Thermo-Calc software AB develops high quality thermodynamic and kinetic databases to predict and simulate accurately multi-component phase behaviour in complex systems. One problem with their Ni-based alloys and superalloy solutions database (TCNI8) is poor description of tungsten partitioning for multi-component nickel based alloys. This work investigates the thermodynamic description of some lower-order systems i.e., Ni-W, Al-Ni-W and Cr-Ni-W by performing key experiments on three binary Ni-W alloys, and two ternary alloys (Al-Ni-W and Cr-Ni-W). Experiments at four different temperatures were carried out in which alloys were homogenized, equilibrated, quenched and investigated to determine the equilibrium solid/liquid compositions. Experimental results are used to validate the thermodynamic descriptions of the liquid and the fcc phase. Unlike ternary Al-Ni-W and Cr-Ni-W, binary Ni-W reproduced the experimental information in a satisfactory way. Ternary parameters for fcc are changed to fit the experimental results of this work. The findings of this work highlight that ternary parameters for the fcc of Al-Ni-W and Cr-Ni-W systems significantly effect the tungsten partitioning values in higher order systems. / Thermo-Calc Software AB utvecklar termodynamiska och kinetiska databaser av hög kvalitet för att korrekt kunna förutsäga och simulera jämvikter och fasomvandlingar i komplexa flerkomponentsystem. Ett problem med deras databas för Ni-baslegeringar och superlegeringar (TCNI8) är att beskrivning av volframpartitionering stämmer dåligt för nickelbaslegeringar. I detta arbete undersöktes den termodynamiska beskrivningen av vissa lägre system, dvs Ni-W, Al-Ni-W och Cr-Ni-W genom att utföra nyckelförsök på tre binära Ni-W-legeringar och två ternära legeringar (Al-Ni-W och Cr-Ni-W). Experimentvid fyra temperaturer utfördes i vilka legeringarna homogeniserades,jämviktsbehandlades, släcktes och undersöktes för att bestämma sammansättning för jämvikt fast fas/smälta. De erhållna experimentella resultaten användes för att validera den termodynamiska beskrivningen av smältan och fcc-fasen. Till skillnad från ternära Al-Ni-W ochCr-Ni-W, reproducerade den experimentella informationen den binära Ni-W-beskrivningen tillfredsställande. Ternära parametrar för fcc justerades efter de experimentella resultaten från detta arbete. Resultaten visar att de ternära parametrarna för fcc i Al-Ni-W och Cr-Ni-W systemen signifikant påverkar volframs fördelning mellan fast fas och smälta i nickelbaslegeringar.

<p>  </p> <p>Concentrated solar power (CSP) is a technology that utilizes focused sunlight to heat a high-temperature medium (such as a molten salt). Heat from this medium can be transferred to a working fluid (such as supercritical CO2) that is then used to drive a turbine to generate electricity. Alternatively, the hot medium/fluid can be pumped into tanks for thermal energy storage (TES), for heat extraction later to generate dispatchable electricity and/or for electricity production at night or on cloudy days. By increasing the fluid temperature to <u>></u>750oC and utilizing TES, CSP can become more cost competitive with fossil-based electricity production. Current CSP systems utilize molten nitrate salts for heat transfer and TES that are known to thermally degrade at temperatures >600oC. To achieve temperatures <u>></u>750oC, molten chloride salts, such as ternary MgCl2-KCl-NaCl compositions, are being considered as heat transfer and thermal energy fluids for next generation CSP plants due to their higher temperature stability, low cost, and availability. </p> <p>In this work, it was demonstrated that MgCl2-containing molten salts are prone to oxidation in ambient air at 750oC, which can enhance corrosion of the containment materials and alter the thermophysical properties of the fluid. An alternative, low-cost, earth-abundant, MgCl2-free, oxidation-resistant molten salt, a eutectic CaCl2-NaCl composition, was developed, along with a corrosion mitigation strategy, to enable the slow growth of protective oxide layers on metals that are resistant to dissolution by such MgCl2-free molten chloride salts. </p> <p>This strategy was expanded to other low-cost, oxidation resistant compositions, such as eutectic BaCl2-CaCl2-KCl-NaCl with tailored chemical and thermophysical properties for CSP and TES. The melting temperature, heat capacity, oxidation resistance, and crystallization behavior were measured for eutectic a BaCl2-CaCl2-KCl-NaCl(17.5-47.8-3.3-31.4 mol%) (BCKN) salt and a MgCl2-KCl-NaCl (40-40-20 mol%) salt. BCKN salt was shown to have a similar melting temperature while having a higher heat capacity and far better oxidation resistance. </p> <p>The corrosion of the nickel-based superalloy Haynes 214 was studied in molten MgCl2-KCl-NaCl (40-40-20 mol%) salt at 750oC under inert atmosphere conditions using a custom-built rotating-disc corrosion testing apparatus that maintained laminar fluid flow on the sample. Non-protective external Cr-, Al-, and Mg- oxide layers were formed on Haynes 214 that were prone to spallation. Internal oxidation of Al was also observed along with Cr depletion zones within Haynes 214.  Corrosion kinetics were evaluated to quantify the role of fluid flow for application of this alloy for use in containment and transportation of this molten chloride salt. </p>

No description available.

La Corrosion Haute Température (HTC), en environnements divers et sévères, d'alliages métalliques toujours plus élaborés en termes de composition et micro-structure, est un sujet industriel et scientifique très complexe. La PhotoElectroChimie (PEC) est une technique de choix pour caractériser les propriétés physico-chimiques et électroniques des couches d'oxydation très hétérogènes formées en HTC. Sur des exemples d'alliages modèles mais représentatifs de la réalité industrielle (aciers duplex, base-Nickel 690), ce travail présente le développement et la validation d'un dispositif expérimental permettant d'appliquer pour la première fois tout l'arsenal des techniques PEC à l'échelle mésoscopique (typiquement 30 µm), ainsi que la validation d'une modélisation originale développée au SIMaP des spectres de photocourants en énergie, qui permet de les décrire et ajuster finement et d'en extraire notamment avec précision les gaps des oxydes semiconducteurs présents dans la couche thermique. / High Temperature Corrosion (HTC), in various and severe atmospheres, of continually more elaborated (composition, micro–structure) metallic alloys, is a rather complex industrial and scientific topic. PhotoElectroChemistry (PEC) acquired a special place in the characterization of physico–chemical and electronic properties of the highly heterogeneous oxidation layers formed in HTC. Through studies of model but industrially representative samples (duplex stainless steel, Ni–base alloy 690), this work presents the development and validation of an experimental set–up allowing for the first time to use the whole set of PEC techniques at the mesoscopic level (typically 30 µm), as well as the validation of an original model of photocurrent energy spectra, developed at SIMaP, allowing to well describe, and accurately fit the latter spectra, and thus yielding, notably, precise bandgap values for the semiconducting components of the thermal scale.

Nickel-based alloys are used in components such gas turbines within the aerospace industry and electric power generation due to its high tensile, rapture and creep strength. Increasing the efficiency of gas turbines are crucial to reduce emissions within the aerospace industry and increasing power gain for electric power generation. Innovation to increase the efficiency relies in part on the development of new nickel-based alloys with beneficial material properties. But also on stable and predictable material behavior during processing and post-processing of the components in the gas turbine. In two prominent material processing fields of precipitation hardened nickel-based alloys, additive manufacturing and welding, strain-age cracking (SAC) is a common phenomenon. SAC is a solid state phenomenon that generally occurs in alloys strengthened with 𝛾′, L12(Pm3m), or 𝛾′′, D022(I4/mmm), phase precipitates during post weld heat treatment or reheating where it manifests as intergranular cracking. Even though the existence of SAC has been known for several decades, its dominant mechanisms are still under considerable debate and the undertaken modeling efforts to gain insight on the phenomenon are virtually non-existent. This study aims to clarify the dominant mechanisms behind strain-age cracking. Breaching this gap would allow for new development for nickel-based alloys within both additive manufacturing and welding. To that extent the goal of this study is to provide tools to aid in clarifying the dominant mechanisms behind strain-age cracking. This is done by implementing the recently developed structural phase-field crystal (XPFC) model and examining the capabilities to model a precipitation event during reheating for a reference binary alloy in two dimensions. To evaluate the strain because of precipitation, a simple method based on the principles of neutron and synchrotron strain scanning is outlined and tested on the limited precipitation event achieved within the study. The XPFC model is capable of modeling precipitation with some restrictions that need further development with extended computational recourses. Lastly, the possibilities to extend the implemented XPFC model to cover nickel-based alloys is discussed.

No description available.

The use of renewable wood-based fuel has been increasing in the last few decades because it is said to be carbon neutral. However, wood-based fuel, and especially used wood (also known as recycled wood or waste wood), is more corrosive than virgin wood (forest fuel), because of higher amounts of chlorine and heavy metals. These elements increase the corrosion problems at the furnace walls where the oxygen level is low. Corrosion mechanisms are usually investigated at the superheaters where the temperature of the material and the oxygen level is higher than at the furnace walls.  Much less work has been performed on furnace wall corrosion in wood or used wood fired boilers, which is the reason for this project.    Tests are also mostly performed under simplified conditions in laboratories, making the results easier to interpret.  In power plants the interpretation is more complicated. Difficulties in the study of corrosion processes are caused by several factors such as deposit composition, flue gas composition, boiler design, and combustion characteristics and so on. Therefore, the laboratory tests should be a complement to the field test ones. This doctoral project involved in-situ testing at the furnace wall of power boilers and may thus contribute to fill the gap. The base material for furnace walls is a low alloy steel, usually 16Mo3, and the tubes may be coated or uncoated. Therefore tests were performed both on 16Mo3 and more highly alloyed materials suitable for protective coatings. Different types of samples exposed in used-wood fired boilers were analysed by different techniques such as LOM (light optical microscopy), XRD (X-ray diffraction), SEM (scanning electron microscopy), EDS (energy dispersive spectroscopy), WDS (wavelength dispersive spectroscopy), FIB (focused ion beam) and GD-OES (glow discharge optical emission spectroscopy). The corrosion rate was measured. The environment was also thermodynamically modelled by TC (Thermo-Calc ®). The results showed that 16Mo3 in the furnace wall region is attacked by HCl, leading to the formation of iron chloride and a simultaneous oxidation of the iron chloride. The iron chloride layer appeared to reach a steady state thickness.   Long term exposures showed that A 625 (nickel chromium alloy) and Kanthal APMT (iron-chromium-aluminium alloy) had the lowest corrosion rate (about 25-30% of the rate for 16Mo3), closely followed by 310S (stainless steel), making these alloys suitable for coating materials. It was found that the different alloys were attacked by different species, although they were exposed in the boiler at the same time in the same place. The dominant corrosion process in the A 625 samples seemed to be by a potassium-lead combination, while lead did not attack the APMT samples. Potassium attacked the alumina layer in the APMT samples, leading to the formation of a low-protective aluminate and chlorine was found to attack the base material.  The results showed that stainless steels are attacked by both mechanisms (Cl- induced attack and K-Pb combination). Decreasing the temperature of the furnace walls of a waste wood fired boiler could decrease the corrosion rate of 16Mo3. However, this low corrosion rate corresponds to a low final steam pressure of the power plant, which in not beneficial for the electrical efficiency. The short term testing results showed that co-firing of sewage sludge with used wood can lead to a reduction in the deposition of K and Cl on the furnace wall during short term testing. This led to corrosion reduction of furnace wall materials and coatings. The alkali chlorides could react with the aluminosilicates in the sludge and be converted to alkali silicates. The chromia layer in A 625 and alumina in APMT were maintained with the addition of sludge. / Förnybara träbaserade bränslen har ökat i användning under de senaste decennierna, eftersom det är koldioxidneutrala. Emellertid är träbaserade bränslen, och i synnerhet använt trä (även känt som återvunnet trä, returträ eller träavfall), mer korrosivt än skogsbränsle, på grund av högre halter klor och tungmetaller. Dessa ökar korrosionsproblemen på eldstadsväggarna, särskilt på platser där syrehalten är låg. Korrosionsmekanismer undersöks vanligtvis på överhettare dvs. på områden där materialets temperatur och syrenivån är högre än vid eldstadsväggarna. Färre arbeten har utförts på eldstadskorrosion i returträ pannor, vilket är motiveringen till detta projekt. Normalt sätt så görs endast i laboratorietester där resultaten är lättare att tolka. I kraftverk är tolkningen mer komplicerad. Undersökningar av korrosionsprocesser försvåras av flera faktorer såsom panndesign, förbränningsegenskaper, rökgassammansättning, beläggningskemi och så vidare. Därför bör laboratorietester kompletteras med fältförsök. Detta doktorandprojekt kan således bidra till att fylla denna brist. Eldstadsväggarna är uppbyggda av flera rör som svetsas samman och de består vanligtvis av 16Mo3 stål. Rören kan vara belagda eller obelagda. Tester har därför genomförts på 16Mo3 samt på höglegerade material vilka är lämpliga som skyddande beläggningar. Olika typer av prov som exponerats i förbränningspannor av returträ analyserades med olika tekniker såsom SEM (svepelektronmikroskopi), EDS (energidispersiv spektroskopi), WDS (våglängd dispersiv spektroskopi), FIB (fokuserad jonstråle) LOM (ljusoptisk mikroskopi), XRD (röntgendiffraktion), och GD-OES (glimurladdning med optisk emissionsspektroskopi). Miljön samt korrosionsprocesser har modellerats termodynamiskt med mjukvaran TC (Termo-Calc®). Resultaten visade att 16Mo3 i eldstadsväggen angrips av väteklorid, vilket leder till bildning av järnklorid och en samtidig oxidation av järnkloriden. Järnkloridskiktet verkade nå ett stationärt tillstånd vad avser tjocklek. Sex veckors prov visade att A 625 (nickelkromlegering) och Kanthal APMT (järnkromaluminiumlegering) hade den lägsta korrosionshastigheten (ca 25-30% av korrosionshastigheten för 16Mo3), följt av 310S (rostfritt stål). Vi har funnit att de olika legeringarna angrips genom olika mekanismer, även om de var exponerade i pannan samtidigt på samma plats. Den dominerande korrosionsmekanismen för legeringen A 625 verkar i huvudsak bero på kalium och bly, medan bly inte attackerar Kanthal APMT. Kalium angriper aluminiumoxidskiktet på Kanthal APMT, vilket leder till bildning av icke-skyddande aluminat medan klor i sin tur attackerar basmaterialet. Resultaten visar att rostfritt stål attackeras genom klor-inducerad korrosion samt kalium och bly i kombination. Reducering av temperaturen kan minska korrosionshastigheten hos 16Mo3. Men denna lägre korrosionshastighet motsvarar ett lågt slutligt ångtryck hos kraftverket, vilket inte är fördelaktigt för elverkningsgraden. De kortare exponeringarna visade att samtidig förbränning av avloppsslam med returträ kan leda till minskad avsättning av kalium och klor i form av alkaliklorider på eldstadsväggarna. Detta ledde till korrosionsminskning av alla studerade material. Dessa alkaliklorider skulle kunna reagera med aluminiumsilikaterna från slammet och omvandlas till alkalisilikater. Detta verkar minska den alkali-inducerade korrosionen på A 625, APMT och 310S. Den aluminiumoxid som bildades på APMT och det kromoxidskikt som bildades på A 625 upprätthölls med tillsats av slam. / <p>QC 20151015</p>