Nanosecond laser surface treatment of steels. Different applications in the fields of nuclear industry

International audienceAmong the numerous laser applications, laser surface melting by using a pulsed-laser is an innovative technology in the field of surface treatments. This technique presents many advantages. It only modifies the surface properties by keeping the mechanical properties of the bulk. It requires neither addition of other compounds nor contact, so it is quite economical and it does not pollute the material. It allows the treatment of complex shapes into closed spaces with difficult access. The laser can work in autonomy that present an interest in the fields of nuclear decontamination.This treatment consists in focusing a nanopulsed laser beam on the surface of the material, leading to the rather immediate melting of the surface through a micron depth, immediately followed by an ultra-fast solidification occurring with cooling rate up to 1010 K/s.By using different techniques of analysis, we showed that the combination of these processes leads to various modifications of surface properties. By combining with dexterity the different laser parameters, it is possible to functionalize the surface or to improve the native properties.Glow discharge optical emission spectrometry (GDOES), XPS and TEM were used to establish the segregation of chemical elements and the growth of a new oxide layer with new properties.XRD with grazing incidence was employed to identify the change of crystallographic structure, SEM was performed to promote the diminution of the surface defects and the microstructure.Applications in fields of nuclear will be presented, especially in terms of pitting corrosion of stainless steel used in secondary circuit, and protection against the nickel release of heat exchanger tubes in the primary circuit coolant

Oxydation de l'acier austénitique 316LN en milieu sodium liquide

National audienc

Chemical interaction of Austenitic and Ferritic Steels with B4C Powder in Liquid Sodium at 600DC

International audienceIn the framework of studies on the control rods lifetime for Sodium Fast Reactor, three commercial steels were exposed to B$_4$C powder in liquid sodium at 600DC for durations up to 3000 h. Analyses by optical and secondary electron microscopy, electron microprobe and glow discharge optical emission spectrometry revealed the formation of borides layers at the surface of the steels and slight carburization underneath. The growth of the boride layers followed parabolic kinetics. The nature of the formed boride layers was in good agreement with thermodynamic equilibrium predicted by Thermo-Calc software. The carburization depths were much lower than the ones obtained in pure carburizing sodium at 600DC. Finally, the carbon penetration depth did not grow with time revealing possible protective character of the boride layers against carbon penetration

Effects of organic amendments on plant-parasitic nematode populations, root damage, and banana plant growth

Nematodes are major pests for crops, including banana. Environmentally friendly methods for managing plant-parasitic nematodes have to be developed, such as organic material application. Our study focuses on the impacts of several organic amendments on banana plants, considering mainly their effect on soil nitrogen supply and soil microbial biomass, and the consequences on plant-parasitic nematode impacts on the plants. A microcosm experiment for 13 weeks was conducted to evaluate four organic materials: sugarcane bagasse, sugarcane sludge, plant residues, and sewage sludge, compared to a control without organic amendment. Input of organic materials led to an important change on nitrogen resource, and plants grew better when the N availability was the highest, but better growth conditions did not necessarily reduce parasitic nematodes impacts on the roots. Damage on the roots depended on plant-parasitic nematode abundance. Three of four tested amendments exhibited a regulator effect on plant-parasitic nematode populations (bagasse, sugarcane sludge, and plant residues). Root growth was not the explanatory factor for this regulation. Only sugarcane sludge led to an overall positive effect on the plant, increasing its growth and reducing its parasitism pressure. The other organic materials exhibited an antagonism between the promoted plant growth and the reduced nematode populations

Nanosecond Laser Surface Treatment Of Steels. Different Applications In The Fields Of Corrosion, Nuclear Industry And Decontamination

International audienceAmong the numerous laser applications, laser surface melting by using a pulsed-laser is an innovative technology in the field of surface treatments. This technique presents many advantages. It only modifies the surface properties by keeping the mechanical properties of the bulk. It requires neither addition of other compounds nor contact, so it is quite economical and it does not pollute the material. It allows the treatment of complex shapes into closed spaces with difficult access. The laser can work in autonomy that present an interest in the fields of nuclear decontamination.This treatment consists in focusing a nanopulsed laser beam on the surface of the material, leading to the rather immediate melting of the surface through a micron depth, immediately followed by an ultra-fast solidification occurring with cooling rate up to 1010 K/s.By using different techniques of analysis, we showed that the combination of these processes leads to various modifications of surface properties. Glow discharge optical emission spectrometry (GDOES) and transmission electronic microscopy (TEM) were used to establish the segregation of chemical elements and the growth of a new oxide layer with new properties.X-Ray diffraction (XRD) with grazing incidence was employed to identify the change of crystallographic structure, scanning electron microscopy (SEM) was performed to promote the diminution of the surface defects and the roughness was also characterized.Applications in fields of nuclear, corrosion, and decontamination will be presented. Those results showed that the new surface properties strongly depend of the laser parameters

Corrosion behaviour of a high strength nickel base alloy in Gas Cooled Reactors (GCR)

International audienceNi-Cr-W alloys are claimed to present high creep strength, a good hot workability together with improved oxidation resistance. Recently developed Haynes 230 could be a promising candidate material for the high temperature structures in Gas Cooled Reactors (GCR). However, corrosion resistance of Haynes 230 is unknown in the reactor specific environment namely impure He up to 850-950DC. Generally speaking the impurities in the cooling helium react with most Cr-containing alloys. They can produce surface scale formation, bulk carburisation and-or decarburization, depending on the gas chemistry, the alloy composition and the temperature. The changes in the bulk carbon content and the associated structural transformations can notably degrade the material mechanical properties and must definitely be precluded. Corrosion properties of Haynes 230 were investigated in a purposely-designed facility under different helium media at about 950DC. Short and longer experiments were carried out in simulated GCR coolant in order to assess the corrosion variability to test conditions. More specifically, the oxide scale formation and a deleterious reaction destructing the protective oxide layer were studied. Main factors impacting on this previous reaction, such as the carbon monoxide partial pressure in the gas atmosphere and the activity of the reactive elements in the alloy were investigated. The reaction mechanism is discussed in the light of published models

Decontamination of metallic surfaces by nanosecond laser ablation

International audienc

Metal decontamination by high repetition rate nanosecond fiber laser: Application to oxidized and Eu-contaminated stainless steel

International audienceThe decommissioning of metallic equipment (pipes, lane surfaces, etc.) contaminated in nuclear installations can consign large amounts of waste to storage and risk workers to radioactive exposure. Here, we study metallic-surface decontamination by laser ablation, which involves ejection and subsequent trapping of surface contamination by subjecting the surface to high-energy laser pulses. We perform laser ablation on oxidized AISI 304L stainless steel samples impregnated with non-radioactive Eu using a high repetition rate nanosecond fiber laser. The oxide layers are with a mean weight percentage of 0.1 to 2% of Eu in the volume of the oxide layer. Glow discharge mass spectrometry (GDMS) is performed to assess the cleaning-treatment efficiency and study the distribution of residual contamination with a Eu-detection limit of 100 ng/g. Our results indicate satisfactory decontamination of up to 97%. We also study the limiting factors and identify the mechanism of penetration of contaminants as induced by thermal effects. Moreover, to understand the ablation mechanism and from the perspective of industrial applications, we analyze the ablated matter to obtain the particle chemical composition and size distributions

Growth of micrometric oxide layers for the study of metallic surfaces decontamination by laser

International audienc