The microstructure evolution and carbide precipitation in a Ti-46Al-8Nb-0.7C alloy as well as its creep properties at intermediate temperatures are investigated by high-energy X-ray diffraction and electron microscopy. The alloy with a nearly fully lamellar microstructure exhibits excellent creep resistance, which could be attributed to the good microstructural stability and strengthening effects from both P-and H-carbides. It is also found that the creep parameters have different effects on the precipitation of the carbides. The overall volume fraction of the carbides shows a positive correlation with the creep temperature and time. However, the thermal stability of Pcarbides in the γ grain interior decreases at a higher creep temperature. The creep stress hardly affects the precipitation and morphology development of the P-carbides. On the contrary, a higher stress can promote the H-carbide formation at the γ/α2 interfaces via α2 lath decomposition in lamellar colonies.
In this work, alloying effects of Mn, Mo, and Cr on the phase transformation behaviors of the orthorhombic and ordered v phases in high Nb-TiAl are investigated. Modulated structures are observed in the Mn and Mo-containing alloys indicating that Mn and Mo cannot hinder the formation of the orthorhombic phase while Cr hinders the formation of the orthorhombic phase completely. For the ordered v phases, small ordered v particles are observed in the Mn-containing alloy. Though Mn cannot hinder the formation of the ordered v phases, the formation temperature of which is decreased to 600 C. No ordered v phases are observed in the Mo and Cr-containing alloys. Two percent of Mo and Cr hinder the formation of the ordered v phases completely. The stabilization effect of Mn, Mo, and Cr on bo phase is mainly a thermodynamic effect.
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