@phdthesis{Wang2014, author = {Wang, Li}, title = {Mechanisms of carbide precipitation and carbon solubility in high Nb containing TiAl Alloys}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-30392}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {TiAl alloys with a high addition of Nb have recently been applied in the aerospace and automotive fields due to their excellent high-temperature properties. The C additions to TiAl alloys have been reported to improve their strength and creep resistance through solid-solution hardening and / or precipitation hardening. In this work powder metallurgy (PM) based Ti-45Al-5Nb-xC (x=0, 0.5 0.75 and 1.0 at. \%) alloys were systematically investigated after different heat treatments. The research is mainly concerned with the temperature range from 800 to 1000ºC which is interesting for processing as well as applications. The results show that the addition of C influences the phase transformations in Ti-45Al-5Nb and that the addition of Nb may influence the carbon solubility in TiAl alloys at high temperatures. The carbon solubility in Ti-45Al-5Nb is > 1.0 at. \% at 1400°C, but between 0.5 and 0.75 at. \% at 1000°C, and less than 0.5 at. \% at 800°C. The carbide precipitation and development of carbide morphology are discussed in great detail. The thermal stability of P-Ti3AlC carbides in Ti-45Al-5Nb-xC alloys is increased, which might be attributed to the addition of high amounts of Nb, or the high amount of carbon, or a combination of both. In heat-treated Ti-45Al-5Nb-0.5C and Ti-45Al-5Nb-0.75C, H-type carbides are not detected to form during annealing. The addition of Nb may increase the formation temperature of the H-Ti2AlC precipitate phase.}, subject = {High Nb containing TiAl alloys; Transmission electron microscope; High-energy X-ray diffraction; Carbide; Thermal stability; Hochniobhaltige TiAl-Legierungen; Transmissionselektronenmikroskopie; Hochenergie-R{\"o}ntgenbeugung; Karbide; Thermische Stabilit{\"a}t; Titanaluminide; Carbide; Temperaturbest{\"a}ndigkeit}, language = {en} }