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 dislo cation gliding atomic planes of (11(1) over bar)(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 interse ction mechanisms was related to the thickness of the incident twin (TI). Wh en 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 o f (11(1) over bar)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 th ickness of the barrier twin (TB), the active intersection mode changes to t he intersection mechanism with the gliding atomic plane of (115)TB The obse rved thickness dependence indicates that active different twin intersection mechanisms need different local stress concentrations near the intersectio n boundary, which increases with increasing TI thickness. A twin intersecti on mainly includes two successive processes that are dislocation dissociati on on the intersection boundary and the dislocation glides in the barrier t win. The local stress concentration needed to activate those intersection m echanisms is related to the difficulties of these two successive processes. The observed sequence in thickness dependence is consistent with the seque nce in difficulty of those intersection mechanisms based on a detailed anal ysis of those two successive processes. (C) 2000 Elsevier Science Ltd. All rights reserved.