a b s t r a c tThe mechanical properties of g-TiAl based alloys are often improved through alloying with niobium and carbon. Depending on composition and heat treatment the details of carbon distribution and the resulting consequences on mechanical properties vary greatly.Here we present a study of the microstructure of Tie45Ale5Nb alloys (in at.-%) with the addition of 0.5e1 at.-% of carbon. We use electron diffraction accompanied by energy dispersive spectroscopy and imaging in the TEM to characterize carbides. These studies are complemented by high-energy X-ray diffraction experiments using synchrotron radiation and by scanning electron microscopy. Carbides are identified in significant numbers in the alloys containing 1 and 0.75 at.-% of carbon but only rarely at 0.5 at.-% C. Our results show that in these alloys carbon in solid solution has a stronger effect on hardness than carbide precipitation.

No abstract

No abstract

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.

No abstract