To cite this article: P. Pareige , B. Radiguet , R. Krummeich-Brangier , A. Barbu , O. Zabusov & M. Kozodaev (2005) Atomic-level observation with three-dimensional atom probe of the solute behaviour in neutron-, ion-or electron-irradiated ferritic alloys, Philosophical Magazine, 85:4-7, 429-441To link to this article: http://dx.The three-dimensional atom probe provides one of the most effective tools to characterize, with near atomic resolution, the solute distribution and the early stage of precipitation in metallic alloys. This paper presents results on the application of this technique to pressure vessel steels and model alloys. It is shown that, in neutron irradiated samples from VVER reactors, after annealing and re-irradiation, no Cu-Si-Mn-Ni-P-enriched clusters form, in contrast to the irradiated but not annealed samples. In the case of model alloys, it is shown that under electron irradiation copper clustering may or may not be observed depending on the type of irradiated materials. On the other hand the microstructures of low and high supersaturated Fe-Cu alloys irradiated under similar Fe-ion irradiations are the same.
Vessel and internal core steels of nuclear power reactors are subjected to energetic neutron irradiation. The production of point defects in the material results from elastic collisions in displacement cascades. On a microscopic scale, changes in the microstructure and local microchemistry are observed in both steels. On a global scale, a shift in the transient ductile to brittle temperature of vessel steels and an increase in the irradiation-assisted stress-corrosion-cracking susceptibility of internal core stainless steels are observed. Also, on a nanometre scale, radiation-induced phase transformation occurs in both steels. A systematic approach has proved its efficiency here to study the specific role of displacement cascades on cluster formation in two different materials: ferritic steels (bcc structure) and austenitic steels (fcc structure). In order to produce the primary knock atom, model ferritic steels containing a small amount of copper as well as a commercial austenitic steel (316) were irradiated using Fe and Ni ions, respectively. The different resulting microstructures are then studied on a nanoscale using tomographic atom probe three-dimensional reconstruction.
Nanoscaled lamellar structures involve complex deformation behaviour at finite strain due to the preserve of a large number of interfaces. The aim of the work is to develop a micromechanical approach based on interfacial operators in the context of statistical continuum mechanics. Using Hill's formalism, constitutive equations at mesoscale (1 μm) are derived from Nemat‐Nasser's finite elastic‐plastic deformation model ]3,5[ and solved numerically by a self‐consistent method ]1[. At micro‐scale (O.1 μm), a thermodynamical process may be defined to describe intrinsic hardening mechanism found to be linearly dependent with the interlamellar spacing's inverse ]4[. Specific crystal plasticity of both phases may then be introduced in the micromechanical approach to obtain a double scale model describing global and local behaviour of a pearlitic ilot under an imposed loading.
Actually, micromechanical approaches give only few references related to glide mechanisms in a lamella and especially load transfer mechanism between lamellae in pearlites. At large strains the concept of interphase barrier has to be introduced and considered as the determinant mechanism of hardening compared with the classical bulk work hardening. A micromechanical approach is used to describe a hardening mechanism related to the growth of dislocation loops inside the ferritic lamellae of pearlite and their locking at the interphase boundary. Using Eshelby-Kro¨ner’s formalism for the resolution of the field equations, the calculation of the Helmholtz free energy related to the (internal) morphological variables allows finding driving forces and the strength of interactions between loops and interfacial walls. Results exhibit a linear dependence between the critical stress and the inverse of the true interlamellar spacing, through a lattice orientation factor relative to the lamellar interphase, as observed experimentally (J. Gil Sevillano, 1991, J. Phys. III, 1, pp. 967–988; G. Langford, 1977, Metallurgical Trans A, 8A, pp. 861–875.
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