INFLUENCE OF LAMELLAR STRUCTURE ON CRACK PROPAGATION IN DUPLEX TiAl ALLOY
层状组织对双相TiAl合金裂纹扩展的影响

In situ TEM technique was employed to observe the influence of lamellar structure on the crack propagation in duplex TiAl alloy. It has been found that both crack tip blunting and crack propagating have connected with the angle included between crack growth and lamellar direction. Only if the crack growth roughly parallel to lamellar direction ,the microcracks may nucleate ahead of the main crack. So, shear ligaments play an important role in toughening TiAl alloy. When the crack growth is perpendicular to lamellae or between perpendicular and parallel to lamellae, the main reasons of lamellar toughening in TiAl alloy owe to that:(1) the lamellar boundary inhibits crack propagation,and(2)the crack tip blunting is caused by the slip of interlamellar boundary. According to the dislocations theory of microcrack nucleation, these phenomena are explained.