High carbon solubility in a gamma-TiAl-based Ti-45Al-5Nb-0.5C alloy and its effect on hardening

摘要

The C distribution within the gamma-TiAl-phase of a Ti-45Al-5Nb-0.5C alloy with near-gamma microstructure was studied by atom probe tomography. In most areas, the C atoms were homogeneously distributed, and only a few C-enriched features were detected, which were presumably Cottrell atmospheres surrounding dislocation cores. The C concentration within the gamma-phase was measured to be approx 0.25 at. percent, which is a factor of 10 higher than the solubility limit reported for other TiAl alloys. The reason for this unusually high C solubility is explained by an existing model, which relates the number of octahedral sites consisting of six Ti atoms to the solubility limit of inter-stitials. The large amount of C in solid solution can explain the results of a recent study which showed that the C-containing alloy had a approx 30 percent increase in yield strength compared with a C-free sheet containing the same Ti, Al and Nb concentrations.