Influence of δ phase precipitation on the stress corrosion cracking resistance of alloy 718 in PWR primary water

The negative influence of δ phase on the intergranular stress corrosion cracking (IGSCC) resistance of alloy 718 is commonly taken for granted. In addition, δ phase formed at low temperature (about 1023 K) do not present the same characteristics than the one formed at higher temperatures (from 1173 to 1273 K). The aim of the present study is then to understand how δ phase precipitation could enhance crack initiation in alloy 718, whatever the form of δ phase is. For that purpose, several heat treatments leading to δ phase precipitation were realized on two alloy 718 heats, one sensitive to IGSCC and the second not. Specific slow strain rate tensile tests carried out on thin tensile specimens in simulated PWR primary medium at 633 K conclusively prove that δ phase has no effect on the intrinsic sensitivity to intergranular crack initiation of tested heats.     

Radiation cross-linking in ultra-high molecular weight polyethylene for orthopaedic applications

The motivation for radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is to increase its wear resistance to be used as bearing surfaces for total joint arthroplasty. However, radiation also leaves behind long-lived residual free radicals in this polymer, the reactions of which can detrimentally affect mechanical properties. In this review, we focus on the radiation cross-linking and oxidative stability of first and second generation highly cross-linked UHMWPEs developed in our laboratory.     

Oxidation and creep failure of alloy 617 foils at high temperature

The microstructure of thermally grown oxides (TGO) and the creep properties of alloy 617 were investigated. Oxidation and creep tests were performed on 100 μm thick foils at 800-1000 °C in air environment, while the thickness of TGO was monitored in situ. According to energy dispersive X-ray (EDX) mapping micrographs observation, superficial dense oxides, chromia (Cr₂O₃), which was thermodynamically unstable at 1000 °C, and discrete internal oxides, alumina (α-Al₂O₃), were found. Consequently, the weight of the foil specimen decreased due to the spalling and volatilization of the Cr₂O₃ oxide layer after an initial weight-gaining. Secondary and tertiary creeps were observed at 800 °C, while the primary, secondary and tertiary creeps were observed at 1000 °C. Dynamic recrystallization occurred at 800 °C and 900 °C, while partial dynamic recrystallization at 1000 °C. The apparent activation energy, Q_app, for the creep deformation was 271 kJ/mol, which was independent of the applied stress.     

Tomographic atom probe characterization of the microstructure of a cold worked 316 austenitic stainless steel after neutron irradiation

For the first time, chemical analyses using Atom Probe Tomography were performed on a bolt made of cold worked 316 austenitic stainless steel, extracted from the internal structures of a pressurized water reactor after 17 years of reactor service. The irradiation temperature of these samples was 633 K and the irradiation dose was estimated to 12 dpa (7.81 × 10²⁵ neutrons.m⁻², E > 1 MeV). The samples were analysed with a laser assisted tomographic atom probe. These analyses have shown that neutron irradiation has a strong effect on the intragranular distribution of solute atoms. A high number density (6 × 10²³ m⁻³) of Ni-Si enriched and Cr-Fe depleted clusters was detected after irradiation. Mo and P segregations at the interfaces of these clusters were also observed. Finally, Si enriched atmospheres were seen.     

Ion beam analysis of materials in the PBMR reactor

South Africa is developing a new type of high temperature nuclear reactor, the so-called pebble bed modular reactor (PBMR). The planned reactor outlet temperature of this gas-cooled reactor is approximately 900 °C. This high temperature places some severe restrictions on materials, which can be used. The name of the reactor is derived from the form of the fuel elements, which are in the form of pebbles, each with a diameter of 60 mm. Each pebble is composed of several thousands of coated fuel particles. The coated particle consists of a nucleus of UO₂ surrounded by several layers of different carbons and SiC. The diameter of the fuel particles is 0.92 mm. A brief review will be given of the advantages of this nuclear reactor, of the materials in the fuel elements and their analysis using ion beam techniques.     

Effect of shot peening on primary water stress corrosion cracking of Alloy 600 steam generator tubes in an operating PWR plant

The effect of shot peening on the primary stress corrosion cracking behavior of thermally treated Alloy 600 steam generator tubes in an operating pressurized water reactor (PWR) plant was analyzed based on pulled tube examinations and in-service inspection eddy current test (ISI-ECT) data. The evaluation was focused on the shape of crack, evolution of the number of new cracks and cracked tube fraction, and variation of crack length and the corresponding eddy current amplitude before and after shot peening. The shape of the crack was changed from a half-elliptical type before shot peening, to an elliptical one with bulging after peening. It was concluded that the shot peening was not effective for retarding both crack initiation and growth for this plant.     

The role of IAEA in coordinating research and transferring technology in radiation chemistry and processing of polymers

The IAEA has been playing a significant role in fostering developments in radiation technology in general and radiation processing of polymers in particular, among its Member States (MS) and facilitate know-how/technology transfer to developing MS. The former is usually achieved through coordinated research projects (CRP) and thematic technical meetings, while the latter is mainly accomplished through technical cooperation (TC) projects. Coordinated research projects encourage research on, and development and practical application of, radiation technology to foster exchange of scientific and technical information. The technical cooperation (TC) programme helps Member States to realize their development priorities through the application of appropriate radiation technology.The IAEA has implemented several coordinated research projects (CRP) recently, including one on-going project, in the field of radiation processing of polymeric materials. The CRPs facilitated the acquisition and dissemination of know-how and technology for controlling of degradation effects in radiation processing of polymers, radiation synthesis of stimuli-responsive membranes, hydrogels and absorbents for separation purposes and the use of radiation processing to prepare biomaterials for applications in medicine.The IAEA extends cooperation to well-known international conferences dealing with radiation technology to facilitate participation of talented scientists from developing MS and building collaborations. The IAEA published technical documents, covering the findings of thematic technical meetings (TM) and coordinated research projects have been an important source of valuable practical information.     

The peculiarities of formation of the metal nanoparticles in irradiated polymer metal complexes

The radiation-induced reduction of metal ions in the films of triple metal polymer complexes of polyacrylic acid-polyethyleneimine-copper(II) or nickel(II) (PAA-PEI-Cu²⁺ or PAA-PEI-Ni²⁺) was studied by EPR and transmission electron microscopy (TEM). It was shown that irradiation of the swollen polymer films in the water-alcohol environment resulted in effective reduction of the metal ions. The exchange between the swollen film and outer environment was found to be an important factor for ion reduction and stabilization of metal particles. EPR data have revealed pronounced effect of the ligand environment on the reduction efficiency. The electron microscopy studies have demonstrated that the dimensions of main fraction of metal particles obtained by the radiation-chemical reduction are in the range of 2-2.5 nm both for Cu and for Ni complexes.     

Degradation of mechanical properties of structural reactor materials induced by formation of stress concentrators

The paper deals with the crack nucleation and stability in strain fields of stress concentrators (e.g. voids, gas bubbles, secondary phase precipitates). A general equation describes critical and subcritical crack length as a function of external (applied loading) and internal (stress concentrator type, normal traction, elastic properties of matrix, etc.) parameters. For the critical crack an analog of the Griffith criterion is found. The reduction of fracture stress due to different types of internal stress concentrators was evaluated.     

External-beam PIXE characterization of volcanic material used in ancient Roman mortars

Volcanic deposits from two volcanic districts, Monti Sabatini (MSVD) and Colli Albani (CAVD), NW and SE of Rome, were analyzed using the particle-induced X-ray emission (PIXE) technique, in order to obtain chemical fingerprints that can be used for provenance studies of filler materials in ancient Roman mortars. The rock samples were mounted on an X-Y stage enabling scanning over the sample surface and irradiated in air with a collimated 3 MeV proton beam. The samples were either analyzed by scanning the beam over a polished surface or they were crushed, ground and homogenized prior to the irradiation. However, scanning over polished sample surfaces avoiding heterogeneities gave quite similar results as scanning over pellet surfaces, especially for the minor and trace elements. This study shows that the deposits of MSVD and CAVD can be distinguished from each other. Several elements or elemental ratios can be used to characterize the districts. Even the individual volcanic deposits of CAVD can be identified.     

Mechanism of elongation of gold or silver nanoparticles in silica by irradiation with swift heavy ions

It has been reported that elongated Au nanoparticles oriented parallel to one another can be synthesized in SiO₂ by ion irradiation. Our aim was to elucidate the mechanism of this elongation. We prepared Au and Ag nanoparticles with a diameter of 20 nm in an SiO₂ matrix. It was found that Au nanoparticles showed greater elongated with a higher flux of ion beam and with thicker SiO₂ films. In contrast, Ag nanoparticles split into two or more shorter nanorods aligned end to end in the direction parallel to the ion beam. These experimental results are discussed in the framework of a thermal spike model of Au and Ag nanorods embedded in SiO₂. The lattice temperature exceeds the melting temperatures of SiO₂, Au and Ag for 100 ns after one 110 MeV Br¹⁰⁺ ion has passed through the middle of an Au or Ag nanorod.     

The effect of a single tensile overload on stress corrosion cracking growth of stainless steel in a light water reactor environment

It has been found that a single tensile overload applied during constant load amplitude might cause crack growth rate retardation in various crack propagating experiments which include fatigue test and stress corrosion cracking (SCC) test. To understand the affecting mechanism of a single tensile overload on SCC growth rate of stainless steel or nickel base alloy in light water reactor environment, based on elastic-plastic finite element method (EPFEM), the residual plastic strain in both tips of stationary and growing crack of contoured double cantilever beam (CDCB) specimen was simulated and analyzed in this study. The results of this investigation demonstrate that a residual plastic strain in the region immediately ahead of the crack tips will be produced when a single tensile overload is applied, and the residual plastic strain will decrease the plastic strain rate level in the growing crack tip, which will causes crack growth rate retardation in the tip of SCC.     

Multianalytical characterization of a blue pigment used in art-crafts from Central Mexico

We report a preliminary characterization of a blue pigment because its color has been associated to objects found from Aztec and Precolumbian times. The pigment was examined before and after its purification by a variety of techniques: Particle Induced X-ray emission (PIXE), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy coupled to energy dispersion spectroscopy (SEM-EDS). The relationship of the chemical composition, the spectroscopic signals and the color are discussed.     

Influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in PWR primary water

The influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in simulated Pressurized Water Reactor (PWR) primary water has been investigated. A-286 microstructure was characterized by transmission electron microscopy for ageing heat treatments at 670 °C and 720 °C for durations ranging from 5 h to 100 h. Spherical γ′ phase with mean diameters ranging from 4.6 to 9.6 nm and densities ranging from 8.5 × 10²² m⁻³ to 2 × 10²³ m⁻³ were measured. Results suggest that both the γ′ phase mean diameter and density quickly saturate with time for ageing heat treatment at 720 °C while the γ′ mean diameter increases significantly up to 100 h for ageing heat treatment at 670 °C. Grain boundary η phase precipitates were systematically observed for ageing heat treatment at 720 °C even for short ageing periods. In contrast, no grain boundary η phase precipitates were observed for ageing heat treatments at 670 °C except after 100 h. Hardening by γ′ precipitation was well described by the dispersed barrier hardening model with a γ′ barrier strength of 0.23. Stress corrosion cracking behaviour of A-286 was investigated by means of constant elongation rate tensile tests at 1.5 × 10⁻⁷ s⁻¹ in simulated PWR primary water at 320 °C and 360 °C. In all cases, initiation was transgranular while propagation was intergranular. Grain boundary η phase precipitates were found to have no significant effect on stress corrosion cracking. In contrast, yield strength and to a lesser extent temperature were found to have significant influences on A-286 susceptibility to stress corrosion cracking.     

Environmentally-assisted cracking behaviour in the transition region of an Alloy182/SA 508 Cl.2 dissimilar metal weld joint in simulated boiling water reactor normal water chemistry environment

The stress corrosion cracking (SCC) and corrosion fatigue behaviour perpendicular and parallel to the fusion line in the transition region between the Alloy 182 Nickel-base weld metal and the adjacent SA 508 Cl.2 low-alloy reactor pressure vessel (RPV) steel of a simulated dissimilar metal weld joint was investigated under boiling water reactor normal water chemistry conditions. A special emphasis was placed to the question whether a fast growing interdendritic SCC crack in the highly susceptible Alloy 182 weld metal can easily cross the fusion line and significantly propagate into the adjacent low-alloy RPV steel. Cessation of interdendritic SCC crack growth was observed in high-purity or sulphate-containing oxygenated water under constant or periodical partial unloading conditions for those parts of the crack front, which reached the fusion line. In chloride containing water, on the other hand, the interdendritic SCC crack in the Alloy 182 weld metal very easily crossed the fusion line and further propagated with a very high rate as a transgranular crack into the heat-affected zone and base metal of the adjacent low-alloy steel. The observed SCC cracking behaviour at the interface correlates excellently with the field experience of such dissimilar metal weld joints, where SCC cracking was usually confined to the Alloy 182 weld metal.