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Accès restreint aux membres de l'Université de Lorraine jusqu'au 2016-10-25; The use of vanadium alloy V-4Cr-4Ti as fuel cladding in the generation IV sodium cooled fast reactor (SFR) is considered with a great interest thanks to its attractive physico-chimicals properties namely: a good compatibility with liquid sodium, a high neutronic transparency,a good mechanical properties even under irradiation. However, the dissolution of oxygen in vanadium leads to its hardening. This behavior imposes, consequently, the use of on external protection as coatings that can be considered as a barrier against oxygen diffusion contained in liquid sodium at very low concentrations (a few ppm). In this work, binary and ternary diffusional silicides coatings are produced mainly by halide activated pack cementation. Their ability to protect the substrate in media simulating a SFR’s conditions, with a low oxidation potential of O2, is proved according to the results of oxidation tests in impure helium at 650 ° C and corrosion in sodium liquid at 550 ° C (CorroNa test at CEA de Saclay). Other air oxidation tests (cyclic, isothermal and creep-bending 3 points) showed good resistance of coatings at temperatures above 900°C due to the formation of a protective layer of SiO2, adherent and compact. In another part of this work, the microstructural stability of the cladding/coating system in accidental conditions is studied. This required the calculation of interdiffusion coefficients using models of multilayer growth as proposed by Wagner and mutual consumption as proposed by Buscaglia. Finally, the isothermal section at 1200 ° C and the liquidus projection of V-Cr-Si system are studied. This step, preliminary to the study of quaternary V-Cr-Ti-Si system, should allow as a perspective the optimization of the architecture of the coating and help to understand the oxidation mechanisms; L’usage de l’alliage de vanadium V-4Cr-4Ti comme matériau de gainage du combustible dans les réacteurs nucléaires à neutrons rapides refroidis au sodium (RNR-Na) représente un intérêt tout à fait particulier de par ses propriétés physico-chimiques attractives à savoir : une bonne compatibilité avec le sodium liquide, une transparence neutronique élevée et de bonnes propriétés mécaniques sous irradiation. Toutefois, la dissolution de l’oxygène dans le vanadium conduit à son durcissement de manière considérable et rend, par conséquence, son utilisation conditionnée par l’utilisation de protection externe moyennant des revêtements faisant office de barrière de diffusion à l’oxygène présent dans le sodium liquide à hauteur de quelques ppm. Au cours de ce travail, des revêtements diffusionnels à base siliciures binaires et ternaires sont élaborés essentiellement par cémentation activée en caisse. Leur capacité à protéger le substrat dans des milieux simulant les conditions d’un RNR-Na, caractérisés par un faible potentiel oxydant de O2, est avérée suite à des tests d’oxydation sous hélium impur à 650°C et de corrosion dans le sodium liquide à 550°C (test CorroNa au CEA de Saclay). D’autres tests d’oxydation sous air (cycliques, isothermes et fluage-flexion 3 points) ont montré la bonne résistance des revêtements à des températures au-delà de 900°C grâce à la formation d’une couche protectrice de SiO2, adhérente et compacte. Un autre volet de ce travail a permis d’aborder la stabilité microstructural du système gaine/revêtement dans les conditions accidentelles. Ceci a nécessité le calcul des coefficients d’interdiffusion en s’appuyant parallèlement sur les modèles de croissance multicouche de Wagner et de consommation mutuelle de Buscaglia. En dernier lieu, la coupe isotherme à 1200°C et la projection liquidus du système V-Cr-Si sont étudiés. Cette étape, préliminaire à l’étude du système quaternaire V-Cr-Ti-Si, doit permettre en perspective l’optimisation de l’architecture du revêtement et aider à la compréhension des mécanismes d’oxydation

The use of vanadium alloy V-4Cr-4Ti as fuel cladding in the generation IV sodium cooled fast reactor (SFR) is considered with a great interest thanks to its attractive physico-chimicals properties namely: a good compatibility with liquid sodium, a high neutronic transparency,a good mechanical properties even under irradiation. However, the dissolution of oxygen in vanadium leads to its hardening. This behavior imposes, consequently, the use of on external protection as coatings that can be considered as a barrier against oxygen diffusion contained in liquid sodium at very low concentrations (a few ppm). In this work, binary and ternary diffusional silicides coatings are produced mainly by halide activated pack cementation. Their ability to protect the substrate in media simulating a SFR’s conditions, with a low oxidation potential of O2, is proved according to the results of oxidation tests in impure helium at 650 ° C and corrosion in sodium liquid at 550 ° C (CorroNa test at CEA de Saclay). Other air oxidation tests (cyclic, isothermal and creep-bending 3 points) showed good resistance of coatings at temperatures above 900°C due to the formation of a protective layer of SiO2, adherent and compact. In another part of this work, the microstructural stability of the cladding/coating system in accidental conditions is studied. This required the calculation of interdiffusion coefficients using models of multilayer growth as proposed by Wagner and mutual consumption as proposed by Buscaglia. Finally, the isothermal section at 1200 ° C and the liquidus projection of V-Cr-Si system are studied. This step, preliminary to the study of quaternary V-Cr-Ti-Si system, should allow as a perspective the optimization of the architecture of the coating and help to understand the oxidation mechanisms, L’usage de l’alliage de vanadium V-4Cr-4Ti comme matériau de gainage du combustible dans les réacteurs nucléaires à neutrons rapides refroidis au sodium (RNR-Na) représente un intérêt tout à fait particulier de par ses propriétés physico-chimiques attractives à savoir : une bonne compatibilité avec le sodium liquide, une transparence neutronique élevée et de bonnes propriétés mécaniques sous irradiation. Toutefois, la dissolution de l’oxygène dans le vanadium conduit à son durcissement de manière considérable et rend, par conséquence, son utilisation conditionnée par l’utilisation de protection externe moyennant des revêtements faisant office de barrière de diffusion à l’oxygène présent dans le sodium liquide à hauteur de quelques ppm. Au cours de ce travail, des revêtements diffusionnels à base siliciures binaires et ternaires sont élaborés essentiellement par cémentation activée en caisse. Leur capacité à protéger le substrat dans des milieux simulant les conditions d’un RNR-Na, caractérisés par un faible potentiel oxydant de O2, est avérée suite à des tests d’oxydation sous hélium impur à 650°C et de corrosion dans le sodium liquide à 550°C (test CorroNa au CEA de Saclay). D’autres tests d’oxydation sous air (cycliques, isothermes et fluage-flexion 3 points) ont montré la bonne résistance des revêtements à des températures au-delà de 900°C grâce à la formation d’une couche protectrice de SiO2, adhérente et compacte. Un autre volet de ce travail a permis d’aborder la stabilité microstructural du système gaine/revêtement dans les conditions accidentelles. Ceci a nécessité le calcul des coefficients d’interdiffusion en s’appuyant parallèlement sur les modèles de croissance multicouche de Wagner et de consommation mutuelle de Buscaglia. En dernier lieu, la coupe isotherme à 1200°C et la projection liquidus du système V-Cr-Si sont étudiés. Cette étape, préliminaire à l’étude du système quaternaire V-Cr-Ti-Si, doit permettre en perspective l’optimisation de l’architecture du revêtement et aider à la compréhension des mécanismes d’oxydation

Agência 1 O avanço da tecnologia tem sido o principal motivo para a produção de novos materiais estruturais associando excelentes propriedades mecânicas, baixo custo de fabricação e aplicações em ambientes diversificados. Entre os materiais mais avançados, as superligas à base de níquel são as que mais se destacam em aplicações envolvendo altas temperaturas. Para estas aplicações é necessário um balanço adequado de propriedades como alta resistência mecânica, alta resistência à fluência, alta resistência à fadiga, alta condutividade térmica, baixa anisotropia de expansão térmica e alta resistência à oxidação. Entre estas ligas estão as a Mar-M246 e a Mar-M247, que possuem Al e Cr em sua composição, responsáveis pela formação de camadas de óxidos Al2O3 e Cr2O3, capazes de aumentarem a resistência à oxidação e corrosão em altas temperaturas. Porém, o uso destas superligas por um longo período de tempo pode provocar a fragmentação dessas camadas de óxido ou a evaporação da camada de Cr2O3 interferindo na integralidade do material. Uma das formas de aumentar a vida útil destas ligas é revesti-las com camadas de alta resistência à oxidação sem que interfiram nas propriedades do substrato. O processo de Cementação em Caixa Ativados por Haletos (HAPC) é um método muito versátil, de baixo custo, utilizado para recobrir diversos materiais, independente de sua geometria. Diante deste cenário, o objetivo deste trabalho foi estudar a deposição de alumínio, um dos mais usados na proteção contra oxidação e corrosão, para formação de camadas de revestimentos pelo processo HAPC sobre a superliga de níquel Mar-M246, que até o momento não foi relatado na literatura aberta. O processo de aluminização foi realizado em quatro diferentes temperaturas, utilizando-se NH4Cl, como ativador, e uma mistura de pós contendo alumínio e alumina. Um estudo termodinâmico, com auxílio do software HSC Chemistry 6.0, contribuiu nas escolhas das temperaturas e ativador, além de se obter um mecanismo de deposição do alumínio na formação da fase de revestimento para o processo a 1000°C. Os resultados mostraram, para todas as temperaturas, uma camada homogênea sem trincas ou poros e de composição química Ni2Al3 e/ou NiAl3. O crescimento do revestimento foi avaliado pela cinética de crescimento em processos de 1 a 16 h, obtendo-se a informação de um crescimento parabólico e uma energia de ativação de 96,55 kJ.mol-1, para o processo de aluminização via HAPC, onde estes revestimentos foram caracterizados via microscopia eletrônica de varredura (MEV). Todos os revestimentos formados em um período de 9 h, em todas as temperaturas estudadas, foram caracterizados via microscopia ótica (MO), MEV, espectroscopia por energia dispersiva (EDS) e difratometria de raios X (DRX), mostrando uma espessura de camada entre 90 a 300 μm. Estes substratos revestidos foram introduzidos em um ensaio de oxidação a 1000°C por 240 horas, revelando uma otimização na resistência à oxidação pela formação da camada de óxido Al2O3, revelando uma redução do ganho de massa em torno de 3,4 vezes para as camadas formadas nos processos HAPC 900 e 1000°C The advancement of technology has been the main reason for the production of new structural materials combining excellent mechanical properties, low manufacturing cost and applications in diverse environments. Among the most advanced materials, nickel-based superalloys are the most prominent in applications involving high temperatures. For these applications, an appropriate balance of properties is required, such as high mechanical strength, high creep resistance, high fatigue resistance, high thermal conductivity, low thermal expansion anisotropy and high oxidation resistance. Among these alloys are MarM246 and Mar-M247, which have Al and Cr in their composition, responsible for the formation of Al2O3 and Cr2O3 oxide scale, useful of increasing resistance to oxidation and corrosion at high temperatures. However, the use of these superalloys for a long period of time can cause the fragmentation of these oxide scales or the evaporation of the Cr2O3, interfering with the integrality of the material. One way to increase the useful life of these alloys is to coating them with scales that are highly resistant to oxidation without interfering with the properties of the substrate. The Halide Activated Pack Cementation (HAPC) process is a very versatile, low-cost method used to coating many materials, regardless of their geometry. In view of this scenario, the objective of this work was to study the deposition of aluminum, one of the most used in the protection against oxidation and corrosion, for the formation of coatings by the HAPC process on the Mar-M246 nickel superalloy, which until now has not been reported in the open literature. The aluminization process was carried out at four different temperatures, using NH4Cl as an activator and a powders mixture containing pure Al and alumina. A thermodynamic study, with the aid of the HSC Chemistry 6.0 software, contributed to the choice of temperatures and activator, in addition to obtaining an aluminum deposition mechanism in the formation of the coating phase for the process at 1000°C. The results showed, for all temperatures, coating without cracks, pores or adhesion failures to the substrate and a layers with Ni2Al3 and/or NiAl3 in chemical composition. The growth of the coating was evaluated by the growth kinetics in processes from 1 to 16 h, obtaining the information of a parabolic growth and activation energy of 96.55 kJ.mol-1, for the process of aluminization via HAPC, where these coatings were characterized by scanning electron microscopy (SEM). All coatings formed in a period of 9 h, at all temperatures studied, were characterized by optical microscopy (MO), SEM, dispersive energy spectroscopy (EDS) and X-ray diffractometry (XRD), showing a layer thickness between 90 to 300 μm. These coated substrates were introduced in an oxidation test at 1000°C for 240 hours, revealing an optimization in the oxidation resistance by the formation of the Al2O3 oxide layer, revealing a reduction in mass gain around 3.4 times for the layers formed in the HAPC 900 and 1000°C processes.