The microstructure of massively transformed alloys was studied by means of conventional and high-resolution electron microscopy. A high density of planar defects (complex antiphase domain boundaries, thermal micro-twins) was observed. The high-resolution electron microscopy confirmed that 2 antiphase-related γ-matrix domains were generally separated by a thin layer of 90º domain, in which the c-axis was rotated through 90º over a common cube axis, with respect to those of the γ-matrix domains. Two crystallographically distinct types of 90º domain were observed to be associated with the complex antiphase domain boundaries. In regions where thermal micro-twins intersected the generally morphologically wavy non-crystallographic complex antiphase domain boundaries, the latter faceted parallel to the {111} twinning-planes of the thermal micro-twins. This local interaction between complex antiphase domain boundaries and thermal micro-twins was associated with the transfer of true twinning shears of 1/6<112]-type from the matrix to the thin 90º domain; thus generating a pseudo-twinned region where the corresponding shears were of 1/6<121] type. Diffusion which was associated with local rearrangement of the atomic stacking was expected to accommodate relaxation of the complex antiphase domain boundaries by faceting on the low-energy {111} planes.

Planar Defects in Massively Transformed Ti-Al Alloys. X.D.Zhang, J.M.K.Wiezorek, M.J.Kaufman, M.H.Loretto, H.L.Fraser: Philosophical Magazine Letters, 1999, 79[8], 519-30