Heat transfer during metal pouring and its solidification in the vacuum furnace have been investigated by experiments using model set of castings of different diameters and insulations. The pouring metal was Inconel 713LC alloy based on nickel. The found data have been used for optimization of the numerical simulation of the thermal regime during the both pouring and solidification phases of the process in vacuum. Numerical simulation of the alloy structure in individual castings has been made by the CAFE module of the ProCast software and obtained results compared with the real structure. The optimized boundary conditions can be used for simulation of real castings.

The topic of this thesis is the formation of microporosity in cast test bars of nickel-base superalloy Inconel 713LC during solidification. The theoretical part consists of nickel alloys, their macrostructure, the method of casting and crystallization of nickel-based superalloys. The second part is devoted to the design of casting conditions, the production of shell molds, the size and shape of grains, evaluation of microporosity by various available methods, comparing the influence of grain size and the proportion of microporosity on the resulting values of the mechanical tests. Experiments were carried out in cooperation with PBS Velká Bíteš and ÚST foundry department.

The Ni-base superalloy, IN-718, has been coated with alumina sols. Coated surfaces, carrying alumina layers having thicknesses between 0.6 μm and 3.6 μm show a significantly reduced oxidation rate when compared with uncoated reference surfaces, even if heating temperature is increased up to 900 °C and heating time is extended to 800 h. Alumina layers were prepared via sol-gel processing using a modified Yoldas procedure to obtain alumina sols. No change in rheological sol behavior was observed for more than 1 year of aging under static conditions at room temperature. Depending on pH value, modified Yoldas sols contain a manifold of Al species, among them Al13 polycations. Thermal evolution of sol derived alumina powders depends on Al speciation of parent sols. Depending on sol composition, both gamma-Al2O3 and eta-Al2O3 occur as intermediate transition aluminas. Phase composition and gas phase velocity influence oxygen permeability of thin layers prepared with modified Yoldas sols.

Das Ziel der Arbeit war die Weiterführung der Substrukturanalyse von plastisch verformten metallischen Werkstoffen mit kubischer Struktur auf der Basis des Disklinationskonzeptes unter Berücksichtigung unterschiedlicher homologer Temperaturen und Stapelfehlerenergien. Die Untersuchungen wurden an Stauchproben von Wolfram, Aluminium und der Legierung Inconel 718 mit Hilfe der TEM, der REM (EBSD) und der röntgenografischen Profilanalyse durchgeführt. Bei allen drei Werkstoffen konnten im Temperatur- und Umformbereich T/Ts<=0,3, Deformation>=0,3 auf der Basis von lokalen TEM-Desorientierungsmessungen Partialdisklinationen identifiziert und ihre Frankvektoren bzw. Defektstärken bestimmt werden. Die Ergebnisse der EBSD-Untersuchungen und der Röntgendiffraktometrie sind mit den TEM-Beobachtungen kompatibel und zeigen, dass die Kombination der drei Methoden für die systematische Substrukturanalyse an stark verformten Werkstoffen gut geeignet ist.

Nickel superalloys are used for high-temperature application in energetic and aerospace industry. They are exposed to aggressive environment at high temperatures with the interactions between fatigue and creep processes, high-temperature oxidation, corrosion and erosion. Lifetime extension of such strained parts while increasing the performance of particular machine is possible by applying protective surface coatings. The subject of this work is to investigate the fatigue failure mechanisms of superalloy Inconel 713LC at 800 °C and to compare these mechanisms between material with a protective coating based on Al-Si and material without coating. The location of initiation fatigue cracks, their propagation and the fatigue crack propagation rate in some areas were analyzed by optical microscopy, scanning electron microscopy and confocal laser scanning microscopy. Based on previous research it was found that the application of the coating AlSi has a positive effect on lifetime of alloy Inconel 713LC. These results were confirmed and estimated in the diploma thesis.

Masters thesis deals with formation of diffusion barrier coatings by means of powder mixtures chemical vapor deposition. Its theoretical part is focused on the problems with diffusion barriers formation, where predominantly three most commonly used methods are introduced, i.e. CVD from powder mixtures, active gasses and slurries. The experimental part of master thesis deals with the formation of nickel-aluminide diffusion barriers on Inconel 713LC superalloy substrate, where was for aluminization used six different powder mixtures at the temperature of 800 °C and dwell of 0, 2 and 5 hours.

No description available.

No description available.

Nickel-based superalloys and tool steels are well-known high-performance alloys due to their extensive use in many different industries. Nickel-based superalloys have found their way into aircraft, aerospace, marine, chemical, and petrochemical industries owing to their excellent high-temperature corrosion and oxidation resistance. On the other hand, tool steels could provide a combination of outstanding corrosion and wear resistance. They can play an important role in cutting and wear applications and manufacturing plastic extrusion and food processing components. Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce these alloys. This technology can successfully tackle conventional manufacturing challenges of highly alloyed materials i.e. segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries (PPBs) in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both Ni-based superalloys and tool steels may affect the fatigue performance of these PM-HIPed products. This licentiate thesis aims to investigate the microstructure and fatigue behavior of two PM-HIPed alloys i.e. Inconel 625 and high-nitrogen tool steel. The results confirm precipitation along PPBs in PM-HIPed Inconel 625; however, no effect was detected in the fractography studies of the high cycle fatigue samples, and tensile properties were comparable with wrought materials reported in the literature. On the other hand, the microstructure of PM-HIPed high-nitrogen tool steel displayed dispersed precipitates and no traces of PPBs. Moreover, in both cases, i.e. very high cycle fatigue of PM-HIPed high-nitrogen tool steel and high cycle fatigue of PM-HIPed Inconel 625, fatigue crack initiation was attributed to the presence of non-metallic inclusions, either individually or agglomerated with precipitates. This underscores the significance of the manufacturing process in fatigue performance. / Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce high-performance alloys. Among the variety of engineering alloys, Nickel-based superalloys and tool steels stand out as well-known high-performance alloys, widely employed across diverse industries. PM-HIP technology can successfully address conventional manufacturing challenges associated with highly alloyed materials, such as segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and the formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both alloys, may affect the fatigue performance of these PM-HIPed products. The present study aims to assess two PM-HIPed alloys, namely Inconel 625 and high-nitrogen tool steel, with a comprehensive examination of their microstructure and fatigue properties. The objectives include examining the microstructural features introduced by the PM-HIP process and understanding how they influence fatigue failure mechanisms in these alloys.

No description available.