation, possibly due to hydride fracture. The interpretation is supported by finite element calculations and scanning electron microscopy of the fracture surface.
arXiv (Cornell University), 2019
Zircaloy-4 is used extensively as nuclear fuel cladding materials and hydride embrittlement is a major failure mechanism. To explore the effect of δ-hydride on plastic deformation and performance of Zircaloy-4, in situ high angular resolution electron backscatter diffraction (HR-EBSD) was used to quantify stress and geometrically necessary dislocation (GND) density during bending tests of hydride-free and hydride-containing single crystal Zircaloy-4 microcantilevers. Results suggest that while the stress applied was accommodated by plastic slip in the hydride-free cantilever, the hydride-containing cantilever showed precipitationinduced GND pileup at hydride-matrix interface pre-deformation, and considerable locallyincreasing GND density under tensile stress upon plastic deformation.
Materials Characterization, 2018
Hydride distribution in a dual-phase hydrided Zr-2.5wt%Nb has been studied. Samples having different prior thermo-mechanical processing history were thermally cycled within a 86 keV X-ray photon beam. The diffraction patterns generated with this technique allow the evaluation of the relative quantity of hydrides within differently oriented grain sets. It was found that hydrides exist primarily within two different α-Zr grain-sets. One grain-set has its {0002} α-Zr direction oriented very close to the hoop direction while the other exists within a plane approximately 20°away from it. During thermal cycling, the proportion or hydrides oriented within different grain sets was shown to change from the distribution associated with the prior thermomechanical processing, to that corresponding to the current thermal cycling conditions. It was also shown that the ability for hydrogen to redistribute in the matrix correlates with the cooling rate of the specimen.
Materialia, 2019
The crystal structures of-hydride in zirconium (Zr) in published literature has been reviewed. The confusion between two reported space groups for-hydride, namely tetragonal P 4 2 / n , and orthorhombic Cccm is then addressed experimentally in combination with crystal structure modelling. Micron-sized hydrides were determined to be-type through electron diffraction in Zr. Electron diffraction patterns (DPs) were acquired along different zones, from which firm criteria for the identification of-hydride was hence established. The lattice parameters of-hydrides were measured along two orthogonal directions, which reveal a non-equal lattice parameter a 0 and b 0 , suggesting an orthorhombic structure. The-hydride formation induced plasticity in the surrounding matrix is determined by TEM characterization, including via in situ dissolution/precipitation studies. The dislocations are characterized to be type < a > dislocations, with various configurations depending on the size of the hydride.
Journal of Applied Crystallography, 2014
This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated -ZrH 1.66 generally follows the (111)//(0001) and [110]//[1120] orientation relationship with the -Zr matrix. The -hydride displays a weak texture that is determined by the texture of the -Zr matrix, and this dependence essentially originates from the observed orientation correlation between -Zr and -hydride. Neutron diffraction line profile analysis and highresolution transmission electron microscopy observations reveal a significant number of dislocations present in the -hydride, with an estimated average density one order of magnitude higher than that in the -Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the -Zr matrix. The present observations provide an insight into the behaviour of -hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of hydrides.
Metallurgical and Materials Transactions A, 2000
X-ray diffraction intensity data from three compositions of zirconium-base alloys, viz. ZIRCALOY-2, ZIRLO, and Zr-25 pct Nb, having extensive application in nuclear industry were recorded using a PHILIPS PW 1730 X-ray diffractometer. Detailed studies using the recorded diffractometer data, keeping in view the recent trends in the powder diffraction analysis, were carried out with a view to evaluating the microstructural paramaters, including domain size, microstrain, faulting probability, and dislocation density. While faulting appears to be absent in all alloys, the average domain size and root-mean-square (rms) strain appear to be smaller compared to pure zirconium. However, both of these parameters, i.e., average domain size and rms strain tend to increase with the addition of Nb, as in ZIRLO, but display a diminishing trend with higher content of Nb, as is evident in the Zr-2.5 pct Nb alloy.
Hydride precipitation and stresses in zircaloy-4 observed by synchrotron X-ray diffraction
2010
The grain stresses within hydrides precipitated in rolled zircaloy-4 plates were determined by synchrotron X-ray diffraction experiments using an 80 keV photon beam and a high-speed area detector placed in transmission geometry. Results showed large compressive stresses (360 ± 20 MPa) in the hydrides along the plate rolling direction. The origin of these stresses was investigated by performing hydride dissolution/precipitation in situ for thermal cycles between room temperature and 400°C. A large stress hysteresis was observed, with a steady decrease on heating and an abrupt change on cooling. The observed stresses are explained by the constraint imposed by grain boundaries on the growth of hydride platelets on the rolling-transverse plane of the rolled plates.