Twin intersection in tensile deformed γ-TiAl intermetallic compounds

Abstract

Intersections of deformation twins in γ-TiAl grains were examined in Ti-47at.%Al alloy specimens tensile-tested at 873 K. Transmission electron microscopy (TEM) revealed 1 / 2 < 1 1 ¯ 0 ] { 111 } dislocations and 1 / 6 < 11 2 ¯ ] { 111 } twins in deformed γ-TiAl grains. Some γ-TiAl grains contained twins on two different {111} planes, which intersect along <110] directions (type-1). No twin intersection along <101] (type-2) was observed, which was often reported in compressed specimens. Results are discussed with the Schmid factor distributions of twinning systems and slip systems. It should be noted that twinning shear in L1 0 structure is limited only in one 1/6< 11 2 ¯ ] movement on a {111}. Considering Schmid factors of possible four twin systems, both type-1 and type-2 twin intersections are expected. Tensile load direction which can activate both twinnings of type-2 intersection can also activate ordinary 1 / 2 < 1 1 ¯ 0 ] { 111 } dislocations. The absence of type-2 intersection suggests that ordinary slip systems were favored in these cases.