Cd Alloy Research Articles

Information on the evolution of severe LWR fuel element damage obtained in the CORA program

In the CORA program a series of out-of-pile experiments on LWR severe accidental situations is being performed, in which test bundles of LWR typical components and arrangements (PWR, BWR) are exposed to temperature transients up to about 2400°C under flowing steam. The individual features of the facility, the test conduct, and the evaluation will be presented. In the frame of the international cooperation in severe fuel damage (SFD) programs the CORA tests are contributing confirmatory and complementary informations to the results from the limited number of in-pile tests. The identification of basic phenomena of the fuel element destruction, observed as a function of temperature, is supported by separate-effects test results. Most important mechanisms are the steam oxidation of the Zircaloy cladding, which determines the temperature escalation, the chemical interaction between UO 2 fuel and cladding, which dominates fuel liquefaction, relocation and resulting blockage formation, as well as chemical interactions with Inconel spacer grids and absorber units ((Ag, In, Cd) alloy or B 4C), which are leading to extensive low-temperature melt formation around 1200°C. Interrelations between those basic phenomena, resulting for example in cladding deformation (“flowering”) and the dramatic hydrogen formation in response to the fast cooling of a hot bundle by cold water (“quenching”) are determining the evolution paths of fuel element destruction, which are to be identified. A further important task is the abstraction from mechanistic and microstructural details in order to get a rough classification of damage regimes (temperature and extent), a practicable analytical treatment of the materials behaviour, and a basis for decisions in accident mitigation and management procedures.

Shape memory and related phenomena

More than half the papers presented at ICOMAT-89 (International Conference on Martensitic Transformations, Sydney, Australia, July, 1989) were concerned with various aspects of the shape memory effect (SME), a relatively new phenomenon associated with a martensitic transformation. Accordingly, a material undergoes a displacive, shear-like martensitic transformation when it is cooled below a certain temperature, Ms. The transformation is completed when a lower temperature, Mr, is reached, where the material is said to be in the martensitic state. When this martensite is deformed (below Mr) it undergoes a strain which is completely recoverable upon heating. The shape recovery (memory) begins at a temperature, As, and is completed at a higher temperature, Af. The Ms, Mr, As and Af temperatures depend upon the particular alloy system, and recovery strains typically range from 2-10%. The martensite in shape memory alloys (SMA's) may also be isothermally induced above the Ms temperature by the application of stress, known as stress-induced martensite (SIM). This martensite disappears (reverses) when the applied stress is removed, resulting in a mechanical type (as opposed to thermal type) shape memory. The formation of SIM and its reversion gives rise to superlastic behavior. The two-way SME combines aspects of the 'one way' SME and SIM formation. Following a variety of thermomechanical treatments a specimen will exhibit a spontaneous shape change upon cooling between Ms and Mr because of microstresses inbuilt during processing. The microstresses effectively function ('program') as the external stress in SIM formation, but since the internal stresses are not released, the martensite will only reverse upon heating, at which time the one way SME operates. The shape memory effect was initially reported in 1951 by Chang and Read who studied a Au-Cd alloy3 I)* Since then many other alloy systems have been found to exhibit SME behavior. A brief history of the shape memory effect can be found in Ref. (2), and an excellent review of the development of SMA's has been provided by Miyazaki and Otsuka. (3) The more practical and engineering aspects of SMA's, which are not covered here, will be found in the book, Engineering Aspects of Shape Memory Alloys, proceedings of an international workshop/conference held in 1988. (4) Additional information on the SME and SMA's can be found in various conference proceedings °-14) and monographs, os-ig) Table 1 presents a brief glossary of shape memory and related phenomena. Apparently recognizing that the rather exotic Au--Cd alloy of Chang and Read °) had little engineering significance, interest in the shape memory remained largely dormant until 1963, when similar

Identification of intermetallic compounds in thin layers of electrodeposited Cu–Cd alloys using electrochemical techniques

AbstractAn attempt was made to analyse the phase structure of thin layers of electrodeposited Cu–Cd alloys using anodic linear sweep voltammetry combined with a potentiostatic pulse technique (ALSV–PPT). The results were compared with data obtained using conventional techniques for phase structure analysis. It was found that application of the conventional X-ray technique (Guinier analysis) is limited, because the grain size of the alloy constituents is too small for compounds to be revealed by X-ray peaks. Electrodeposited alloys could be successfully analysed using that method only after subsequent thermal treatment. Diffraction patterns from transmission electron micrographs of very thin foils (of the order of 20–50 nm) of electrodeposited 75Cd–25Cu (at.-%) alloy revealed the presence of CuCd3 intermetallic compound having a grain size of ~20 nm. By comparing all the results, the distribution of the various intermetallic compounds present at various stages in the electrodeposition of thin (up to 10 μm)...

Identification of intermetallic compounds in thin layers of electrodeposited Cu–Cd alloys using electrochemical techniques

Identification of intermetallic compounds in thin layers of electrodeposited Cu–Cd alloys using electrochemical techniques

Temperature and Grain Size Dependence of Yielding and Fracture of Pd–2 wt% Cd Alloy

Etude de l'effet de la taille de grain et de la temperature sur les parametres d'ecrouissage de cet alliage. On se place dans l'intervalle de temperature 443 a 503 K

Free energy change of off-eutectic binary alloys on solidification

A formula for the free energy difference between the undercooled liquid phase and the stable solid phase is derived for off-eutectic binary alloys in which the equilibrium solid/liquid transition takes place over a certain temperature range. The free energy change is then evaluated numerically for a Bi-25 at. pct Cd alloy modeled as a sub-subregular solution.

The structure of CuCd alloys obtained electrolytically under galvanostatic conditions

The structure of CuCd alloys obtained from an ethylenediamine electrolyte was studied in the range of current densities from D k = 0.01 to 2.0 A dm −2 and for a mean thickness of the deposited layer of 20 μm. An analysis was made of the chemical and phase compositions of the alloys, the sizes of crystallites and lattice distortions, the solubility of cadmium in sopper and the surface morphology. Depending on the current density, either single-phase alloys (α-phase) or two-phase alloys (α-phase + cadmium-enriched phase or α-phase + Cu 2Cd) are formed. The size of the α-phase crystallites decreases with an increase in current density so that amorphous alloys are obtained above D k = 0.5 A dm −2 . The maximum solubility of cadmium in copper is about 22 at.%. The structure of the alloys obtained under galvanostatic conditions is compared with that of alloys previously obtained under potentiostatic conditions.

The hP1-type phases in alloys of cadmium, mercury, and indium with tin

The hP1-type phases in alloys of Cd, Hg, and In with Sn are stable in the valence electron concentration interval 3.80–3.95. Following a rule of Raynor, the axial ratioc/a decreases with increasing valence electron concentration,Nb/at. Using lattice constant measurements the rule is confirmed, and by using density measurements the absence of constitutional vacancies is verified. Thec/a→Nb/at relation of the hP1 phases is similar toc/a→Nb/at of InSnm (0<m<0.1) and In3Sn. A bonding-type proposal, explaining the stability of these structures and the dependence of their axial ratio on valence electron concentration, is derived.

Superplasticity in single-phase Zn-0·25 wt. % Cd alloy

A single-phase Zn-0·25 wt. % Cd alloy was prepared with the mean grain sized¯≈ 1μm. Superplastic characteristics (Amax=320% andmmax>0·4) were established at room temperature at the strain rates.ɛ≈10−4s−1. Because of the absence of any second phase particles the fine-grained structure was not stable and an intense grain coarsening was observed both during the long-term ageing and during straining at room temperature. The increasing temperature accelerated this grain coarsening and suppressed the superplastic behaviour. Nevertheless, the stress relaxation tests suggested that the superplastic behaviour might be expected at higher temperatures in coarser grained specimens, too, but at substantially lower strain rates.

High-resolution electron microscopic study on long-period superstructures with 6H stacking sequence in Au3Cd alloys

Atomic arrangements of long-period superstructures in Au–24.5at.%Cd alloy with the basic h.c.p. structure have been investigated by high-resolution electron microscopy. The alloy shows one-dimensional or two-dimensional long-period superstructures in the close-packed plane with a 6H stacking sequence, depending on heat treatments. It is shown that the two-dimensional incommensurate superstructure with a period larger than 9a0 is composed of domains of the hexagonal commensurate structure (M = 9) separated by the antiphase-boundary zone in which 33/2a0 × 2a0 × 3c0 orthorhombic structure is formed (a0, c0 being the lattice parameters of the h.c.p. structure). Microstructures of the alloy annealed at 620 K with the one-dimensional long-period superstructure and of the alloy quenched from 770 K showing diffuse scattering have also been investigated by high-resolution electron microscopy.

Crystal Structure of &amp;gamma;&lt;SUB&gt;2&lt;/SUB&gt;&amp;prime; Martensite in Au-47.5 at%Cd Alloy

Crystal structure of the γ2′ martensite in a Au-47.5 at%Cd alloy has been analyzed by the single crystal X-ray diffraction method. The lattice constants were a=0.4859(11), b=0.3151(1) and c=0.4766(1) nm. The space group was Pcmm, with 4 atoms in the unit cell as Ölander reported. The structure was refined by the full-matrix least squares method to a final R factor of 4.7%, noticeably improved from that of Ölander. Moreover, the amount of shift of each atom from the ideal stacking positions in the hcp structure was discussed by using a hard sphere model of atoms; e.g. atoms in each layer are not arranged centro-symmetric.

Study of Rubber-Like Behaviour in a Au-47.5at% Cd Alloy by Synchrotron-Orbital Radiation

Study of Rubber-Like Behaviour in a Au-47.5at% Cd Alloy by Synchrotron-Orbital Radiation

Preconcentration of Trace Elements in Aluminum Alloys Using a Chelating Ion-Exchanger and Determination by ICP-AES

The Hyphan resin, a chelating ion-exchanger, is used to preconcentrate several metals (Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Ti, and Zn) in aluminum alloys, before analysis by ICP atomic emission. The recovery of the preconcentration procedure is 100% for most metals. The accuracy of the method is evaluated by analysis of ALCAN and NIST standard reference materials. The results are in good agreement with the certified values. The preconcentration method can be used in a batch or in a flow analyzer mode in conjunction with an ICP/atomic emission spectrometer.

Kinetics of cellular dissolution in a CuCd alloy

Dissolution of the cellular precipitate by cell boundary migration has been studied in a Cu-2 at.% Cd alloy in the temperature range 777–878 K. Microstructural observations have revealed that the process of dissolution begins at the original position of the grain boundary as well as the cell boundary. The steady state rate of cell boundary migration decreased with decreasing temperature of dissolution and became zero at approximately 770 K, which is about 30 K below the equilibrium solvus temperature. The boundary diffusivities were determined at a number of temperatures by using the theory of Petermann and Hornbogen modified for dissolution. The diffusivity values calculated from the experimental data are seven orders of magnitude higher than the corresponding volume diffusivities. From the temperature dependence of the diffusivity, an activation energy of 157 kJ mol −1 is obtained, which is about three-quarters of the activation energy for the bulk diffusion of Cd into Cu. From the diffusivity and activation energy values, it can be concluded that the diffusion of Cd along the migrating grain boundaries control the dissolution of the cellular precipitate in this alloy.

Bainite formation in a silver-cadmium alloy

The changes in X-ray diffraction intensity and internal friction within and beyond the incubation period of bainitic transformation on the isothermal TTT diagram in a silver-cadmium (43.3 wt pct Cd) alloy were studied. Experimental results show that the parent-phase X-ray diffraction intensity and the internal friction value increase immediately at the beginning of isothermal holding and that the internal friction reaches its maximum value,Q−1max within the incubation period. It then gradually decreases. It is suggested that the prebainitic transformation within the incubation period is the nucleation process of bainite.

Long range order, antiphase domain structures, and the formation mechanism of α1 (“Bainite”) plates in A CuZnAl alloy

The inheritance of long range order during the β 2 (B2) or β 3 ( L2 1) → α 1 (“Bainite”) transformation in a Cu-26.67Zn-4Al (wt%) alloy has been demonstrated. The associated antiphase domain (APD) structures in the α 1, plates were studied by TEM dark field imaging using both nearest-neighbor (NN) and next-nearest-neighbor (NNN) superlattice reflections. At temperatures below the β 2 → β 3 ordering temperature, both NN and NNN APDs are inherited by the α 1, plates during their initial formation and subsequent early stage plate thickening. NNN order is lost, although NN order and its APD structure are preserved in subsequently thickened layers of the plates. As a result, the α 1 ordered structure is composite, consisting of an 18R central region and an ordered 9R surrounding outer layer. At temperatures above the β 2 → β 3 transition temperature, the parent β 2 possesses only NN order. Similar inheritance of NN order and associated APDs is also found at lower transformation temperatures. The observed evolution of long range order and the APD structure of the α 1 plates strongly suggests that both the initial transformation and early growth stages of the plates involve a shear mechanism. Long range diffusion, which is effectively confined to the NNN sublattice due to the presence of NN order at the interface, eventually takes over and controls subsequent plate thickening. The thickness of the 18R central zone in α 1 plates decreases significantly with increasing transformation temperature, implying that the shear-diffusional transition is shifted to an earlier transformation stage as the transformation temperature becomes increasingly higher than the martensitic transformation temperature, M s . The lifetime of long range order in the α 1, plates also decreases with increasing transformation temperature, as internal diffusion in the plates is enhanced. The implications of these observations are discussed and compared with earlier results on similar transformations in binary CuZn and AgCd alloys. Accordingly, it is believed that, for the first time, an aggregate of substantial documentation has been obtained for the case where a solid state phase transformation begins by a shear mechanism and ends up being dominated by classical diffusion. This behavior can be rationalized in terms of ordering temperatures in relation to the M s temperature of a given alloy. The essential point in this case, is that a “mixed” transformation is clearly involved, the description of which in classical terms, e.g. shear or diffusion controlled, depends upon the time frame of observation during the course of total transformation.

On the mechanism of martensite nucleation

The martensitic transformation in the following two model systems, Fe-30 at.% Ni and In-5.25 at.% Cd, was studied by X-ray diffraction and metallography in order to answer the following question: does the nucleation of martensites occur by a soft mode mechanism or by classical heterogeneous nucleation? The model systems used were sphere shaped single crystals with diameters between 30 and 114μm. In order to prevent the nucleation of martensite at or near the free surfaces, the Fe-30 at.% Ni and In-5.25 at.% Cd spheres were coated with a thin, coherent Ni-rich or Cd-rich surface layer, respectively. In the FeNi-system, the surface coating suppressed martensite formation in the entire crystal whereas no change was noticed in the InCd alloy. This result rules out a soft mode nucleation mechanism for martensite in FeNi and suggests a non-classical (e.g. a soft mode) process in In-5.25% Cd.

Oxide particle densities in internally oxidised Ag-Cd alloys: Part 2 Alloys with ternary additions

The densities of oxide particles are studied as a function of depth below the surface of internally oxidised Ag–9·5 at.-%Cd alloys with additions of ~0·2 or 2 at.-%Al, Mn, Ni, Sn, or Zn. Because of its low diffusivity and low free energy of oxide formation, Ni has no influence on particle density. Tin forms needlelike oxides and reduces the particle density as a result of geometric effects. Zinc has a marked effect on particle shape with platelike precipitates which coalesce during subsequent precipitation of CdO, but does not greatly affect particle density. Both Al and Mn increase particle density up to two orders of magnitude. Planar size distributions are presented which indicate that two types of nucleation site are present in the Mn containing alloys. In the alloy containing 0·15 at.-%Al the Al2O3 particles are too fine to act as nuclei for CdO precipitation; two types of band both with a narrow size distribution of CdO particles, but with slightly different size and largely different density are formed. Heterogeneous nucleation and depletion of the centre region of sample sheets, both of which result from the counterdiffusion of the oxidising elements, are shown to have a great influence on particle density, resulting in a more homogeneous distribution of particle densities over the sample cross-section than that predicted by available theories.MST/900b

Oxide particle densities in internally oxidised Ag–Cd alloys: Part 1 Effect of heterogeneous nucleation in alloys with high Cd content

It is shown by quantitative evaluation of scanning electron micrographs that there is disagreement between predictions of particle density on the basis of classical theory of internal oxidation and experimental results for Ag–Cd alloys with a medium Cd content at some depth below the surface and with high Cd content over most of the specimen cross-section. It is hypothesised that a transition from homogeneous to heterogeneous nucleation takes place by which the particle density is increased. Nucleation sites are formed by agglomeration of vacancies enriched in front of the oxidation zone because of counterdiffusion of Cd which, in turn, is accelerated by the high defect concentration. Most of the experimental results can be qualitatively explained by considering these effects.MST/900a

Pulse-plating of AuCuCd alloys—I. Experiments under controlled mass transport conditions

Pulse-plating of AuCuCd alloys under controlled steady state and non steady state mass transport conditions has been studied using an additive free cyanide electrolyte and a rotating hemispherical electrode. Average current densities ranged from 10 mA cm −2 to 1 A cm −2, pulse current densities from 50 mA cm −2 to 10 A cm −2 and pulse times from 0.2 to 100 ms. The influence of applied pulse parameters on alloy composition was determined. In addition, potential transient were measured and the resulting deposits were studied optically and/or with the scanning electron microscope. Results show that the composition of the deposited alloys and their aspect depends strongly on the choice of applied pulse-parameters.