TEM investigation of twin intersection in a Ti–45Al–9Nb–2.5Mn alloy deformed at room temperature

Three penetration mechanisms of the type-I twin intersection with the dislocation gliding atomic planes of (111)TB, (001)TB, and (115)TB respectively have been observed in a high-Nb containing TiAl base alloy by high resolution TEM. It was found that the active mode of those intersection mechanisms was related to the thickness of the incident twin (TI). When the TI is very thin such as 2–3 nm, the active intersection mode usually is the intersection mechanism with the dislocation gliding atomic planes of (111)TB; when the TI gets thick, the active intersection mode moves to the intersection mechanism with the gliding atomic planes of (001)TB; as the TI becomes thick enough such as 15 nm which is similar to the thickness of the barrier twin (TB), the active intersection mode changes to the intersection mechanism with the gliding atomic plane of (115)TB. The observed thickness dependence indicates that active different twin intersection mechanisms need different local stress concentrations near the intersection boundary, which increases with increasing TI thickness. A twin intersection mainly includes two successive processes that are dislocation dissociation on the intersection boundary and the dislocation glides in the barrier twin. The local stress concentration needed to activate those intersection mechanisms is related to the difficulties of these two successive processes. The observed sequence in thickness dependence is consistent with the sequence in difficulty of those intersection mechanisms based on a detailed analysis of those two successive processes.