Creep mechanisms of fully-lamellar TiAI based upon interface sliding

Deformation mechanisms of fully lamellar TiAl with a refined microstructure (y lamellae: 100 - 300 nm thick, a2 lamellae: 10 ~ 50 nm thick) crept at 760°C have been investigated. As a result of a fine structure, the motion and multiplication of lattice dislocations within both y and a2 lamellae are limited at low creep stresses (< 400 MPa). Therefore, the glide and climb of lattice dislocations are insignificant to creep deformation. The cooperative motion of interfacial dislocations on y/a. 2 and y/y interfaces (i. e. interface sliding) is proposed to be the dominant deformation mechanism at low stresses. Lattice dislocations impinged on lamellar interfaces are found to be the major obstacles impeding the motion of interfacial dislocations. The number of impinged lattice dislocations increases as the applied stress increases and, subsequently, causes the pileup of interfacial dislocations along the interfaces. Accordingly, deformation twinning activated by the pileup of interfacial dislocations is proposed to be the dominant deformation mechanism at high stresses (> 400 MPa). © 1999 Materials Research Society.