Zr Single Crystals Research Articles

Oxidation characteristics of basal ( [formula omitted]) plane and prism ( [formula omitted]) plane in HCP Zr

The oxidation characteristics of (0 0 0 2) basal plane and (1 1 2 ̄ 0) prismatic plane of an unalloyed Zr were investigated. From the Zr crystal bar, the specimen representing a single crystal was prepared to be coarse enough to have its grain be 4×4×1 mm 3 in size. After identifying the crystallographic orientations and planes by X-ray diffraction (XRD), the samples were cut out in such a way as the cutting planes could correspond to the desired crystallographic planes. Oxidation tests were carried out in water at 360 °C. The oxidation rate of the (1 1 2 ̄ 0) prismatic plane was faster than that of the (0 0 0 2) basal plane. The analysis of oxide using the synchrotron XRD revealed that the oxide grown at the basal plane had the preferred (2 0 0) plane in mono-ZrO 2, while the oxide at the prismatic plane grew at both the (2 0 0) and (0 0 2) planes of mono-ZrO 2. In addition, the oxide layer that had formed at the basal plane having only one preferred growth plane exhibited a high fraction of columnar oxide and a relatively wide range of protective barrier layer. These results mean that the characteristics of the preferred planes of mono-ZrO 2 play an important role on the oxidation rate of Zr single crystal.

Determination of dislocation densities in HCP metals from X-ray diffraction line-broadening analysis

X-Ray diffraction (XRD) line-broadening analysis has been performed on highly textured Zr-2.5Nb specimens which had been deformed in tensile tests to produce well-controlled dislocation structures. An iterative deconvolution method has been applied to extract the broadening function for the material, using as standards, a Zr single crystal and a 0 pct deformed specimen. In both cases, for specific tensile tests, a significant contribution to the basal line braodening was observed, which was clearly not directly related to the dislocation structure generated by the deformation, i.e., so-called c-component dislocations having a component of their Burgers vectors perpendicular to the basal plane. Calculations showed that the extent of basal line broadening cannot be attributed to the secondary effect of strain from a-type dislocations, i.e., dislocations with Burgers vectors parallel with the basal plane. It is concluded that most of the line broadening observed was the result of intergranular strain distributions. These distributions are most prominent for grains oriented with their c-axes perpendicular to the tensile-deformation axis and resulted in basal-plane line broadening even when there were few, if any, c-component dislocations present.

The deformation of Nb-Zr-N single crystals containing zirconium nitride particles I. Mechanical properties

Abstract Two groups of Nb–Zr single crystals with different zirconium contents (up to about 1 at.% Zr) were made using an electron-beam floating-zone apparatus. Alloys containing ZrN dispersions were obtained by internal nitridation of Nb–Zr single crystals. The mechanical properties of the alloys were measured over the temperature range 4.2–373 K. All tests were carried out in compression using a testing machine with an integral helium cryostat. Differential tests were used to study the effect of the ZrN particles upon the thermal part of the flow stress. It was found that the overall strengthening of the materials was about 100 MPa and that probably only a fraction of this was due to the ZrN particles directly. The shapes of the stress-strain curves were similar to those of Nb–N interstitial alloys with negative hardening rates in most cases in contrast with the high hardening rates often observed in precipitation-hardened alloys. The thermal stress was very similar to that found in the pure metal and the results indicate that the fundamental deformation mechanism of niobium is not changed by the presence of the precipitates.

The deformation of Nb–Zr–N single crystals containing zirconium nitride particles I. Mechanical properties

Abstract Two groups of Nb–Zr single crystals with different zirconium contents (up to about 1 at.% Zr) were made using an electron-beam floating-zone apparatus. Alloys containing ZrN dispersions were obtained by internal nitridation of Nb–Zr single crystals. The mechanical properties of the alloys were measured over the temperature range 4.2–373 K. All tests were carried out in compression using a testing machine with an integral helium cryostat. Differential tests were used to study the effect of the ZrN particles upon the thermal part of the flow stress. It was found that the overall strengthening of the materials was about 100 MPa and that probably only a fraction of this was due to the ZrN particles directly. The shapes of the stress-strain curves were similar to those of Nb–N interstitial alloys with negative hardening rates in most cases in contrast with the high hardening rates often observed in precipitation-hardened alloys. The thermal stress was very similar to that found in the pure metal and t...

Irradiation-driven solute redistribution in Zr alloys

Zr-2.5Nb, with four different Fe concentrations, Zircaloy-2 and a Zr(Fe) single crystal have been irradiated with energetic Ar + ions (mostly 1.5 MeV) to fluences ⩽10 21/m 2 (≈100 dpa). The resulting enhancement of the α-phase Fe solubility has been measured as a function of dose, dose-rate and specimen temperature. Most of the chemical analyses were done by electron microprobe. At 50 and 300°C there was a discernible increase in α-phase Fe for Zircaloy-2, but not for Zr-2.5Nb. Between 411 and 469°C the Fe levels in the α-phase of both alloys increased to ≈2500 ppma from prior-irradiation levels of ≈70 ppma: in Zr-2.5Nb thin foils there was a corresponding drop of the β-phase Fe concentrations from about 1.5 to 0.4 at.%.

Kinetics of concurrent desorption and diffusion into the solid: D/Zr(0001)

Rapid adsorbate diffusion into the solid is known to suppress the desorption yield measured in a thermal desorption experiment. We show that this suppression can be controlled (at least partly) by pulsed-laser heating at rates in excess of 1010 K/s. As an example, we analyze the D/Zr system. In this case, deuterium adsorbed on a surface rapidly diffuses into the bulk of Zr with increasing temperature, and the deuterium desorption probability measured with conventional heating rates (β⩽100 K/s) is as low as ≈10−4 for polycrystalline Zr foils (deuterium desorption is not observed at all from single-crystal Zr from which dissolved H/D has been removed). Heating the Zr(0001) surface by pulsed-laser thermal excitation with β≃1011 K/s is demonstrated to result in the increase of the deuterium desorption probability up to approximately 0.01. To interpret this observation, general equations for describing associative desorption accompanied by adsorbate diffusion into the solid are simplified by employing the specifics of the temperature-programmed kinetic regimes with a linear increase of temperature. The desorption yield calculated without any adjustable parameters is in good agreement with the experimental results.

The study of hydrogen segregation on Zr(0001) and Zr(1010) surfaces by static secondary ion mass spectroscopy, work function, Auger electron spectroscopy and nuclear reaction analysis

The segregation of hydrogen on Zr(0001) ad Zr(1010) surfaces was studied by static secondary ion mass spectroscopy (SSIMS), Auger electron spectroscopy (AES), work function measurement and nuclear reaction analysis (NRA). It was found that hydrogen has a strong tendency to segregate on these Zr surfaces. The heats of segregation, measured by SSIMS which was calibrated by NRA, are 10.1 kcal mol−1 on Zr(0001) and 10.7 kcal mol−1 on Zr(10110). The valence-band-related AES of Zr indicated that the modification of the Zr valence band by the segregation of hydrogen is similar to that resulting from the formation of surface hydride; this is connected with the strong tendency for hydrogen to segregate. The diffusion coeffients of hydrogen along 〈0001〉 and 〈1010〉 directions in a Zr single crystal were measured by the kinetics of surface segregation. It was found that the diffusion along 〈0001〉, D = 0.034exp(−9565/RT)mm2 s−1, is slower than that along 〈1010〉, D = 0.173exp(−8887/RT)mm2 s−1, i.e. by about one order of magnitude. This may be explained by the difference in the atomic density on (0001) and (1010) faces and the partition functions of the activated states in these two diffusion paths. It was found that dissolved oxygen enhances the diffusion of hydrogen.

SIMS studies of the corrosion of zirconium

The integrity of CANDU pressure tubes is critically dependent on the protectiveness of the oxide film formed on its surface. The actual protective layer may be only a few nanometres in thickness. In an on-going investigation of the properties of the protective oxide film, and the relationship of these properties to the corrosion behaviour of the pressure tubes, SIMS has become an important component of the analytical methods used. In this paper, examples will be given showing the application of static and dynamic SIMS to the study of the interaction of O 2 and H 2 with single-crystal Zr and the diffusion of H and O in Zr, the application of dynamic SIMS to the characterization of D- or H-containing species in pressure tube oxides, and the effects of incorporation of impurities into the oxide. These studies will be related to the current understanding of CANDU pressure tube corrosion.

A Mössbauer study of single-crystal Zr-0.065 at% 57Fe

Single crystals of Zr-0.065 at% Fe (95% 57Fe), from a common parent, have been studied by Mössbauer spectroscopy, using both transmission and conversion-electron modes. In the “as grown” state the Fe is present as the meta-stable phase, t-Zr 2Fe. Vacuum annealing, in the range 795–973 K, results in gradual decomposition of t-Zr 2Fe and the diffusion of Fe from the bulk to the surface, where it forms the stable Zr 3Fe phase. The kinetics of Zr 3Fe formation show fair accord with the known diffusion properties of Fe in α-Zr. Some results for other dilute Zr(Fe) single crystals are reported.

High resolution studies of the solid state amorphization reaction in the ZrCo system with the atom probe/field ion microscope

ABSTRACTThe atom probe/field ion microscope is introduced as a new powerful investigation device to study the early stages of the solid state amorphization reaction (SSAR). A bilayer of Zr and Co was condensed under UHV conditions on W wire tips and analyzed in a field ion microscope (FIM) combined with an atom probe (AP). The reaction of Co with Zr has been studied at room temperature. FIM pictures and AP analysis have shown that even at low temperatures an amorphous phase is formed at the Zr/Co interface and in the Zr grain boundaries. In these areas concentration profiles have been taken on a nanometer scale. Most likely, the extended solid solution of Co found in α- Zr grain boundaries causes the formation of the amorphous phase. Further, Rutherford backscattering spectrometry (RBS) suggests that even point defects and dislocations at the surface of an α- Zr single crystal are sufficient to initiate the SSAR between a polycrystalline Co layer vapour- deposited onto that single crystal.

Ion-channeling investigations of nitrogen in zirconium

In this study, ion-channeling techniques were used to determine the lattice sites of N in the a-Zr hexagonal close-packed (hep) structure and the effect of trapping irradiation-produced defects at the N atoms. A Zr single crystal was implanted along 〈112̄0〉 at 293 K with 300 keV 15N 2 ions to a fluence of 2.2 × 10 15 ionscm −2. The position of 15N atoms in the Zr lattice was studied using measurements of yields of 1H ions (incident energy 800 keV) backscattered from the Zr atoms and the alpha-particle yields from the nuclear reaction 19N(p, α) 12C. Dechanneling of the protons in the Zr crystal provided information on changes in the overall defect concentration during the irradiation and annealing stages. Information was obtained for the 〈112̄0〉 and 〈101̄0〉 channels. The 15N ion implantation resulted in an appreciably larger yield of a particles when the 1H ion beam was incident along 〈112̄0〉 compared to that found for incidence along 〈10 1 0〉. Angular scans through 〈112̄0〉 also indicated an appreciable peaking in the α-particle yield at the aligned 〈112̄0〉 position. These observations indicated that the N atoms occupied the octahedral interstitial positions in the α-Zr hep lattice. Subsequent to the 15N implantation, the Zr crystal was irradiated at 35 K with 800 keV 4He ions to fluences of 1.8 × 10 16 and 9.1 × 10 16 ionscm −2, followed by post-irradiation annealing in both instances. No appreciable displacement of the N atoms from their lattice sites was detected after these irradiations, or during annealing up to 423 K. Hence N atoms in octahedral sites are very stable and their position remains essentially unaltered during subsequent defect formation and migration, at least up to 423 K.

Evidence against amorphous phase formation by the solid state reaction of iron on single-crystal Zr(0001) in ultrahigh vacuum

Thin polycrystalline 57Fe films were deposited in ultrahigh vacuum onto a well ordered Zr(0001) single-crystal surface characterized by low-energy electron diffraction and Auger electron spectroscopy, and were investigated in situ by conversion electron Mössbauer spectroscopy (CEMS). In contrast to the case of a polycrystalline triple layer of 1000 Å Zr/200 Å 57Fe/150 Å Zr, the formation of amorphous Fe-Zr was not observed on the ordered single-crystal surface upon annealing at around 660 K. Furthermore, iron film deposition onto an ion-beam irradiated, damaged Zr(0001) surface held at 660 K during deposition resulted in the formation of intermetallic crystalline Zr 3Fe, and not These results prove that the presence of zirconium grain boundaries is an essential requirement for the nucleation of amorphous Fe-Zr by a solid state reaction. Surface defects at the zirconium surface seem to promote nucleation of the thermodynamically more stable intermetallic compound Zr 3Fe.

Solute diffusion in α-Zr: Rutherford backscattering and secondary-ion mass spectrometry study

Abstract Substitutional diffusion coefficients D of Hf, Ta and Pb have been measured α- Zr single crystals and the diffusion profiles analysed by Rutherford backscattering (Hf, Ta and Pb) and secondary-ion mass spectrometry (Hf). Measurements were made either parallel (D ‖) or perpendicular (D‖ ) to the specimen c axis. Although the main study is concerned with the influence of Fe on the diffusion of Hf, Ta and Pb at 1100 K, some preliminary data are also reported for Pb and Ta at 872 and 1000 K. The initial measurements at 1100 K show that D(Ta)>D(Hf)>D(Pb); the Zr specimens used for these measurements were then treated to reduce the Fe content (65–30 at.p.p.m.) and the diffusion coefficients remeasured. With one exception, D‖ for Hf, the diffusion coefficients fell by a factor of about two with the decrease in Fe concentration; D‖ for Hf fell by about an order of magnitude. All the D values measured at 1100 K for Hf, Ta and Pb lie in the range 4 × 10−19-3 × 10−17m2s: those for Hf, and their dependence on the Fe concentration (with the exception of the low-Fe D datum), are notably similar to α-Zr self-diffusion values presented in a very recent study. Together, the results are considered in terms of intrinsically normal diffusion with enhancement of the more slowly diffusing species by an Fe-associated defect. A comparison of solute D values measured in α-Zr, where Fe levels have not been deliberately reduced, shows that substitutional solute diffusion increases with decreasing size and valence.

Convergent Beam Electron Diffraction Zone Axis Pattern Map of Zirconium

The purpose in obtaining zone axis pattern map (zap map) from a given material is to provide a quick and reliable tool to identify cristaline phases, and crystallographic directions, even in small particles. Bend contours patterns and Kossel lines patterns maps from Zr single crystal in the [0001] direction have been presented previously. In the present communication convergent beam electron diffraction (CBED) zap map of Zr will be shown. CBED patterns were obtained using a Philips microscope model EM300, which was set up to carry out this technique. Convergent objective upper pole piece for STEM and some electronic modifications in the lens circuits were required, furthermore the microscope was carefully cleaned and it was operated at a vacuum eminently good.CBED patterns in the Zr zap map consist of zero layer disks, showing fine details within them which correspond to intersecting set of higher order Laue zone (HOLZ) deficiency lines.

Fast diffusion and nucleation of the amorphous phase in Ni–Zr films

The nucleation of the amorphous phase by solid-state reactions has been investigated on single-crystal Zr films grown by molecular beam epitaxy and covered in situ with either polycrystalline Ni, amorphous (a-) NiZr, or single-crystalline Zr99N01 films. Interfacial reactions were investigated by backscattering analysis or secondary ion mass spectroscopy. The amorphizing reaction occurred only in the specimen with the a-NiZr over layer, although fast Ni diffusion through the single-crystalline Zr layer was observed in all three specimens. The nucleation behavior of a-NiZr is attributed to the combination of high-Ni and low-Zr mobility in crystalline Zr.

Evidence for a nucleation barrier in the amorphous phase formation by solid-state reaction of Ni and single-crystal Zr

In an ultrahigh vacuum (UHV) environment, thin poly crystalline Ni films have been deposited on a Zr (112) single-crystal surface. In contrast to the case of poly crystalline Ni and Zr films, formation of amorphous Ni—Zr is not observed upon annealing at 300 °C for 11.5 h. The possible presence of an oxide or an amorphous phase diffusion barrier is ruled out and therefore the lack of a reaction must be due to a reaction barrier at the single-crystal Zr/ Ni interface. Either ion mixing of the interface with 400 keV, 5 × 1015 Xe+ /cm2, or deposition of a poly crystalline Zr layer in between the Zr single crystal and the Ni overlayer can overcome this reaction barrier. These results indicate that grain boundaries in polycrystalline Zr play an important role in amorphous Ni—Zr formation by a solid-state reaction.

Sign of the electric field gradient at111Cd in Zr and Sb

The Β-γ TDPAC technique was applied to111Ag implanted in Zr and Sb metal single crystals in order to determine sign and magnitude of the quadrupole interaction at the site of111Cd in these metals. An analysis of the data taken at 293K yielded ΝQ=+15.4(6) MHz for111Cd in Zr and ΝQ=−107.5(20) MHz for111Cd in Sb. From these values electric field gradients of +7.3(8)×1016 V/cm2 and −5.56(62)×1017 V/cm2 for Cd in Zr and Sb are derived respectively.

Détermination comparative du profil de concentration en oxygène dissous dans le zirconium après oxydation à 800°c par émission ionique secondaire et par la réaction nucléaire 16O(d, p) 17O

The emission yields of secondary ions Zr +, ZrO + in Zr—0 solid solutions, bombarded with Ar +, were plotted as a function of the oxygen content. The ionic ratio ZrO +/Zr + could be correlated to the hardness of the Zr—O solution but does not vary linearly with C O/C zr. For samples bombarded with heavy ions TaF + 3, sputtering and ionization yields of the different species make uniform: the Z rO +/Zr + ratio varies linearly with C o / C zr . Diffusion gradients in oxidized Zr single crystals determined by SIMS are consistent with profiles obtained by nuclear microanalysis.

The Yield Drop at or Below 423k in Zr Single Crystals and in Ti

Yield drops were obtained in interrupted tensile and compression tests performed on zirconium single crystals between 262 and 362 K. Near 295 K, where most tests were performed, a minimum yield drop was obtained for an aging performed near the internal stress. For positive stress relaxations and a constant aging time, this yield drop increased linearly with the stress relaxed during aging. This result indicates a significant portion of the yield drop is caused by dislocations gliding to pinning points, which are most probably forest dislocations. A similar behaviour was observed for polycrystalline titanium at 423 K. The yield drops observed in the single crystals at 295 K, after aging at zero stress, increased linearly with the logarithm of the aging time in contrast to the time-independent Haasen-Kelly effect observed in polycrystalline material. Résumé Nous avons mesuré la hauteur des crochets de vieillissement après écrouissage sur des monocristaux de zirconium, lors d'essais de traction ou de compression entre 262 et 362 K. Prés de 295 K, où la plupart des essais ont été faits, c'est un vieillissement près de la contrainte interne qui donne Ie plus petit crochet. Pour des relâchements positifs de contraintes et un temps de vieillissement constant, il y a une relation linéaire entre la hauteur du crochet et la contrainte relâchée lors du vieillissement. Ce résultat démontre qu'une partie importante du crochet est causée par des dislocations qui glissent aux points d'ancrages, ceux-ci étant probablement des dislocations de forêt. Dans des essais à 423K sur du titane polycristallin, nous avons aussi obtenu une relation linéaire entre la hauteur du crochet et le relâchement de la contrainte. La hauteur des crochets obtenus pour les monocristaux de zirconium à 295 K, suite à un vieillissement à contrainte nulle, augmente linéairement avec le logarithme du temps de vieillissement, et donc ne peut pas être expliqué simplement par l'effet Haasen-Kelly observé sur des éprouvettes polycristallines.

The Yield Drop at or Below 423k in Zr Single Crystals and in Ti

Yield drops were obtained in interrupted tensile and compression tests performed on zirconium single crystals between 262 and 362 K. Near 295 K, where most tests were performed, a minimum yield drop was obtained for an aging performed near the internal stress. For positive stress relaxations and a constant aging time, this yield drop increased linearly with the stress relaxed during aging. This result indicates a significant portion of the yield drop is caused by dislocations gliding to pinning points, which are most probably forest dislocations. A similar behaviour was observed for polycrystalline titanium at 423 K. The yield drops observed in the single crystals at 295 K, after aging at zero stress, increased linearly with the logarithm of the aging time in contrast to the time-independent Haasen-Kelly effect observed in polycrystalline material. Résumé Nous avons mesuré la hauteur des crochets de vieillissement après écrouissage sur des monocristaux de zirconium, lors d'essais de traction ou de compression entre 262 et 362 K. Prés de 295 K, où la plupart des essais ont été faits, c'est un vieillissement près de la contrainte interne qui donne Ie plus petit crochet. Pour des relâchements positifs de contraintes et un temps de vieillissement constant, il y a une relation linéaire entre la hauteur du crochet et la contrainte relâchée lors du vieillissement. Ce résultat démontre qu'une partie importante du crochet est causée par des dislocations qui glissent aux points d'ancrages, ceux-ci étant probablement des dislocations de forêt. Dans des essais à 423K sur du titane polycristallin, nous avons aussi obtenu une relation linéaire entre la hauteur du crochet et le relâchement de la contrainte. La hauteur des crochets obtenus pour les monocristaux de zirconium à 295 K, suite à un vieillissement à contrainte nulle, augmente linéairement avec le logarithme du temps de vieillissement, et donc ne peut pas être expliqué simplement par l'effet Haasen-Kelly observé sur des éprouvettes polycristallines.