The heat-treating industry is in need of heat- treatment furnace materials and fixtures that have a long service life and reduced heat capacity. Based on microstructural analysis of components that were used until failure in carburization furnace application, it was found that the primary reason for failure was the excessive carburization that leads to “metal dustingâ€� and subsequent cracking. Aluminizing is widely used to increase the high temperature oxidation and carburization resistance of nickel- based alloys. In this dissertation, RA330, RA602CA, 304L/316L, Inconel 625 alloys were selected to study their performance in an industrial carburization furnace for times up to two years. These alloys were exposed in both the as-fabricated and aluminized condition. The test samples were exposed to Cp=0.7-1.3% carburizing atmosphere at approximately 900℃ for 3 months, 6months, 12months, 18 months and 24months. The oxidation properties and oxide stability at high temperatures will be presented. In addition, the analysis of microstructural development during long term exposure experiments in an industrial carburizing furnace will be presented. These samples were characterized using optical and scanning electron microscope, EBSD, and x-ray diffraction. It was found that the aluminized alloys exhibited lower weight gain and carbon uptakes.

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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.

Today’s transportation highly depends on hydrocarbon fuels, and reducing the weight could help a lot in reducing the air pollutants and carbon footprints in the environment to comply with the strict regulations set by reputable standard organizations in the world. Utilizing lightweight materials in automobile parts is one of the key factors to succeed in meeting the goals defined in the standards. Replacing the conventional single material component with a multi-material component having the same geometry but lighter weight could help the automakers to achieve these goals. Compound casting is one of the methods to produce such components. The aluminum alloy/ductile iron bimetal component produced by compound casting was investigated. During the production of the experimental sample of the compound casting, component two parameters were considered, melt-to-solid volume ratio and pre-heat temperature of the solid insert. The results showed that the increasing melt-to-solid volume ratio caused the formation of a stronger metallurgical bond between the two materials compared to the lower melt-to-solid volume ratio. However, pre-heating the solid insert under the atmospheric condition caused the formation of iron oxide layers on the surface, and as a result, no metallurgical bonding was formed, no matter which melt-to-solid volume ratio was used during the production process. So, inspired by AlFin process, the solid inserts were first dipped inside the aluminum alloy bath with the target temperature of 750 °C for two extended periods, 15 minutes and 30 minutes, to ensure that the preliminary metallurgical bonds were formed at the interface surfaces without disturbance by the surrounding atmosphere. To make the experimental components and to develop the metallurgical bonds, the aluminized inserts were then quickly placed inside the sand molds, and the cast alloy was poured inside the molds and around the inserts immediately after placement. In this way, although the formation of the aluminum oxide layer was unavoidable on the surfaces of the aluminized inserts, there was still liquid aluminum alloy melt underneath, which could be easily washed away during the pouring of the cast alloy.Nevertheless, the metallurgical bonds in the compound casting products having a lower melt-to-solid volume ratio didn’t withstand the shear loads and only the product having a higher melt-to-solid volume ratio with the aluminized insert dipped for a longer time could resist against the loads. In addition to the mechanical strength of the experimental products, their metallurgical bonds were specified and characterized using microscopic examination and EDS analysis. The successful results of the experimental product were then proposed to modify the design of a model from the automobile industry, called the truck wheel hub. / Dagens transport beror starkt på kolvätebränslen, och att minska vikten kan hjälpa mycket att minska luftföroreningar och kolavtryck i miljön för att följa de strikta regler som ställts av ansedda standardorganisationer i världen. Att använda lätta material i bildelar är en av de viktigaste faktorerna för att lyckas uppfylla de mål som fastställs i standarderna. Att ersätta den konventionella komponenten med enstaka material med en komponent med flera material som har samma geometri men lättare vikt kan hjälpa biltillverkarna att uppnå dessa mål. Gjutning av föreningar är en av metoderna för att producera sådana komponenter. Aluminiumlegeringen / segjärn-bimetalkomponenten framställd genom sammansatt gjutning undersöktes. Under framställningen av det experimentella provet av gjutning av föreningen beaktades komponent två parametrar, volymförhållandet smält till fast material och förvärmningstemperaturen för det fasta insatsen. Resultaten visade att det ökande smält-till-fasta volymförhållandet orsakade bildandet av en starkare metallurgisk bindning mellan de två materialen jämfört med det lägre förhållandet mellan smält och fast volym. Förvärmning av den fasta insatsen under atmosfäriskt tillstånd orsakade emellertid bildningen av järnoxidskikt på ytan, och som ett resultat bildades ingen metallurgisk bindning, oavsett vilket smält-till-fast volymförhållande användes under produktionsprocessen . Så, inspirerad av AlFin-processen, doppades de fasta insatserna först in i aluminiumlegeringsbadet med måttemperaturen 750 ° C under två långa perioder, 15 minuter och 30 minuter, för att säkerställa att de preliminära metallurgiska bindningarna bildades vid gränsytans ytor utan störningar av den omgivande atmosfären. För att tillverka de experimentella komponenterna och för att utveckla de metallurgiska bindningarna placerades sedan de aluminiumiserade skärmen snabbt inuti sandformarna, och den gjutna legeringen hälldes in i formarna och runt insatserna omedelbart efter placering. På detta sätt, även om bildningen av aluminiumoxidskiktet var oundvikligt på ytorna på de aluminiumförsedda insatserna, fanns det fortfarande flytande aluminiumlegeringssmälta under, vilket lätt kunde tvättas bort under hällningen av den gjutna legeringen.Icke desto mindre tål de metallurgiska bindningarna i de sammansatta gjutprodukterna med ett lägre volym-till-fast volymförhållande inte skjuvbelastningarna och endast produkten med ett högre smält-till-fast volymförhållande med den aluminiumiserade insatsen doppades under en längre tid kunde motstå mot lasterna. Förutom de experimentella produkternas mekaniska styrka specificerades och karakteriserades deras metallurgiska bindningar med mikroskopisk undersökning och EDS-analys. De framgångsrika resultaten av den experimentella produkten föreslogs sedan att modifiera utformningen av en modell från bilindustrin, kallad truckhjulnavet.