19 th International Symposium on Zirconium in the Nuclear Industry P. Vizcaino, A. V. Flores, M. A. Vicente, J. R. Santisteban, G. Domizzi, A. Tolley, A. Condó, J. Almer Characterization of Hydrides and the α -Zr Matrix in Zirconium Alloys Effects of Stresses, Microstructure and Neutron Irradiation on Hydride Texture, Terminal Solid Solubility and Dislocation Structure Monday May 20 to Thursday May 23 2019 The Midland; Manchester United Kingdom
OUTLINE Experimental • Design of the experiments: APS, LNLS, TEM, etc. • Materials under study: characterization • Data reduction and analysis Results • Hydride texture/matrix texture ✔ Effect of an applied stress ✔ Link between microscopic and mesoscopic scales (Perovic´s model) • Effects of stress on the solubility limit • Hydride dislocation densities by TEM and HRTEM observations • Hydride dislocation densities by synchrotron X-ray diffraction General Conclusions
Materials under study: APS experiments Zr-2.5Nb CANDU type Hydride blister grown in the laboratory: X-yay beam scan microstructure, axial surface scheme Sample for X-ray diffraction 3 mm Blister 4 mm Radial Hoop Axial
Materials under study: APS experiment Hydride morphology before Zr-2.5Nb CANDU type microstructure the in-situ experiment axial surface L2: 130 wt-H ppm Four dog-bone samples hydrided: 44, 55, 67 and 130 H-wtppm Hoop E1: 55 wt- H ppm
Materials under study: other experiments Neutron irradiated (~10 22 neutrons/cm 2 ) and unirradiated Zircaloy-4 Fully recrystallized microstructure Deuterided i) Planar sheet: 5 x 4 mm for irradiated XRD in the Bragg-Brentano Zircaloy-4, ~ geometry at LNLS, Brazil Axial 400 H eq -ppm) Hoop SEM image of a ii) Thin foil: φ~3 mm for TEM Zircaloy-4 and HRTEM highly hydrided sample TEM, Zircaloy-4 iii) Unirradiated fully hydrided. recrystallized and hydrided 10μm Red thin foil was also prepared arrows for TEM and HRTEM indicate studies, ~ 3000 H-wtppm) hydrides.
APS 1-1D x-ray beam station. Experimental setup for the cylindrical specimens containing the hydride blister Experimental setup Pole figures • Beam energy: 80 Kev, monochromatic beam • Running around a diffraction ring (angle χ ) • Beam size: 300 x 300 μ m • CCD image obtained in 0,1 sec (2048 x 2048 pixels corresponds to scan along two parallel lines that virtually cross the center of the pole of 200 x 200 μ m 2 ) figure (radial direction). • Cylindrical specimen of hydrided (blister) Zr-2.5Nb • Rotation of the specimen around the radial with principal axes in the three directions, radial, direction ( ψ ) reflects as a rotation of the hoop and axial lines around the center of the pole figure. The X-ray beam goes through the cylindrical sample and an area detector collects the diffracted rings. The cylindrical sample is rotated along the radial direction (ψ) in angle y from -90 to 90º in 5º steps
LNLS (Brazilian Synchrotron) XRD#1 beam station TEM Bariloche Atomic Center, Experimental setup for the Bragg-Brentano experiments Arg. • Geometry: θ -2 θ , 0.05 o step, 20 º≤ 2 θ≤ 130º Unirradiated Zircaloy-4: • Photon beam of 8.08 keV two orientation relationships for the • λ = 1.542484Å ( Δλ =0.000001Å) hydrides with the α -Zr matrix: [0002] α // [111] δ and (1 1-2 0) α // (-2 2 0) δ Radial (c) (a) (b) 2 2 Sample 0 Axial-Hoop plane 2 0 2 Sample 0 holder 2 2 (c) Hydride peaks 1 1 2 0 Close to a blister ( α -Zr and δ -hydride are ~ 50%): 1 0 1 0 1 1 0 200 nm ✔ δ -(200) peak is 0 (b) considerably wider than the α -(10-11), TEM images and SAD patterns from hydrides and Zircaloy-4 matrix. (a) Hydride with orientation but , relationship [0002 ]α // [111 ]δ and (1 1 -2 0 )α// (2- ✔ instrumental resolution 2 0 )δ (b) SAD pattern of a hydride with Z= 111. (c) is identical due to the SAD of the matrix with Z= 0002. close proximity between the α and δ peaks
APS experiments: data reduction Four main phases are identified, the α, β and ω phases of Zr and the δ− hydride, with varying intensities for different azimuthal angles, due to the crystallographic texture of all phases. Specimen L2 (130 wt H-ppm), unloaded condition The position, integrated area and FWHM of all peaks observed in each diffractrogram were defined by least-squares fits, in order to define texture, elastic strains and dislocation densities of the δ -hydride, as described below. Images were transformed into 72 “traditional” 2 θ diffractograms by slicing the rings azimuthally with an angular section of 5 o
RESULTS Hydride texture/matrix texture: crystallographic texture of delta hydride within the blister, ~90% of δ -hydride phase blister interface ~50% of δ -hydride phase outside the blister (in the parent material), with a concentration of ~200 wt ppm H At first glance, the three pole figures display a similar pattern regardless of the position and the very different hydride concentrations and morphologies A closer look shows: ✔ a nearly perfect orthorhombic symmetry, ✔ those measured where hydrides appear as a minority phase display certain degree of asymmetry (~15 o to de radial direction) Texture of the α -Zr matrix plays the major role in the structure of the hydride ODF
RESULTS Hydride texture/matrix texture: crystallographic texture of delta hydride We have determined many intensity pole figures for α -Zr phase They were used to produce the orientation distribution function (ODF) of the α -Zr phase Hydride ODF: the orientation relationship [0002] α //[111] δ, (11-2 0) α //(20-2) δ has been applied to all the crystal orientations composing the α -Zr ODF , weighted by their intensities The agreement between experimental and calculated pole figures is extremely good, confirming that the hydride-parent crystal relation [0002] α //[111] δ and (1 1-2 0) α //(2 0- 2) δ is by far the most commonly observed Identical precipitation probability in all α− Zr grains regardless of its orientation (perhaps explain the observed asymmetries)
RESULTS Crystallographic texture of delta hydride Asymmetries can be explained in terms of a texture simplified model assuming four texture components: Basic texture components of a Zr-2,5Nb pressure tube Colored points indicate the positions of the components in the ODF of the microstructure Regions of the α -(0002) and δ -(111) pole figures where the ideal orientations of the synthetic ODFs manifest on a recalculated figure pole of a blister
RESULTS Crystallographic texture of delta hydride Interesting to note the rotation of ~15 o from the hoop direction a change in the texture component precipitation probability implies Far from the blister, Blister: 90% hydride low H content This confirms that, although the texture of the α -Zr Explanation in terms of the Perovic’s model [*]: does plays a role in precipitation of circumferential For circumferential hydrides far from the blister or radial hydrides, its connection with the actual morphology of hydride clusters is not the elastic strain field that appears in the straightforward : it involves a complex interplay with matrix after hydride precipitation makes the Radial the morphology of α -grains, the type of grain arrangement of h tilted hydrides (b) energetically boundaries and other factors such as external and Hoop more favorable over arrangements h hoop (a) or internal stresses and the detailed spatial distribution h Radial (c) Perovic´s representation of circumferential of defects and radial hydrides in a Zr-2.5Nb pressure tube precipitated in α -Zr grains of either [*]. V. Perovic • G.C. Weatherly • C.J. Simpson. Hydride precipitation in m hoop , m tilted or m radial orientations α/β zirconium alloys. Acta Metall. Vol. 31. No. 9, (1983), pp 1381-1391.
APS 1-1D x-ray beam station. Experimental setup for dog-bone experiment • Beam energy: idem • Beam size: idem The cycles (three) from room temperature up to • CCD image idem 400 o C were performed without stress (A), at 130 • Dog-bone specimens of Zr-2.5Nb with principal Mpa (B) and at 225 Mpa (c) keeping them 5´ at axes in the three directions, radial, hoop and 400 o C. axial • Samples were placed in a MTS tensile test machine • NO SAMPLE ROTATION POSSIBLE Unstressed (L2), Cooled stressed at 225 circumferential hydrides Mpa (L2), circumferential and radial hydrides
Four dog-bone samples hydride samples 44 H- wtppm 55 H- Hoop wtppm 67 H- wtppm 130 H- wtppm
RESULTS Effect of external stress on the texture of the δ -hydride Before After During the experiments the dog-bone specimens remained at a fixed orientation: the white dotted Reorientation implies: circle contains the observed orientations ✔ Favoring hydride precipitation in h Hoop or h tilted instead of other orientations ✔ Changes in the intensity of the d -hydride spots in the pole figures but not in the position ✔ Turning energetically favorable some Perovic´s cluster arrangements of radial hydrides
Recommend
More recommend
