Tensile behavior of a TiAl intermetallic alloy at 750°C based on in-situ observational tests

High Nb containing TiAl alloys with FL, DP, NG microstructures were investigated based on the in-situ tensile tests at 750 degrees C. The results showed that, DP structure had the comparatively better tensile properties among structures investigated with yield strength of 637MPa and elongation of 4.7%, NG structure properties was slightly inferior to that of DP structure. FL structure had the same yield strength as DP structure, but its tensile strength was the lowest and almost no ductility. In-situ SEM observation during tension showed that, Both of NG and DP structures had similar deformation characters. When the stress up to a certain value that was 737MPa for NG and 850MPa for DP during the tensile tests. The micro cracks initiation and growth occurred. The amount of microcracks increased and the microcracks were widely distributed with load increasing. In FL structure, Microcracks initiation and propagation were too fast to be clearly observed before the specimens fractured. SEM observation showed that the microcracks mainly distributed along interlamellars and lamellar colony boundaries perpendicular or being a larger angle to the load axis in FL structure. The microcracks in grain boundaries coalesced and growed, which was a dominant mechanism of tensile failure for NG structure alloy. The intermittent microcracks were formed in DP structure which initiated due to the coalescence of voids.