Incorporation of Y2O3 Particles into 410L Stainless Steel by a Powder Metallurgy Route

Addition of yttria to steels has been proposed for the fabrication of oxide-dispersion-strengthened materials for nuclear power applications. We have investigated materials prepared from 12 Cr martensitic stainless steel, AISI 410L, produced by powder metallurgy. Materials were produced with and without yttria addition, and two different sizes of yttria were used, 0.9 µm and 50 nm. Tensile and mini-creep tests were performed to determine mechanical properties. Optical microscopy, SEM, TEM, and EDX analysis were used to investigate the microstructures and deformation mechanisms and to obtain information about non-metallic inclusion particles. SiO2, MnS, and Y2Si2O7 inclusion particles were observed. An SiO2 and Y2O3 interaction was seen to have occurred during the ball milling, which impaired the final mechanical properties. Small-angle neutron scattering experiments showed that the matrix chemistry prevented effective dissolution of the yttria. © The Author(s) 201

Relationship between the yield strength-fracture toughness balance and the multiscale microstructure of a maraging stainless steel for aircraft applications

Two grades of Fe-Cr-Ni-Al-Ti-Mo maraging steels, with a different titanium content, were investigated. Particular attention was given to the correlation between the precipitated phases and the yield strength. Synchrotron X-ray diffraction, small-angle neutron scattering and atom probe experiments were performed to determine the crystal structure, shape, size distribution, chemical composition, particle number density and volume fraction of precipitates. Both alloys show a strong increase in strength after an aging treatment, which is attributed to the co-precipitation of two different intermetallic phases. Strengthening by a single precipitation of &beta;-Ni (Al,Ti) particles induces a saturation of yield strength around 1600 MPa above a volume fraction of 6 %. The improvement of yield strength is then obtained by introducing a nanoscale co-precipitation of &eta;-Ni3(Ti,Al) phase.</jats:p

Parametric study of 15Cr / 15Ni austenitic steels swelling behavior under irradiation using cluster dynamics

International audienceAs part of the research program on generation IV reactors, CEA is developing new grades of austen-itic steels for the fuel cladding of Sodium Fast Reactors (SFR). Austenitic stainless steels show ex-cellent properties in SFR’s extreme operating conditions: corrosive environment, high operating tem-perature (400-700 ° C) and highly energetic neutron flux. However, the appearance of the swelling phenomenon under irradiation limits cladding lifespan. The most optimized French grade is AIM1, a 15Cr-15Ni austenitic stabilized steel, which sustain doses up to 100 displacements per atom (dpa)

Strain-induced dissolution of Y-Ti-O nano-oxides in a consolidated ferritic ODS steel

International audienceThe present study aims at showing the influence of severe plastic deformation on highly stable Y-Ti-O nano-oxides present in ODS ferritic alloys used for nuclear applications. An innovative strain path implying alternated compressions was used to deform the material up to an equivalent plastic strain of 13. Energy Filtered Transmission Electron Microscopy and Small Angle Neutron Scattering revealed the strain-induced dissolution of the Y-Ti-O nano-oxides. It appears to be the first time that dissolution of such particles is clearly observed after plastic deformation. By heating the material, it is also possible to re-precipitate the nano-oxides. These results show a strong analogy with the mechanical alloying of ODS powder

Atomic-scale computer simulation study of the interaction of Cu-rich precipitates with irradiation-produced defects in α-Fe

Copper-rich precipitates can nucleate and grow in ferritic steels containing small amounts of copper in solution and this affects mechanical properties. Growth kinetics, composition and structure of precipitates under irradiation are different from those under thermal ageing, and also vary with type of radiation. This implies that the interaction between radiation defects, i.e. vacancies, self-interstitial atoms (SIAs) and their clusters, and precipitates is influential. It is studied here by atomic-scale computer simulation. The results are compared with those of elasticity theory based on the size misfit of precipitates and defects, and the modulus difference between bcc iron and bcc copper. It is found that SIA defects are repelled by precipitates at large distance but, like vacancies, attracted at small distance. Copper precipitates in iron can, therefore, be sinks for both vacancy and interstitial defects and hence can act as recombination centres under irradiation conditions. A tentative explanation for the mixed Cu–Fe structure of precipitates observed in experiment and the absence of precipitate growth under neutron irradiation is given. More generally, agreement between the simulations and elasticity theory suggests that the results are not artefacts of the atomic model: both vacancy and interstitial defects in metals may bind to precipitates with weaker cohesion than the matrix

Influence of Donor Age and Species Longevity on Replicative Cellular Senescence

The replicative life span of cell strains obtained from multiple explants from the same individual is highly variable, additional variability is added when strains are obtained from different individuals. This variability is probably due to both technical issues and heterogeneity inside the tissues. Notwithstanding these limitations, many scientists searched for an inverse relationship of proliferative potential and donor age. Reviewing this literature, we conclude that this inverse correlation is likely more dependent to developmental stages than to aging per se; i.e. cells taken from a developing organism have higher replicative capacity than cells taken from an adult. Replicative senescence has been studied also across species searching for a positive relationship with longevity. Recently it has been show that when specific culture conditions (mainly low oxygen tension) are applied, strains from several species appear immortals. Moreover, for species that do present cellular senescence, it seems that replicative capacity relates primarily to species adult body mass more than to longevity