The fracture behaviour of intermetallic TiAl alloys with and without warm pre-stressing

摘要

The fracture behaviour of near-gamma (NG) and fully lamellar (DEL) intermetallic TiAl alloys with and without warm pre-stressing (WPS) is investigated by testing three point bending specimens with fatigue precracks at room temperature and at 700 deg C. Detailed fractographic observations and FEM calculations are carried out to find the critical step of cleavage fracture. The results show that the cleavage fracture is induced by direct propagation of the pre-crack and that the stress at the crack tip is the decisive controlling factor. The WPS process improves the fracture initiation toughness of both the NG and the DFL microstructure, but deteriorates slightly the increase of the K-resistance curves, especially for the DFL microstructure. The compressive residual stress induced by WPS plays the main role in improving the fracture initiation toughness.