Effect of microstructure and chemical composition on localized corrosion resistance of a AISI 304L stainless steel after nanopulsed-laser surface melting

International audienc

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

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

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

Laser additive manufacturing applied to nuclear components repair and Co-based materials replacement in friction areas

International audienceLaser additive manufacturing is a recent technology that turns a CAD modelled object into a physical one, layer by layer, by addition of projected melted metallic powders. The process is compatible with a vast array of metals and complex geometries and provides a good metallurgical quality. The potential of this process for nuclear industry materials has been assessed on two applications, nuclear components repair and friction resistant coatings using Ni-based alloys instead of Co-based alloys. For generation II&III reactors, repairing presents an advantage over part replacement in terms of cost and delay. Indeed, a number of nuclear components with complex geometries are unique and the difficulty to reproduce them in a timely manner with standard shaping methods results in a more global unavailability. We report about repair of defects on Stellite®6 parts using laser cladding technology.In fast neutron reactors, parts subjected to wear conditions are usually made of cobalt-based alloys. Cobalt may however be released and activated into 60Co, thus contaminating the primary circuit. Hence the motivation to use cobalt-free alloys. Also, the laser cladding process can increase the performances of nickel-based hardfacing materials compared to the standard PTAW coating process.In both cases we have observed occurrences of crack formation. A correlation between process parameters, structural properties of the projected materials and crack formation was found. We describe how the process parameters control the inherent extensive thermal cycling and consequently the properties of the final material, and we propose a methodology to avoid crack formation. The great flexibility of the laser projection process opens the door to deposition with composition gradients that allows avoiding cracks by accommodating the inducing strain inside the material

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

International audienc

Development of laser cleaning for metallic equipment

International audienc

Traitements de surface avec et sans apport de matiere pour le nucleaire - Modification de surface par laser, PVD et CVD

International audienceDans le contexte actuel d'optimisation du parc actuel et futur et de l'allongement de la duree de vie des centrales et des installations du cycle, la problematique de duree de vie des materiaux est cruciale. Les problematiques de vieillissement et de reactivite (corrosion) constituent un defi majeur dans l'industrie nucleaire. Pour relever l'ensemble de ces defis, les technologies innovantes dans le domaine des procedes de traitements de surfaces avec ou sans apport de matiere sont des solutions prometteuses d'autant plus que ces dernieres ont connu un developpement significatif ces dernieres annees.Parmi les technologies de traitement de surface etudiees au Service d'Etudes Analytiques et de Reactivite des Surfaces (SEARS) de la DEN (Division de l'Energie Nucleaire), les techniques par laser sont historiquement presentes grace aux competences du LISL (Laboratoire d'Ingenierie des Surfaces et Lasers). Une premiere appartient a la famille des traitements sans apport de matiere. Elle consiste a venir frapper une surface avec un laser dont les proprietes sont judicieusement choisies pour que la matiere presente soit fondue voire ejectee. En pilotant les caracteristiques du faisceau laser incident les proprietes de surface peuvent etre modifiees. Il est par exemple possible de former une couche barriere d'oxydes, d'homogeneiser des phases et d'augmenter la teneur en certains elements chimiques voire de modifier la structure cristallographique ce qui peut conduire a une augmentation de la durete. Les applications de ce procede sont le renforcement de la resistance a la corrosion par piquration d'aciers 304L ou la limitation du relachement de nickel en milieu primaire au niveau des generateurs de vapeur. Enfin, l'ejection de matiere provenant de la surface traitee peut etre maximisee pour utiliser ce traitement comme une technique d'ablation surfacique pour le demantelement ou la maintenance d'installations, son point fort etant la possibilite de decontaminer des composants a distance.Les autres traitements de surface concernent des methodes avec apport de matiere. Parmi les technologies etudiees, certaines passent par un etat gazeux de la matiere. Suivant si la phase gazeuse se condense ou se decompose a la surface du composant a revetir, on parlera de PVD (condensation) ou de CVD (decomposition avec reaction chimique). Ces techniques sous vide sont majoritairement employees pour deposer des revetements protecteurs afin d'augmenter les performances et les durees de vie de composants en milieux extremes (haute temperature, irradiation, oxydation, corrosion ou encore usure abrasive). On peut citer les developpements actuels avec Areva pour les EATFs (Enhanced Accident Tolerant Fuels) concernant les gaines de combustible nucleaire qui, avec un revetement protecteur, resisteraient bien mieux a des hypothetiques conditions accidentelles de perte de refrigerant primaire

Embedding of luminescent pigments within 316L stainless steel matrix by laser powder bed fusion for optical functionalities.

International audienc

Embedding of YAG:Ce within 316L stainless steel matrix by additive manufacturing for corrosion monitoring.

International audienc