Role of Interfacial Dislocations on Creep of a Fully Lamellar TiAl

Deformation mechanisms of a fully lamellar TiAl (γ lamellae: 100 ~ 300Ênm thick, α2 lamellae: 10 ~ 50 nm thick) crept at 760¡C have been investigated. It was found that, as a result of a fine structure, the motion and multiplication of dislocations within both γ and α2 lamellae are limited at low creep stresses (< 400 MPa). Thus, the glide and climb of lattice dislocations have insignificant contribution to creep deformation. In contrast, the motion of interfacial dislocations on γ/α2 and γ/γ interfaces (i.e. interface sliding) dominates the deformation at low stresses. The major obstacles impeding the motion of interfacial dislocations was found to be lattice dislocations impinging on lamellar interfaces. The number of impinging lattice dislocations increases as the applied stress increases and, subsequently, causes the pileup of interfacial dislocations on the interfaces. The pileup further leads to the formation of deformation twins. Deformation twinning activated by the pileup of interfacial dislocations is suggested to be the dominant deformation mechanism at high stresses (> 400 MPa).