The sub-structures of a lamellar alloy which had been deformed at 760C were studied. The deformation had involved low (138MPa) stresses, applied up to large strains (1.5%), or high stresses (518MPa) applied up to small strains (0.67%). During creep, interfacially gliding dislocations were initially retarded by intrinsic barriers (such as ledges in the interface) or extrinsic barriers (such as the reaction of lattice dislocations with interfaces), thus resulting in a dislocation pile-up configuration. With further deformation, deformation twins were formed, and dislocation emission from interfaces also occurred. It was found that a critical local stress was required in order to initiate deformation twins; which were suggested to form via a stair-rod cross-slip mechanism. This critical stress could be provided by an interfacial dislocation pile-up.

Formation of Deformation Twins in a Crept Lamellar TiAl Alloy J.G.Wang, L.M.Hsiung, T.G.Nieh: Scripta Materialia, 1998, 39[7], 957-62