Abstract: By means of in-situ tensile tests of fully lamellar TiAl based alloys, the analysis of experiment data, scanning electron microscope (SEM) S-520 observation of fracture surface, the tensile fracture process and fracture mechanism of TiAl alloys are investigated. The result of in-situ tensile experiment reveals that cracks are initiated directly from the notch root for the straight notch specimens, and the fracture mechanism is that the main crack is initiated, propagated and connected, when the main crack extends to a length, which acts as a Griffiths crack and matches the loading stress which the crack propagates catastrophically through entire specimen. Cracks initiate at interfaces between lamellae and lamellar interface is the most weakest part. Fracture surface is composed of the trans-lamellar fracture and inter-lamellar fracture, trans-lamellar fracture is dominant. For flat in-situ tensile specimen or those with a big circle arc gauge at a higher applied load, a number of large cracks are produced along lamellar interfaces within the gauge-limited volume of tensile specimens. With increasing applied load, microcracks propagate and connect, the final crack develops at a most heavily damaged section within the gauge-limited volume by passing through the remaining ligaments among the interlamellar cracks. For most specimens, fracture process is the crack direct initiation process. Once a crack is produced, the specimen will fracture. It is also to say the strength of the material is very higher, and crack initiation and damage are more difficult.

Key words: Fracture mechanism, In-situ tensile, TiAl-based alloys