The goal of this dissertation is to obtain some insights into understanding the relationship of “processing-microstructure-property” for layered-ternary ceramics by developing new processing methods, investigating the microstructure and high-temperature corrosion mechanism of several representative systems. The better understanding of this relationship will contribute to both the scientific research and practical applications.1. A new set of orientation relationship (OR) between Ti5Si3 and TiC was determined. High-resolution Z-contrast scanning transmission electron microscopy observations revealed that Ti3SiC2 nucleated within the twin boundary of TiC. These investigations extend the understanding of the formation mechanism of Ti3SiC2 to the atomic-length level.2. The microstructures and high-temperature oxidation properties of Ti-Al-C compounds were studied. It seems that Ti3AlC2, TiC, and Ti2AlC share close microstructural relationship and that their mechanical properties and corrosion resistance can be tuned by tailoring the microstructure. The diffusion of carbon throuth TiAl twin boundaries promotes the dissolution of TiAl laths and leads to the formation of Ti2AlC. The Al2O3 oxide scale shares a well crystallize interface with the Ti3AlC2 substrate following two specific sets of ORs. Ti2AlC suffers from serious hot corrosion attacks under molten Na2SO4 salt. The high-temperature hot corrosion resistance of Ti3AlC2 and Ti2AlC was significantly improved by a simple pre-oxidation treatment.3. A method that offers the advantages of short processing time, low applied pressure and high product purity were found to synthesizes the fully dense and single-phase Ti2AlN. Ti2AlN experiences a rapid oxidation above 900oC because the activity of Al in Ti2AlN is too low to form a protective Al2O3 scale.4. Single-phase bulk Cr2AlC ceramic was fabricated. Atomic-scale characterization with a chemical sensitivity was achieved using high-resolution Z-contrast imaging. Electron energy loss spectroscopy analyses revealed that the Cr-C bond was characterized by strong s type bonding. Cr2AlC, AlCr2, and Al8Cr5 share coherent or semi-coherent interfaces following specific sets of ORs. The unique crystal structure and bonding properties enable the selective oxidation of Al within Cr2AlC. A protectively Al2O3-rich scale efficiently retards the further corrosion of the Cr2AlC substrate. 5. The crystal structure of a new Ta4AlC3 phase was determined and a full set of crystal structure parameters for this compound was presented. OR between TaC and Ta2AlC, and a general OR between binary cubic MX carbides/nitrides and layered-ternary carbides/nitrides was proposed. A series of new phases were identified. The bonding strength of Ta-C bonds is higher than that of Ta-Al bonds. Consequently, the bulk modulus of layered-ternary Ta-Al-C compounds increases with the increasing of Ta-C fraction (or Ta/Al ratio).6. The space group of both Zr2Al3C4 and Zr3Al3C5 was determined to be P63/mmc. TEM analyses show that Al could reduce the twin boundary energy of ZrC and lead to the formation of ternary Zr-Al-C ceramics. The microstructural evolution of Zr-C slab and Al-C unit during the formation of ternary Zr-Al-C compounds was illustrated. First-principle calculations revealed that the bonding strength of the Zr-Al bond was comparable to that of the Zr-C bond within ternary Zr-Al-C ceramics, which contributes to the high-retained elastic stiffness at elevated temperatures.
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