Добірка наукової літератури з теми "Slurry aluminizing"

The corrosion behavior of aluminized Type 310S stainless steel (SS) in the wet seal of molten carbonate fuel cells was investigated. Coupons of Type 310S SS were aluminized by two different aluminizing methods: thermal spray and slurry-coating. In both types of samples Fe and Cr diffused readily into the Al layer at 650 °C. At first this interdiffusion is limited to the interfacial area. With time, Fe and Cr aluminides precipitate in the Al layer. The slurry-coated layer contains a higher concentration of FeAl and Fe3Al than does the thermal spray layer. Consequently, the slurry-coated layer also displays a greater degree of corrosion than the thermal spray layer.

Copper and its alloys with high electrical and thermal conductivity are a group of widely used engineering materials in numerous applications. In order to improve the tribological properties of copper substrate, an electroplating nickel layer was firstly deposited on copper substrate, subsequently these electroplated specimens were treated by slurry pack cementation process at 900°C for 12 h using a slurry mixture composed of TiO 2 as titanizing source, pure Al powder as aluminzing source and also a reducer for titanizing, an activator of NH 4 Cl and albumen (egg white) as cohesive agent. The effect of Al content on the microstructure and the properties of the coating has been studied. The results showed that an intermetallic Ni - Ti ( Al ) compound/ Ni graded layer was formed on copper substrate after slurry pack cementation process. With the rise of Al content in slurry mixture, the microhardness of the graded coating increased and the friction coefficient decreased from 0.35 to 0.18, at the same time, the slurry pack process gradually transited from the titanizing process to an aluminizing one. Correspondingly the main phases of the coating were changed from Ni - Ti intermetallic compounds into Ni - Al ones.

One of the surface modification processes for high-temperature oxidation resistance is slurry aluminizing process, forming protective layer of alumina (Al2O3). However, several important parameters such as annealing times and temperatures should be intensively considered. The objective of this study is to improve the process of slurry aluminide coating of ferritic stainless steels type AISI430 (16%Cr) combat to high-temperature oxidation. The specimens were cut, then ground, and finally sprayed with slurry mixture (Al powder + polyvinyl alcohol (PVA)). They were annealed in Ar at 1100°C for 15 minutes in order to eliminate PVA and form aluminide on their suface. The protective layer Al2O3 was finally formed in the temperature range of 900-1100 °C for 15-60 minutes. The cyclic oxidation tests were performed at 1000 °C for 24 hours. The surface morphology were then examined by XRD, SEM equipped EDS. The results showed that all oxidation kinetics of coated specimens were parabolic. The oxidation rate of uncoated specimens was apparently higher than that of coated specimens. Comparing with all coated specimens, the oxidation rate decreased with the increasing temperature and annealing time. In this study, the coating process at 1100°C for 60 minutes exhibited the lowest oxidation rate due to the most complete layer of Al2O3. The surface morphology showed the formation of continuous layer of Fe2Al5 and Al2O3, acting as barrier layer to oxide growth. Effect of temperature and time on oxidation resistance were discussed in this study.

La sélection des matériaux utilisés dans les moteurs aéronautiques est un enjeu majeur pour assurer la sécurité des passagers, optimiser les performances de l’avion et maîtriser les coûts. Dans les parties les plus chaudes des moteurs (i.e. chambre de combustion et turbine), les pièces sont généralement constituées de superalliages à base nickel en raison de leurs excellentes propriétés mécaniques à haute température. Vulnérables aux phénomènes de corrosion et d’oxydation à haute température, les superalliages doivent la plupart du temps être revêtus afin de prolonger leur durée de vie (ingénierie de surface). La composition chimique et l’architecture des revêtements sont alors adaptées en fonction du régime de température et des phénomènes de dégradation rencontrés (i.e. corrosion à chaud, oxydation et/ou érosion). En vue de répondre aux nouvelles réglementations environnementales, de nouvelles voies de synthèse et de fonctionnalisation sont à l’étude comme alternatives aux procédés industriels actuels. Dans le cadre du projet Européen « PARTICOAT », le LaSIE a démontré la faisabilité d’élaborer des systèmes barrières thermiques complets (couche de diffusion + barrière thermique) en une seule étape à partir de barbotines (« slurries ») à base aqueuse contenant des microparticules d’Al. Dans cette étude, l’ajout de Cr comme dopant a été étudié. L’addition de Cr a permis d’abaisser l’activité de l’Al lors de l’étape d’aluminisation et de limiter les réactions exothermiques entre Al et substrat à base de nickel. L’optimisation des ratios entre Al et Cr a permis d’obtenir différentes microstructures de revêtement. Diverses architectures de dépôts ont également pu être testées grâce à la souplesse d’élaboration des revêtements par barbotines. L’influence de l’atmosphère (Ar, air) et celle des conditions de traitement thermique ont également été étudiées. Enfin, la durabilité des revêtements développés au cours de la thèse a été évaluée au cours d’essais de corrosion à chaud et d’oxydation
The selection of materials is of utmost importance in gas turbine engines to ensure the security of the passengers, optimize the performances of the aircraft and be cost efficient. In the hottest region of the engines (i.e. combustion chamber and turbine), the components are usually made of nickel-based superalloys. These materials can resist to high mechanical loads at high temperature but are vulnerable to aggressive environments. Therefore, nickel-based superalloys are usually coated to increase their durability in the engine (surface engineering). The chemical composition and the coating architecture are carefully adjusted depending on the temperature regime and the mechanisms of degradation encountered (hot corrosion, oxidation and/or erosion). New synthesis routes and functionalization are currently developed as alternative solutions to industrial processes. As a promising alternative approach, different studies were carried out in the LaSIE laboratory under the European project “PARTICOAT” and confirmed the possibility to elaborate complete thermal barrier systems (diffusion coating + thermal barrier coating) from Al-containing water-based slurries. In this work, the role of Cr as a doping agent was investigated. The addition of Cr decreased the thermodynamic activity of Al upon aluminizing and limited the exothermic reactions usually reported between Al and nickel-based materials. Different architectures of coatings were obtained thanks to the flexibility and the adaptability of the slurry coating process. The gas composition (Ar, air) and the heat treatment conditions were also investigated. Finally, the high temperature resistance of the slurry coatings developed during this work was evaluated under hot corrosion and oxidation conditions

La sélection des matériaux utilisés dans les parties chaudes des moteurs aéronautiques ou dans les centrales de production d’énergie est devenue un enjeu crucial au vu des impératifs écologiques et économiques. L’un des composants critiques de ces systèmes sont les aubes de turbine dont la tenue mécanique est assurée par la nature des substrats employés (aciers et superalliages à base nickel). Cependant, leur tenue environnementale nécessite l’application de revêtements protecteurs source d’Al capables de former de barrières d’oxyde (Al2O3) imperméables à l’attaque externe par oxydation et corrosion aux hautes températures. L’épuisement de l’Al pour former l’oxyde et par interdiffusion avec le substrat conduit inexorablement à la perte de protection. Ainsi, des structures spécifiques de revêtement telles les barrières de diffusion peuvent alors être mises en place pour augmenter la durée des vies des aubes au détriment de leurs propriétés mécaniques et de coûts élevés de fabrication et environnementaux. Durant cette étude, des nouvelles voies originales de synthèse des revêtements de diffusion d’aluminium « autorégénérants » ont été étudiées. Ces revêtements disposent d’une structure composite, avec une matrice de phases intermétallique (NixAly) renforcée par des microréservoirs constitués d’un cœur (NixAly) et d'une paroi en Al2O3 à travers laquelle l’Al du cœur peut ravitailler la matrice et maintenir une concentration globale en Al suffisamment élevée dans la matrice capable de former la couche externe protectrice d’Al2O3.Nos études démontrent que les réactions aluminothermiques entre du NiO et l’Al permettent de former un tel revêtement autorégénerant avec une barrière de diffusion à l’interface substrat/revêtement lorsque le Ni est initialement pré-oxydé à 1100°C pendant 2h. Néanmoins, aucun compromis n’a été trouvé pour former des revêtements sans NiO résiduel qui pourrait compromettre l’adhérence du revêtement au substrat. En revanche, une voie électrochimique permet d’incorporer de microparticules d’Al3Ni2 dans des électrodépots de Ni. A la suite d’un traitement d’aluminisation par barbotine, les microparticules préoxydées s’incorporent de manière homogène dans un revêtement de β-NiAl. Après traitement d’oxydation isotherme à 1000°C durant 48h, ce revêtement par voie électrodéposition + aluminisation présente une teneur en aluminium supérieure à 40 at%, ce qui est supérieur à un revêtement de diffusion absent de microréservoirs démontrant ainsi le caractère autorégénerant des nouveaux revêtements
The selection of materials used in the hot parts of aeronautical turbines or in power plants has become a crucial issue in view of ecological and economic imperative. Turbine blades are amongst the most critical components. Their mechanical resistance is ensured by the substrate itself (steels and Ni alloys and superalloys). However, their low environmental resistance requires the application of protective coatings delivering Al to form oxide barriers blocking the external oxidative and corrosive attack. Upon exposure at high temperatures, Al depletes from the coating by oxidation to grow the oxide scale and by interdiffusion with the substrate’s elements resulting in the loss of protection. Some specific coating structures like the diffusion barriers have been investigated in the past but the overall mechanical properties are lowered and the fabrication and environmental costs are high. Therefore, a pioneering and original investigation has been conducted to synthesize “self-regenerating” aluminum diffusion coatings. These coatings are characterized by a composite structure whereby the matrix made of NixAly intermetallic phases is strengthened with microreservoirs made of NixAly core and an Al2O3 shell through which Al diffuses out to maintain the adequate Al concentration in the matrix, hence to stabilize the external protective Al2O3 scale.Our studies demonstrate that the aluminothermic reactions between NiO and Al lead to the formation of such a self-regenerating coating with an interdiffusion barrier at the coating/substrate interface whenever Ni is preoxidized at 1100°C for 2h beforehand. However, all the coatings sintered through this method possess residual NiO, which may compromise their adherence to the substrate. In contrast, the use of electrochemical methods allows to incorporate Al3Ni2 microparticles in the NI electrodeposits. With a subsequent slurry aluminizing treatment, the preoxidized particles incorporate homogeneously in a β-NiAl coating matrix. After exposure at 1100°C for 48h in air, the Al content in the self-regenerating coatings is greater than 40 at% as opposed to the micro-reservoirs-free aluminide coating allowing to demonstrate the self-regenerating property of these new coatings

Pack aluminizing and vapor-phase aluminizing (VPA) are common methods for producing protective coatings on aero and industrial gas turbine hot section components. SermAlcote® slurry aluminization is an alternative to many industrial pack and vapor-phase aluminizing processes. SermAlcote® slurry aluminization processes are designed to meet existing commercial specifications while offering significant improvements in cost, quality and turntime over competitive aluminizing processes. Advantages of this processing route include simplified masking, shorter thermal processing cycles, improved diffusion capacity (no powder, simplified racks), and elimination of powder handling/storage concerns. Unlike conventional slurry aluminizing methods, the SermAlcote® process produces very uniform diffused aluminide coatings over a very wide range of applied slurry amounts. This simplifies the manufacturing process and produces high degree of process repeatability and uniformity. Data and examples are presented in order to describe the characteristics of SermAlcote® slurry aluminization processes for producing aluminide coatings, platinum-modified aluminide coatings, and over-aluminized MCrAlY coatings.

Hot section gas turbine parts need protection against oxidation and hot corrosion. The essential element is Al to build the protective Al2O3. Al can be applied on the gas path surfaces by overlay techniques or by diffusion of Al into the base material — the “aluminizing”. Aluminizing can be done by slurry, pack cementation, out of pack, or by “pure” CVD. Additional elements can be added to the aluminide. The different techniques are discussed under the aspects of advantage/disadvantage, limits and possible coating structures.