Studies On Precipitation Reaction And Dislocation Microstructures Of TiAl Based Intermetallic Compounds

TiAl based intermetallic compounds are very promising candidates as high temperature structural materials due to their high specific strength, good oxidation resistance and high modulus. However, their practical application is still hindered by the poor ductility at room temperature, the fast creep rate and the insufficient strength at high temperature. It has been illustrated that the mechanical properties of the dual-phase TiAl alloys are superior to that of single-phase TiAl alloys, the former consist ofγ-TiAl with L10 tetragonal structure andα2-Ti3Al with D019 hexagonal structure. At present, microstructural control and alloying are the main methods to improve the properties of TiAl based alloys.In this work, we studied the Ti-Al-Ag and Ti-Al-Nb alloys system. Ti-54at.%Al-2at.%Ag and Ti-54at.%Al-4at.%Ag was aged at 1073K for different time, then precipitation reaction was observed in the two alloys. The transmission electron microscopy (TEM) was employed to research systematically the kinetic process of the precipitation reaction, crystallographic characteristics of phase transformation and precipitation strengthening, including the composition of the matrix and the precipitates, the morphological evolution of the precipitates, the growth and coarsening mechanism of the precipitates, the interface structure between the matrix and the precipitates, the habit plane of the precipitates. We also studied the microstructure of Ti-48at.%Al-xNb(x=1, 3, 5and 10at.%) and analyzed the...