Dislocation Loop Formation and Growth under In Situ Laser and/or Electron Irradiation

Vacancies and interstitial atoms are primary lattice (point) defects that cause observable microstructural changes, such as the formation of dislocation loops and voids in crystalline solids. These defects' diffusion properties determine the phase stability and environmental resistibility of macroscopic materials under ambient conditions. Although in situ methods have been proposed for measuring the diffusion energy of point defects, direct measurement has been limited. In this study, we propose an alternative in situ method to measure the activation energy for vacancy migration under laser irradiation using a pulsed laser beam from a laser-equipped high-voltage electron microscope (laser-HVEM). We made in situ observations that revealed the formation and growth of vacancy dislocation loops in an austenitic stainless steel during laser irradiation. These loops continued to grow when thermal annealing was performed after laser irradiation at the same temperature. We anticipate that laser-HVEM will provide a new method for investigating lattice defects

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

International audienceFor 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

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

International audienceFor 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

Lessons learned from baffle bolt replacements regarding irradiation-induced creep behaviour

An overall maintenance policy for managing ageing of PWR vessel internals, subject to high neutron fluence, was launched by EDF during the 90’s. It involves four main activities that are dependent on:− Safety Analysis, − R&D Program, − In-Service Inspection and/or Maintenance Program, − Metallurgical Examinations. The purpose of this paper is to analyze field data obtained from baffle to former bolts replacement operations using materials properties obtained from R&D programs. We show that following highly anticipative R&D, a comprehensive approach can be established to account for irradiation creep behavior of baffle bolts. The approach relies on (i) irradiation-creep law established by means of irradiated pressurized tubes for SA-304 and CW-316, (see presentation from J. Garnier in the conference),(ii) measurement of removal torques of baffle bolts recorded during their replacement, (iii) metallurgical examination of bolts, (iv) knowledge of dose distribution within the components and (v) modeling of the mechanical behaviour of the bolts. It is concluded that torque values measured during removal of baffle to former bolts can be explained by irradiation- induced creep experimental laws

Sintering of ferritic and austenitic nanopowders using Spark Plasma Sintering

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Irradiation creep of SA 304L and CW 316 stainless steels: Mechanical behaviour and microstructural aspects. Part II: Numerical simulation and test of SIPA model

International audienceA cluster dynamic model has been adapted to test the Stress Induced Preferential Absorption of Defect (SIPA) on Frank loops hypothesis concerning irradiation creep, to reproduce quantitatively both microstructure evolution and its stress induced anisotropy and macroscopic creep rate. It is concluded that SIPA on Frank loops model can account for the observed defects structure, but is unable to reproduce quantitatively the creep rate. (C) 2011 Elsevier B.V. All rights reserved