No description available.

No description available.

Single crystals of iron with 20, 28 and 40 at. % aluminium were deformed in compression at room temperature. The later two alloys were deformed also at temperatures in the range of yield stress anomaly. Room temperature deformation was carried under the atomic force microscope (AFM) and the evolution of surface was recorded in-situ. Samples deformed at elevated temperatures were investigated by AFM after the deformation. Dislocation structures in deformed samples were then investigated in transmission electron microscope (TEM). Observations of surface (AFM) and bulk (TEM) are compared. Results of both techniques mutually agree and support the interpretation of observed phenomena. Several original analysis methods were developed. Most notably the stereographic reconstruction, which was applied to dislocation structures and carbide particles present in investigated alloys. Model explaining the distribution of carbide particle axes is presented. Powered by TCPDF (www.tcpdf.org)

Aluminetos de ferro pertencem a uma classe de materiais interessantes por combinarem excelente resistência à oxidação com boas propriedades mecânicas em temperaturas moderadas a altas (até 500°C). Estes materiais, contudo, em temperatura ambiente, possuem baixa ductilidade (menos de 5% de alongamento à tração), característica correlacionada a efeitos ambientais, o que dificulta seu processo de conformação. A fundição é uma via de processamento tradicionalmente aplicada às ligas frágeis (por exemplo, ferro fundido cinzento), sendo necessário conhecer as propriedades termoquímicas da liga para que as peças fundidas sejam livres de defeitos atribuídos ao processo, como a formação de poros e rechupes. Neste trabalho foram investigadas três ligas distintas de intermetálicos, Fe28Al, Fe28Al6Cr e Fe28Al6Cr1Ti, sob a influência de diferentes condições de solidificação. Para estas três composições de liga, observou-se a redução do tamanho de grão em até 60% pela adição de Al-5Ti-1B como inoculante ao metal fundido. As ligas foram produzidas em condições laboratorias (forno de indução com capacidade máxima de 2 kg e proteção sob fluxo de Ar), bem como em escala industrial (forno de indução com capacidade de 100 kg). O processo em escala industrial resultou em peças de fundição com pequena quantidade de defeitos, sendo este um indicativo da capacidade de produzir peças destes aluminetos de ferro diretamente pelo processo de fundição. A técnica de tomografia de raios X auxiliou na mensuração da contração linear (~6%) e tendência à formação de defeitos. Além da caracterização microestrutural das ligas produzidas, este trabalho, ao relatar processo de fundição em escala industrial, inclui uma discussão sobre a reatividade do metal fundido e o material refratário que reveste o forno de indução. Dessa forma, os dados obtidos permitem averiguar a fundibilidade de ligas da família FeAl pelo uso de forno de indução. / Iron aluminides are good candidates for applications at moderate to high temperatures (up to 500 °C) because they combine excellent oxidation resistance with good mechanical properties. However, these materials have low ductility at room temperature (less than 5% traction elongation), a characteristic correlated to environmental effects, which hinders their conformation process. Casting is a processing route traditionally applied to brittle alloys (eg, gray cast iron), it is necessary to know the thermochemical properties of the alloys to reduce the formation of defects attributed to the casting process, such as the formation of pores, scar and blows. In this work, three different alloys of intermetallic (Fe28Al, Fe28Al6Cr and Fe28Al6Cr1Ti) were investigated under the influence of different solidification conditions. For these three alloy compositions, grain size reduction by up to 60% was observed by the addition of Al-5Ti-1B as an inoculant to the molten metal. The alloys were produced under laboratory conditions (induction furnace with a maximum capacity of 2 kg and protection under Air flow), as well as industrial scale (induction furnace with capacity of 100 kg). The industrial scale process resulted in castings with a small number of defects, which is an indication of the ability to produce mechanical parts of these iron aluminides directly by the casting process. The X-ray tomography technique assisted in the measurement of linear contraction (~ 6%) and tendency to defect formation. In addition to the microstructural characterization of the alloys, this work includes a discussion about the reactivity of the molten metal and the refractory material coating the induction furnace. In this way, the obtained data allow to investigate the FeAl alloys castability by the use of induction furnace.

Thesis (M. Sc. ( Physics)) -- University of Limpopo, 2020 / In this work, we present first-principles calculation on the structural, thermodynamic, mechanical and electronic stabilities of Fe-Al and FeAl-X (X: Pt, Pd, Ru and Ag) alloys at lower and high temperatures. These systems have recently attracted a lot of attention for both scientific and possible technological application in turbines, Steel-It coating, energy sector, boilers, pipes and automotive parts as a potential replacement of steel due to their excellent resistance to oxidation at high temperatures. However, they suffer limited room temperature ductility and a sharp drop in strength above 873 K. We determined the lattice parameters, heats of formation, elastic constants, bulk to shear moduli, density of states, phonon dispersion curve and X-ray diffraction pattern for binary and ternary system at various concentrations between 0 ≤ x ≤ 10. Furthermore, the lattice expansion, elastic constants, Gibbs free energy, X-ray diffraction pattern and radial distribution function were done on the most stable systems to determine the melting point of FeAl-X ternary systems. A systematic investigation was performed on the stability of the Fe-Al alloys at zero K. We employed CASTEP code to evaluate the thermodynamic, elastic and electronic stability. Virtual crystal approximation was used to determine various atomic concentrations (0 ≤ x ≤ 5) of both Pt and Ru; this allowed more precise predictions on the materials’ behaviour. Further analysis was done on the density of states to describe the behaviour of each phase near the Fermi level; these phases were observed at different percentage compositions. A supercell approach, DMol3 was also used to evaluate these systems at a larger scale (0 ≤ x ≤ 50). VASP and LAMMPS codes were used to determine the stability of these FeAl-X ternary systems at concentrations (0 ≤ x ≤ 10). It was found that the equilibrium lattice parameters of the binary systems are in good agreement to within 2% with the available experimental data. The heats of formation showed that β2 FeAl phase was the most energetically stable system since it displayed the lowest value compared to all other binary systems. This observation accord well with the experimental phase diagram. It was also confirmed from the corresponding electronic DOS behaviour near the Fermi level. Furthermore, the shear modulus (C’) of these Fe-Al binary systems, i.e. FeAl, Fe2Al5, Fe4Al13, Fe5Al8, Fe2Al and FeAl3 were found to be positive fulfilling the condition of stability. The Fe2Al5 system was found to be the second most stable phase, followed by the monoclinic structure Fe4Al13. This observation was confirmed from the total DOS (where the Fermi level falls in the pseudogap, condition of stability). We further employed virtual crystal approximation and supercell approaches to model various atomic compositions at 0 ≤ x ≤1 and 0 ≤ x ≤ 50 for Ag, Pt, Pd and Ru. The heats of formation, density of states and elastic constants were determined to describe the structural, thermodynamic and mechanical stability of these systems. It was found that the addition of Ag, Pt, Pd and Ru enhances the stability at lower atomic percentage composition below 0.5%. Interestingly, the addition of Pt and Ru was found to significantly improve the ductility of the ternary FeAl-X compound for 0.2 and 0.5 at. % compositions. These systems showed that the Fe-sublattice was the preferred doping site with promising improvement in strength on the properties. It was further deduced that Ag and Pd stabilize the FeAl-X system at atomic percentage compositions of 0.5 and 0.7 respectively. Furthermore, a molecular dynamics-based LAMMPS-EAM was employed to model Fe50-XXXAl doped systems with either Ag, Pt or Pd. The lattice site preferences of the dopant were deduced from their energy landscape. More importantly, Ag and Pd doped systems gave comparable transition temperatures to experimental findings of 1273 K and 1073 K, respectively. Their thermodynamic and mechanical stability trends showed promising properties for industrial applications, displaying stability at a high temperature below 1300 K. This was evident for Ag, Pt (0.5 at %) and Pd (0.7 at %) doping as was the most stable systems with respect to Cij, ΔG, and RDF’s which indicated to influence the elastic instability above 1200 K as well as the ductility of these systems. The XRD confirmed that the doped systems preserved the structural symmetry as expected.

La première partie de ce manuscrit est consacrée à l’étude des microstructures et des microségrégations, héritées de la solidification des alliages ternaires Fe-Al-Ti, Fe-Al-Zr et quaternaires Fe-Al-Ti-Zr. Pour améliorer la compréhension des phénomènes ayant lieu au cours de la solidification et disposer d’un outil permettant de prédire les phases formées au cours de la solidification, une description thermodynamique du coin riche en fer du système quaternaire Fe-Al-Ti-Zr est proposée dans une seconde partie. A partir de l’ensemble des données expérimentales et bibliographiques disponibles concernant les équilibres de phases dans les différents systèmes ternaires, une description thermodynamique de chacun des systèmes ternaires est effectuée. Les systèmes Fe-Al-Zr et Fe-Ti-Zr ont été complètement décrits à l’aide du logiciel ThermoCalc. Le système ternaire Fe-Al-Ti a fait l’objet d’une description partielle. Les résultats obtenus permettent de proposer une première description thermodynamique du coin riche en fer du système quaternaire Fe-Al-Ti-Zr. Des séquences de solidification ont également été calculées à partir de cette description pour les alliages ternaires Fe-Al-Zr et quaternaires Fe-Al-Ti-Zr et comparées aux résultats expérimentaux / The first part of this work deals with the study of the microstructures and micro-segregations phenomena, inherited from the solidification on Fe-Al-Ti, Fe-Al-Zr and Fe-Al-Ti-Zr alloys. To improve our understanding of the phenomena occurring during the solidification process and to dispose of a predictive tool of the phases formed during the solidification process, a thermodynamic modeling of the iron rich corner of the Fe-Al-Ti-Zr quaternary system is proposed on a second part. From the data available in this work and in the literature, a thermodynamic modeling of each of the constituting ternaries systems is performed. Fe-Al-Zr and Fe-Ti-Zr ternaries systems were fully modeled using the ThermoCalc software. The Fe-Al-Ti ternary system is only partially modeled. These results allowed us to propose a first description of the iron rich corner of the Fe-Al-Ti-Zr quaternary system. Solidification sequences were calculated from this thermodynamic model for Fe-Al-Zr ternaries and Fe-Al-Ti-Zr quaternaries alloys and compared to our experimental results

This work deals with issues of preparation of intermetallics based on iron, nickel and titanium aluminides. It works with an idea of preparation of bulk material by reaction synthe-sis from kinetic spraying deposits by cold spray. Theoretical part is concerned with phases and compounds of these aluminides for structural applications, their characteristics and present fabrication. In experimental part there are studied microstructures created by annealing of deposits.

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This thesis deals with reaction synthesis of materials Fe–Al, Fe–Cu and Fe–Ni from cold spray. In literature analysis are introduced these systems and for each system there is brief description of binary equilibrium diagram. Furthermore here are some short explanations of diffusion, Kirkendall effect and other possible processing technologies of intermetallic materials. In experimental part, samples of sprayed materials were annealed and then microstructural changes were investigated. This thesis contains photographs of microstructure, results from scanning electron microscopy, X-ray, and measurements of microhardness.