A study of active deformation systems in titanium alloys: dependence on alloy composition and correlation with deformation texture

Active glide and twinning systems have been studied by transmission electron microscopy (TEM) in samples of three Ti-alloys, T40 (Ti+ 1000 ppm O), T60 (Ti +2000 ppm O) and TiAl6V4 deformed up to 5% by uniaxial or biaxial tension. The aim of the work was to understand more clearly which glide systems are activated during deformation of polycrystalline material and how they are related to the formation of the cold rolling textures. In order to estimate the stresses necessary for the activation of the observed glide systems, the resolved shear stresses for the different deformation systems were calculated from measured crystal orientations. The main results are: in TiAl6V4 [a], basal slip has a lower critical resolved shear stress, tau(c), than prismatic slip. [c+a] pyramidal glide shows a very low tau(c), which is up to two times larger than that for prismatic slip. Nevertheless, [c+a] glide systems were only rarely activated and twinning systems were never activated. Therefore, deformation with c-components may be accommodated by beta-phase deformation or grain boundary sliding. The observed c-type texture is due to the strong basal glide. In T40, tau(c), for <c+a> glide is up to 13 times higher than that for prismatic glide. However, [c+a] glide and twinning were strongly activated, leading to the observed t-type texture. In T60, the high oxygen content completely suppressed twinning and strongly reduced [c+a] glide. The less developed t-type texture is due to the combination of [c+a] and basal glide. (C) 2002 Elsevier Science B.V. All rights reserved.