Laser-directed energy deposition (L-DED) is a key enabling technology for the repair of high-value aerospace components, as damaged regions can be removed and replaced with additively deposited material. While L-DED repair improves strength and fatigue performance compared to conventional subtractive techniques, mechanical performance can be limited by process-related defects. To assess the role of oxygen on defect formation, local and chamber-based shielding methods were applied in the repair of 300M high strength steel. Oxidation between layers for locally shielded specimens is confirmed to cause large gas pores which have deleterious effects on fatigue life. Such pores are eliminated for chamber shielded specimens, resulting in an increased ductility of ∼15%, compared to ∼11% with chamber shielding. Despite this, unmelted powder defects are not affected by oxygen content and are found in both chamber- and locally shielded samples, which still have negative consequences for fatigue.

One of the most important parts of a hybrid reactor is the cladding because it should withstand high temperatures, neutrons with high energy, high neutron flux, as well as provide the first security contention. Besides, the material should have good mechanical properties to remove the heat. Although, the cladding material choice will have a great influence on criticality calculations. In previous works on ADS there is no cladding used, therefore in this paper it is tested different cladding materials based on SS-316, ODS, T91 and 15-15Ti used in nuclear reactors, to study the variations on the fuel depletion and variations on the neutronic parameters. The results using the cladding are compared with the one obtained without using it. The best material choice is based on the neutronic parameters that presents the closest behavior to the ADS simulated without clad.

The annealing behavior of three HSLA steels is studied using the combined techniques of EBSD-KAM and Sub-grain Method. These techniques have been successfully used to assess the annealing behavior of AK, IF and other high strength steels. Stored energy maps in the hot band, cold rolled and after annealing are constructed and analyzed. The combined usage of the Sub-grain Method and EBSD-KAM techniques are employed to calculate and compare the evolution of the stored energy and recrystallization behaviour during the annealing of Ti-bearing, Nb-bearing, and V-bearing HSLA steels. Orientation dependent stored energy distribution maps at different annealing stages are constructed and analysed. The results show that the stored energy distribution through the thickness of the samples is not uniform and is independent of the steel composition. Similarly the recrystallization behaviour is strongly related to the initial microstructural condition and particularly to the grain boundary character distribution of the steels.

Carbide precipitation within low carbon AISI H13 hot work tool steel that had either been quenched at 80 °C or cryogenically treated at −196 °C prior to tempering has been examined using micrometer-scale synchrotron diffraction mapping. Vanadium-rich cubic M8C7 carbide, lattice parameter of approximately 0.8610 nm, not identifiable using laboratory powder x-ray diffraction (PXRD), was found to be present in all samples. The concentration of this phase was greatest in the rapidly cooled cryogenically treated sample. However, all cryogenic treatments resulted in greater carbide concentrations than in the quenched sample. In addition rapid cryogenic cooling by immersion in liquid nitrogen (N2), as compared with slow cooling to −196 °C over a 3 h duration, results in greater order within the carbide phase subsequent to tempering, as interpreted by analysis of unit cell size variation, and the smallest stress, as interpreted by diffraction peak full width half maximum height distributions.

Over the last few years there have been significant developments in the field of three-dimensional atom probe (3DAP) analysis. This article reviews some of the technical compromises that have led to different instrument designs and the recent improvements in performance. An instrument has now been developed, based around a novel reflectron configuration combining both energy compensation and focusing elements, that yields a large field of view and very high mass resolution. The use of laser pulsing in the 3DAP, together with developments in specimen preparation methods using a focused ion-beam instrument, have led to a significant widening in the range of materials science problems that can be addressed with the 3DAP. Recent studies of semiconductor materials and devices are described.

Selon la composition chimique et la température, les aciers présentent deux phases à l'équilibre : austénite et ferrite. La solubilité quasi nulle du carbone et de l'azote dans la ferrite à température ambiante favorise la précipitation de carbures et/ou de nitrures pouvant conduire au durcissement de la matrice.Pour les fortes teneurs en carbone, apparaît une phase eutectoïde dure, la perlite, constituée de lamelles de ferrite et de cémentite (carbure de fer). Les aciers ferrito-perlitiques (matrice ferritique avec des îlots de perlite) présentent une limite d'élasticité élevée avec des potentialités d'allongement importantes ; un durcissement complémentaire peut être obtenu par écrouissage (par exemple, les aciers steel cord).Un refroidissement rapide de l'austénitique conduit à des phases métastables dures : la martensite et la bainite. Selon la teneur en carbone et le schéma de refroidissement, on obtient généralement des structures multiphasées à matrice ferritique ; la transformation martensitique se produisant avec un changement de volume, la limite d'élasticité est affectée par la formation de ce constituant. Dans certains cas particuliers, l'austénite résiduelle après refroidissement se transforme progressivement en martensite durant la déformation. Cet effet TRIP (Transformation Induced Plasticity – Transformation induite par la plasticité) permet l'obtention d'une résistance élevée avec une ductilité importante.Ainsi, il est possible d'obtenir différentes familles d'acier couvrant un large domaine d'utilisation. La modélisation de leur comportement mécanique doit permettre de définir les structures optimales pour une tenue mécanique visée.

This work concerns the use of parallel electron energy loss spectroscopy (PEELS) to investigate the detection, distribution, and quantification of carbon in various steel microstructures generated by rapid cooling rates or by isothermal transformation. The feasibility of detecting C in steels containing very small amounts of carbon was first examined by calculating the minimum detectable mass fraction for a variety of binary Fe-C alloy specimen thicknesses and microscope conditions. These theoretical studies indicated that the detection of carbon in steel microconstituents containing about 0.01 wt.% (or even less) was easily possible with an analytical transmission electron microscope equipped with a LaB6 emitter and a PEEL spectrometer. These theoretical calculations seemed to be reasonable, as it proved possible to make a quantitative PEELS study of the partitioning between the microconstituents ferrite, retained austenite, and martensite found in an ultralow carbon (0.03 wt.%) steel weld metal provided care was taken to avoid hydrocarbon contamination. Studies of both carbon and molybdenum segregation to ferrite/martensite interfaces in an isothermally transformed Fe-C-Mo alloy were also carried out in order to investigate the nature of the “solute drag” effect in this alloy system.