Deformation of lamellar structure in TiAl-Ti3Al two-phase alloys

Abstract

Polysynthetically twinned (PST) crystals of TiAl(γ)-Ti₃Al(α₂) two-phase alloys with five different orientations were deformed in compression and in tension in the temperature range from- 196 to 1100°C. Deformation structures in gamma domains of six different orientation variants in each specimen were examined by transmission electron microscopy, and operative slip and/or twinning systems were determined. No significant change in the operative deformation modes was observed up to 800°C. On the basis of these results, macroscopic plastic strain tensors of PST crystals were derived. They were found to describe well the anisotropic deformation of PST crystals. The anisotropy of deformation is typically observed when the loading axis is parallel to the lamellar boundaries. The normal strain in the direction perpendicular to the lamellar boundaries is zero or much smaller than that in the direction parallel to the lamellar boundaries. Strain continuity at domain and lamellar boundaries is one of the most important factors in determining not only operative slip and/or twinning systems for each orientation variant in the gamma phase but also the yield stress and tensile elongation of PST crystals.