Hydride Plates Research Articles

Research on the hydrogenation behavior of magnetocaloric La0.8Ce0.2Fe11.51Mn0.19Si1.3 hot-pressed plates

The fabrication of La(Fe, Si)13Hy plates is very challenging owing to the poor mechanical stability. In this work, La(Fe, Si)13 plates synthesized by hot-pressing remain mechanically robust after optimizing the hydrogenation process. The hydrogenation behavior was investigated through characterizing the phase structures and magnetocaloric effects of La0.8Ce0.2Fe11.51Mn0.19Si1.3 hydride plates. The saturated hydrogenation plates exhibit the large magnetic entropy change (12.98 J/kg·K), excellent mechanical properties (bending strength ∼ 213 MPa) and good stability under the conditions of the hydrogenating temperature of 593 K, the pressure of 0.13 MPa for 210 min.

The deformation and burst behavior of Zircaloy-4 cladding tubes with hydride rim features subject to internal pressure loads

This study is motivated by the desire to conduct a separate effects test replicating specific aspects of an in-pile pulse reactor test on high exposure light water reactor (LWR) fuel rods. The principal purpose of the tests was to determine whether temperature and or hydrogen concentration thresholds exist in assessing the vulnerability of a stress relieved zirconium alloy cladding tubes to low strain ruptures. A secondary objective was to determine whether observations of the cladding stress during deformation could aid in the understanding of the crack formation and propagation in cladding tubes with hydride rim features. The study utilized artificially hydrided Zircaloy-4 cladding tubes and an isothermal, internal pressure test that was controlled with an in-situ strain measurement. The test results show a clear transition in failure vulnerability between room temperature and 150 °C. Below 150 °C, cladding tubes rupture at very low uniform plastic strain—even at relatively modest cladding hydrogen levels. At and above 150 °C, cladding tubes only rupture at low uniform plastic strain if the cladding hydrogen content is greater than 500 ppm and usually experience at least some modest amount of plastic deformation prior to rupture. Post-test metallographs from non-ruptured cladding tubes show numerous primary cracks forming in the hydride rim and arresting at the metal/hydride interface. This observation combined with the decrease in bulk yielding of hydrided cladding tubes when compared to fresh non-hydrided tubes leads to the conclusion that the fracture stress of the hydride rims is related to and bounded by the yield stress of the zirconium metal. Some evidence is presented for a change in crack propagation mechanism from one of void formation on hydride plates and linkage at temperatures below 150 °C to more classical ductile shearing beneath the primary crack tip at temperatures above 150 °C. This apparent change in crack propagation mechanism may help explain the observed temperature and hydrogen concentration thresholds.

Simultaneously realizing good volumetric entropy change and mechanical strength of La0.8Ce0.2Fe11.51Mn0.19Si1.3Hy plates

It is hard to get a high-strength La(Fe, Si)13-based hydrides owing to the brittle feature of hydrides. In this work, we fabricated the La0.8Ce0.2Fe11.51Mn0.19Si1.3 plates through hot pressing at 1323 K for various time. Subsequently, the saturated hydrogenization is achieved at 593 K in H2 atmosphere of 0.13 MPa for 210 min. The microstructure and magnetocaloric properties were investigated by an X-ray diffractometer, a scanning electron microscope and the Versa-Lab. Under magnetic fields of 0–2 T, the maximal volumetric entropy change is 91.4 mJ/(cm3·K) at 297 K for the hydride plates. The hydride plate simultaneously has excellent mechanical properties with the maximum bending strength of 213 MPa, which suggest that the hot pressing followed by hydrogenation could be an effective route of fabricating La(Fe, Si)13-based hydrides for the potential application in the magnetic refrigerator.

Formula omitted][formula omitted] morphology prediction of Zr hydride precipitates using atomistically informed Eshelby’s ellipsoidal inclusion

We energetically predicted the morphology of Zr hydride precipitates in a hexagonal close-packed (HCP) Zr matrix. Considering Zr hydride precipitates as ellipsoids, we used Eshelby’s ellipsoidal inclusions to calculate the elastic energy increment due to the presence of Zr hydride precipitates in the Zr matrix, in which the elastic anisotropy and inhomogeneity of the elastic constants between Zr and Zr hydride were considered. We compared the difference in the elastic energy increment between the ellipsoidal inclusions with different shapes: plates (mimicked by penny-shape ellipsoids), needles (mimicked by longitudinal ellipsoids) and sphere, and orientations to detect the stable structure with the minimum elastic energy increment. Eigenstrains of each Zr hydride and elastic constants of Zr hydrides and HCP Zr for Eshelby’s ellipsoidal inclusion analysis were determined using atomistic simulations based on a density functional theory calculation, achieving a parameter free abinitio morphology prediction. The morphology predictions were implemented for two cases: with and without shear components of eigenstrain (w/ and w/o shear). The 〈12̄10〉 longitudinal needle for the γ hydride (w/o shear) and plate (or disk) on the plane, which is 20° to 30° tilted about 〈12̄10〉-axis from basal plane (0001), for δ and ε hydrides (w/ shear) were successfully predicted as stable shapes and orientations of the precipitates under zero external stress conditions, qualitatively consistent with experimental observations. The external circumferential tensile stress on the basal plane reduces the elastic energy of [0001] parallel Zr hydride plates, which is also qualitatively consistent with the reoriented δ hydride precipitates observed in the experiment. On the other hand, predicted external stress for the reorientation of Zr hydride is quite high, around 10 GPa. This is inconsistent with experimental observation and further investigation is necessary. Generally, our predictions based on elasticity theory appear qualitatively consistent with experimental observations, suggesting an elastic origin of the morphology of Zr hydride precipitates in the HCP Zr matrix.

Nanoindentation study of hydride diffusion layer in commercial pure titanium

In this work, the mechanical properties of hydride diffusion layer were thoroughly researched by nanoindentation technique. For the first time, the clear section microstructure of hydride diffusion layer was revealed under scanning electron microscope with complicated interactions of hydride plates near the interface between hydride layer and titanium matrix. The hydride layer section has higher hardness and lower modulus towards titanium matrix due to the hard nature and easier crack nucleation of hydride precipitation. Besides, the hardness of titanium matrix shows considerable anisotropy. The anisotropic hardness of sample surface was studied before and after hydrogen charging. The hardness of titanium matrix decreases with the increase of deviation angle between c-axis and surface normal. The hydride layer formed in the titanium grain with more favorable orientation for hydride transformation tends to possess higher indentation hardness.

Study on the mechanical properties and microstructure of Zr-2.5wt%Nb pressure tube material

In order to study the mechanical properties and the anisotropy of a Zr-2.5 wt%Nb pressure tube material, tensile tests along the principal tube directions, which are axial, transverse and radial, were performed at room temperature using a pressure tube. The effect of tube length was evaluated, by using samples from the tube's back-end, middle, and front-end. Strong anisotropy among the principal directions was found, and increased strengths were obtained with increased distance from the front-end location. Microstructure analysis by X-ray diffraction, electron backscatter diffraction, and scanning electron microscopy indicated that increasing defect density along the tube was the main reason for the increasing strength. Although texture mainly determined the anisotropy of the tensile strengths, the ratio between the axial and radial strengths could be considerably altered by hydride plates. Depending on how the hydride plate was placed with regard to the deformation direction, the yield strength and strain hardening ability were reduced differently by the hydride. The deterioration effect of the hydrides did not show linear dependency on the hydrogen contents due to other microstructure variations. We had a brief discussion about which parameters might result in the non-linear change found in the deterioration along the tube.

Mechanical and magnetocaloric properties of La(Fe,Mn,Si)13Hδ/Cu plates prepared by Cu-binding prior to hydrogenation

La(Fe,Si)13Hδ hydrides with large magnetocaloric effect (MCE) have been demonstrated as promising magnetic refrigerants around room temperature. To meet the shape requirements in a refrigerator, hot-pressing technique was usually employed. However, hydrogenation prior to hot-pressing is inappropriate sometimes because the dehydrogenation occurs at about 450 K, and the incorporation of large amount of metal as binder often makes the MCE reduce a lot. Here, we report a new way to prepare the metal-bonded LaFe11.4Mn0.3Si1.3Hδ hydride plates as thin as 0.5 mm by metal-binding prior to hydrogenation instead. By adding a small amount 4 wt% of Cu, LaFe11.4Mn0.3Si1.3/Cu plates were firstly prepared. Afterwards, hydrogen absorption can be still conducted because lots of holes and naked surfaces still left, which favor hydrogen atoms into lattice. As a result, saturated hydrogenation can be achieved. The MCE keeps large, and good mechanical properties and thermal conductivity have been demonstrated.

Hydrogen-Induced Phase Transformation and Microstructure Evolution for Ti-6Al-4V Parts Produced by Electron Beam Melting

In this paper, phase transitions and microstructure evolution in titanium Ti-6Al-4V alloy parts produced by electron beam melting (EBM) under hydrogenation was investigated. Hydrogenation was carried out at the temperature of 650 °C to the absolute hydrogen concentrations in the samples of 0.29, 0.58, and 0.90 wt. %. Comparative analysis of microstructure changes in Ti-6Al-4V alloy parts was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Furthermore, in-situ XRD was used to investigate the phase transitions in the samples during hydrogenation. The structure of Ti-6Al-4V parts produced by EBM is represented by the α phase plates with the transverse length of 0.2 μm, the β phase both in the form of plates and globular grains, and metastable α″ and ω phases. Hydrogenation to the concentration of 0.29 wt. % leads to the formation of intermetallic Ti3Al phase. The dimensions of intermetallic Ti3Al plates and their volume fraction increase significantly with hydrogen concentration up to 0.58 wt. % along with precipitation of nano-sized crystals of titanium δ hydrides. Individual Ti3Al plates decay into nanocrystals with increasing hydrogen concentration up to 0.9 wt. % accompanied by the increase of proportion and size of hydride plates. Hardness of EBM Ti-6Al-4V alloy decreases with hydrogen content.

Excellent mechanical properties and age stability of hydrogenated La0.8Ce0.2Fe12.5Mn0.2Si1.3Hδ plates with extra Fe

Herein, hydrogenated La0.8Ce0.2Fe12.5Mn0.2Si1.3Hδ plates as thin as 0.4–0.6 mm with extra Fe were prepared, whereupon the microstructure, mechanical properties, age stability, and magnetocaloric effect (MCE) were systematically investigated. It was demonstrated that the introduction of extra α-Fe largely enhanced the mechanical properties. The bending strength was about 61 MPa for a single 0.6 mm-thick plate, while the compressive strength was as much as 352 MPa for the stacked plates. Meanwhile, the hydride plates showed considerable MCE around room temperature. The maximal entropy change was 14.2 J/kgK around its Curie temperature TC = ∼298 K and the effective refrigeration capacity was 284 J/kg under a magnetic field change of 0–5 T. Moreover, the hydride plates exhibited excellent age stability and good thermal conductivity. No age splitting occurred, even when the plates were held at room temperature for more than one year, owing to full hydrogenation. Finally, room-temperature thermal conductivity was as large as 9.5 Wm−1K−1. All of these results demonstrate that the hydride plates with extra Fe are desirable magnetic refrigerants, which is beneficial to increase the working efficiency in a device.

Formation of iron hydride in α-Fe under dislocation strain field and its effect on dislocation interaction

Atomistic simulation of hydride formation under dislocation strain field piled up at inclusions in α-Fe was performed using a new Finnis–Sinclair-type embedded atom method potential. Two 1/2 [111] (101¯) edge dislocations were introduced in BCC α-Fe to study the effects of dislocation interaction on the formation of hydride. Our simulation demonstrated that the interaction of dislocation-inclusion could produce ultrahigh stress that resulted in the formation of iron hydride. In addition, the dissociation of one of the two 1/2 [111] edge dislocations into [001]+1/2 [111¯] two perfect dislocations can occur under a large applied shear (5%) or smaller shear (0.5%) when a hydride plate forms, despite the dissociation not satisfying the energy condition of dislocation reaction. The [001] perfect dislocation is usually considered the origin of cleavage on {100} planes, which is not stable without large applied load or hydrogen. In our model, the densities of both dislocation and inclusion on the glide plane could be changed to correspond to the dislocation density and inclusion (carbide) density in real martensitic steels. The results indicated that low dislocation density and small size of inclusions could prevent the formation of hydride. From these findings, tempering was suggested asa measure of preventing hydrogen embrittlement because proper tempering can effectively reduce the residual stress caused by quenching, precipitate dispersive and fine carbides (inclusion) and, in addition, decrease dislocation density in quenching and tempering martensitic steels.

In situ synchrotron X-ray diffraction study of hydrides in Zircaloy-4 during thermomechanical cycling

The d-spacing evolution of both in-plane and out-of-plane hydrides has been studied using in situ synchrotron radiation X-ray diffraction during thermo-mechanical cycling of cold-worked stress-relieved Zircaloy-4. The structure of the hydride precipitates is such that the δ{111} d-spacing of the planes aligned with the hydride platelet face is greater than the d-spacing of the 111 planes aligned with the platelet edges. Upon heating from room temperature, the δ{111} planes aligned with hydride plate edges exhibit bi-linear thermally-induced expansion. In contrast, the d-spacing of the (111) plane aligned with the hydride plate face initially contracts upon heating. These experimental results can be understood in terms of a reversal of stress state associated with precipitating or dissolving hydride platelets within the α-zirconium matrix.

피복관 냉각에 의한 지르코늄 합금 피복관 수소화물 재배열 특성

김명수 ・김현길2 ・민수정1 ・김규태1,* 동국대학교 에너지환경대학 한국원자력연구원 경수로핵연료기술개발부 Cladding Cooling Rate-Dependent Hydride Reorientation and Configuration Myeong-Su Kim, Hyun-Gil Kim, Su Jeong-Min, and Kyu-Tae Kim* Dongguk University, College of Energy & Environment, Gyeongju 780-718, Korea Nuclear Convergence Technology Division, Daejeon 305-353, Korea Abstract: The effects of cooling rates from 400 to 200 °C on hydride reorientation were investigated using ring specimens of 250 ppm and 500 ppm H Zr-Nb cladding tubes. For no stress conditions with cooling rates of 2.5 and 25.0 °C/min, the 250 ppm H specimens show that hydride plates are reprecipitated only in a circumferential direction during the cooling from 400 to 200 °C, but the hydride plates appear to be much shorter for the 25.0 °C/min cooling rate. However, the 500 ppm H specimens show that hydride plates are reprecipitated as a mixture of circumferential and radial hydride plates for the 25.0 °C/min cooling rate. This mixed hydride plates may be caused by a blocking effect of circumferential hydrides undissolved on the one hand and by a considerable tensile hoop stress locally generated by a large difference in the cooling rates between outer and interior layers on the other hand. For 150 MPa tensile hoop stress conditions with a cooling rate of 2.5 °C/min, the 500 ppm H specimens show a relatively shorter radial hydride plates than the 250 ppm H specimens, which may be explained by a blocking effect of undissolved circumferential hydride plates in the 500 ppm H specimens. Tensile tests for the specimens experiencing the cooling from 400 to 200 °C under the 150 MPa hoop stress conditions indicate that there is little impact of hydrogen content on ultimate tensile strengths but the 250 ppm H specimens generate less plastic elongation and more noticeable cleavage fracture than the 500 ppm H specimens, which may be caused by relatively longer radial hydride plates in the former. †(Received November 27, 2012)

Influence of stress field of expanding and contracting plate shaped precipitate on hydride embrittlement of Zr-alloys

The stress fields of expanding (precipitation) and contracting (dissolution) hydride plates were computed by finite element method using Zr–H solid solution and hydride properties at 25, 200 and 400°C for fully and semi-constrained hydride plates. For the first time simultaneous hydride expansion and matrix contraction and vice-versa have been considered in a simulation of hydride precipitation and dissolution, respectively. It was observed that a fully constrained expanding hydride plate exerts a tensile stress field in the matrix close to the edge of the hydride plate while a partially contracting hydride plate exerts a tensile stress field in the hydride plate as well as a large compressive stress in the surrounding matrix close to the edge of the hydride plate. It is suggested that a compressive stress component in the matrix acting normal to a partially shrinking hydride plate could possibly explain an enhanced resistance to hydride embrittlement of Zr-alloy at elevated temperature.

Face-centered tetragonal titanium hydrides in fine-grained commercial pure (grade 2) titanium

Face-centered tetragonal (fct) titanium hydride was observed by transmission electron microscopy in commercially pure (CP, grade 2) fine-grained (FG) titanium produced by severe plastic deformation (SPD) and annealing. This γ-fct titanium hydride has a c/a ratio of 1.08. It was found that the γ-fct hydride possesses inherent orientation relationships with the FG hexagonal close-packed (hcp) α-Ti matrix, namely (110)γ∥(101¯0)α, [001]γ∥[0001]α, [1¯14]γ∥[1¯21¯6]α and [1¯12]γ∥[12¯13¯]α. The fct titanium hydride plates within hcp matrix have the thickness of 10–150nm and length of 50nm–3μm while the matrix grains have the size of 50nm to 3μm. The fct titanium hydride was found to be very scarce in this Ti and the relationship between the length of γ-fct hydride and grain size of the hcp matrix has also been discussed.

δ-Hydride Habit Plane Determination in α-Zirconium at 298 K by Strain Energy Minimization Technique

Hydrogen in excess of solid solubility precipitates as hydride phase of plate shaped morphology in hcp α-Zr with the broad face of the hydride plate coinciding with certain crystallographic plane of α-Zr crystal called habit plane. The objective of the present investigation is to predict the habit plane of δ-hydride precipitating in α-Zr at 298 K using strain energy minimization technique. The δ-hydride phase is modeled to undergo isotropic elasto-plastic deformation. The α-Zr phase was modeled to undergo transverse isotropic elastic deformation but isotropic plastic deformation. Accommodation strain energy of δ-hydride forming in α-Zr crystal was computed using initial strain method as a function of hydride nuclei orientation. Hydride was modeled as disk with round edge. Contrary to several habit planes reported in literature for δ- hydrides precipitating in α-Zr crystal, the total accommodation energy minima at 298 K suggests only basal plane i.e. (0001) as the habit plane.

A theoretical and experimental study of hydrides in zirconium alloys

A method developed for computing the critical length and thickness of hydride plates formed in delayed hydride cracking (DHC) in zirconium alloys is considered. The model is based on analyzing the distribution of tensile stresses in the plane of a sharp normal tensile crack. The characteristics of hydrides formed due to DHC in reactor tubes produced from alloy Zr-2.5% Nb are determined experimentally. The results of the computation agree well with experimental data.

Formation of titanium hydride in Ti–6Al–4V alloy

Use of hydrogen as a temporary element in titanium alloys is an attractive approach for enhancing processability, and also for modification of microstructures and thereby improving final mechanical properties. In this article, microstructures, phases and phase transformations in Ti–6Al–4V alloy specimens containing 0.1, 0.3 and 0.5 wt.% hydrogen has been investigated using optical microscopy, XRD and TEM. It was shown that there are fcc δ titanium hydride plates precipitated in the specimens containing hydrogen 0.302 and 0.490 wt.%. Simultaneously, mass orthorhombic martensite α″ has been found in the specimens as well as δ hydride. One eutectoid transformation mechanism from β H to δ hydride and α based on diffusion transformation theory was presented.

Critical length and thickness of hydride plates with delayed hydride cracking in zirconium alloys

A method for calculating the critical length and thickness of hydrides with delayed cracking in commercial zirconium alloys is developed. The critical characteristics of hydride precipitates are estimated for pipes made of the alloy Zr-2.5%Nb. It is shown that the theoretical results agree with the experimental data.

Microstructural study of hydride formation in Zr–1Nb alloy

Hydriding of Zr–1Nb alloy having a microstructure comprising equiaxed α grains and a uniform distribution of spherical particles of the β-phase has been carried out in this study. The specimens were hydrided by gaseous charging method to different hydrogen levels. The microstructures of hydrided samples were examined as a function of hydrogen content. The formation of δ-hydride in slow cooled specimens and formation of γ-hydride in rapidly cooled specimens has been studied with their morphology, habit plane and orientation relationship with the α matrix in view. The habit planes of either type of hydride phase has been determined and compared with those observed in other Zr–Nb alloys. The orientation relationship between the α matrix and the δ-hydride was found to be the following: (0 0 0 1) α ∥( 1 ̄ 1 1 ̄ ) δ and [1 1 2 ̄ 0] α ∥[1 1 0] δ . The orientation relationship between the α matrix and the γ-hydride was of the following type: (0 0 0 1) α ∥(0 0 1) γ and [1 2 ̄ 1 0] α ∥[1 1 ̄ 0] γ . The internal structure of both types of hydride has been examined. The effect of the presence of the spherical β-phase particles in the α matrix on the growth of the hydride plates has been investigated.

Use of solid state protonic conductors for oxygen potentiometric sensor at room temperature

The use of oxygen sensors based on oxygen conductors such as stabilized zirconia is restricted at temperatures 300°C. Oxygen sensors operating at room temperature are however required for many purposes, especially in environmental and biological analyses. We have therefore studied the realization of a simple solid state sensor for oxygen at room temperature, which utilizes a thin film of pellicular zirconium phosphate or NAFION as protonic conductor, a titanium hydride plate as solid state reference electrode and a sensing catalytic electrode of Pt. Such a sensor is based on the H 2-O 2 mixed potential which is produced at the sensing electrode when short pulses of current are applied. Potential measurements are periodically performed after a suitable delay time forms the end of each pulse. The potential is a linear function over a large range of log P o 2 , while, in the most favourable conditions, the sensitivity limit is of a few parts per millions.